Advanced Application of Nanotechnology to Industrial Wastewater 9819932912, 9789819932917

Table of contents :
Contents
Nano-biotechnology-Based Solution to the Age-Old Problem of Spent Wash Causing Water Pollution in the Vicinity of Distilleries
1 Introduction
2 Colourants in Distillery Wastewater
3 Melanoidins
4 Melanoidins and Food
5 Melanoidin Formation
6 Treatment Technologies for Decolourization of Distillery Effluent
7 Treatments Based on Physicochemical Methods
7.1 Adsorption
8 Oxidation Processes
9 Coagulation and Flocculation
10 Membrane Treatment
11 Biological Methodology-Based Treatment
12 Anaerobic Digestion
13 Treatment Using Aerobic Means
14 Treatment by Activated Sludge
15 Biocomposting
16 Other Treatments
17 Microbial Treatment
17.1 Bacterial Systems
18 Immobilized Microbes
19 Nanomaterials for Waste Water Treatment
20 Conclusion
References
Application of Nanomaterials in Heavy Metals Remediation from Wastewater
1 Introduction
2 Silver Nanomaterials
3 Carbon Nanomaterials
4 Titanium Dioxide Nanomaterials
5 Iron Nanomaterials
6 Iron Oxide Nanomaterials
7 Conclusion
References
Application of Metallic Nanoparticles for Industrial Wastewater Treatment
1 Introduction
2 Modern Application of Nanotechnology in Decontamination of Water
2.1 Carbon Nanotubes (CNTs) in Wastewater Treatment
2.2 Metal Nanomaterials and Their Uses for Industrial Wastewater
3 Wastewater Treatment Using Photocatalysis
3.1 TiO2 Nanomaterials as Photocatalyst
3.2 Nanomaterials for the Membrane to Improve the Efficiency
3.3 Antimicrobial Activity of Metal/Metal Oxide Nanomaterials
3.4 UV/TiO2 Photocatalysis and Its Application Toward Drug Removal
3.5 AgNPs Photocatalyst and Its Usage in Recalcitrant Pollutants Removal
4 Conclusions and Overview
References
Zero-Valent Nanomaterials for Wastewater Treatment
1 Introduction
2 Types of Nanomaterials in Wastewater Treatment
2.1 Nanoscale Zero-Valent Iron (nZVI)
2.2 Immobilization of ZVI onto Supports
2.3 Doping of ZVI with Other Metals
3 Zero-Valent Iron for Wastewater Treatment
3.1 Heavy Metal Removal by ZVI
3.2 Photocatalysis for Removal of Organic Pollutants
4 Current Challenges and Future Perspectives
5 Conclusion
References
Photocatalytic Treatment of Soft Drink Industry Wastewater Using Supported/Immobilized Nanophotocatalysts
1 Introduction
2 Characteristics of SDIW
3 Conventional Treatment Technologies for SDIW
4 Advanced Oxidation Processes for SDIW Treatment
5 Photocatalysis
6 Modification and Immobilization of Photocatalysts
7 Photocatalytic Treatment of SDIW Using Modified Photocatalyst
8 Conclusion
References
Chemical Nanosensors for Monitoring Environmental Pollution
1 Introduction
2 Components of a Nanosensor
3 Principles of Functioning of Chemical Nanosensors
4 Classification of Chemical Nanosensors
4.1 Electrochemical Nanosensor
4.2 Nanowired-Based Chemical Sensors
4.3 Raman Scattering Chemical Nanosensors
4.4 Piezoelectric Nanosensors
4.5 Immunochromatographic Strip Nanosensors
5 Advantages of Chemical Nanosensors Over Conventional Approaches in Environmental Monitoring
5.1 Reports on the Use of Chemical Nanosensors in Environmental Monitoring
6 Conclusion
References
Nanotechnology for Bioremediation of Industrial Wastewater Treatment
1 Introduction
2 Water Pollution: Major Sources
2.1 Fertilizers and Pesticides
2.2 Water Pollution Due to Industries
2.3 Polythene and Plastic Bags
2.4 Polluted Groundwater
3 Conventional Method Used in Industrial Wastewater Treatment and Purification
3.1 Filtration by Micro Membrane
3.2 Sedimentation
3.3 Filteration by Sand
4 Nanotechnology Used for Bioremediation of Industrial Wastewater Treatment
4.1 Nanophotocatalysts
4.2 Nanofilteration Membranes
4.3 Nanaoadsorbents
4.4 Nanomaterials
4.5 Ultrafiltration
4.6 Nanomotors and Sensoring
5 Microorganisms Involved in Nanotechnology for the Treatment of Wastewater
6 Enzyme Technology Assisted with Nanotechnology
7 Conclusion and Futuer Prespective
References
Nanoadsorbents for Treatment of Wastewater
1 Introduction
2 Wastewater
3 Major Contaminants in Wastewater
3.1 Heavy Metals
3.2 Dyestuff
3.3 Pharmaceutical
3.4 Inorganic Pollutants
3.5 Radioactive Waste
4 Wastewater Treatment
4.1 Physical Treatment of Wastewater
4.2 Chemical Treatment of Wastewater
4.3 Biological Treatment of Wastewater
5 Adsorption
6 Nanotechnology
7 Nanoadsorbent
7.1 Carbon-Based
7.2 Metal Oxide Nanoparticles
7.3 Metal Nanoparticles
7.4 Polymeric Adsorbents
7.5 Metal Organic Framework
7.6 Magnetic Nanoadsorbents
8 Future Prospects
9 Conclusion
References
Nanofiltration Technique for the Treatment of Industrial Wastewater
1 Introduction
2 Filtration Using Membrane
2.1 Reverse Osmosis
2.2 Ultrafiltration
2.3 Nanofiltration
3 Characteristics, Advantages, and Disadvantages of Nanofiltration Membranes
3.1 Characterization
3.2 Advantages
3.3 Disadvantages
4 Modifications of Nanofiltration Membrane
4.1 Surface Coating
4.2 Graft Polymerization
4.3 Metallic Nanoparticle Impregnated NF Membranes
5 Wastewater Treatment Using Nanofiltration Membrane
5.1 Dye Removal
5.2 Heavy Metal Removal
5.3 Organic Pollutants Removal
6 New Advancement in Nanofiltration Membrane
6.1 Nanocomposite Nanofiltration Membrane for Industrial Wastewater Treatment
6.2 Nanocomposite Hollow-Fibre Nanofiltration Membrane for Wastewater Treatment
6.3 Aquaporin Based NF Membranes
6.4 Nanofiltration Membrane Bioreactor
6.5 Stimuli-Responsive Nanofiltration Membrane
7 Future Outlooks in NF Membrane Technology for Wastewater Treatment
8 Conclusion
References
Technological Advancement in the Synthesis and Application of Nanocatalysts
1 Introduction
2 Structural Features of Nanocatalyst
3 Different Types of Nanocatalyst
3.1 Homogeneous Nanocatalyst
3.2 Heterogeneous Nanocatalyst
3.3 Nanocarbon Catalyst
3.4 Bio-derived Nanocatalysts
4 Progress in Synthesis of Nanocatalysts
4.1 Conventional Approaches for the Synthesis of Nano Catalysts
4.2 Green Synthesis Approach for the Synthesis of Nanocatalysts
5 Emerging Applications of Nanocatalysts
5.1 Application of Nanocatalysts in Biofuel Production
5.2 Application of Nanocatalysts in Water Treatment
5.3 Application of Nanocatalysts in Agriculture
5.4 Application of Nanocatalysts in Fuel Cell
5.5 Application of Nanocatalysts in Drug Delivery
6 Commercial Aspects of Nanocatalysts
7 Challenges and Future Perspectives
8 Conclusions
References
Metallic Nanoparticles and Bioremediation for Wastewater Treatment
1 Issues of Water Resources Pollution, Water Treatment, and Management
2 Sources and Impacts of Water Pollutants
3 Current Methods and Techniques for Water Pollution Management
4 Bioremediation Approach for Polluted Waters
5 Nanoscience and Derived Applications
6 Nanotechnology as an Advanced Technique (NTs)
7 Classification of Nanoparticles (NPs)
8 Metallic Nanoparticle: Ag and Fe
9 Bimetallic Ag/Fe Core–Shell Nanoparticle for Water Treatment
10 Uses of Nanomaterials in the Remediation of Pollutants and Water Purification
11 Future Potential Application
References
Phytonanoremediation of Metals and Organic Waste in Wastewater Treatment
1 Introduction
2 Impact of Water Pollution
3 Biosynthesis of Green Nanoparticles
4 Sources of Green Nanoparticles
4.1 Algae-Assisted Nano-particle Synthesis
4.2 Plant Synthesized Nanoparticles
5 Application of Nano-phytoremediation in Wastewater Treatment
5.1 Nanobioremediation of Heavy Metals
5.2 Nano Bioremediation of Organic Compounds
6 Conclusion
References
Production and Application of Porous Ceramic Membrane for Water and Wastewater Treatment—A Case Study in Vietnam
1 Introduction
2 Procedures for Making Porous Ceramic Filter
3 Porous Ceramic Filter Produced from Kaolin and Rice Husks
4 Porous Ceramic Filter Produced from Kaolin Mixed with Corn Cobs
5 Porous Ceramic Filter Produced from Kaolin Mixed with Coconut Fiber
6 Porous Ceramic Filter Produced from Kaolin Mixed with Bagasse
7 Effect of Furnaced Temperature and Time on the Properties of Porous Ceramic Filters
8 Surface Properties of Porous Ceramic Filter
9 Conclusions and Remarks
References
Nanomaterials in Wastewater Management
1 Introduction
2 Wastewater Composition and Source Composition
3 Nanomaterials in Wastewater Treatment
3.1 Metal Nanoparticles
3.2 Zeolites
3.3 Carbon Nanotubes
3.4 Nano-membranes
4 Nano-informatics for Wastewater Treatment
5 Conclusions and Future Prospects
References
Cyclodextrin-Based Material for Industrial Wastewater Treatments
1 Introduction
2 Cyclodextrin-Based Polymers
2.1 Removal of Organic Pollutants
2.2 Removal of Heavy Metals
2.3 Removal of Textile Waste
2.4 Removal of Pharmaceutical Waste
3 Conclusion
References
Application of Nanomaterials for the Removal of Heavy Metal from Wastewater
1 Introduction
2 Water Pollution
3 Heavy Metals: Types, Sources, and Toxicity
4 Nano Adsorbents: Synthesis Routes
5 Nano Adsorbents in Heavy Metal Remediation
5.1 Carbon-Based Nano Adsorbents
5.2 Polymer Based Nano Adsorbents
5.3 Metal Oxide Nano Adsorbents
5.4 Magnetic Nano Adsorbents
6 Nano Adsorbent Recovery and Reutilization
7 Conclusion and Future Directions
References
Technological Interventions for Wastewater Treatment: Monitoring and Management
1 Introduction
2 Interventions in Wastewater Treatment
2.1 Electrochemical Technologies
3 Nanotechnology in Wastewater Treatment
3.1 Application of Nanotechnology in Wastewater Treatment
4 Conclusion
References

Citation preview

Maulin P. Shah   Editor

Advanced Application of Nanotechnology to Industrial Wastewater

Advanced Application of Nanotechnology to Industrial Wastewater

Maulin P. Shah Editor

Advanced Application of Nanotechnology to Industrial Wastewater

Editor Maulin P. Shah Environmental Microbiology Lab Ankleshwar, Gujarat, India

ISBN 978-981-99-3291-7 ISBN 978-981-99-3292-4 (eBook) https://doi.org/10.1007/978-981-99-3292-4 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Contents

Nano-biotechnology-Based Solution to the Age-Old Problem of Spent Wash Causing Water Pollution in the Vicinity of Distilleries . . . Shipra Jha, Prachi Kapoor, Christine Jeyaseelan, and Debarati Paul

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Application of Nanomaterials in Heavy Metals Remediation from Wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ayushi Singh, Sonal Chaudhary, Ajit Varma, and Shalini Porwal

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Application of Metallic Nanoparticles for Industrial Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ardhendu Sekhar Giri, Vishrant Kumar, and Sankar Chakma

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Zero-Valent Nanomaterials for Wastewater Treatment . . . . . . . . . . . . . . . . Arindam Sinharoy and Priyanka Uddandarao Photocatalytic Treatment of Soft Drink Industry Wastewater Using Supported/Immobilized Nanophotocatalysts . . . . . . . . . . . . . . . . . . . Anil Swain, Neelancherry Remya, and Abhishek Patil Chemical Nanosensors for Monitoring Environmental Pollution . . . . . . . Abel Inobeme, Charles Oluwaseun Adetunji, Alexander Ikechukwu Ajai, Jonathan Inobeme, John Tsado Mathew, Alfred Obar, Munirat Maliki, Nkechi Nwakife, and Chinenye Eziukwu

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Nanotechnology for Bioremediation of Industrial Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Manisha Kumari, Jutishna Bora, Archna Dhasmana, Sweta Sinha, and Sumira Malik Nanoadsorbents for Treatment of Wastewater . . . . . . . . . . . . . . . . . . . . . . . . 133 Pratik V. Tawade, Samyabrata Bhattacharjee, and Kailas L. Wasewar Nanofiltration Technique for the Treatment of Industrial Wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Niladri Shekhar Samanta, Piyal Mondal, and Mihir Kumar Purkait v

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Contents

Technological Advancement in the Synthesis and Application of Nanocatalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Prangan Duarah, Pranjal P. Das, and Mihir K. Purkait Metallic Nanoparticles and Bioremediation for Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 Elham M. Ali and Ahlam S. El-Shehawy Phytonanoremediation of Metals and Organic Waste in Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 Garima and Navneeta Bharadvaja Production and Application of Porous Ceramic Membrane for Water and Wastewater Treatment—A Case Study in Vietnam . . . . . . 263 Khac-Uan Do, Xuan-Quang Chu, and Hung-Thuan Tran Nanomaterials in Wastewater Management . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Lavaniya Nagrath, Hina Bansal, and M S Smitha Cyclodextrin-Based Material for Industrial Wastewater Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Amara Lakshmi Lasita, Pallavi Pradhan, Nilesh S. Wagh, and Jaya Lakkakula Application of Nanomaterials for the Removal of Heavy Metal from Wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 P. Priya, N. Nirmala, S. S. Dawn, Kanchan Soni, Bagaria Ashima, Syed Ali Abdur Rahman, and J. Arun Technological Interventions for Wastewater Treatment: Monitoring and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353 Anurag Singh, Prekshi Garg, Prachi Srivastava, and V. P. Sharma

Nano-biotechnology-Based Solution to the Age-Old Problem of Spent Wash Causing Water Pollution in the Vicinity of Distilleries Shipra Jha, Prachi Kapoor, Christine Jeyaseelan, and Debarati Paul

Abstract Distillery spent wash is the unwanted residual liquid waste generated during alcohol production, and pollution caused by it is one of the most critical environmental issues since this wastewater has very high COD (~1,10,000–1,90,000 mg/ L) and BOD (~50,000–60,000 mg/L). Despite environmental guidelines imposed on effluent quality, untreated or partially treated effluent is released into waterbodies, and with its characteristic colour and odour, it threatens water quality all over the world. The threat posed by gradually increasing volumes of distillery waste or spent wash and also strong rules and regulations with respect to effluent disposal has initiated the development of newer and effective processing of effluent in cost-effective manner. Many clean-up techniques have been practiced traditionally and have been innovated by including novel approaches for bioremediation to treat this spent wash. With the enhancement in science and technology, urbanization also contributes to an increase in the load of toxic waste in the environment. The existing methods are not efficient to remove contaminants from the environment. Due to the distinctive properties of nanomaterials and their applications in various fields, they are gaining attention from researchers in bioremediations fields. Hence, nanomaterials are immobilized with microorganisms to clean the environmental pollution. In this chapter, we will discuss the use of nanomaterials for the removal of contaminants. Keywords Distillery spent wash · Environmental pollution · Bioremediation · Nanomaterials

S. Jha · P. Kapoor · C. Jeyaseelan (B) · D. Paul (B) Amity University Uttar Pradesh, Sec 125, Noida 201313, India e-mail: [email protected] D. Paul e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_1

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1 Introduction Molasses distilleries have been designated as a “Red category” industry by MOEF (Ministry of Environment of Forests (MOEF) because of their tremendous pollutioncausing potential (Tiwari et al. 2007). Large quantities of wastewater are released by these distilleries that amounts to about 8 to 15 L alcohol (rectified spirit). The standard set-back faced during the treatment of this dark brown coloured spent wash (distillery effluent), containing approximately 2% recalcitrant melanoidin pigment, is its resistant nature that fails most of the common natural microbial degradation and other biological treatments (Pakouki et al. 2008). Melanoidin compounds are benign and destructive for existing soil/water microbiota. The other concomitant issues are due to increased BOD (Biological Oxygen Demand), COD (Chemical Oxygen Demand), acidity, and toxicity by phenolic substances (Dahiya et al. 2001). This spent wash has pH in the range of 4·0–4·3, BOD in the range of 52–58, COD in the range of ~92–100 kg/m3 , and suspended solids in the range of 2–2·5 kg/m3 . In 2003, Central Pollution Control Board (CPCB), which is responsible for national environmental compliance, specifically directed that zero discharge into inland surface water bodies should be targeted by the end of 2005. There are many reports (Thakker et al. 2006) to demonstrate the bioremediation of melanoidins contained in the spent wash using white–rot fungi possessing lignin-degrading enzymes since these ligninolytic enzymes have non-specific substrate requisite resulting in degradation of harmful melanoidin pigments. An extremely diverse range of enzymes demonstrate melanoidin degradation activities, e.g. manganese peroxidase, lignin peroxidase, H2 O2 producing enzymes, and laccase (Gold and Alic 1993). Remediation techniques of various designs have been applied to ameliorate the dangers posed by melanoidin pollution which is a substantial environmental problem. Starting from physicochemical methods to biological methods using immobilized or free microbial cells have been employed. Yet the problem ceases to find an effective and sustainable technology. Here the chemistry of the pollutant and various methods used for removal of the pollutant and future prospects have been described.

2 Colourants in Distillery Wastewater The wastewater from molasses obtained by alcoholic fermentation has a high concentration of brown pigment. The colour is negligibly degraded by the conventional treatments and can also be added during anaerobic treatments, owing to the repolymerization of compounds. The following are the four major classes of compounds contributing to the colour of molasses: 1. Phenolic, polyphenolic, and flavonoid compounds derived from cane plants mostly are yellow to brown and exist in the plant as non-coloured compounds and are oxidized to coloured state in juice either by enzymes or by chemical oxidation.

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2. Caramel compounds are formed by the decomposition of sucrose. 3. Compounds like melanoidins which are formed by the reaction of sugar and amine compounds contribute to dark brown colour besides hydroxymethyl furfural (colourless) rapidly decomposing to dark when sugar is heated in acidic conditions. 4. Degradation of fructose. The contribution to the colour of the effluent is mainly because of the factors such as phenolics (tannic and humic acids) from the feedstock, caramels from overheated sugars, melanoidins from Maillard reaction of proteins (amino groups) with sugars (carbohydrates), and furfurals from acid hydrolysis (Rani et al. 2019). During the heat treatment, the Maillard reaction, a non-enzymatic reaction takes place followed by the formation of compounds known as Maillard products. The reaction proceeds effectively at more than 50 °C and is favoured at pH 4–7 (Morales and Jiménez-Pérez 2001). Melanoidins are among the final products of the Maillard reaction and are complex compounds whose structures are not fully understood. Melanoidin is one of the biopolymers which is not really decomposed by the action of microorganisms and is widely distributed in nature. Melanoidins have antioxidant properties, which makes them toxic to a number of aquatic micro and macroorganisms (Kitts et al. 1993).

3 Melanoidins Melanoidins are natural products obtained by the condensation of sugars and amino acids and are generally dark brown to black in colour. They are Maillard reaction products, which is a non-enzymatic browning reaction (Plavsi´c et al. 2006). Melanoidins naturally have a wide distribution in food (Painter 1998) and drinks and are widely discharged in huge amounts by several agro-based industries, especially from distilleries using sugarcane molasses and fermentation industries as contaminants (Kumar and Chandra 2006; Gagosian and Lee 1981). It is assumed that the melanoidins do not have a definite structure as the elemental composition and chemical structures of melanoidins have a large dependence on molar concentration and the nature of parent reacting compounds and conditions under which reactions take place such as pH, temperature, heating time, and solvent system used (Ikan et al. 1990).

4 Melanoidins and Food Melanoidins are the end products of Maillard reaction that are significantly important ingredient of the foodstuffs and play a considerable role in thermal food processing. Melanoidins are abundantly present in bakery products, coffee, beer, and other foodstuffs including malt, honey, milk, wine, and more.

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Coffee: Melanoidins are a significant ingredient of coffee, which is a typical refreshment broadly devoured everywhere in the world. Approximately, 25% of the coffee’s dry matter comprises melanoidins which play a crucial part in specific organoleptic properties and viscosity of coffee. The chemical components in coffee beans are proven to be a part of Maillard reaction products. The amount of carbohydrate groups, reducing sugars, proteins, and phenolic compounds present in coffee are responsible for the composition of melanoidins. Phenolic compounds in the coffee are released during intestinal digestion, which are either covalently bonded or non-covalently bonded to the core of melanoidins. Coffee melanoidins are generally high molecular weight melanoidins with 59% of the composition, while the rest 41% is the low molecular weight melanoidins. The amount of lower molecular weight melanoidins are experimentally proven to remain unchanged while the higher molecular weight melanoidins are increased on prolonged roasting of coffee beans (Rivero et al. 2005, Nunes and Coimbra 2010). Beer: During the malting and brewing processes of beer, melanoidins are formed and they act as antioxidants with polyphenols. They affect the flavour, colour, and viscosity of different kinds of beer. Melanoidins are believed to be protective against DNA damage which is due to the reactive oxygen species. Dark-coloured beers have a relatively higher content of melanoidins than blond beers, and thus show a more enormous effect to protect against DNA damage (Rivero et al. 2005). Bakery Products: Owing to the antioxidant activity and the ability to influence colour and texture properties, the presence of melanoidins is also detected in bakery products like breads, biscuits or muffins. They are useful in increasing the shelf-life of these foods and also improve the growth of Bifidobacteria by utilizing melanoidins as a carbon source (González-Mateo et al. 2009). However, the persistence of melanoidins by evading degradation causes them to escape various stages of wastewater treatment plants, and eventually, they enter our environment.

5 Melanoidin Formation Melanoidins are produced due to the polymerization of reactive species when the Maillard reaction occurs. Different types of chemical processes occur including cyclization, rearrangement, retroaldolization, dehydration, isomerization, and condensation, and thereafter the brown nitrogen-rich polymer and copolymer, known as melanoidin is formed. The molecular weight of coloured compounds increases as browning continues. The complexity of the Maillard reaction has been considerably studied during recent years and new important pathways and key intermediates have been established (Martins et al. 2001). Melanoidins are acidic compounds having a negative charge. When temperature and the reaction time increase, the total C also increases, resulting in the unsaturation of this molecule. The more the degree of polymerization, the more the intensity of colour developed. This amount of pigment formation can be measured

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by determining its optical density at about 420 nm, which then reflects the extent of the Maillard reaction. Hayase et al. showed C3 sugar formation during early browning phases and the compound methylglyoxal dialkylamine was identified. Fay and Brevard (2004) discovered the formation of stable Amadori compounds, (N-substituted 1-amino-1deoxyketoses) during initial Maillard reaction steps. The study showed that these stable class of Maillard intermediates, produced in the initial stages of Maillard reaction, were because corresponding N-glycosyl amines showed Amadori rearrangements. The chemical rearrangement reactions were christened because Mario Amadori was the first person who established this condensation reaction between aromatic amine and D-glucose. This reaction gave rise to structurally different isomers: (i) a labile N-substituted glycosylamine and (ii) stable N-substituted 1amino-1-deoxy-2-ketose. The Maillard reaction may be the source of marine fulvic and humic acid formation where sugars condense with amino acids or proteins. The basic components or building blocks of humic substances are found to be heterocyclic moieties rather than benzenoid structures which are of aromatic nature. The similarity in the formation of C3 imine has been found to be similar to a large extent to the C2 imine formation, as reported by Hayashi et al. (1986). Due to this, there could be an increase in the amount of Amadori products formed as well as a decrease in the amount of glucosylamine. It has been observed in the glucose-nbutylamine system that there is a production of C3 compounds and a similar process increases the C3 compounds by a reaction between n-butylamine and Amadori products. These results showed that the chances of a reaction of Amadori compounds is a possibility which leads to the formation of C3 compounds. A vast amount of research has been reported on the Maillard reaction, yet the mechanism by which melanoidins are formed at the end of the process is obscure. However, the formation of melanoidin through Maillard amino-carbonyl reaction can be clarified by the mechanism proposed in the review mentioned above. One of the major thrust areas of scientific research these days is water pollution control. In general, coloured organic compounds impart only a minor fraction of organic load to wastewaters, but their colour makes them aesthetically unacceptable. Particularly, colour removal has become a major area of scientific interest according to the various related research reports. A number of decolourization techniques have been recorded in the past couple of decades and a few of them have been accepted by some industries also. It is needed to find out cost-effective alternative treatments for removing dyes and colourants from large volumes of effluents, like the biological or integrated systems. Since colour is a visible pollutant, industrial or domestic water should not be possessing colour and should be removed as soon as it appears. Colourless effluents laden with toxic and hazardous pollutants may not be objectionable to the common man but the discharge of even lesser toxic-coloured effluents is often objected by the people owing to the assumption that colour indicates pollution. Therefore, it is not surprising to note that coloured wastewater is now considered to be a pollutant that needs to be treated before discharge. Various colouring agents such as dyes, inorganic pigments, tannins, lignins, etc. usually impart colour. Chemically, more than 8000 different types of dyes are currently manufactured,

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the biggest consumers of these dyes being the textile industries (Rajgopalan 1990), paper and pulp industries, Kraft bleaching, dye and dye intermediates industries, tanneries, pharmaceutical industries, industries which are probably the most potential contributors to the pollution. Among the major adverse effects associated with the discharge of dark colour wastewater into rivers and lakes is the reduction of photosynthetic activity as less sunlight can penetrate into the water. Additionally, the temperature of the water increases leading to lower concentrations of dissolved oxygen.

6 Treatment Technologies for Decolourization of Distillery Effluent Several technologies have been explored for reducing the effect of pollution of sugarcane molasses wastewater. The majority of these methods decolorize the effluent by either concentrating the colour into the sludge or by breaking down the coloured molecules. These treatment technologies are discussed in detail in the following section.

7 Treatments Based on Physicochemical Methods 7.1 Adsorption One of the physicochemical treatment methods is adsorption on activated carbon, widely employed for the elimination of colour and specific organic pollutants. Activated carbon is a well-known adsorbent because of its microporous structure, large surface area, high capacity of adsorption, and large surface reactivity potentials. Earlier studies on decolourization of molasses wastewater constitutes adsorption on commercial as well as indigenously prepared activated carbons (Satyawali and Belakrishanan 2008). Decolourization of synthetic melanoidins using activated carbon made using sugarcane bagasse was compared to decolorization via commercially available activated carbon (Ahmed et al. 2020). The adsorptive capacity of the different activated carbons was found to be quite comparable.

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8 Oxidation Processes This process is mainly initiated through oxidation by ozone, which is used in the treatment of dyes, phenolics, pesticides, etc. because of its ability to destroy hazardous organic contaminants. This method is reported to give 80% decolourization and 15– 25% COD reduction, with enhanced biodegradability of the wastewater. However, ozone can only decolourize the chromophore group and not the dark-coloured polymeric compounds of wastewater. Ozone with UV radiation is reported to increase effluent degradation with respect to COD. Another process of oxidation involves a combination of wet air oxidation and adsorption for the removal of sulphates from the distillery spent wash. Photocatalytic oxidation has also been studied for some time, which uses solar radiation and TiO2 as the photocatalyst, which is very effective and leads to the complete mineralization of effluent to CO2 and H2 O (Almomani et al. 2018).

9 Coagulation and Flocculation Colloids are minute particles that remain apart due to certain forces acting between them. The process of coagulation destabilizes these forces by neutralization. The negative charge or zeta potential on the colloidal particles can be minimized by using cationic coagulants which introduce positive electric charges. This leads to the formation of larger particles, by the collision of particles, called flocs. The flocs help to combine the particles into agglomerates or larger clumps by the action of polymers which act as bridges, and the process is termed flocculation. The aggregation takes place when there is the formation of a bridge between the segments of the polymer chain. The cost of chemicals and the problem of sludge disposal indicates that coagulation is an expensive process.

10 Membrane Treatment Various pilot trials were carried out on distillery spent wash using the process of hybrid nanofiltration (NF) and reverse osmosis (RO) which is a recent study reported by Nataraj et al. (2006). The process of nanofiltration helped to remove the colloidal particles as well as colour. A reduction of 80% and 45% of dissolved solids and chloride concentration, respectively, was also observed with a pressure of 30–50 bar being maintained as optimum for the feed. The removal of colour and COD have been found to be effective by physiochemical methods. The disadvantages of these methods were high operation costs, generation of excessive amount of sludge, which was difficult to dispose of, use of large amounts of chemicals, and sensitivity to variable water input. Looking at the advantages and

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disadvantages of the reported treatment technologies, it can be shown that a single method would not be effective for the complete removal of molasses from wastewater. Thus, different technologies, based on their effectiveness at various stages can be used sequentially to grant an overall comprehensive approach for the treatment of water containing molasses.

11 Biological Methodology-Based Treatment Aerobic or anaerobic treatment of molasses-containing wastewater is practiced widely; a combined methodology also works in many cases, since it involves the advantages of both protocols. Anaerobic method of treatment is more prevalent using special reactor designs with high speed of treatment and they have been employed at pilot level or large-scale level for complete operation. The effluent from anaerobic treatment is then treated aerobically; a plethora of microbes have been explored and employed for aerobic treatment for the safe discharge of the treated effluent. The melanoidin pigment gets removed by the microbial agents during biological treatment after the pigments are concentrated in the sludge. Both partial or complete degradation of colouring agent is possible for the colour molecules. Such methodologies have been discussed in detail in the following section.

12 Anaerobic Digestion The first step for treating spent wash (stillage) is usually anaerobic digestion and is widely practiced. The treatment strategy transforms a major chunk of the COD, i.e. about >50%, in the form of biogas, which then gets utilized as plant fuel. Thus, the energy required for providing aeration in the stirred tank or aerated reactors gets saved during anaerobic treatment. Nowadays, effluent treatment is popularly done using anaerobic methods effective removal of over 90% COD and between 80 to 90% BOD; 85 to 90% biochemical energy may also get recovered because of biogas formation. Although open lagoons can remove BOD to the maximum extent, still the largest amount of biomethane is produced by using a upflow anaerobic sludge blanket (UASB) bioreactor. We have discussed this in detail under the microbial treatment section.

13 Treatment Using Aerobic Means Anaerobic treatment of distillery effluent holds large amounts of organic compounds and these, therefore, cannot be directly discharged. Partially treated effluents have high degrees of COD, BOD, and other suspended solids, which can cause reduced

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availability of important mineral ions to plants. This is because the organic matter traps minerals and immobilize them. These compounds may also become phytotoxic substances while they are being decomposed. Strict rules and regulations with respect to discharging coloured effluent may deter industries from directly discharging the anaerobic-treated effluent having lower COD (Nandy et al. 2002). For these reasons, treatment of effluent using aerobic means is being employed for decolourizing melanoidin and also to reduce the COD and BOD. A wide variety of microbes, e.g. bacteria in pure or mixed forms, yeast, cyanobacteria, and fungi are being discovered with the ability to mineralise and degrade melanoidin pigment in the wastewater, thereby decolorizing this wastewater before discharge. The aerobic methods have been described in the microbial treatment section.

14 Treatment by Activated Sludge Wastewater is commonly treated via the activated sludge method and this area has always attracted immense research targeting improved efficiency and vigour during the treatment process by innovation in reactor configuration and performance. Few studies here show the importance of research. The aerobic SBR (sequencing batch reactor) is a popular and effective solution for the treatment of effluents that are generated by small-scale wineries. These treatment systems included primary settling tanks, followed by an intermediate retention trough, and then a couple of storage tanks, and finally the aerobic treatment tank. An initiation time of about 7 days was provided for aerobic degradation which resulted in about 93% removal of COD along with ~97.5% removal of BOD. Various species of microbes are employed during the activated sludge process, especially mixed cultures are utilized. On the other hand, few researchers believed in the increased effectiveness of pure cultures for enhancing aerobics systems during treatment processes. Aerobic treatment and the conventional activated sludge treatment are widely employed for colour removal and COD removal from spent wash released by molasses-based distilleries. But the protocol is energy inefficient and the pigments do not get satisfactorily removed. Several pure bacterial, fungal, and algal cultures specifically capable of decolorizing melanoidins from stillage/spent wash (wastewater sugarcane molasses distillery) have been studied for developing suitable bioprocesses to degrade melanoidins from the molasses wastewater. It has been observed that fungal decolourization was slower and less efficient due to its prolonged growth cycle and moderate rates of decolourization; bacterial decolourization was generally faster and more efficient. However, it has been reported that mixed communities completely mineralize the melanoidin pigment using a combination of metabolic pathways contributed by the individual strains. Bacterial consortia may be considered a superior choice for wastewater treatment because microbes metabolize or co-metabolize the pigments for gaining energy, thereby enhancing the efficiency of decolourization. There is a disadvantage faced in all studies involving microbial population that adequate supplement of nutrients is necessary and the effluent has

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to be diluted for optimal microbial action and desired results eventually. Therefore, it is necessary to explore other efficient microbes for decolorizing/degrading the effluent such that the microbes can use it as nutrient sources in the raw form, without dilution. Additionally, field or pilot/commercial scale studies should be planned and encouraged, instead of being limited to laboratory-scale investigations.

15 Biocomposting Biocomposting uses aerobic microbes that mediate activated bioconversion via an aerobic pathway, where carbonaceous compounds are broken down by heterotrophic microorganisms. The degradation process and rate depend on the bioavailability of organic sources and inorganic substances that are essential for their growth. Composting is efficient, especially for converting wet substances to forms that are readily taken up by microbes. In the process of doing so, organic materials get stabilized and pathogens or disease-causing organisms are warded off, apart from proper drying of wet starting substances. During the process of composting, carried out under aerobic conditions, the thermophilic degradation of organic waste matter happens at about 40–60% moisture content and results in the formation of relatively stable, humus-like materials (Kannan and Upreti 2008).

16 Other Treatments Some other physicochemical methods applied for treating distillery effluent have been reported by various studies. Applying radiation technology involves combining electron beam treatment and coagulation using Fe2 (SO)3 , resulting in decreased optical absorption in the UV region. Ultrasound technology is also one of the methods for treating distillery spent wash, which enhances the biodegradability of the effluent. Catalytic thermolysis to remove BOD and COD is also reported to be an efficient method. This process is reported to form settleable solid residue with a slurry having significant filtration characteristics. The residue is used as a fuel in combustion furnaces and the ash formed is mixed with organic manure to be used in agriculture. Numerous physicochemical methods including adsorption, coagulationflocculation, oxidation, Fenton’s oxidation, ozonation, electrochemical oxidation using combinations of electrodes and electrolytes, nanofiltration, reverse osmosis, ultrasound, and distinct combinations of these methods are presently being used in the treatment of distillery effluent. However, these methods also come with some drawbacks involving excessive chemical use, sludge formation, high operational cost, and disposal issues (Chaudhari et al. 2008; Pikaev et al. 2001). The figure below shows the various methods used for effluent treatment (Fig. 1).

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Melanoidin degradation

Physico-chemical treatment

Adsorption Coagulation Flocculation Oxidation process Membrane treatment Evaporation Combustion

Enzymatic treatment

Peroxidases Oxidoreductases Cellulolytic enzymes Cyanidase Proteases Amylases

Biological treatment

Anaerobic treatment/Reactors

Aerobic treatment

Bacterial treatment Fungal treatment

Treatment by other microorganisms

Fig. 1 Showing the various methods employed for the treatment of spent wash

17 Microbial Treatment 17.1 Bacterial Systems Bacteria capable of both bioremediation and decolourization of molasses wastewater have been isolated. Different bacterial isolates are employed in decolourization of molasses-based distillery wastewaters. Some of these studies are also discussed in detail in the following section. Five bacterial strains were isolated from sewage and then acclimatized to grow and degrade increasing concentrations of melanoidin from distillery waste. The isolates were made capable enough to be able to decolourize by 80% in 4–5 days, with no supply of air. The products left majorly when the biodegradation process completed was bacterial biomass, carbon dioxide gas, and volatile acids under thermophilic and anaerobic conditions. Strains DP1, DP2, DP3, DP4, and DP5 were isolated from a soil sample and selected as the candidate strains for melanin degradation studies. From taxonomical studies, the DP1 strain belonged to the genus Bacillus, most closely resembling Enterobacter sp. The strain decolorized 60% of molasses pigment within 5 days at 38 °C under anaerobic conditions, and also decolourization was seen when grown in the presence of air. During the experiments under all treatments or melanoidin concentrations tested, the pigment was decolorized effectively by DP1, to above 40% within 2 days. The Aeromonas sp., thereafter reduced the COD by 44% and an algal bioassay then evaluated the spent wash quality prior to treatment and afterwards.

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It was seen that spent wash caused more eutrophication before treatment than after the treatment was over. Typically, the bacterial decolourization might need the supply of mixed cultures for decolorizing molasses-based wastewater, through a combination of metabolic modes of individual strains of bacteria or other microbes. Therefore, mixed culturebased studies for the degradation of different effluents have been reported by many scientists in cases of textile effluents, distillery waste treatment, and so on. Since the catabolic activities of microbes within mixed consortia can complement each other, the syntrophic interaction present within the mixed communities can result in the proper mineralization of effluent.

18 Immobilized Microbes Immobilization is a phenomenon that fixes the cells into a matrix in four different ways including adsorption, entrapment, encapsulation, and covalent binding. a] Adsorption is the physical coordination between the surface of water-insoluble matrix and microbes. The microbes mainly adhere to the matrix surface with the bond formation including hydrogen bonds, ionic bonds, and van der Waals forces. But due to the weak interaction, the rate of leakage from the matrix surface is high in the adsorption method. b] Encapsulation is an irreversible method of immobilization. In this method, the biological material is encapsulated in various spherical membranes with controlled permeability. Encapsulation enhances efficiency and provides protection from leakage. c] Covalent binding is another immobilized technique based on bond formation between cells and inorganic carriers, and d] Entrapment method is mainly based on binding the cells within the matrix. This method is used for immobilizing the microorganism and prevents them from matrix leakage. The entrapment method is very fast and requires moderate conditions for the reaction to take place. Different forms of the matrix can be used for immobilization including alginate, agar, cellulose gelatine, polystyrene, and collagen (Bayat et al. 2015). Microorganisms multiples easily by using a wide range of nutrition with the different environmental conditions and are commonly present everywhere in the habitat (Rahman et al. 2006; Leon et al. 1998). Due to nutrient adaptability, microorganisms can be explored in the area of bioremediation. Bioremediation is a bacterial activity that can treat, utilize, and break down toxic forms into non-toxic forms. Microorganisms play a very important role to protect the ecosystem from toxic contamination. From the research studies, it has been found that immobilized microbes are a very important and promising phenomenon to clean up the contaminant from the air, water, and soil (Stolarzewicz et al. 2011; Argin-Soysal 2004). The activity of microorganism is affected by many factors including temperature, pH, duration, nutrients, moisture, soil structure, pollutant concentration, and the presence or absence of oxygen. Large amounts of wastewater production and their treatment for the removal of hazardous components is becoming the biggest problem. There is much scientific

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evidence that indicates that conventional water treatment can poorly remove toxic components. Conventional methods have adverse effects on microbial communities that exist in water. And the removal of hazardous components become the biggest challenge for scientists (Groboillot et al. 1994; Trelles and Rivero 2013; Gardin and Pauss 2001). Immobilizations of microbes are gaining interest in the field of wastewater treatment. Immobilization is not only restricted to the fermentation industry, but also physically confined to microbes including Alginate, gelatin, cellulose, agarose, polyester, and collagen. Immobilized microbes have been used for the elimination of pollutants, formation of chemicals, and pollutant treatment (Lopez et al. 1997) The immobilized microbes are considered as principle components for bioremediation (Table 1). Immobilizing the degrading strains of microbes within biofilms and upon bio flocs may be considered crucial steps for anaerobic degradation. This is due to the number of advantages of immobilization, e.g. better activity, more effective COD depletion percentage at shorter hydraulic retention period, and also more adaptability or tolerance to impeding effects of toxic or organic loads of waste water. The immobilized system may have other problems when the effluent contains compounds, e.g. phenols, that may be toxic to microbes and cause inhibition of their metabolic pathways. Due to the seasonal variations in these industries and also due to the absence of microbes that are capable of anaerobic degradation, extended time is required to start-up the Table 1 Microorganisms immobilized with different nanomaterials Types of microorganism

Immobilized with nanomaterial

Interact with contaminant

References

Aspergillums niger

Sodium alginate

Hydrocabon, crude oil

Dallago (2015)

Bacillus subtilis

Chitosan-sodium alginate

Oil based paints

Penicillium chrysogenum

Sodium alginate

Toluene, Phenol compounds, Aromatic hydrocarbon, xylene, benezene

Mahendiran et al. (2013)

Industrial dyes

Herrera-ERstrella and Guevara-garcia (2009), Gadd (1986)

Penicillium ochrochloron

Pseudomonas aeruginosa

Multiwalled carbon Heavy metal, copper, nickel, nanotube Textile dye

Bacillus cereus

Calcium alginate

Bacillus coagulan Sodium alginate

Diesel oil Crude oil, diesel oil

Staphylococcus aureus

Metal nanoparticles Textile effluent

Staphylococcus, Enterobacter

Alginate

Pesticides

Pankaj (2012)

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entire process. H2 S gas formation in anaerobic bioreactors results due to the reduction of sulphur compounds. Many environmental factors influence microbes that are involved in wastewater treatment and also speed up or deter the rates of biochemical reactions. The important parameters are availability of nutrients, toxicants, temperature, pH, and dissolved organic load. If the organic load is high, wastewater may be diluted using tap water such that it stands near to typical effluent which can be safely released by a wastewater treatment plant. Sadly, the spent wash normally does not get relieved of its high levels of COD, BOD, solids, etc. even after anaerobic treatment, and thereby falls short of the effluent standards proposed by Central pollution Control Board (CPCB) in India.

19 Nanomaterials for Waste Water Treatment The evolution of nanotechnology has opened a new path for wastewater treatment. Due to their smaller size and high surface-to-volume ratio, nanomaterials include nanocomposites, carbon-based nanomaterials, and oxide-based nanomaterials, and have been explored for the treatment of wastewater (Brady-Estevez et al. 2010). Nanomaterials have strange physical, chemical, and biological properties which enhance their utilization in water treatment areas (Lengke et al. 2006). The fabrication of nanomaterials from microorganisms indicates eco-friendly bioremediation. Bolade et al. (2020) reported that due to the redox potential and non-toxic nature, iron nonmaterial is used for remediation (Table 2). The execution of an immobilized nano-based system for wastewater treatment requires less infrastructure (Qu et al. 2013). For the removal of organic pollutants, heavy metals contaminants, oil, disinfectants, pathogens, and inorganic pollutants extensive range of nonmaterial have been tested (Tiwari et al. 2008; Amin et al. 2014). Due to the economic point of view and competition with conventional wastewater treatment methods, nanotechnology should be controlled and explored properly. The research studies show wide interactions of nanomaterial with a biological system for wastewater treatment along with toxicity effect on the physiological activity of microorganisms (Bhavya et al. 2021; Das et al. 2012; Jain et al. 2006). During the wastewater treatment, nano-based systems play a very important role in membrane biofilm formation and biofouling control. Recently, with the incorporation of nanomaterials including silver nanoparticles, TiO3 , Al2 03 , nano-Ag, and CNTs in ultrafiltration membrane system for the enhancement of thermal and mechanical stability, to increase membrane hydrophobicity to make the membrane fouling resistance, includes Ag-nanoparticles devices named Aquapure and MARATHON system (Elmi et al. 2014; Kiser et al. 2009; Mukherjee et al. 2002). The application of CNTs which has antimicrobial activity included in distribution pipes and storage tank to protect them from corrosion and microbial contamination (Musee et al. 2011; Mohanpuria et al. 2008).

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Table 2 Different nanomaterials used for bioremediation Types of nanomaterials/ nanosorbents

Observations

Target analyte

Application

References

Magnetic NPs

Non-toxic

Organic compounds and heavy metals

Easy to separate and no sludge production

Panda et al. (2021)

Dendrimers

Toxicity depends Organic on surface pollutants, charge and size Heavy metals

No sludge production and easy to separate

Dayana et al. (2021)

TiO2

Toxic at micron sized

Organic pollutants

Insoluble in water Chen and Mao and photostable (2007)

Nanoclay

Non-toxic

Dyes, Hydrocarbons, Anions, organic pollutants, and heavy metals

Higher sorption Salam et al. capacity, stability, (2017) and lower cost

Nanomembranes

Non-toxic

Inorganic and organic substances

Works at low pressure

Kariim et al. (2020), Kumar et al. (2019)

Gold nanorods

Non-toxic

Toxic mercury and trace pollutants like pesticides

High surface area and mesoporous characteristic

Ramkumar 2018, Mahajan et al. 2020

Carbon nanotubes

Becomes toxic when sized exceeds 15 ug/ cm

Anions, heavy metals, and organic pollutants

High chemical stability

Engel (2016)

Metal composite

Time and concentration Dependent

Metal pollutants

Higher selective and metal uptake

Ahmad (2021)

Graphite oxide

efficient and stable

Dyes

Higher surface area, thermal conductivity, chemical stability

Perreault et al. (2015); Kumar et al. (2019)

Nano aerogels

Time and concentration dependent. Poor thermal stability

Uranium

Used in high- and low-temperature environments

Christophe (2020)

Nano iron oxide

Non-toxic

Toxic pharmaceuticals

High adsorption and antibacterial properties

Polymer fibres

Non-toxic

Arsenic and toxic metal

Oil remediation

Micelles

Non-toxic

Organic pollutants

Higher affinity for Shedbalkar and hydrophobic Jadhav (2011)

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20 Conclusion Scientific reports are showing various microorganisms including algae, bacteria, and fungi that are used successfully for the removal of heavy metal pollutants from waste effluent. However, due to scarcity of nutrients, supplements, absences of suitable reactor system, loss of enzymes, microbial treatment for decolorizing and biodegrading the waste material has limitations. To overcome these limitations, scientists explore different nanomaterials along with the microbes for the removal of pollutants from the environment. The research study shows that it is important to screen, identify, isolate, and characterize the microbes to get better results to clean up the environment. In modern technology, scientists progressively exploring nanomaterials to get improved results for bioremediations. Globally, due to increasing drinking water demands, nanomaterials including nanostructure, nanosystem, and nanosorbents are eco-friendly, faster, and more competent for large-scale wastewater treatment. Further, there is a need to develop, synthesize, and formulate the nano-based immobilized system to handle the cost constraints for a commercialized approach for bioremediation.

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Pikaev AK, Ponomarev AV, Bludenko AV, Minin VN, Elizar’eva LM (2001) Combined electronicbeam and coagulation purification of molasses distillery slops. Features of the method, technical and economic evaluation of large scale facility. Radiat Phys Chem 61:81–87 Plavsi´c M, Cosovi´c B, Lee C (2006) Copper complexing properties of melanoidins and marine humic material. Sci Total Environ 366(1):310–319 Qu XL, Brame J, Li Q, Alvarez JJP (2013) Nanotechnology for a safe and sustainable water supply: enabling integrated water treatment and reuse. Acc Chem Res 46(3);834e843 Rahman RNZ, Ghazali FM, Salleh A et al (2006) Biodegradation of hydrocarbon contamination by immobilized bacterial cells. J Microbiol 4:354–359 Rajagopalan S (1990) Water pollution problem in textile industry and control. In: Trivedy RK (Ed) Pollution management in industries,–Environmental Pollution, Karad, India, pp 21–45 Ramkumar J (2018) Nanomaterials as sorbents for environmental remediation. Arch Nano Op Acc J 1(4):71–74. https://doi.org/10.32474/ANOAJ.2018.01.000116 Rani N, Sangwan P, Joshi M, Sagar A, Bala K (2019) Microbes: a key player in industrial wastewater treatment Rivero D, Perez-Magarino S, Gonzalez-Sanjose ML, Valls-Belles V, Codoner P, Muniz P (2005) Inhibition of induced DNA oxidative damage by beers: correlation with the content of polyphenols and melanoidins. J Agric Food Chem Salam MA, Kosa SA, Al-Beladi AA (2017) Application of nanoclay for the adsorptive removal of Orange G dye from aqueous solution. J Mol Liq 241:469–477 Satyawali Y, Balakrishnan M (2008) Wastewater treatment in molasses-based alcohol distilleries for COD and color removal: a review. J Environ Manage 86(3):481–497 Shedbalkar U, Jadhav J (2011) Detoxification of malachite green and textile industrial effluent by Penicillium ochrochloron. Biotechnol Bioprocess Eng 16:196–204 Singh G, Bakshi S, Bandyopadhyay KK, Bose S, Nayak R, Paul D Enhanced biodegradation of melanoidin pigment from spentwash using PDMS-immobilized microbes via ‘repeated addition’ strategy. Biocatalysis Agricu Biotechnol 33:101990 Thakker AP, Dhamankar VS, Kapadnis BP (2006) Biocatalytic decolorisation of molasses by Phanerochaete chrysosporium. Bioresour Technol 97(12):1377–1381 Tiwari PK, Batra VS, Balakrishnan M (2007) Water management initiatives in sugarcane molasses based distilleries in India. Res Conserv Recycl 52:351–367 Tiwari DK, Behari J, Sen P (2008) Application of nanoparticles in waste water treatment. World Appl Sci J 3(3):417–433 Trelles JA, Rivero CW (2013) Whole cell entrapment techniques. Methods Mol Biol 1051:365–374

Application of Nanomaterials in Heavy Metals Remediation from Wastewater Ayushi Singh , Sonal Chaudhary , Ajit Varma , and Shalini Porwal

Abstract In recent decades, the development of new and engaging technologies has resulted in a considerable volume of harmful effluents. Industrial wastewaters from a range of industries are a major source of contamination in bodies of water. Pollutants present in wastewater include organic and inorganic contaminants, heavy metals, and non-dissolving chemicals. The environment is severely harmed by such pollutants. As a result, new and imaginative ways and technology to eliminate them must be explored. Nanomaterials have been suggested as promising pollutant-removal candidates in recent years. A wide range of low-cost nanomaterials with unique characteristics are presently available. In this case, nano-absorbents are excellent materials. Heavy metal contamination is frequent in both subterranean and surface waterways. Heavy metals have recently been the subject of several researches. The utilization of nanomaterials to remediate heavy metals from industrial wastewater has been the focus of this chapter. Keywords Nanomaterials · Wastewater · Heavy metals · Detoxification · Pollutants

1 Introduction Water is one of the most recurrent natural resources on the planet, and it is necessary for all humans’ existence and progress. Water demand is rapidly increasing as a result of fast urbanization and industrialization, and water scarcity has become a pressing issue for developing countries to handle. Various sectors, including battery production, mining, toxins, and electroplating, release a large amount of hazardous effluent. Pollutants in wastewater have a wide range of negative effects on living things and A. Singh · S. Chaudhary · A. Varma · S. Porwal (B) Amity Institute of Microbial Technology, Amity University, Sector-125, Noida, Uttar Pradesh, India e-mail: [email protected]

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_2

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the environment. It turned out to be a more efficient and cost-effective method of treating industrial wastewater. The types of contaminants found in industrial effluent are determined by the manufacturing process. Pollutants found in industrial wastewater typically include excessive amounts of organic compounds, elevated pH levels, dangerous heavy metals, extreme salinity, and increased turbidity due to the presence of inorganic chemical impurities. Industrial wastewater treatment includes adsorption, flotation, chemical precipitation, membrane filtration, flocculation, and coagulation. These wastewater treatments are sometimes inefficient in removing certain contaminants, such as hazardous heavy metals. Wastewater is produced by a variety of sources, including residential, commercial, industrial, and agricultural lands. The composition of wastewater is highly variable, and it is mostly governed by the source from which it is generated. Solutes, heavy metals, metal ions, ammonia, and gases, as well as complex organic compounds such as excreta, plant material, food, protein, natural organic matter, and nitrate found in surface water, groundwater, and/or industrial water, are common constituents of wastewater. Industrial waste is often categorized into two types: hazardous and nonhazardous. Nonhazardous industrial wastes are made from cardboard, plastic, iron, glass, stone, and organic waste and pose no environmental or health risks. Hazardous wastes, on the other hand, are industrial wastes that might harm human health or the environment, such as flammable, biodegradable, and hazardous materials. Industrial waste is divided into three categories: wastewater, solid trash, and air leakage. There is some overlap in the physical qualities of the components present in all three groups since wastewater can contain suspended solids and suspended liquids, and solid waste precipitation can comprise gas, liquid, and some liquids. Particles and air exposures can be made up of a fluid that emits air and a substance called particle emission. Industrial trash with a high percentage of non-recyclable or recyclable metals is usually an excellent candidate for landfill, or garbage disposal in the ground. These elements may constitute harm to living beings and the environment if they are not treated before disposal, hence it is critical to treat wastewater before disposal. For wastewater treatment, a variety of physical, chemical, and biological treatment procedures are used. To date, a variety of studies on nanomaterials have been done to develop applications for heavy metal water treatments, and they show tremendous potential as an irreplaceable choice for adsorbing heavy metals from wastewater. These qualities are highly effective for removing heavy metals from polluted wastewater. Wastewater treatment is divided into three categories based on the type of nanomaterial used: nano-adsorbents, nanomembranes, and nano-catalysts. The following are some of the most prevalent wastewater sources: ● Municipal/domestic wastewater: wastewater discharged from residences, foundations such as schools and medical clinics, and business offices such as retail centres, restaurants, and so on. ● Industrial wastewater: industrial processes that remove wastewater, such as the pharmaceutical, textile, and poultry industries.

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● Infiltration/inflow: water that enters the sewer in the long run through establishment channels, leaking pipes, submerged manholes, groundwater invasion, and other sources. ● Rainfall runoff and snowmelt are examples of stormwater. Nanotechnology was one of the most significant developments of the twenty-first century. Nanomaterials must have a well-organized structure, be capable of filtering, be compact in size, and have a high surface-to-volume ratio. Effects on the surface region, huge quantum tunnel effects, tiny size effects, and quantum effects are some of the unique aspects of nanomaterials at the nanoscale. Nanostructured adsorbents are also employed in wastewater treatment because they are more efficient and react more quickly. Magnetic nanoparticles are being developed for the adsorption of metals and organic molecules are also used to remove industrial contaminants from groundwater, such as bisphenol-A, phthalates, and alkylphenols. Green nanotechnology is a novel word coined in the modern period. Green technology’s major goal is to have as little health and environmental dangers as possible. Nanomaterials are defined as materials with a dimension of 1–100 nm. Nanomaterials are important because of their unique features, such as adsorption, a high surface-to-volume ratio, catalytic activities, and reactivity. Nanomaterials have a large surface area due to their small size, which makes them very compatible. These characteristics add to their unrivalled adsorption capability and reactivity, making them ideal for heavy metal ion removal Basu and Ghosh (2013). Industrial pollution is still a major contributor to the degradation of the ecosystem around us, including the water we drink, the air we breathe, and the land we live on. Industrialization’s expanding power not only consumes enormous amounts of agricultural land, but also causes environmental and land damage (Fig. 1).

2 Silver Nanomaterials Silver nanoparticles, in the form of colloidal silver, are commonly employed. Silver nanoparticles have been successfully employed as antibacterial agents against naturally occurring microbes (Reidy et al. 2013). Silver nanomaterial disrupts vital biological components of microorganisms, resulting in pathogenic microbe mortality. Cell lysis occurs when nanomaterial attaches to the cell membrane. In hospitals, the silver nanomaterial is utilized to purify water for community use. They have been utilized as a replacement for chlorine in filtering (Parthasarathi and Thilagavathi 2009). Silver nanomaterials have the ability to reduce biofouling and act as an effective disinfectant in the elimination of E. coli and other pathogens in sewage and wastewater treatment (Amin et al. 2014). By inserting high porosity filters, Ag nanomaterials can be employed more efficiently (Quang et al. 2013). Silver nanoparticles destroy pathogenic bacteria by causing physical disturbance and oxidative stress to disrupt essential cellular components. They are the most promising for water disinfection since they are cost-effective and have significant antibacterial activity.

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Environment

Electronics

Healthcare

Application of nanomaterials Soil health

Textiles

Agriculture

Biomedical

Fig. 1 Application of nanomaterials in different sectors

Silver nanoparticles generated by chemical reduction were included using PolyEther-Sulphone (PES) microfiltration membranes, and the microorganisms present near the membrane were not active enough (Ferreira et al. 2015). The standard for silver in drinking water set by the Environmental Protection Agency (EPA) and the World Health Organization (WHO) was higher than the silver loss from silver nanoparticles (Dankovich and Gray 2011).

3 Carbon Nanomaterials Carbon nanoparticles, which are made from the most abundant element carbon, are widely utilized in water filtration. Carbon nanoparticles have the ability to regenerate, allowing the adsorption capacity of spent carbon to be regenerated and the cost-effectiveness of activated carbon to be determined. However, some adsorption capacity will be lost during regeneration (Dhermendra et al. 2008). The discovery of the first fullerene in 1985 ushered in a new era in carbon nanotube (CNT) synthesis (Kroto et al. 1991). The first carbon nanotube (CNT) was created in 1991 (Iijima 1991). Carbon nanotubes (CNTs) are made from graphite by arc discharge, laser ablation, or chemical vapour deposition from carbon-containing gas. CNTs have attracted

Application of Nanomaterials in Heavy Metals Remediation …

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a lot of attention in recent years because of their hydrogen bonding, hydrophobic interactions, ion exchange, and electrostatic interactions with wastewater contaminants. Because of their exceptional adsorption of organic and inorganic contaminants, researchers are now focused on incorporating CNTs into a variety of devices. Carbon nanotubes (CNTs) are made from graphite by arc discharge, laser ablation, or chemical vapour deposition from carbon-containing gas. CNTs have attracted a lot of attention in recent years because of their hydrogen bonding, hydrophobic interactions, ion exchange, and electrostatic interactions with wastewater contaminants. Because of their exceptional adsorption of organic and inorganic contaminants, researchers are now focused on incorporating CNTs into a variety of devices. CNTs have been found to be effective sorbents for a variety of polar and nonpolar organic chemicals, including 1,2- dichlorobenzene, atrazine, butane, Dichloro Diphenyl Trichloroethane (DDT), dioxin, peptone, and a-phenylalanine, and other polar and nonpolar organic chemicals. The use of synthetic CNT-based membrane filters with hollow cylinders and radially aligned CNT walls to remove bacteria and viruses from contaminated water has proved successful (Srivastava et al. 2004). Heavy metals discharged into the aquatic environment and absorbed in living tissues must be removed from the water, which can be done with multi-walled CNTs whose adsorption capability can be improved by oxidizing them with nitric acid (Sayes et al. 2004). CNTs have a high sorbent capacity for organic chemicals like polycyclic aromatic hydrocarbons, phenolic compounds, endocrine disruptors, and antibiotics (Yang et al. 2012). CNTs have good mechanical strength, high sorption capacity, and hydrophilicity for some pharmaceutical chemicals such as diclofenac sodium and carbamazepine, and these compounds can be destroyed during the regeneration process (Wei et al. 2013). CNTs are sometimes mixed with other metals to improve their properties, resulting in an increase in the amount of oxygen, nitrogen, or other groups on the surface of CNTs, which improves their dispersibility and increases their specific surface area (Adeleye and Keller 2014). The interstitial gaps and grooves in CNTs provide high adsorption sites for organic molecules, and CNT bundles with bigger pores have a high adsorption capacity for bulky organic compounds (Ji et al. 2009). CNTs are better adsorbents for heavy metals because of their short intraparticle diffusion distance and readily accessible adsorption sites (Li et al. 2003a) (Table 1).

4 Titanium Dioxide Nanomaterials TiO2 nanomaterials, which are less expensive than other nanomaterials, are now employed to remove many sorts of pollutants from wastewater. TiO2 nanoparticles have a number of advantages, including high photosensitivity, availability, nontoxicity, and environmental friendliness (Carp et al. 2004). Humans are less hazardous to TiO2 nanomaterials, which produce photocatalytic reactive oxygen species. TiO2

26 Table 1 Wastewater treatment using different nanomaterials and their target analyte

A. Singh et al.

Nanomaterials

Treatment mechanism

Target analyte

Titanium dioxide

Photocatalysis

Pollutant (organic)

Iron

Reduction and adsorption

Pollutants (organic), heavy metals, anions

Nanoclay

Adsorption

Pollutants (organic), heavy metals, anions

Nanotube

Adsorption

Pollutants (organic), heavy metals, anions

Dendrimers

Encapsulation

Pollutants (organic), heavy metals

Micelles

Adsorption

Pollutants (organic)

Nanofiltation and nanomembranes

Nanofiltration

Inorganic and organic substances

can be used to create nanotubes and nanowires. TiO2 has an antagonistic action at concentrations ranging from 0.1 to 1 gm in 1 L (Ibhadon and Fitzpatrick 2013). ● Metal Organic Chemical Vapor Deposition (MOCVD) can be used to make titanium dioxide ● Process of Sol–Gel ● Precipitation of hydroxides from salts for wet chemical synthesis. TiO2 nanowire membranes can be used for photocatalytic oxidation as well as filtration of organic contaminants. The TiO2 microsphere, a new form of a catalyst made using a sol spraying calcination process, settles quickly in its aqueous suspensions under gravity. These TiO2 microspheres were found to be effective in photodegrading salicylic acid and sulfosalicylic acid, and they were said to have a lot of potential for wastewater treatment (Li et al. 2003b). TiO2 also has a high oxidative potential, as well as being biologically and chemically inert. Under the impact of solar and artificial light, many organic pollutants such as insecticides, dyes, polymers, and phenolic contaminants have been destroyed by photocatalysis employing nanosized TiO2 (Ahmed et al. 2011). TiO2 requires ultraviolet radiations for excitation in order to induce charge separation inside the particles. Because TiO2 has such poor selectivity, it may destroy a wide range of contaminants (Ohsaka et al. 2008). Metal doping has been shown to improve the photocatalytic activity of TiO2 , with silver attracting the most attention for doping (Mu et al. 1989). Doping with anions, on the other hand, is thought to be more cost-effective and ideal for industrial applications (Fujishima et al. 2008). TiO2 nanoparticles have the ability to adsorb metals such as Pb, Cd, Cu, Zn, and Ni at pH 8 (Engates and Shipley 2011), according to Engates and Shipley. Visible light-triggered TiO2 nanoparticles have received a lot of attention in

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Table 2 TiO2 nanomaterial in different pollutants removal Nanomaterial

Target analyte

Photocatalyst dose

Remediation efficiency

References

TiO2

Nitrobenzene

0.1 M

100

Mansoori et al. (2008)

TiO2

Methyl orange

3 g/L

100

Mansoori et al. (2008)

TiO2

Rhodamine 6G

0.1% (w/w)

90

Mansoori et al. (2008)

TiO2

Parathion

1000 mg/L

70

Zhang et al. (2006)

TiO2

Benzene

5g

72

Chuang et al. (2008)

TiO2

Phenol

1.8 g/L

TiO2

Rhodamine B

TiO2

100

Mansoori et al. (2008)

50 mg/50 ml

97

Mansoori et al. (2008)

Toluene

5g

71

Mansoori et al. (2008)

TiO2

Basic dye

1.22 g/L

80

Wu et al. (2006)

TiO2

4-chlorophenol

25 mg/100 ml

99

Shah (2020)

TiO2

Procion red MX-5B

(2 mg) TiO2 (30%)

98

Shah (2021)

the previous decade (Asahi et al. 2001). For example, mesoporous materials degrade organic substances when exposed to visible light. It has been revealed that Au/TiO2 nanocomposite microspheres exist (Wang et al. 2012) (Table 2).

5 Iron Nanomaterials In wastewater treatment, iron nanoparticles are commonly employed. The majority of the therapy done using iron nanoparticles is based on a reductive dehalogenation process. Nanoparticles of iron are inexpensive, and when they react with pollutants, they turn into hydroxides, which act as flocculants. Contamination removal, both inorganic and organic (Klacˇanová et al. 2013). The hydrophobic membrane that surrounds the zinc nanomaterial acts as a protective covering for it, as it would otherwise react with impurities and reduce the nanomaterial’s capacity (O’Hara et al. 2006; Paek et al. 2006). As a solid sorbent, iron oxide nanomaterials with a large surface area and strong reactivity bond with solid and colloidal contaminants in water. When elemental iron is combined with a metal catalyst such as nickel, palladium, or platinum, a bimetallic nanomaterial is formed, which improves the redox reaction kinetics (Zhang and Elliot 2006; Fu et al. 2006). Depending on the mobility of the

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contamination, iron nanoparticles can be utilized to treat it. Mobile contaminations and immobile contaminations can both be treated using iron nanomaterials. Mobile iron is employed for static pollutant bodies and is directly injected upstream for treatment (Crane and Scott 2012). Some pollutants, such as Ar(III/V), U(VI), and Se(VI), can be lowered to a lower oxidation state when immobilized on an iron surface (Crane et al. 2011). Fe0 can be oxidized by H2O or H+ in anaerobic settings, resulting in Fe2+ and H2, which can be employed as possible reducing agents for pollutants (Wang et al. 2014). Adsorption, reduction, precipitation, and oxidation by iron nanoparticles have efficiently removed halogenated organic chemicals, nitroaromatic compounds, metalloids, and inorganic anions such as phosphates and nitrates.

6 Iron Oxide Nanomaterials The use of iron oxide nanoparticles in wastewater treatment has drawn interest due to its high sorption capacity, ease of operation, resourcefulness, and availability. The most frequent silver oxides are maghemite and nonmagnetic hematite (Cornel and Schwertmann 1996). Magnetism, an unusual property that aids in water filtration, can impact the physical properties of pollutants in water. When magnetic separation is combined with adsorption, it has been widely applied in water treatment and environmental remediation (Ambashta and Sillanpää 2010). Various ligands, such as Ethylene Diammine Tetraacetic Acid (EDTA), L-glutathione, mercaptobutyric acid, and meso-2,3-dimercaptosuccinic acid, are used to improve the adsorption capacity of iron oxide nanoparticles (Warner et al. 2010). The magnetic characteristics of iron oxide, together with adsorption performance, could provide a promising method to wastewater treatment. When compared to other conventional approaches, the physical, chemical, and magnetic features of iron oxide nanoparticles make it a more efficient and cost-effective solution (Babel and Kurniawan 2003). By absorbing visible light, iron oxide nanoparticles can operate as a good photocatalyst. The photocatalytic activity of iron oxide nanoparticles is responsible for the formation of electron-hole pairs through the small band gap (Bandara et al. 2007). The photodegradation of Congo red dye by iron oxide nanoparticles synthesized by thermal evaporation and co-precipitation is an example of photocatalysis for safe and effective wastewater treatment (Khedr et al. 2009). Iron oxide nanomaterial can also be used for immobilization. Because of their chemical inertness and favourable biocompatibility, iron oxide nanomaterials have been widely employed in immobilization techniques (Sulek et al. 2010). The mechanism of contaminant removal by iron oxide nanoparticles is explained by many phenomena such as electrostatic interaction, selective adsorption, ligand combination, and surface binding. Adsorption occurs for both inorganic and organic pollutants via a surface binding mechanism in which the contaminants diffuse into the adsorbent or are adsorbed for further interaction. Iron oxide nanomaterials have been demonstrated to be a highly promising substrate when combined with biotechnology (Dinali et al. 2017).

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7 Conclusion Because of population growth, extended droughts, climatic changes, and other factors, water security is crucial in many significant areas of the universe. According to the literature review, wastewater or water treatment with nanomaterials is becoming a popular research topic. Water makes our planet better when compared to other planets. However, the general availability of pure water is a factor in the current and unsurprising demand for water. In many parts of the world, drinking water resources are insufficient to meet household developmental, fundamental, or basic needs. There is a dearth of pure water in some areas to meet the basic demand for sanitation, and human water needs are clearly a breaking point in terms of human and other animal well-being. Academics, research institutes, research fellows, and young scientists must find a new approach to break free from these limitations. This universe faces numerous challenges in doing so, particularly in light of a changing and environmentally conscious future; population growth is driving community expansion, globalization, and urbanization. Nanomaterial treatment for water contaminants is growing more popular, and it is dramatically improving in this advanced time due to the world’s dire water and freshwater shortages. Nanomaterials have a wide range of physical and chemical properties, making them good candidates for water purification. The type of nanomaterial used for wastewater treatment is determined by factors such as location, availability, practicality, and economic conditions. Nanomaterials solve the challenges that old and conventional methods encounter by providing cost-effective, environmentally sustainable, and time-saving solutions. Nanomaterials can be used as sorbents to remove heavy metals at high concentrations with good selectivity. Because of these characteristics, they are useful in therapeutic technologies. Nano remediation can be used to clean up larger contaminated locations, which minimizes cleanup time and contaminant concentration. Metal oxide-containing nanomaterials are useful tools in biosensors and biosorbents because they act as immobilization carriers. Nanomaterials have the ability to identify diseases and other newly identified chemicals in wastewater by acting as sensors due to their size and other features. Nanocomposite materials are another application of nanomaterials that benefits both the host and the nanomaterial. Polymers, biopolymers, activated carbons, and minerals can all operate as hosts, allowing loaded nanomaterials to be more stable and dispersed. More research is being done to better understand the interaction between immobilized nanoparticles and their hosts, as well as to construct multifunctional nanomaterials. Nanomaterials are particularly promising for wastewater treatment, given the present rate of development.

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Yang Y, Wang H, Li JX, He BQ, Wang TH, Liao SJ (2012) Novel functionalized Nano-TiO2 loading electrocatalytic membrane for oily wastewater treatment. Environ Sci Technol 46(12):6815– 6821 Zhang WX, Elliot DW (2006) Applications of iron nanoparticle in groundwater remediation. Remediation 16(2):7–21 Zhang YZ, Wang X, Feng Y, Li J, Lim CT, Ramakrishna S (2006) Coaxial electrospinning of (fluoresceinisothiocyanate-Conjugated bovine serum albumin)-Encapsulated poly (ε-caprolactone) nanofibers forsustained release. Biomacromolecule 7:1049–1057

Application of Metallic Nanoparticles for Industrial Wastewater Treatment Ardhendu Sekhar Giri, Vishrant Kumar, and Sankar Chakma

Abstract Most of the time, the water discharged from several chemical and process industries is contaminated by varieties of organic pollutants like dyes, pharmaceutically active compounds, pesticides, etc. The toxic heavy metals and other impurities present in wastewater cause multiple issues in the aquatic environment. A huge amount of contaminated wastewater has been discharged from several manufacturing processes without proper supervision. Depending upon the different manufacturing processes, the typical contaminants are originated and mixed in industrial wastewater. Organic pollutants having severe pH, high salinity, toxic heavy metals, and high turbidity in the presence of inorganic impurities are found in industrial wastewater. In the field of environmental science and engineering, metallic nanoparticles (NPs) are considered as new functional materials with the ability to enhance wastewater treatment. Water purification is recognized as a significant area in terms of the applications of nanotechnology. The synthesis of nanomaterials with different characteristics is one of the important attributes of such an application. The development of nanomaterials based on different processes for the remediation of environmental pollutants is a challenging area due to the toxic nature of these contaminants. Many technology inventors suggested that several cost-effective methods for the removal of harmful contaminants present in water can be improved by nanotechnologies. The excellent characteristics of nanomaterials resulting from superior catalytic activities, nanoscale size, and adsorption properties as well as high reactivity have been the subject of active research and development globally in recent years. In this chapter, the different types of nanocatalysts and their engineering applications for developing a sustainable environment have been described. Keywords Wastewater · Industrial effluent · Nanomaterials · Advanced oxidation processes · Photocatalysis A. S. Giri (B) · V. Kumar · S. Chakma (B) Department of Chemical Engineering, Indian Institute of Science Education and Research, Bhopal 462066, Madhya Pradesh, India e-mail: [email protected] S. Chakma e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_3

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1 Introduction Water is the most useful and important natural resource for living beings on the earth. However, water scarcity has been observed in the last few decades due to continuous urbanization and climate change. The ground and surface water are also contaminated due to the constant accumulation of pollutants like pathogens, heavy metals, organic and inorganic materials, or other contaminants originating from different sources generated because of improper treatment (Crane and Scott 2012). As a result, the whole ecological system is affected. Hence, there is a constant need for advanced, effective, and economical water treatment processes, especially for drinking purposes as the most important generous goal, which is still a major challenge for the twenty-first century. This challenge has been mitigated due to the use of extraordinary water resources, and recycling of industrially contaminated water has developed into a new form of water resources. Limitations of traditional water and contaminated water treatment technologies meet up adequate water quality and supply to the environment and human needs within their limit (Feldmann et al. 2008). The present condition demands developing varieties of modern technologies to produce clean and affordable water after the treatment of harmful pollutants that may cause numerous diseases to human beings or in the aquatic environment (Liang et al. 2005). To assist water problems that are to be solved by different technical challenges and need to improve processes gained from nanotechnology that gives us new opportunities to develop skills (Liu et al. 2008). Nanomaterials are generally 100 nm in diameter having one or more dimensions. Several materials as a result show unique and outstanding properties in terms of their strength, conductivity, rate of reactivity, and electricity increase significantly (Bai et al. 2020). These nanoscale materials with newly discovered properties have set up amazing areas of study in terms of enhancing the water quality and health. The use of nanotechnology shows not only its ability to overwhelm the different challenges associated with traditional expertise for the treatment of contaminated water but also discover the novel technology for the treatment of industrially contaminated water in respect of financial feasibility and its reuse. In this chapter, we have discussed the recent advances in the field of application of nanotechnology for industrial wastewater treatment. The use of nanomaterials for treating polluted water is significantly discussed based on their economical processes. Likewise, the application of nanotechnology is associated in terms of wastewater treatment.

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2 Modern Application of Nanotechnology in Decontamination of Water Many recent advances have been developed on different NPs (bioactive nanoparticles, nano-sorbents, nanostructured catalytic membranes, nanocatalysts, and molecularly imprinted polymers (MIPs)) and have been used for eliminating varieties of organic, inorganic solutes, and toxic metal ions from industrial wastewater as shown in Fig. 1. Nanoparticles (NPs) have potential applications for water treatment and have significant potential to overcome the current challenges of the present situation (Crane and Scott 2012). NPs show size-dependent properties like higher adsorption capacity, high reactivity, and higher dissolution activity due to a higher surface-tovolume ratio that can be used for treating the contaminated water discharge from the different local industries without proper supervision. In addition to that, some other unique properties of NPs such as quantum captivity, superparamagnetic and semiconducting properties also influence the catalytic efficiency for improvement of the water treatment process. Figure 2 shows the pathways for the origin of drugs and their metabolites in the environment (Feldmann et al. 2008).

Fig. 1 Nanotechnology and its engineering application in water treatment

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A. S. Giri et al. Human being Drugs Waste

Elimination on Hospitals and Private Households

Veterinary Drugs

Drug Industries and medications

Fish Dairy farm

Drugs for MedicinalThera py

Contaminated water

Fertilizer, Composts

Adsorbed sludge

Soil

Surface Water

Drinking Water

Groundwater

Fig. 2 Different pathways for the origin of drugs and their metabolites in the ecosystem

2.1 Carbon Nanotubes (CNTs) in Wastewater Treatment The carbon nanotubes (CNTs) may eventually transform the future in the areas of nanotechnology due to their smooth cylindrical-shaped macromolecules with a small radius in the range of nm and a length in the range of μm (Iijima et al. 1991; Bethune et al. 1993). The wall surfaces of these CNTs are made of carbon atoms with a hexagonal lattice enclosed by fullerene-like shapes. Apart from this, another reason for the effectiveness of CNTs in water treatment is the presence of highly active sp2 orbital carbon sites that interact strongly with aromatic rings containing organic pollutants (electron-donor property) via π–π and van der Waals interaction mechanisms. CNTs also inspire innovative applications apart from their physical, chemical, electrical, and structural properties for focusing on the water pollution problems. CNTs established new fields of nanotechnologies, especially in water treatment applications like catalysts, adsorbents, filters, or membranes. CNTs get accumulated in the aqueous phase due to their hydrophobicity in nature and promote the adsorption process of organic molecules onto their surface. As very powerful adsorbents, this property of CNTs has attracted a lot of attention to the removal of different organic compounds from water. For example, polynuclear aromatic hydrocarbons (PAHs), chlorobenzenes and chlorophenols (Peng et al. 2003; Cai et al. 2005), herbicides such as sulfur derivatives (Zhou et al. 2006), phthalate esters, dioxin (Long and Yang 2001), DDT and its metabolites (Zhou et al. 2006), PBDEs, trihalomethanes (Cai et al. 2005), bisphenol A and nonylphenol, dyes (Fugetsu et al. 2004), pesticides (thiamethoxam,

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imidacloprid, and acetamiprid) (Zhou et al. 2006), atrazine (Zhou et al. 2006), and dicamba (Biesaga and Pyrzynska 2006). Functionalized CNTs have been used for the copolymerization process with crosslinked nanoporous polymers and showed a very high adsorption–desorption capacity for a variety of organic pollutants like nitro-phenol and trichloroethylene (Salipira et al. 2007). However, a purification technique is also required to remove the unbind amorphous carbon particles from the surface of the CNTs to improve the adsorption capacity (Gotovac et al. 2006). The cylindrical external surface of the CNTs shows higher active sites for effective adsorption and it was also found to have no inner cavity, as well as inter-wall space of CNTs that, contributed to adsorption purpose (Yang and Xing 2007). However, adsorption–desorption hysteresis can be observed in the case of fullerene (a spherical hollow shape allotrope of carbon) but it is irreversible (Yang and Xing 2007). Typically, nanosized metal oxides (Pacheco et al. 2006) and natural nanosized clays (Yuan and Wu 2007) are mainly used for metal removal and their corresponding inorganic ions from the aquatic environment. Hydroxylated and oxidized CNTs are also good adsorbers for the detection of metal ions such as Pb (Li et al. 2006), Cu (Liang et al. 2005), Ni (Lu and Liu 2006), and Cd (Liang et al. 2004), which are very commonly detected in contaminated water discharged from different industries. The perfect multi-walled CNTs can also be used for the adsorption of organometallic compounds that were found to be tougher than the CNTs containing carbon black (Munoz et al. 2005). Several studies have reported using modified CNTs for the removal of heavy metals including Cd (Vukovic et al. 2010), Cu (Li et al. 2010), Ni and Sr, Pb (Vukovic and Marinkovi 2011), Cr (Atieh 2011), Ur (Schierz and Zanker 2009), and a mixture of metal ions (Cu, Zn, Cd, and Ni) (Salam et al. 2011) from different industrial contaminated water.

2.2 Metal Nanomaterials and Their Uses for Industrial Wastewater NPs produced by the combination of different metal–metal oxides are used largely for removing different metal ions from industrial wastewater. Metal nanoparticles are predictable components in bioremediation, notably in contaminated water, due to their faster rate of kinetics, flexibility for modification, and high rate of adsorption ability in both in-situ and ex-situ applications (Ajith et al. 2021). Fe2 O3 withmetal oxides include nanosized (Feng et al. 2012), MgO (Gao et al. 2008), Ag NPs (Fabrega et al. 2011), TiO2 (Luo et al. 2010), CuO (Goswami et al. 2012), CeO (Cao et al. 2010) and providing superior surface area and specific affinity. The low solubility of these oxides made them environmentally friendly for the removal of common metals and also produces less/no secondary pollution. Aggregated metal oxide NPs are used to

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elucidate the feasibility of arsenate removal by packed bed columns from water (Hristovski et al. 2007). Batch experiments were performed with 16 commercial nanopowders (Fe2 O3 , ZrO2 , TiO2 , and NiO) in four water matrices, which were selected based on well-fitted parameters obtained from Freundlich adsorption isotherm kinetics to establish the highest level of arsenate removal from contaminated water in the environments. Singh et al. (2011) explored that porous ZnO NPs remove several toxic metal ions like Hg2+ , Cu2+ , Co2+ , Ni2+ , Cd2+ , Pb2+ , and As3+ originated from industrially contaminated water. It was reported that ZnO nano-assemblies show deeper attraction towards Pb2+ , Hg2 , and As3+ ions due to their high electro-negativity, and they show signs of better removal efficiency (64% Hg2+ , 98% Pb2+ , and 97.5% As3+ ). Also, several reports have been reported on magnetic oxides as nanoadsorbents, especially Fe3 O4 , which is used for the removal of various toxic metal ions from industrial wastewater, such as Pb2+ , Ni2+ , Cu2+ , Cr3+ , Cd2+ , Co2+ , Hg2+ , and As3+ (Zhao et al. 2010; Wang et al. 2012; Liu et al. 2008). The adsorption efficiency of different transition series metal ions by Fe3 O4 NPs is not only dependent on pH and temperature but effectively also on the amount of the adsorbent and the growing time (Shen et al. 2009).

3 Wastewater Treatment Using Photocatalysis In the presence of a catalyst, stepping up of a photoreaction is referred to as ‘Photocatalysis’. A photocatalyst during the chemical reaction gets consumed or does not change itself. Photoreaction is initiated by solar or UV light that is absorbed by the substrates like homogeneous or heterogeneous catalysts. The organic pollutants are degraded in the presence of UV light-assisted photo-catalyst and transformed into non-toxic products such as H2 O, CO2, and other inorganic products. The photocatalytic activity changes with the ability of the catalyst to generate electron–hole pairs in a photo-generated catalytic reaction which produces hydroxyl radicals (• OH) and degrades pollutant molecules present in the wastewater through different secondary reactions as shown in Fig. 3. These pretreatment techniques have been used for toxic and non-biodegradable contaminants to enhance their biodegradability. As a refining step, photocatalysis can also be used to treat typical recalcitrant organic pollutants. The rate of kinetics for the cleavage of different pollutants present in industrial wastewater is generally found due to limited light intensity and photocatalytic activity, which are the major obstacles to its broad application. SiO2 , TiO2 , ZnO, WO3 , CdS, ZnS, SrTiO3 , SnO2, and Fe2 O3 can be used as photocatalysts. The most commonly used nanomaterials as photocatalysts are presented in Table 1 with their bandgap energy. Xu et al. (2012) have suggested that nanomaterials show different behaviors in terms of their mechanical, chemical, electrical, magnetic, optical properties, and distinct quantum effects as compared to their bulk form. As a photocatalyst, nanomaterials have recently achieved excellent interest from researchers. The mechanism

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Fig. 3 General mechanism for the degradation of toxic pollutant degradation through nanophotocatalysts

Table 1 Various photocatalysts and their bandgap energy (Bhatkhande et al. 2002)

Photocatalyst

Bandgap energy (eV)

Photocatalyst

Bandgap energy (eV)

TiO2 (rutile)

3.0

TiO2 (anatase)

3.2

Si

1.1

ZnO

3.2

Fe2 O3

2.2

SrTiO3

3.4

SnO2

3.5

CdS

2.4

ZnS

3.7

α–Fe2 O3

3.1

WO3

2.7

WSe2

1.2

for any photocatalytic reaction is associated with the following five basic steps (Bai et al. 2020): • • • • •

Diffusion of contaminants to the photocatalyst surface. Adsorption of impurities/contaminants on the photocatalyst surface. The reaction of adsorbed contaminants. Desorption of products from the photocatalyst surface. Removal/diffusion of products from the photocatalyst surface.

3.1 TiO2 Nanomaterials as Photocatalyst In heterogeneous photocatalytic processes, TiO2 is mostly preferred material due to its good photoactive behavior and high level of non-toxic nature, large bandgap, and stability. Many reports have been published based on the photo-absorption and photocatalytic properties of TiO2 in the presence of UV light (Pang and Abdullah

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2013). At different temperatures stated to be at 150 °C, the photocatalytic activity of TiO2 was explored for showing its highest activity towards the decontamination of water (Xie et al. 2010). Both surface modification of the crystalline structure of a few rare-earth metal ions (e.g., Nd, Gd) and doping with different transition metal ions like Ag, Fe, Bi, and V could enhance the photocatalytic activity of TiO2 , as they could significantly affect both the rate of interfacial electron transfer and charge carrier recombination (Li et al. 2010). As an efficient catalyst, Fe-doped TiO2 NTs have been used to decontaminate the real industrial/textile wastewater containing a mixture of organic dyes including both disperse and reactive dyes as compared to TiO2 , NTs, and TiO2 powder (Pang and Abdullah 2013). The improvement of photocatalytic activity of TiO2 doped with different nonmetals such as C, S, N, and B under visible light has also been depicted in the literature (Liu et al. 2012). Under visible light, a complete photo-degradation of methylene blue after 120 min has been reported in the presence of carbon self-doped TiO2 sheets (Cheng et al. 2012). Ju et al. have also explored a higher catalytic activity with 3–5% N– and S–doped TiO2 NPs for the degradation of methyl orange at pH 4.0 under solar light irradiation.

3.2 Nanomaterials for the Membrane to Improve the Efficiency Typical physical separation techniques followed by biological treatments have been used for the removal of suspended particles and dissolved pollutants or other contaminants present in industrial wastewater. In addition to these, many evaporative techniques have also been used for the same. Membrane separation as an alternative technique for selectively permeable barriers, with different pore sizes, is used to treat the wastewater by passing the water molecules through the pores. But a wide range of particulate is required to dissolve the mixtures, depending on their nature. The membrane filtration processes based on the membrane pore sizes are grouped according to the size of the particles they can retain. The details of the different membranes with their specification are presented in Table 2. However, the efficacy of many membranes can be improved by improving the flux or by decreasing membrane fouling. One of the best techniques to improve membrane efficiency is by introducing nanoparticles with antifouling and antimicrobial properties. This process can increase selectivity and flux (by increasing hydrophobicity). A coupled application of membranes with different NPs can thus decrease the energy requirement and the use of chemicals that are used in membrane cleaning purposes and optimize the cost issues. To improve the membrane performance, it can be functionalized with NPs and this method is moderately new. Several different conditions have been employed to explain different technologies like NPs-enhanced, nano-enhanced, nano-activated, nano-functionalized membranes, and so on. However, to prevent any ambiguity, the terminology should be normalized. Recent studies have focused on membrane

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Table 2 Different types of membranes and their characteristics Filtration type

Particle size

Contaminants removed

Operating pressure ranges

Microfiltration (MF)

0.1–10 μm

Bacteria and suspended particles 0.2–2.0 bar

Reverse osmosis (RO)

Ca. 0.0001 μm Impurities, including monovalent 20–120 bar ions

Ultrafiltration (UF)

Ca. 0.003–0.1 μm

Colloids, polysaccharides, proteins, most bacteria, and viruses

1–4 bar for cross-flow, 0.2–0.4 bar (dead-end and submerged)

Nanofiltration (NF)

Ca. 0.001 μm

Natural organic matter, multivalent ions associated with the hardness of water

5–25 bar

nanotechnology for the synthesis of NPs surrounded by different inorganic or polymeric membranes for multifunctional purposes. For multifunctional applications like photocatalytic activity (e.g., bimetallic NPs, TiO2 , ZnO), antimicrobial activity testing (for example, nano-Cu and CNTs), these functional nanomaterials are generally synthesized by metal oxide NPs (e.g., TiO2 , Al2 O3 and zeolite). The main objective using of NPs in the membrane is to prevent the membrane from fouling and need to improve water permeability by enhancing the hydrophilic nature of metal oxide. In the field of photocatalytic reactions, membranes have also special attention due to their rapid application towards the degradation of organic contaminants under solar/UV light and their continuous discharge in industrial wastewater without loss of nano-photocatalyst. Different nanomaterials have been used to prepare the photocatalytic membrane. The TiO2 /Al2 O3 composite membranes supported on polymer and metallic membranes (Kim et al. 2003) and doted polymer membranes containing TiO2 particles entrapped membranes were studied for wastewater treatment (Molinari et al. 2004). However, membranes used in the various photocatalytic reactions may conflict with various scientific problems such as lesser photocatalytic activity, deterioration of membrane structure, and loss of deposited TiO2 layer over a long time. Different types of polymeric membranes have been integrated with the monoor bi-metallic catalysts such as nano-sized zero-valent iron (nZVI) and noble metals supported on nZVI for the degradation of chlorinated contaminants (Wu et al. 2005).

3.3 Antimicrobial Activity of Metal/Metal Oxide Nanomaterials The microbial-contaminated water is also a major threat to public health. With the development of microorganisms resistant to multiple antimicrobial agents, there is increased demand for improved disinfection methods (Barnes et al. 2006). In the field of current innovations in nano-biotechnology, the ability to prepare nanomaterials

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with a specific size and shape is expected to be used for the improvement of sterile agents in the field of industrial wastewater treatment. Materials show an efficient and responsible tool for improving biocompatibility with their reduced size (Kim et al. 2007). Due to the size of comprising particles with nanoscale dimensions, the biological activity of a variety of NPs changes. The particle size of NPs and their antibacterial activity affected the operating behaviors and are mostly associated with killing the bacteria or slowing down their growth.

3.3.1

Ag Nanoparticles

Silver nanoparticles (AgNPs) make themselves an excellent candidate for a few daily activities due to their unique physical and chemical properties, and their antimicrobial and anti-inflammatory properties for various purposes in the therapeutic field. Nevertheless, many studies have reported that nano-silver can apparently improve the environment and help in developing sustainability (Panyala et al. 2008). AgNPs have broad-spectrum antibacterial actions and are non-toxic in nature even at low concentrations in the human body (Baker et al. 2005). It has been explored that both Ag-based compounds and Ag+ ions are found to be toxic and possess strong biocidal effects on different species of bacteria that are present in different industrial water (Lara et al. 2010). Rai et al. (2009) suggested that AgNPs are effective for broad-spectrum biocides against a variety of drug-resistant bacteria, which makes them a potential candidate for the application in pharmaceutical products originating from different drug industries. AgNPs may help to prevent the transmission of drug-resistant pathogens in different clinical environments (Yamanaka et al. 2005). Recently, many hybrids of AgNPs showed an effective antimicrobial surface coating agent property with different amphiphilic macromolecules (Aymonier et al. 2002). AgNPs can be a powerful bactericidal agent even at extremely low concentrations (Mishra and Kumar 2009). Likewise, AgNPs are used as antimicrobial additives in the fabrication of medical devices for showing no significant toxicity against human-developed monocyte cell lines (Martinez-Gutierrez et al. 2010).

3.3.2

Au Nanomaterials

AuNPs with a higher permanence present in contact with many biological fluids and their variety of surface modifications with spherical shape are not efficiently toxic to living cells, even though taken into them (Connor et al. 2005; Peracchia et al. 1997). The advantage of AuNPs is that it is being used to enhance antimicrobial activities for protein-based like ampicillin and fluoroquinolone class drugs (Chen et al. 2006). A new study revealed that AuNPs have an efficient toxic effect against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. By increasing the permeability of the cell wall in bacteria, novel particles are generating ‘holes’ in their cell walls causing the leakage of cell substances and ultimately happening to cell death (Rai et al. 2010).

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Fig. 4 Photographs of oil removal from oil–water mixture using PDMS modified sponge at different time: a 0 s, b 5 s, c 10 s, d 15 s, and PDMS-luffa-TiO2 nanosponge at e 0 s, f 5 s, g 10 s, h 15 s. (Adapted from Khan et al. 2019)

Gupta and Kulkarni (2011) reported diesel oil separation from oil–water mixture using PDMS modified AuNPs. Remarkably, the spent material can be redeveloped by employing heat at 300 °C for 30 min in the presence of air. The composite was also used for removing sulfur (S) containing compounds like thiamazole via chemisorption onto the AuNPs. Another study showed that PDMS-luffa-TiO2 nanosponge can remove oil completely from oil–water mixture within 15 s of treatment as shownin Fig. 4 (Khan et al. 2019).

3.3.3

CuO Nanomaterials

As a killing agent, CuO nanoparticles were efficiently used with a wide range of bacterial pathogens growth in wastewater. But high strength of CuO NPs is required to attain a bactericidal effect (Ren et al. 2009). The time-kill trials showed that the Gram-negative strains have a greater sensitivity towards CRO NPs combined with nano–Ag. Experiments have been conducted to evaluate the ability of CuO NPs surrounded by a variety of polymer materials. This implies that a release of ions into the local environment is needed for optimizing the antimicrobial activity (Cioffi et al. 2005). CuO NPs show antimicrobial activity against Klebsiella pneumonia, Shigella strains, Bacillus subtilis, and Salmonella paratyphi (Ren et al. 2009).

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3.4 UV/TiO2 Photocatalysis and Its Application Toward Drug Removal It is a well-established approach where the semiconductor material gets excited in the presence of UV or solar light to produce an electron hole (e− cb – h+ vb ) pair (Eq. 1), which ultimately implies in the detoxification of pollutants (in air or water system). Electrons from the valence band (VB) are pushed to the conduction band (CB), which generates a hole (h+ vb ) in the VB of the semiconductor. The drug molecule adsorbed on the surface of the semiconductor can be reduced and oxidized by the photo-generated electron (e− ) that travels to the surface of the catalyst without recombination. On the other hand, molecular oxygen reacts with electrons generated from the conduction band (e− cb ) is adsorbed onto the surface to generate superoxide radical anions (O2 −• ) (Eq. 2), while h+ vb reacts with water molecule adsorbed on the surface of the catalyst to form HO• ad radicals (Eq. 3). + TiO2 + hν → e− cb + hvb

(1)

−• e− cb + O2 → O2

(2)

+ • h+ vb + H2 O → H + HOad

(3)

TiO2 is usually used as a nano-photocatalyst because of its high photocatalytic activity, low toxicity, high oxidation capacity, low cost, easily available, and chemical stability under UV light (λ < 380 nm) (Leonidas et al. 2007). Rutile and anatase are the most commonly used crystal structures of TiO2 NPs consisting of 80% anatase and 20% rutile, which is considered a standard photocatalyst. Different organic pollutants can undergo photo-reactions through oxidative degra•− • dation with h + vb , O2 and HOad radicals as well as through reductive cleavage by electrons induced by CB. At ambient conditions, lower mass transfer limitations using NPs are the key advantages of UVPC in the presence of UV/solar irradiation. UVPC is efficient for the destruction of a wide range of organic pollutants into non-toxic compounds such as CO2 and H2 O as the end products (Chakma and Moholkar 2014). The major factors influencing UVPC are catalyst dose, initial pollutant loading, irradiation time, reactor design, solution pH, temperature, light intensity, and common ion effect of ionic species. The amount of photon transfer may be reduced into the medium by using an excess amount of catalyst. But the design of the reactor should assure the uniform irradiation of light on the catalyst surfaces.

3.4.1

Influence of TiO2 on 4-MAA Decomposition in UVPC

In a study, the degradation has been performed at different concentrations of TiO2 from 0.5 to 1.0 g/L at a fixed pH of 2.5. The results are shown in Fig. 5. There was

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N O

N N

O

O DIPY

S

Na+ OH

Hydrolysis

N

N

N

N

N

N NH2

O

O

N H

4-MAA

4-AA

HN O 4-FAA

O

N N HN O

CH O

4-AAA

Fig. 5 Chemical structure of dipyrone drug and its metabolic pathways

a sharp increase in 4-MAA degradation in the presence of a 1.0 g/L TiO2 dose that showed the maximum removal of 88.6% in 45 min. The higher TiO2 dose (>1.0 g/L) suppressed the removal efficiency due to the saturation of the availability of active sites for effective adsorption. It is due to the combined effect of the working conditions of the reactor, particle morphological behavior, and UV exposure (Bahnemann et al. 2007). Higher TiO2 concentration enhances the formation of HO• radicals on the surfaces (Bahnemann et al. 2007). However, a high concentration of NPs promoted particle aggregation, which eventually hindered the penetration of light in the reactor inside, thus reducing degradation efficiency (Sohrabi and Ghavami 2008a, b).

3.4.2

Degradation Mechanism Pathways of DIPY Degradation by TiO2

The photo-catalyst degradation of dipyrone (DIPY) drug as 4-MAA metabolite forms in the presence of TiO2 NPs that are characterized by the formation of HO• radical, which acts as the common oxidants and is mostly accountable for the decomposition of organic pollutants present in the water (Fig. 5). However, the extent of the

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degradation of drug molecules and their intermediates formed generally depends on the process parameters such as pH variation, Fe2+ to H2 O2 ratio, TiO2 catalyst dose, etc. The development of the degradation mechanism for the DPY molecule is to discover the possible routes of 4-MAA as metabolite degradation by HO• generated in this heterogeneous catalytic process. Due to the presence of more H2 O, soluble sulphonate group (-SO3 H) in 4-MAAwith mass number in terms of mass to charge ratio (m/z = 218.11) containing a pyrazolines structure is yielded at once and was found to be separated by an isocratic mobile phase in a reverse-phase HPLC column. MS spectra validated based on mass to charge (m/z) ratio are recorded using 4isopropyl antipyrine (m/z 231.3) as an internal standard (Ojha and Rathod 2009). The nitrogen (N) atom in pyrazolinone moiety is the most preferred site for the HO• attacking and releasing aniline as a byproduct (Pignatello et al. 2006). It was produced due to hydroxylation of the aromatic ring by the addition of HO• radical. N–atom from –NH–NH– moiety is mostly removed in the form of N2 and NH3 around 70 and 7% of the stoichiometric amount (Calza et al. 2005).

3.4.3

Biodegradability and Toxicity of 4-MAA and Its Degradation Products

The biodegradability of typical organic contaminants is determined by the ratio of biochemical oxygen demand under 5 days incubation period to chemical oxygen demand (BOD5 /COD) (Tekin et al. 2008). It is known as the biodegradability index (BI). Usually, pharmaceutically active compounds and personal care products’ contaminated water are considered to be relatively biodegradable with BOD5 / COD > 0.4 (Tang and Tassos 1997). An aqueous solution of 50 ppm DIPY shows initial BOD5 and COD as 3.75 and 41.3 mg/L, respectively. It indicates that the DIPY molecule is non-biodegradable in nature with a BOD5 /COD ratio of 0.1. TiO2 NPs as a photocatalytic process (UVPC) under UV-irradiation showed about 20% higher BOD5 /COD enhancement than UV/H2 O2 process (Giri and Golder 2014). It was about 10% greater than the corresponding drug remediation. BOD5 / COD results showed lower value in UVP and UVPC compared to Fenton and photoFenton processes due to unreacted 4-amino antipyrine (4-MAA) and intermediate products. Beltran et al. (1999) suggested that a mainly higher extent of conjugation due to the formation of chelate complexes of three different heavy metals improves the biodegradability of the organic pollutants. It has been found that newly formed daughter products acting as chelating agents significantly lower their biodegradability (Kummerer et al. 2000).

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3.5 AgNPs Photocatalyst and Its Usage in Recalcitrant Pollutants Removal AgNPs were prepared by using flavonoids present in the plant extract of Tabernaemontana divaricate (Fig. 6) and are also used for treating recalcitrant pollutants from different industrial wastewater. Figure 6 shows the degradation of 4-aminopyridine (4-AP) and its isomeric compounds. A mixture of 4-AP and plant extract was kept in dark to complete the adsorption and reach equilibrium. After that, the solution was kept under the irradiation of visible light for 2 h. The degradation efficacy (%) of 4AP in the presence of AgNPs was investigated by changing the initial concentrations of 4-AP, AgNPs dose, and pH. The photocatalytic activity of AgNPs was evaluated against 4-AP. The maximum removal efficiency of 48% has been observed for the 4-AP under an optimal condition (AgNPs of 1.6 g/L, 4-AP 5 mg/L, and pH 7) after exposure of 2 h. The degradation efficiency was decreased with increasing the concentration of 4-AP from 2 to 25 mg/L due to the overloading of pollutants onto the surface of NPs, which affected the reduction in photodegradation. The pH of the solution played a significant role in photoreaction, and the pH of 4-AP has been varied from pH 3 to pH 7 with the corresponding optimal conditions of 4-AP (5 mg/L), Ag NPs (1.6 g/ L), and reaction time of 2 h. It was found that there was an increasing rate of 4-AP removal onto AgNPs with an increase in pH from 3 to 7. At neutral pH, the cleavage of 4-AP onto AgNPs was found to be higher due to more stable dispersion and higher electrostatic force of attraction between 4-AP and NPs.

Fig. 6 Synthesis of AgNPs from flavonoids present in plant extract of Tabernaemontana divaricate

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4 Conclusions and Overview Both nanotechnology and nanomaterials as cost-effective, highly efficient, and ecofriendly methods have gained attention in the past few decades for the remediation of different organic and inorganic contaminants from the aquatic environment. NPs with many specific properties make them a favorable candidate for decontamination of water discharge from different industries. With the additional advantage of high adsorption selectivity and capacity, NPs have been used to remove varieties of metal ions at a very low concentration level. Adsorption is an easy physiochemical method that can be applied for the elimination of heavy metal ions from water. In this chapter, we have described the various groups of NPs like carbonaceous, polymer-based materials, metal, and metal oxides that are used as potent adsorbents for heavy metal removal and remediation of different organic pollutants (pesticides, drugs, dyes, etc.) under UV/solar light. Due to their good mechanical strength and small size, they could easily be separated from other metal ions. The toxicity of NPs shows a significant effect on both human and aquatic life and should be eliminated. The nanomaterialrelated literature concerned with the use of these in real-time studies is insufficient and has a lack of studies on their use in the practical wastewater treatment plant. A good understanding has been portrayed here of the interaction mechanism between the nanomaterials and drug (DIPY) molecule. However, the risk and influence of NPs on the environment cannot be ignored.

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Zero-Valent Nanomaterials for Wastewater Treatment Arindam Sinharoy and Priyanka Uddandarao

Abstract Wastewater from various industries majorly includes organic pollutants and heavy metals. They pose a serious threat to the environment because they are toxic and not biodegradable. In this scenario, metallic nanoparticles such as gold, silver, platinum, iron, copper and selenium are explored for wastewater treatment. However, nanoscale zero-valent iron (nZVI), representing the forefront of technologies, has been considered as promising material, due to its high reducibility and strong adsorption capability. ZVI is typically applied as a reductant and is capable of transforming, degrading or sequestering a variety of contaminants. ZVIs can be applied as either a single or a bimetallic system as well as advanced oxidation processes (AOPs). Moreover, core–shell type nanoparticles are a type of biphasic materials which have an inner core structure and an outer shell made of different components. Organic shells, consisting in most cases of polymers, proteins or complex sugars, can improve the performance of inorganic nanoparticles by enhancing their biocompatibility, acting as anchor sites for molecular linkages, or protecting them from oxidation. In this chapter, we will be focusing on the role of zero-valent iron and hybrid metallic nanoparticles in wastewater treatment due to their ability for the removal of various pollutants with a special emphasis on adsorption and photocatalysis. Further, this chapter focuses on challenges addressing the treatment and future trends. Keywords Adsorption · Core · Shell · Heavy metal removal · Photocatalysis · Zero-valent iron

A. Sinharoy (B) · P. Uddandarao Department of Microbiology, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_4

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1 Introduction Water pollution is one of the major concerns of the modern world which is linked with rapid urbanization and industrialization even in the remotest and most undeveloped parts of the world and is associated with poor planning for such developmental activities. The demand for clean water supply has increased by many folds over the past few decades, however, urban authorities are unable to keep pace with such high demands. Furthermore, due to rampant pollution of ground and surface water sources even the available clean water reserves are shrinking on a regular basis. These pollutants include heavy metals such as chromium, cobalt and selenium, and organic compounds like chlorinated solvents, nitrates, dyes, arsenic, phenol, halogenated, and nitroaromatic compounds (Sun et al. 2006). The necessity for a reliable and safe water supply is driving developing countries to create new and cost-effective water/wastewater purification and treatment systems (Ombaka et al. 2020; Gil-Díaz et al. 2020). Traditional and advanced treatment methods such as flocculation, Fenton’s oxidation, membrane filtration, adsorption, phytoremediation, bioremediation, photochemical, ion exchange, electrochemical oxidation, electrolytic precipitation, and ozonation have drawbacks such as sludge production and disposal, contaminants transfer from one phase to another and formation of byproducts. Therefore, the removal of synthetic chemicals remains an issue of serious concern. Along with the development in other scientific fields, the synthesis, characterization and application of engineered nanomaterials has also been revolutionized with nanoparticles being synthesized from new materials and with novel shapes and sizes. These novel nanoparticles have found application in all fields imaginable including catalytic reactions, advanced electronic devices, sensors, biomedical fields for both detection and therapeutics, pollutant detection and remediation, etc. (Sun et al. 2007). Among these wide-ranging applications, this chapter is dedicated toward environmental pollutant mitigation using nanoparticles for preventing water pollution and to help with the clean-up of already polluted water sources. For this purpose, the zero-valent nanoparticles are gaining attention due to their environmental remediation capability for various pollutants. They are used as reducing agents and are capable of transforming or degrading a variety of contaminants, which are often found in groundwater and soil. The zero-valent (nZVI)-based technologies act as reductant and are involved in various environmental oxidation–reduction reactions (Deng et al. 2020). This chapter focuses on the recent advances of nZVI and their use in the adsorption/photocatalysis for the treatment of hazardous contaminants. Further reports about immobilization of nZVI onto support and doping of ZVI with other metals are discussed.

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2 Types of Nanomaterials in Wastewater Treatment 2.1 Nanoscale Zero-Valent Iron (nZVI) The zero-valent iron (nZVI) nanoparticles have a typical core–shell configuration. The core is predominantly made up of zero-valent or metallic iron, with the mixed valent [i.e. Fe(II) and Fe(III)] oxide shell forming the metallic iron oxides. As iron is commonly found in the environment as iron(II) and iron(III) oxides, whereas nZVI is a synthesized material, so far, uses of nZVI have mostly centered on its electron-donating capabilities (Mortazavian et al. 2018). nZVI is moderately reactive in water under ambient conditions and can serve as a good electron donor, making it a flexible remediation material. The nZVI serves as a reducing agent, supplying electrons directly to the pollutant for degradation or assisting activities that require electrons for degradation. The direct reactivity of zero-valent iron with groundwater pollutants can provide an abiotic degradation pathway. The reactivity and mobility of nZVI are greatly influenced by its size, surface, capping substance, oxide layer or support material, and manufacturing method. The technique of synthesis chosen is also determined by the application needs of nZVI (Galdames et al. 2020). Because of its high surface energy and magnetic characteristics, bare nZVI are extremely reactive, estimated to be 10–1000 times more reactive than granular ZVI (Vilardi et al. 2019). nZVI is a moderate reducing reagent with a typical reduction potential of 0.44 V (Khuntia et al. 2019). It is also affordable and non-toxic. nZVI can oxidize organic contaminants in the presence of oxygen dissolved in water. It reacts with O2 to form H2 O2 in the first reaction. As a result, produced hydrogen peroxide is reduced to water by ZVI or can react with Fe2+ , resulting in hydroxyl radicals.

2.2 Immobilization of ZVI onto Supports Immobilization of ZVI nanoparticles onto different support systems has been explored in many of the previous studies. This immobilization improves the performance of ZVI nanoparticles as the aggregation and reduction of ZVI could be prevented or at least reduced due to their immobilization. Moreover, immobilization provides stable sites for reaction to take place which is better for the removal of these pollutants. The materials on which ZVI was immobilized were different such as carbon, carbon nanotube, activated carbon, granular carbon, fly ash, resins, polystyrene, silica, graphene oxide and different clay materials (Wu et al. 2020). Depending upon the materials, various methods were used for the synthesis and immobilization of ZVI onto these porous materials. Such porous materials are used for immobilization because they have a larger surface area, and unique structural and property-wise benefits. For example, many of these materials are good adsorbents, and many have good photocatalytic and oxidation–reduction properties which can

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itself be beneficial for any wastewater treatment. Following are some of the examples of ZVI immobilization in different materials along with the methods used. Immobilization of ZVI nanoparticles within ion exchange resin was carried out with two polymers (polystyrene resins) composed of the same backbone but different surface functional groups, i.e. N–S and Cl–S (Jiang et al. 2011). For the immobilization of ZVI in the ion exchange resin, beads of two different polymeric resins were prepared and added to the ferric chloride solution. The ferric chloride solution contained hydrochloric acid for N–S beads, and for Cl–S beads; the ferric chloride solution was in ethanol–water (2:3 by volume) mixture. After shaking the beads in respective solutions, the solution was decanted and following washing with alcohol to remove water suspended in sodium borohydride solution to reduce entrapped iron to Fe0 . This final step was carried out in an ultrasonic bath, and following the reaction beads were vacuum dried to obtain ZVI-immobilized ion exchange resin beads. In another study, ZVI nanoparticles were incorporated into electrospun polymer nanofibrous mat for copper removal (Xiao et al. 2011). The mat was prepared using electrospinning of a polymer mixture containing polyacrylic acid and polyvinyl alcohol, and was further strengthened using multiwalled carbon nanotubes (crosslinking at 145 °C). Such prepared mat was further suspended in ferric solution to take up iron which was then reduced to Fe0 with borohydride. Such prepared material showed higher copper removal. A similar enhancement of heavy metal removal property was also reported in a study with ZVI-supported anion exchange (D201) polymer (Liu et al. 2017a). The method used for the synthesis of ZVI-supported ion exchange resin was also similar to previous studies. The ferric iron was first loaded into the resin and then reduced to zero-valent iron with borohydride. In another study, ZVI and zeolite hybrid was prepared by first mixing iron chloride and zeolite together by mechanical agitation (Zhou et al. 2015). In the subsequent step, the adsorbed ferric iron was reduced to Fe0 with sodium borohydride solution. Thus, prepared material was washed with ethanol and stored under vacuum. Jia and Wang (2013) reported montmorillonite-supported ZVI nanoparticles to prevent its aggregation. This study found that heterogeneous nucleation is better than homogeneous nucleation for the synthesis of ZVI and its reactivity as heterogeneous nucleation produces smaller sized ZVI nanoparticles. The localization ZVI in the inner layers of montmorillonite is better for its stability than on the material’s surface, from where higher loss was reported. Petala et al. (2013) used ZVI supported on mesoporous silica (MCM-41) for hexavalent chromium removal from wastewater. In this method, the ferric chloride solution in ethanol was added to MCM-41, and the solvent was evaporated at 80 ºC. Following this step, the ferric iron bound to MCM-41 is reduced to zero-valent iron using a sodium borohydride solution. After the reaction is complete, the particles were washed with ethanol and vacuum dried before being used. In a method to synthesize nickel-zero-valent iron immobilized biochar, paper mill sludge was converted to biochar first by pyrolyzing it at a high temperature of 700 ºC (Devi and Saroha, 2015). The ZVI was produced by reducing ferrous sulfate with sodium borohydride. The resulting ZVI was immobilized on the biochar by suspending the reactant in CTMB solution along with ZVI and stirring the solution

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at 1000 RPM. Further, Ni coating on the material was performed by suspending the ZVI immobilized biochar into a nickel chloride solution and sonicating it to complete the reaction. Vogel et al. (2019) reported ZVI-activated carbon complex synthesis using ferric nitrate as the iron source. In this method, the activated carbon particles were mixed in a ferric solution, dried and then converted using a thermal method by heating at 700 to 850 °C. The resulting dried material contained 20% ZVI nanoparticles and 55% activated carbon. In a study, a different approach was taken for the immobilization of ZVI onto biochar where chitosan was used to adhere the ZVI particles (Zhou et al. 2014). In this procedure, the chitosan was dissolved in acetic acid in which the ZVI particles were suspended before biochar was added to the mixture. To this solution, NaOH was added under stirring conditions and once the reaction was completed, the excess reactants were washed before the ZVI-immobilized biochar particles could be recovered, dried and applied for experimental investigation. Liu et al. (2017a, b) prepared ZVI immobilized fly ash-based adsorbent for the removal of lead and chromium. In this study, fly ash, bentonite, coke and iron ore tailings were mixed in a 1:2:2:2 ratio along with dried seaweed (Enteromorpha prolifera) biomass (1% by weight) in a blender for proper mixing. Cylindrical-shaped pellets were formed from this mixture, dried at 105 ºC and sintered at 900 ºC. The resulting materials were used for adsorptive removal of heavy metals from wastewater. In another study, ZVI-supported chitosan was prepared using chitosan-obtained shrimp shell wastes (Ahmadi et al. 2017). This extracted chitosan was dried and added to acetic acid solution to dissolve, to which a ferric chloride solution was added. This mixed solution was reduced by adding borohydride solution dropwise. Once the solution turned black, the reaction was stopped, and the precipitates were washed with ethanol and dried at 100 ºC. Zhou et al. (2018) used a novel compound, i.e. waste rock wool to immobilize ZVI nanoparticles for the removal of Cr(VI). Waste rock wool was surface functionalized using hydrochloric acid. Then the activated waste rock wool was added to ferrous sulfate solution, and the iron was reduced to zero-valent iron using a borohydride solution. The resulting composite materials were washed with deionized water, alcohol and vacuum dried. Moreover, the results found that this immobilization of ZVI prevented its aggregation and improved its chromium removal performance. The waste rock wool with a higher surface area was an ideal candidate for ZVI impregnation. The addition of zero-valent iron imparted magnetic property to the adsorbent and could be easily separated from the solution.

2.3 Doping of ZVI with Other Metals Similar to the immobilization strategy, the main reason for doping other metals, particularly transition metals in ZVI, is to prevent their agglomeration. This doping strategy also helps in preventing the ZVI to be oxidized and improving its reactivity. The doping of transition metals to ZVI improves the degradation of organic pollutants

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through dehalogenation by acting as a hydrogen catalyst or by producing reactive electrons. This way, the reaction rate and kinetics of pollutant degradation improve. Lai et al. (2014) studied copper doping to zero-valent iron to form bimetallic nanoparticles in which a different Cu amount was doped ranging from 0.05 to 1.81 g per G of Fe. The study reported that the copper doping improved the catalytic activity of ZVI at a concentration < 0.89 g Cu/g Fe. The degradation of p-nitrophenol was very high (98%) at optimum conditions which was much higher than only ZVI-based reaction. In a different study, the incorporation of bismuth into ZVI nanoparticles increased its reactivity (Murtaza et al. 2019). In this method, the ferrous sulfate and bismuth nitrate solution was prepared in a water–ethanol mixture, and reduced using sodium borohydride solution. The governing mechanism for this removal was through the reduction of Cd(II) to Cd0 , and the addition of bismuth improved this cadmium removal by 11%. In order to improve catalytic degradation of hexachlorobenzene, silver doping was done to ZVI at 0.05–0.45% concentration (on weight basis) (Nie et al. 2013). The results showed that a small amount of Ag doping is effective with an optimal value of 0.09%, whereas the addition of more amount of Ag reduced the reactivity of ZVI due to covering the active site on the nanoparticle surface. In another study, nickel doping to produce nickel/iron bimetallic nanoparticles was carried out using the ball milling method (Xu et al. 2012). The results showed bimetallic particles have much higher dechlorination efficiency for 4-Chlorophenol. The nanoparticles were found to be much more stable at pH 6, with very high recyclability without losing any reactivity. In a similar work, Krishnan et al. (2021) examined the efficiency of palladium doping to ZVI nanoparticles immobilized polyurethane support for degradation of azo dye RED ME4BL. The study found the Pd-doped ZVI could effectively degrade (92% removal efficiency) the azo dye and doping improved the process efficiency. Koutsospyros et al. (2012) performed a comparative study between copper and nickel for preparing bimetallic nanoparticles with iron to be used for the degradation of various explosive compounds (RDX, TNT, HMX, etc.). The results showed that there was no significant difference between the Cu and Ni doping on the kinetics of degradation of these pollutants, however, Fe–Cu particles were highly effective for degradation of all the compounds. Wang et al. (2022) explored copper doping to iron nanoparticles for the reactive removal of hexavalent chromium. These zero-valent Cu and Fe were introduced to montmorillonite support material for preventing their release during the experimental study. The results showed that bimetallic nanoparticles had improved reactivity with a higher amount of chromium removal. He et al. (2016a) demonstrated improved degradation of polychlorinated biphenyls by palladium-doped ZVI nanoparticles. In this study, EDTA was used as a ligand for enhancing the performance of the nanocomposite.

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3 Zero-Valent Iron for Wastewater Treatment 3.1 Heavy Metal Removal by ZVI Heavy metals such as lead, cadmium, zinc, nickel, copper, chromium and arsenic have serious detrimental effects on the environment. The sources of heavy metals in the environment are primarily industrial activity related to mining, coal burning, petroleum refinery, steel plants, etc. (Sinharoy et al. 2020a). The release of these heavy metals untreated into the surface water bodies creates hazardous effects on all the components of the ecosystem. Moreover, due to their recalcitrant and nonbiodegradable nature, they persist in nature for longer duration causing more harm to the environment (Sinharoy and Lens 2020). Hence, various strategies including chemical precipitation, adsorption, membrane separation, filtration, evaporation, reverse osmosis, electro dialysis, electro coagulation, etc. have been explored for removing heavy metals from wastewater (Sinharoy and Pakshirajan 2019; Sinharoy et al. 2020b). However, among these strategies, the use of ZVI has gained a lot of traction recently due to their high degree of heavy metal removal which can often reach complete removal (Table 1). Furthermore, due to the magnetic nature of ZVI, its separation following the treatment is easier (Wu et al. 2020). To improve the performance of ZVI for heavy metal removal, different strategies such as surface modification, or forming conjugate with porous/semiporous materials and clay minerals are also implemented (Zou et al. 2016). The mechanism involved in the heavy metal removal using ZVI nanoparticles is adsorption and reduction (Tarekegn et al. 2021). In addition, some studies that have shown oxidation, aggregation, ion exchange, etc. can also be involved in the removal of heavy metals from wastewater by ZVI nanoparticles (Zou et al. 2016; Jacob et al. 2020). Adsorption is a well-known mechanism used for heavy metal removal. ZVI nanoparticles are suited for adsorption due to their high amount of active sites and functional groups on its surface which helps in heavy metal interaction with the nanoparticles (Wu et al. 2020). There are many studies of adsorption-based removal of heavy metals using ZVI nanoparticles. Boparai et al. (2011) studied cadmium (25– 450 mg/L) removal using ZVI nanoparticles with an adsorbent dosage of 500 mg/ L. The results showed very high cadmium removal with 769.2 mg/g of adsorption capacity. According to the authors, the adsorption mechanism is chemisorption. Statham et al. (2015) reported excellent copper and zinc removal with ZVI nanoparticles with adsorption capacities of 2.2–4.5 and 0.15–0.28 mg/g of ZVI for Cu and Zn, respectively. Xi et al. (2010) studied the mechanism of lead removal using ZVI nanoparticles. The Pb removal obtained in this study was very high (99.9%) at optimum conditions within just 15 min of reaction along with 401.8 mg/g of adsorption capacity at 0.05 g of ZVI dosage. The XPS analysis of the ZVI samples before and after the adsorption process showed that both forms of lead, i.e. Pb0 and Pb(II) are present on the ZVI surface. These findings indicated that the removal mechanism involved rapid adsorption followed by partial reduction of lead to form lead oxide precipitate on the ZVI surface.

25 °C

4.0

4.5–5.0

6.5

nZVI

nZVI

nZVI-immobilized ion exchange resin

25 °C

25 °C

25 °C

Room temp

7.0

1.0–8.0

7.0

5.0

NR

nZVI (α-Fe2 O3 )

ZVI supported on biochar

ZVI-chitosan composite

ZVI supported on anion exchange polymer (D201)

ZVI-supported biochar with chitosan

25 °C

20, 30 and 40 °C

ZVI immobilized on 1.0–11.0 fly ash-based compound

25 °C

25 °C

Temperature

pH

Material

Pb(II), Cr(VI) and As(V)

Cu(II)

Cd(II)

Pb(II)

As(III) and As(V)

Pb(II) and Cr(VI)

As(III) and As(V)

Pb(II), Cu(II) and Cd(II)

Pb(II)

Heavy metal used

40 mg/L Pb(II), 53 mg/L Cr(VI) and 21 mg/L As(V)

20 mg/L

10 mg/L

10–200 mg/L

0–200 mg/L

100–1000 mg/L

5 mg/L

0.01 mM

200 mg/L

Initial concentration

> 93% of Pb(II), 70–95% of As(V) and 26–40% Cr(VI)

88.3%

99.8%

51.7–97.3%

87–94%

NR

99.6%

> 99%

99.9%

Removal percentage

Table 1 Heavy metal removal by adsorption with zero-valent iron (ZVI) and ZVI-based materials

Du et al. (2013)

Eglal and Ramamurthy (2015)

Xi et al. (2010)

References

NR

NR

142.8 mg/g

77.5 mg/g

(continued)

Zhou et al. (2014)

Liu et al. (2017b)

Ahmadi et al. (2017)

Dada et al. (2017)

95 mg/g for As(III) Tang et al. and 47 mg/g for (2011) As(V)

Maximum Liu et al.( 78.13 mg/g for Pb 2017a) and 15.70 mg/g Cr

121 mg/g for As(III) and 125 mg/g for As(V)

270 mg/g for Cu, 170 mg/g for Pb, 110 mg/g for Cd

401.8 mg/g

Adsorption capacity

60 A. Sinharoy and P. Uddandarao

Room temp

3.0 and 5.0

ZVI-supported mesoporous silica (MCM-41)

NR: not reported

35 °C

4.0

nZVI-zeolite composite

Temperature

20–50 °C

pH

2.0–10.0 ZVI-supported functionalized waste rock wool

Material

Table 1 (continued)

Cr(VI)

Pb(II)

Cr(VI)

Heavy metal used

6 mg/L

100 mg/L

10–200 mg/L

Initial concentration

100% for pH 3

96%

100% for 10–40 mg/L

Removal percentage

NR

806 mg/g at 1000 mg/L Pb(II)

197.69 mg/g

Adsorption capacity

Petala et al. (2013)

Kim et al. (2013)

Zhou et al. (2018)

References

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Reductive removal of heavy metals using ZVI is also reported in the literature. In this case, ZVI acts as an electron donor and heavy metals as an electron acceptor. But this interaction is dependent upon the properties of ZVI and heavy metals. Moreover, this reduction process can take place either directly by reaction with heavy metals or in a two-step process where first adsorption takes place which is followed by a reduction reaction. This type of reduction process reduces the valence of heavy metals to a more stable form and often mimics their reduction in a natural environment. For instance, Cheng et al. (2021) reported the reductive removal of hexavalent chromium to trivalent chromium using ZVI particles. Liu et al. (2015) reported that among the different mechanisms involved in lead removal using magnesium hydroxidesupported ZVI particles, 47% was due to a reduction reaction which was confirmed to form Pb0 elements following the reduction of Pb(II). In a similar work by Zhou et al. (2015), trivalent antimony was reduced to its elemental form to a very high degree (>80%) by ZVI nanoparticles supported on zeolite. Liu et al. (2017b) studied copper removal using a ZVI nanoparticle supported on an anion exchange polymer (D201). In this work, the copper removal significantly improved (~50% increase) due to its immobilization onto ion exchange resin. The copper was adsorbed and precipitated onto the polymeric beads, and further reduced to Cu0 by reacting with ZVI present in the beads. Moreover, complete regeneration of the ion change beads containing ZVI could be achieved with Cu removal performance being restored to its original form. The development of reactors capable of continuous operation is essential for the application of ZVI nanoparticles and ZVI-based materials for heavy metal removal on an industrial scale. There are few studies in the literature which have demonstrated the capability of ZVI nanoparticles under continuous operation. Among the continuous heavy metal removal setup, column experiment is the most common type of study conducted on a lab scale to analyze the heavy metal removal capacity of the adsorbent. Kishimoto et al. (2018) used an experimental setup containing a 10 mm acrylic column with 15 g of ZVI for zinc removal. The study obtained a 74% overall removal for zinc. Further study was conducted on desorbing zinc from ZVI using citric acid with recovery capacity ranging 36–77% for 0.1–10 mM citric acid concentration. In a different strategy, Madaffari et al. (2017) constructed a column containing a mixture of ZVI and lapillus (a type of unconsolidated volcanic rocks) in different ratios for the removal of nickel. The maximum Ni removal efficiency of 99.7% was obtained at a 50:50 ratio for ZVI and lapillus. However, the next two removal values were not far behind with 99.6% (10:90 ratio) and 99.4% (30:70). The potential of ZVI is greatly highlighted in this work, as even the presence of 10% ZVI in the column filling is able to remove more than 99% of the heavy metal from the influent wastewater. Large-scale installation with ZVI has also been reported for treating real industrial effluent. For example, a 60 m3 ZVI-based reactor was installed in Jiangxi province (China) for treating highly corrosive and heavy metal-containing wastewater from a copper processing plant (Li et al. 2017). The reactor was fitted with pH and ORP monitoring and controlling strategies. This ZVI-based treatment system was used as a pre-treatment step for removing arsenic (110 mg/L) and heavy metals. Apart

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from arsenic, other heavy metals present in the wastewater are Cu in large quantities (103 mg/L), and small amounts of Pb (0.35 mg/L), Sb (8.7 mg/L), Ni (0.67 mg/L), Se (4.6 mg/L) and Zn (0.38 mg/L). The performance of the reactor was excellent with more than 99.5% removal of As and other pollutants over a long period of time (>1 year). In another study, a zero-valent iron-based treatment system was installed in a uranium mill tailings site to remove heavy metals and radioactive compounds (As, Mn, Mo, Se, U, V and Zn) from groundwater located at Durango (Colorado, USA) (Morrison et al. 2002). There were two types of configurations used at this place, one with plates with ZVI powder bounded with aluminosilicate and the other one with granular ZVI mixed with steel wool as a packing material. The treatment unit performed excellently with > 97% removal for As, Se, U, V and Zn. However, Mn and Mo showed slightly less removal with 85% and 67%, respectively. The effluent concentration of these pollutants was far less than what was present in the influent stream which confirmed the suitability of the treated water to be safely released into the environment.

3.2 Photocatalysis for Removal of Organic Pollutants For the photocatalysis, nZVI nanoparticles, nZVI immobilized with supports and nZVI doping with metal/metalloids are used as catalysts (Table 2). The majority of organic pollutants include synthetic compounds present in wastewater from the textile, printing, leather, paper, food and pharmaceutical industries; these are hazardous even at very low concentrations (Kumar et al. 2015). There are several approaches such as biological oxidation, membrane filtration, adsorption and heterogeneous photocatalysis (Bokare and Choi, 2009) which are used for the removal of organic pollutants from an aquatic medium. Apart from nanosize, ZVI can also be synthesized in microscale sizes. However, the presence of an innate passive layer in microscale ZVI reduces their efficiency compared to nanoscale ZVIs. Moreover, the specific surface area of nanoscale particles is higher than the microscale particles due to the specific surface area being indirectly proportional to the particle size. This property increases the effectiveness of the microscale particles with better treatment efficiency (Shih et al. 2010). To exemplify this improved property of the nanoscale particles, one study reported nanoscale ZVI could be able to degrade 90% of a dye within 24 min of reaction time within which microscale particles could only degrade just 25% under the same reaction condition. Each hue of dye used in the textile industry has a distinct chemical structure. The dye molecules are great electron acceptors and the nZVI particles are good electron donors. In the aqueous medium, the nZVI particles reduce to Fe2+ and Fe3+ ions, and the hydroxyl, hydrogen ions produced during the reduction process react with dye molecules to cause the chromophore link to break (Mesa-Medina et al. 2021). To decolorize the dye molecules, the nZVI particles must also break the auxochrome link, and the ensuing intermediate organic compounds must be mineralized into

Acid Red 1 and acid Green 25 Methyl orange, para-nitrophenol, Congo red, Rhodamine B and Methylene Blue

Chemical vapor deposition technique

Precipitation method

Precipitation method

Precipitation method

Fe7 S8 /Fe3 O4 coated zero-valent iron

Zero-valent iron

Melia Azedarach impregnated Co and Ni zero-valent metal nanoparticles

Zero-valent iron/titanium dioxide based on activated carbon

Iron nanoparticles Biosynthesis using using Trigonella Trigonella foenum-graecum seed extract foenum-graecum seed extract

Orange(II)

Precipitation method

Zero-valent Nano-Iron-Doped TiO2

Methyl orange dye

2,4-Dichlorophenoxyacetic acid

Nitrophenols

Rhodamine B

Hydrothermal method

Nano-zero-valent iron@BiFeO3 /g-C3 N4

Pollutant

Synthesis

Catalyst

25.0 mg/L

221.04 mg/L

MO (16.3 ppm), PNP (13.9 ppm), CR (34.8 ppm), RB (4.79 ppm), MB (3.19 ppm)

50 mg/L

20 mg/L

250 mg/L

10 mg/100 mL

Pollutant concentration

Table 2 Photodegradation efficiencies for specific pollutants achieved with nZVI-based catalysts

87%

86.37%

MO (81%), PNP (93%), CR (92%), RB (97%), MB (96%)

AR1 (91.60%) and AG25 (98%)

51% TOC removal

88%

97%

(continued)

Radini et al. (2018)

Baloochi et al. (2018)

Ahmad et al. (2020)

Bhatti et al. (2020)

Niu et al. (2021)

Badmus et al.( 2021)

Rahman et al. (2021)

Degradation efficiency References (%)

64 A. Sinharoy and P. Uddandarao

0.1 mM

Precipitation method

Chitosan membrane/zinc phthalocyanine support for the synthesis of zero-valent metal nanoparticles

4-nitrophenol, methyl orange and congo red

25 mg/L

Biosynthesis using methyl orange Cupressus sempervirens leaf branches

Iron-based nanoparticles

0.1 mM

Methyl orange, congo red, methylene blue and acridine orange and 4-nitrohphenol, 2-nitrophenol, 3-nitrophenol and 2,6-dinitrophenol

Precipitation method

Chitosan-titanium oxide fibers supported zero-valent nanoparticles

Pollutant concentration

Pollutant

Synthesis

Catalyst

Table 2 (continued)

> 90%

95%

MO (97.9%), CR (98.2%), MB (96%), AO (90%) and 4-NP, 2-NP 3-NP, 2,6-DNP (100%)

Ali et al. (2017)

Ebrahiminezhad et al. (2018)

Ali et al. (2018)

Degradation efficiency References (%)

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CO2 , H2 O and inorganic ions to achieve complete degradation. It is evident that the color removal process is affected significantly by pH (Liu and Wang 2019). Due to protonation at a low pH value, the iron particles act as an electron donor, hence converting ions into atoms. Resultantly, the chromophoric group is reduced and converted into amines via intermediate formation. As the solution gets more acidic, the H+ concentration increased, thus, iron particles donated more electrons and the color removal process was enhanced. There are studies which focus on the immobilization of nZVI onto supports, for example, Wang et al. 2016 reported tetracycline degradation using nZVI on polydopamine surface-modified biochar. As biochar is a carbon-rich pyrogenic material, it shows very high adsorption due to its high surface area and has a quite higher rate of degradation due to the presence of higher porosity to achieve enhanced adsorption capacity to organic contaminants (Mandal et al. 2020; Ahmaruzzaman 2021; Ruan et al. 2022). Further, nZVI was immobilized on the organobentonite which could rapidly and completely dechlorinate pentachlorophenol to phenol with an efficiency of 96.2%. Generally, organobentonites are produced by replacing the metal cations in bentonite interlayers with organic cations. The quaternary alkylammonium in the form of (CH3 )3 NR+ is used most extensively, where R is a long alkyl chain (Li et al. 2011). In addition, nZVI immobilized by Enteromorpha prolifera-basedactivated carbons were applied for chloramphenicol treatment (Wu et al. 2018). The modified nZVI exhibited excellent removal capacity for 545.25 mg/g because of the synergetic effects of adsorption and degradation of the nZVI-activated carbon system. Immobilization of nZVI onto graphene matrix can restrain aggregation of iron particles, contributing to its enhanced performance toward ternary nanocomposite of magnetic nZVI/graphene–TiO2 nanowires (Wang et al. 2018). The usage of nZVI/ graphene–TiO2 nanowires showed superior activity in the removal of metronidazole (99.3%) compared with TiO2 nanowires (43.0%) and graphene–TiO2 nanowires (67.6%) (Raez et al. 2021). Heterogeneous photocatalysts are renewable, low-cost, efficient and simple-toimplement advanced oxidation processes. Chemical processes and catalyzers used in advanced oxidation processes generate free radicals. nZVI could produce the required oxygen vacant surface for absorption in the visible spectrum of electromagnetic radiation by the TiO2 . The associated excess electrons on nZVI can be transferred to the surface oxygen electron of the TiO2. This may result in the delocalization of the surface electron in TiO2 and cause a significant increment in electron density. The decoloration of 88% observed for orange(II) under simulated solar light was possible in 20 min at pH 2 (He et al. 2016b). Zhang et al. in 2020 for the first time reported a nanocomposite prepared from graphitic carbon nitride and nZVI with superior catalytic activity for methylene blue removal efficiencies of 99.2% in 120 min. Graphitic carbon nitride is a metal-free polymeric photocatalyst that is very promising for utilizing solar energy with excellent structural stability, owing to its suitable bandgap of 2.7 eV. Graphitic carbon nitride doped with nZVI achieved high degradation efficiency of 98.5% for tetracycline due to the formation of a heterogeneous photo-Fenton system (Sheng et al. 2016; Wang et al. 2019). Hua et al. (2014) found that the nZVI and N co-modified TiO2 (nZVI/N–TiO2 ) nanotube arrays have an

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improved photocatalytic property under visible light. A similar report was also made by Yu et al. (2013) where the rate of phenol degradation with nZVI/N–TiO2 under visible light was higher than the rate constants obtained using different combinations of titanium oxide compounds, namely N–TiO2 , nZVI/TiO2 and TiO2 under the same experimental conditions. The reason behind this observation is attributed to the fact that the electron transfer is much better in nanoscale ZVI spheres than the other compounds (Hsieh et al. 2010).

4 Current Challenges and Future Perspectives The ZVI-based treatment systems for wastewater treatment have shown promising potential, and due to this many research and review articles have come up in recent times. However, there are a few challenges regarding its commercialization and application on an industrial scale. Firstly, most of the studies reported in the literature are conducted using lab-scale setups and controlled environments. There will be many challenges to replicating these lab-based results on a pilot or industrial scale with real wastewater. As the large variations in physico-chemical parameters of real wastewater along with many organic/inorganic co-pollutants present in real wastewater will surely affect the performance of ZVI, hence, to overcome this challenge more studies should be conducted using real wastewater and efforts should be taken to upscale the lab-based experimental setups. Another challenge is the release of ZVI particles into the environment along with treated effluent. The ZVI like any other nanoparticle has a detrimental effect on living beings as well as on the overall environment. Hence, their release should be strictly monitored and controlled. The immobilization or entrapment of ZVI on support materials could prevent their release to a certain extent, but it could not be stopped completely. To ensure no ZVI is released from treatment plants, probably an additional setup can be installed which will help in separating ZVI from effluent after treatment. Due to the magnetic nature of ZVI particles, a setup with magnetic properties could be an ideal choice. Although this could increase the installation cost, considering the additional benefits, it will be an intelligent decision. Agglomeration of ZVI particles is another issue that creates a lot of difficulty in their commercial application. Immobilization, doping with transition metals and coating them with different active compounds can prevent such problems. Rapid oxidation is another problem for ZVI particularly in aerobic environments, which requires special care for their storage and application. These ZVI and ZVI-based compounds work best under an anaerobic environment. Non-target specificity of ZVI during their reaction also possess a challenge in their application as in many cases some other compounds (than the target ones) can be preferentially adsorbed on its surface. Moreover, they have a very narrow pH range for their optimal reactivity. Due to this reason, pH adjustment of the wastewater need to be performed in many cases whose pH lies beyond this optimum range. Furthermore, continuous mixing in ZVI-based system is essential to bring the pollutants in contact with ZVI for their

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effective removal. This need for mixing can require additional energy consumption, although this could be minimal in comparison to many other conventional treatment systems. It is also difficult to determine the exact mechanism involved in pollutant removal using ZVI particles, as in many cases a combination of different processes such as adsorption, oxidation–reduction and precipitation are involved in removing a particular pollutant. Furthermore, estimating the role of each of the individual processes in the removal of a typical pollutant is challenging, and requires sophisticated instrumentations. This could be taken up as an objective for future study. Moreover, better understanding of mass transfer aspects and reaction kinetics for ZVI-based pollutant degradation could be helpful for its application in real field scenarios.

5 Conclusion Nanotechnology is an interdisciplinary field of study involving science, engineering and technology at the nanoscale level. Since its conceptualization in the 1950s, this field of research has come a long way and has found its application potential in almost all fields of science. Application of nanomaterials in wastewater treatment using different approaches and mechanisms has currently developed from a lab scale to a large industrial level. Among the different nanomaterials, ZVI-based systems provide a promising treatment technology for contaminated water. Treatment of both organic and inorganic wastewater has been demonstrated using ZVI particles. Due to their high surface area and high reactivity, they are utilized as an efficient tool for treating various wastewater. The high treatment efficiency achieved using ZVI for various pollutants is much more than obtained using conventional treatment, encouraging its commercial use. The magnetic properties of ZVI could provide a strategy for their separation after treatment. Moreover, immobilization on different support materials, doping with other metals and coating with active compounds can improve the performance of ZVI particles. These modifications also help in overcoming some of the drawbacks of pristine ZVIs. However, for their successful commercial application, more number of experimental studies using a pilot scale should be conducted. Furthermore, a better understanding of their removal mechanism, reaction scheme and environmental implications will help in their universal application.

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characterization, optimization and modeling approach. Journal of Water Supply: Research and Technology—Aqua, 66(2), 116–130. Ahmaruzzaman M (2021) Biochar based nanocomposites for photocatalytic degradation of emerging organic pollutants from water and wastewater. Mater Res Bull 140:111262 Ali F, Khan SB, Kamal T, Alamry KA, Asiri AM (2018) Chitosan-titanium oxide fibers supported zero-valent nanoparticles: highly efficient and easily retrievable catalyst for the removal of organic pollutants. Sci Rep 8(1):1–18 Ali F, Khan SB, Kamal T, Anwar Y, Alamry KA, Asiri AM (2017) Anti-bacterial chitosan/zinc phthalocyanine fibers supported metallic and bimetallic nanoparticles for the removal of organic pollutants. Carbohyd Polym 173:676–689 Badmus KO, Wewers F, Al-Abri M, Shahbaaz M, Petrik LF (2021) Synthesis of Oxygen Deficient TiO2 for Improved Photocatalytic Efficiency in Solar Radiation. Catalysts 11(8):904 Baloochi SJ, Nazar ARS, Farhadian M (2018) 2, 4-Dichlorophenoxyacetic acid herbicide photocatalytic degradation by zero-valent iron/titanium dioxide based on activated carbon. Environ Nanotechnol Monit Manage 10:212–222 Bhatti HN, Iram Z, Iqbal M, Nisar J, Khan MI (2020) Facile synthesis of zero valent iron and photocatalytic application for the degradation of dyes. Materials Research Express 7(1):015802 Bokare AD, Choi W (2009) Zero-valent aluminum for oxidative degradation of aqueous organic pollutants. Environ Sci Technol 43(18):7130–7135 Boparai HK, Joseph M, O’Carroll DM (2011) Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles. J Hazard Mater 186(1):458–465 Cheng Y, Dong H, Hao T (2021) CaCO3 coated nanoscale zero-valent iron (nZVI) for the removal of chromium (VI) in aqueous solution. Sep Purif Technol 257:117967 Dada AO, Adekola FA, Odebunmi EO (2017) Kinetics, mechanism, isotherm and thermodynamic studies of liquid phase adsorption of Pb2+ onto wood activated carbon supported zerovalent iron (WAC-ZVI) nanocomposite. Cogent Chemistry 3(1):1351653 Deng M, Wang X, Li Y, Wang F, Jiang Z, Liu Y, Gu Z, Xia S, Zhao J (2020) Reduction and immobilization of Cr (VI) in aqueous solutions by blast furnace slag supported sulfidized nanoscale zerovalent iron. Sci Total Environ 743:140722 Devi P, Saroha AK (2015) Simultaneous adsorption and dechlorination of pentachlorophenol from effluent by Ni–ZVI magnetic biochar composites synthesized from paper mill sludge. Chem Eng J 271:195–203 Du Q, Zhang S, Pan B, Lv L, Zhang W, Zhang Q (2013) Bifunctional resin-ZVI composites for effective removal of arsenite through simultaneous adsorption and oxidation. Water Res 47(16):6064–6074 Ebrahiminezhad A, Taghizadeh S, Ghasemi Y, Berenjian A (2018) Green synthesized nanoclusters of ultra-small zero valent iron nanoparticles as a novel dye removing material. Sci Total Environ 621:1527–1532 Eglal MM, Ramamurthy AS (2015) Removal of Pb (II), Cd (II), Cu (II) and trichloroethylene from water by Nanofer ZVI. Journal of Environmental Science and Health, Part A 50(9):901–912 Fu F, Dionysiou DD, Liu H (2014) The use of zero-valent iron for groundwater remediation and wastewater treatment: a review. J Hazard Mater 267:194–205 Galdames A, Ruiz-Rubio L, Orueta M, Sánchez-Arzalluz M, Vilas-Vilela JL (2020) Zero-Valent Iron Nanoparticles for Soil and Groundwater Remediation. Int J Environ Res Public Health 17(16):5817 Gil-Díaz M, Álvarez MA, Alonso J, Lobo MC (2020) Effectiveness of nanoscale zero-valent iron for the immobilization of Cu and/or Ni in water and soil samples. Sci Rep 10(1):1–10 He D, Ma X, Jones AM, Ho L, Waite TD (2016a) Mechanistic and kinetic insights into the ligandpromoted depassivation of bimetallic zero-valent iron nanoparticles. Environ Sci Nano 3(4):737– 744 He X, Aker WG, Pelaez M, Lin Y, Dionysiou DD, Hwang HM (2016b) Assessment of nitrogen– fluorine-codoped TiO2 under visible light for degradation of BPA: implication for field remediation. J Photochem Photobiol, A 314:81–92

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Photocatalytic Treatment of Soft Drink Industry Wastewater Using Supported/ Immobilized Nanophotocatalysts Anil Swain, Neelancherry Remya, and Abhishek Patil

Abstract Soft drink industries demand a huge quantum of freshwater for soft drink production as well as other activities involved in manufacturing such as bottle washing, floor cleaning, cooling, etc. The wastewater produced at the end of these operations is very complex and organic in nature as a result of the use of numerous chemicals throughout those processes. Various biological treatment technologies have been employed for soft drink industry wastewater (SDIW) treatment; however, their application is often limited due to long treatment time, inefficient removal of bio-refractory compounds and maintaining control over process factors such as pH, temperature as well as high operating cost, require controlled operating conditions and in certain cases post-treatment. Advanced Oxidation Processes (AOPs) provide a promising solution for complete and efficient degradation of many organic and inorganic contaminants, including bio-refractory compounds, to give non-toxic end products. Photocatalysis is one of such AOPs, which can ensure complete mineralization of organic contaminants with lesser reaction time and non-toxic by-products. Modification of photocatalyst through doping, combining semiconductors and supporting on suitable materials further increases photocatalytic activity with added advantages like recovery and reusability of photocatalyst after treatment. This chapter aims to discuss the suitability of photocatalysis for the treatment of SDIW using supported/ immobilized nanocatalysts, the contaminant degradation mechanism involved as well as methods to enhance the efficiency of the photocatalytic system. Keywords Soft drink industry wastewater · Treatment · Advanced oxidation process · Photocatalysis · Immobilized catalyst

A. Swain · N. Remya (B) · A. Patil School of Infrastructure, Indian Institute of Technology Bhubaneswar, Argul, Odisha, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_5

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1 Introduction Global scenario of ever-increasing urbanization, industrialization and population growth has led to the stress in the demand for freshwater for various domestic as well as industrial activities. Even though the agricultural sector consumes the highest quantity of water at present, the scenario is subject to change in near future owing to the growing industrial development (Alkaya and Demirer 2015). Food and beverage industries require tremendous amounts of freshwater, which accounts to more than two-thirds of the abstracted freshwater worldwide. Soft drink industry is gaining a significant attention recently due to high productivity and increasing consumption and demand of carbonated soft drinks in market. About 80% of these drinks is constituted by water. Moreover, water is required for various stages of soft drink manufacturing such as cleaning and cooling, wherein the majority of the water is required for washing of bottles, leading to the generation of large quantity of wastewater (Ait Hsine et al. 2005). In order to achieve the goals of water demand management and efficient effluent treatment, soft drink industries need to adopt appropriate treatment technologies that can enable the reuse of treated effluent further for industrial processes, thus allowing to enhance sustainability as well as economic advantages (do Nascimento Jr et al. 2021). Various biological and physico-chemical treatments are currently being applied and studied for soft drink industry wastewater (SDIW) treatment. The present chapter focuses on applicability and limitations of these conventional treatment technologies and the suitability of photocatalytic treatment as a promising new alternative for the same.

2 Characteristics of SDIW A variety of activities associated with manufacturing result in the production of SDIW. As a result, it contains a wide variety of compounds and chemicals from various stages, making it a complex effluent. It often includes wastewater from soft drink manufacturing processes such as bottle washing, filter back-washing, bottling machine cleaning, and cleaning of equipment, floors, and pipework during flavour changes. It also typically includes extra and discarded soft drinks. Additionally, it comprises surfactants/detergents for washing that give the SDIW inorganics, as well as lubricants required for machine components. The main components of soft drink syrup are sugars, fruit juice concentrates, sweeteners, preservatives, salts, and other ingredients. The industrial process of making syrup frequently results in the production of concentrates that are high in sucrose; as a result, this process is typically regarded as the most polluting procedure. Since sugars are easily soluble in the discarded syrup, they contribute high BOD and COD in SDIW thus increasing organic concentration. Additionally, it has been noted

Photocatalytic Treatment of Soft Drink Industry Wastewater Using … Table 1 Characteristics of SDIW (Ait Hsine et al. 2005; Matoši´c et al. n.d.; Sheldon and Erdogan 2016)

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Wastewater parameter

Reported concentration ranges

Chemical oxygen demand (COD)

25–145,000 mg/L

Biochemical oxygen demand (BOD)

130–150 mg/L

Total suspended solids (TSS)

26–38,000 mg/L

Total dissolved solids (TDS)

750–1200 mg/L

Total nitrogen (TN)

20–1180 mg/L

Total phosphorus (TP)

130–250 mg/L

pH

3.4–11

that almost 62% of the total organic matter in SDIW is soluble (Ait Hsine et al. 2005). Characteristics of SDIW are mentioned in Table 1.

3 Conventional Treatment Technologies for SDIW Table 2 enlists the conventional treatment technologies adopted for SDIW treatment. Treatment of SDIW through coagulant-aided filtration using a combination of anionic surfactant sodium dodecyl sulphate (SDS) and non-ionic surfactant Triton X-100 (TX-100) was evaluated. Transmembrane pressure (TMP), operation duration, surfactant concentration, and the ratio of TX-100 to SDS were all considered in the process. The results showed a maximum COD, TDS, and turbidity removal efficiency were 81.3%, 56.7%, and 99.5%, respectively (Namaghi and Mousavi 2014). High-rate anaerobic treatment using a newly-inoculated extended granular sludge bed (EGSB) reactor for the treatment of SDIW exhibited a maximum COD removal rate above 3000 kg/d, and COD removal efficiencies of >85%. The HRT for the treatment process was 29 h (Cuff et al. 2018). Similar treatment process EGSB with different initial characteristics of SDIW with HRT 12 hr, upflow 0.85m/h and OLR of 11 COD/m3 d had an efficiency of 93% COD removal. MBR anaerobic treatment showed COD removal of 87% with HRT 0.41 h and the combined four-stage ultrafiltration unit with anaerobic, anoxic, and aerobic biological treatment followed by membrane separation unit resulted in 95% COD removal efficiency of SDIW within 3.3 h. (Sheldon and Erdogan 2016). A novel combined jet loop-airlift bioreactor (air flow rate at 4 L/min) was constructed which is specialized to permit simultaneous carbon and nitrogen removal from SDIW. The achievement was a COD removal efficiency of around 98% and a TN removal efficiency of approximately 84%. This procedure needed 11h of HRT and moderate air flow rate. (Gholami et al. 2020). Application of physical or mechanical treatment techniques is constrained by high quantities of soluble organic materials in SDIW which escapes the treatment system. Theoretically, SDIW should be biodegradable and treated using biological methods

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Table 2 Different conventional methods applied for SDIW treatment Sl. No

Treatment method

Optimum Removal operating condition efficiency (%)

References

1

Micellar-enhanced ultrafiltration (MEUF) for SDIW treatment using sodium dodecyl sulphate (SDS) and Triton X-100 (TX-100)

Transmembrane pressure = 3 bars, HRT = 0.25 h, SDS = 8.15 nM, TX-100 = 0.25 nM

COD = 81.3; TDS = 56.7; Turbidity = 99.5

(Namaghi and Mousavi 2014)

2

Expanded granular sludge bed (EGSB) reactor

HRT = 11–29 h, Organic loading rate (OLR) = 1.5 kg COD/ m3 d

COD > 85

(Cuff et al. 2018)

3

ESGB anaerobic treatment

HRT = 12 h, Upflow = 0.85 m/ h, OLR = 11 COD/m3 d

COD = 93

(Sheldon and Erdogan 2016)

4

Multi-stage membrane bioreactor (MBR)

HRT = 0.41 h, OLR = 2.3 kg COD/m3 d

COD = 87

5

Integrated EGSB/MBR (UF-MBR)

HRT = 3.3 h, COD = 95 DO = 2–3.7 mg/L, OLR = 3.1 kg COD/m3 d

6

Integrated jet loop-airlift bioreactor

HRT = 11 h, COD = 98; Air flow rate = 4 l/ TN = 83.6 min

(Gholami et al. 2020)

a This

signifies that the composition, concentrations, or other relevant parameters of SDIW were different for each treatment method or advanced oxidation process evaluated in the respective tables. By indicating this variability with an asterisk, we aim to highlight the importance of considering the specific characteristics of SDIW when assessing the performance and suitability of different treatment approaches

as these techniques are thought to be economical and environmentally beneficial (Redzwan and Banks n.d.). It is clear that the standard biological treatment procedures are highly effective in removing COD, like UF-MBR 95% COD removal. But such techniques often need high HRT, which makes the entire treatment procedure exceedingly time-consuming and, in certain situations, generation to secondary contaminants. It has also been found that conventional treatments are not suited to the removal of pollutants with limited degradability, such as dyes and other biorefractory pollutants. It is also challenging to maintain optimal operational conditions for biological processes like high-rate anaerobic treatment, which depend on a number of parameters such as HRT, OLR, etc. So, we may think of alternative solutions to these conventional treatment methods to address their drawbacks.

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4 Advanced Oxidation Processes for SDIW Treatment Recently, there has been a lot of attention paid to the role that advanced oxidation processes (AOPs) can play in this area. AOPs were first proposed for the treatment of potable water in the 1980s, which was defined as the oxidation processes involving the generation of hydroxyl radicals (•OH) in sufficient quantity to effect water purification. Afterwards, the AOP concept has been extended to the oxidative processes with sulphate radicals (SO4 − ). AOPs concluded as the oxidation processes that make use of free radicals by their generation at low pressure as well as temperature in order to oxidize the pollutants/contaminants and convert them into considerably lesser toxic substances or even mineralize them completely to give end products like CO2 , H2 O and certain inorganic ions (Titchou et al. 2021a and b). Due to their superior effectiveness in pollutant degradation and full mineralization, these methods have shown to be a significant improvement over traditional treatment system. In addition, they are not waste-selective, have rapid reaction rates, can efficiently oxidize pollutants, and produce no by-products. Overall, we may categorize these processes into two types: homogeneous and heterogeneous. To be more precise, AOPs can be represented as a set of chemical processes (Fenton, ozonation), physical processes (sonolysis, cavitation), photochemical processes (O3 /UV, photoperoxidation, photoelectrolysis, etc.) and electrochemical processes (electro-Fenton, peroxi-coagulation, Fered-Fenton, etc.) (Garrido-Cardenas et al. 2020; Muniyasamy et al. 2020; Sharma et al. 2018; Titchou et al. 2021aand b; Zazou et al. 2019). The pollutant degradation during the AOP mainly occurs as a result of generation of highly reactive species, called free radicals. Each free radical has its specific mechanism for pollutant degradation, which is generally determined by the analysis of degradation by-products. One of the examples of such species is •OH, which has very high reduction potential and is known to act upon target pollutants such as nitrate, bicarbonate, sulphate, phosphate, etc. non-selectively to completely mineralize them into H2 O and CO2 . Some other examples of reactive oxidizing species are superoxy radicals (O2 − •), peroxymonosulphate (PMS) radicals (SO5 − •), hydroperoxy radicals (HO2 •), etc. (Titchou et al. 2021a and b). In essence, AOPs are used in water and wastewater treatment to eliminate both organic and inorganic contaminants and transform them into less toxic or even completely non-toxic end products. Few AOPs used for SDIW treatment are analyzed in Table 3. The use of bittern (by-product of salt production processes) as a coagulant was done in studying application of electrocoagulation and COD and BOD removal at different percentages of bittern. The results showed that the addition of 0.5% bittern to 5L of real SDIW sample gave the highest efficiencies of COD and BOD removal. The highest COD removal efficiency obtained was nearly 98% at treatment time of 6 h and that for BOD was 95% at 2 h (Julaika et al. 2019). A combination of adsorption as well as electrocoagulation was tested for SDIW treatment. The study also determined optimum conditions for electrocoagulation such as electrode distance and voltage. It was observed that colour was reduced by 51.3%, TSS by nearly 70% and COD by 56.3% solely by electrocoagulation process. Further

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Table 3 Different AOPs for SDIW treatment Serial number

Treatment method

Optimum condition

Time (h)

Removal efficiency (%)

References

1

Electrocoagulation by using bittern as a coagulant

0.5% bittern

6 2

COD = 98.31 BOD = 95

(Julaika et al. 2019)

2

Combination of electrocoagulation and adsorption using activated carbon (AC)

Inter-electrode distance 2 cm, 12 V and monopolar AC = 10 mg/L

2.5

COD = 92.15, TSS = 90.12, Colour = 98.66

(Muryanto et al. 2018)

3

Electrocoagulation without pre-treatment by calcium-modified clinoptilolite zeolite (modified with CaCl2 )

Current 14 intensity = 3 A; pH = 12

COD = 98, TOC = 94, Turbidity = 98, Colour = 100

(Victoria-Salinas et al. 2019)

4

Electrocoagulation with pre-treatment by calcium-modified clinoptilolite zeolite (modified with CaCl2 )

Current 6 intensity = 2 A; pH = 12

COD = 100, TOC = 89, Turbidity = 98, Colour = 100

5

Electrocoagulation with pre-treatment by calcium-modified clinoptilolite zeolite (modified with CaCl2 )

Current 10 intensity = 3 A; pH = 12

COD = 98, TOC = 94, Turbidity = 98, Colour = 100

6

Photo-Fenton

H2 O2 = 4000 mg/L; Fe(II) = 375 mg/L

2

Before addition of sulphate TOC = 54

7

Photo-Fenton with H2 O2 = persulfate radical-bases 4000 mg/L; Fe(II) = 375 mg/L;

4

After addition of sulphate TOC = 76

8

Ozone (O3 )

O3 flowrate 5.2 g/h

1

O3 COD = 9, Colour = 62.06

9

Ozone-peroxide (O3 -H2 O2 )

O3 flowrate 5.2 g/h

1

COD = 10, Colour = 84

(Expósito et al. 2016)

(García-Morales et al. 2012)

(continued)

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Table 3 (continued) Serial number

Treatment method

10

Ozone-coagulant O3 flowrate 1 Polyaluminum chloride 5.2 g/h (PAC) PAC (0.01–0.08) mg/ L

COD = 15, Colour = 62.06

11

Ozone, followed by PAC and then ozone

O3 flowrate 5.2 g/h PAC = 0.03 mg/L

1

COD = 16, Colour = 88

12

Electrocoagulation

pH 8, current intensity = 1.5 A, current density = 30 Am−2

6

COD = 38, TOC = 27

13

Electrooxidation

pH 8, current intensity = 1.5 A, current density = 30 Am−2

6

COD = 75, TOC = 70

14

Electrocoagulation coupled electrooxidation

pH 8, current intensity = 1.5 A, current density = 30 Am−2

6

COD = 85, TOC = 75; TP = 89; TN = 84; Colour = 100

Optimum condition

Time (h)

Removal efficiency (%)

References

(Linares Hernández et al. 2017)

a This

signifies that the composition, concentrations, or other relevant parameters of SDIW were different for each treatment method or advanced oxidation process evaluated in the respective tables. By indicating this variability with an asterisk, we aim to highlight the importance of considering the specific characteristics of SDIW when assessing the performance and suitability of different treatment approaches

enhancement in removal efficiencies was observed when adsorption with activated carbon was adopted and the removal efficiencies were increased to 98.66% for colour, 92.15% for COD and 90.12% for TSS with 10 g/L of activated carbon (Muryanto et al. 2018). A successful attempt was made to explore the treatment of SDIW utilizing the electrooxidation method and to optimize the process by performing pre-treatment of wastewater using calcium-modified clinoptilolite zeolite (modified with CaCl2 ). Electrooxidation without any pre-treatment gave very high removal efficiency: TOC, colour, turbidity, and COD removal efficiencies were 94.05, 100, 98.64, and 98% after 14 h of treatment at pH of 12 and 3 A of current intensity. However, when pretreatment was performed, the treatment period could be reduced to 6 h at a current intensity of 2A in order to remove 100% of the colour, 89.30% of the TOC, 100%

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of the COD, and 98.53% of the turbidity, respectively. As the physico-chemical quality of treated waters is significantly improved, they can be reused for a variety of purposes, such as washing and cooling. The study concluded that this coupled process is highly advantageous for achieving fair levels of efficiency in a shorter treatment time, and that it can ensure the reusability of the treated water (Victoria-Salinas et al. 2019). The suitability of photo-Fenton process for the treatment of wastewater from the SDIW was examined, along with ways to increase its effectiveness with sulphate radical-based AOP. With the use of neural networks and a factorial design of trials, the best conditions for the process were determined. The photo-Fenton method accomplished almost 54% mineralization within 2 h, and the addition of persulphate increased the efficiency to 76% during the following 2 h. In addition, an increase in temperature from 30 to 65 °C over the course of 2 h for the thermal activation of persulphate resulted in a roughly 10% improvement in mineralization. In addition, it was found that the TOC removal slowed in the last phases of treatment due to the development of oxalic acid and the poor reactivity of acetic acid (Expósito et al. 2016). A comparison among ozonation (O3 ), ozonation-peroxide (O3 -H2 O2 ) and ozonation-coagulation with polyaluminium chloride/PAC (O3 -PAC) was done for SDIW treatment. Four configurations were tested: simple ozonation, ozonation with peroxide addition, ozone followed by coagulation and then again by ozonation and coagulation followed by ozonation. It was confirmed that in terms of discolouration, COD as well as turbidity removal, the combined coagulation-ozonation process showed the highest efficiency whereas the ozone-peroxide treatment was the least efficient (García-Morales et al. 2012). Electrochemical AOPs, mainly electrocoagulation and electrooxidation coupled with boron-doped diamond Cu system, were applied for the treatment of SDIW samples. The study revealed that electrocoagulation process could only achieve nearly 38% COD and 27% TOC removal efficiency; the reason for such less efficacy reported was the possible inhibition of oxidation of organic matter due to the presence of inorganic species such as sulphates, phosphates, etc. in high concentrations and formation of complex ions with copper. On the other hand, electrooxidation process yielded considerably higher removal efficiencies—more than 75% COD removal and 70% TOC removal for treatment time of 6 h and almost 94% COD and 85% TOC removal for 12 h of treatment. By coupling both these processes together, the efficiencies obtained were 75% for COD removal, 89% for total phosphorus removal, 84% of total nitrogen removal, and 100% of colour removal, thus indicating greater effectiveness of this coupled treatment system for SDIW treatment (Linares Hernández et al. 2017). In spite of their superior efficacy against organic and inorganic pollutants as compared to other conventional biological and physicochemical processes, the majority of the homogeneous AOPs reviewed here for treatment have certain practical limits. For instance, the application of the Fenton process has a number of disadvantages, including an increase in operational costs when higher concentrations of Fenton reagent are required for higher contaminant concentrations, the practical

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handling and storage of H2 O2 , the difficulty in regenerating catalysts in reagents, the inapplicability of the process in cases of high alkalinity or sludge with a high buffer intensity, and the production of a large quantity of iron sludge in the process (Titchou et al. 2021a and b). Other physico-chemical AOPs, such as sonolytic ozonation, also have limitations, such as the inability to scale up the process to an industrial level due to higher capital and operational costs for ultrasonic devices/transducers, and a decrease in efficiency when dealing with a large volume of wastewater. Therefore, such processes need adequate reactor design and optimization. (Merouani and Hamdaoui 2019). Furthermore, electrochemical AOPs such as electrocoagulation and electrooxidation continue to be challenging to execute on an industrial scale. In order to scale these processes up to an industrial level, it is necessary to focus further on many factors such as reactor design, electrode configurations, process mechanisms, identification of optimal conditions, etc. In addition, the operating cost and energy consumption of these procedures when utilizing a non-renewable energy source may impede their use. One of the biggest disadvantages of electrocoagulation is the electrode passivation, which is caused by the creation of a protective layer of mostly metal oxides during the reaction on the metal surface (Al-Raad and Hanafiah 2021). When employing homogeneous AOPs for the treatment of SDIW, it is necessary to take into account the aforementioned factors. Heterogeneous photocatalysis might be an alternate approach to circumvent these restrictions.

5 Photocatalysis Photocatalysis (Fig. 1) harnesses photon energy and transforms it to chemical energy, and it has tremendous promise for various applications, including water and wastewater treatment. This process is extremely efficient in degrading a wide variety of organic pollutants, ultimately mineralizing them into carbon dioxide and water (Ahmed and Haider 2018). In contrast to other water treatment methods, such as coagulation and flocculation, photocatalysis totally destroys pollutants, as opposed to changing them from one phase to another. On the basis of the physical state of reactants, photocatalysis might be divided into two categories, namely homogeneous and heterogeneous photocatalysis. Homogeneous photocatalysis is the process in which the photocatalyst and the reactant are in the same phase (i.e., gas, solid, or liquid). In homogeneous photocatalysis, free radicals are generated by illuminating homogeneous molecules of oxidizing agents dissolved in water or another liquid, such as hydrogen peroxide (H2 O2 ) and ozone (O3 ). Ozonation (UV/O3 ), photo-Fenton processes (Fe2+ and Fe2+ /H2 O2 ), UV/ H2 O2 , and UV/H2 O2 /O3 are some of the well-known processes (al Mayyahi and Ali Abed Al-Asadi n.d.). Despite the fact that homogeneous photocatalysis has several benefits, such as high oxidation characteristics, rapid reaction, it is not often used in photocatalytic applications. This is because it is challenging to separate the photocatalysts from the solution, the photocatalysts have a poor reusability potential, product purification is required, and almost homogenous photocatalysts absorb narrowly

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Source of hν

Energy

Conduction band (-)

Excitation by photon

e-

Free radicals

Recombination

Valence band (+)

Pollutant Degradation

CO2 + H2O

Free radicals

+

h

OH

Fig. 1 Photocatalysis

within the solar spectrum (Zakria et al. 2021). In addition, photocatalytic activity and stability of homogeneous photocatalysts are constrained by the molecular nature of their structures, which is inherently unstable (Huang et al. 2020). In heterogeneous photocatalysis, the catalyst is totally separate from the reactants. On the basis of band gap energy, i.e., the energy difference between the valence band and the conduction band materials is divided into three categories, namely, insulator (band gap where electrons cannot jump from valence band to conduction band), semiconductor (narrower band gap), metal or conductor (no band gap and electrons move in the space between atoms). Typically, heterogeneous photocatalysts are composed of semiconductors (i.e., metal oxides), as semiconductors can absorb light to stimulate the flow of electrons, resulting in the production of reactive species. Heterogeneous photocatalysis often refers to the photocatalytic process. This process involves hydroxy radicals (•OH) and other reactive oxidizing species that are generated when a photocatalyst, usually a semiconductor, is irradiated with visible light, which results in the excitation of electrons from valence band to conduction band forming electron–hole pairs and generation of reactive oxygen species (ROS) due to the reaction of electrons and holes with atmospheric O2 and H2 O (wastewater). ROS react with target organic compounds to degrade or convert into harmless byproducts. The series of reactions occurring in photocatalysis is explained in Eqs. 1–6 (Kurian 2021). Photocatalyst + hν → e− + h +

(1)

h + + H2 O → H + + O H −

(2)

h + + O H − → •O H

(3)

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2e− + O2 + 2H + → H2 O2

(4)

e− + H2 O2 → •O H + O H

(5)

Organic contaminants + •O H + O2 → C O2 + H2 O + degradation by − pr oducts

(6) It has been illustrated that heterogeneous photocatalysis is one of the most promising techniques for removing organic pollutants from water. The relatively large band gap energy of few metal oxide-based heterogeneous photocatalysts requires the use of ultraviolet, although visible light contains 2–3% UV light, the use of visible light reduces photoactivity. In addition, after the charge separation and migration of photogenerated carriers, electron–hole recombination might occur, resulting in inadequate photocatalytic activity to treat the target pollutants and post-treatment separability of photocatalyst from treated water. In the field of environmental treatments, the electronic band structure alterations and charge separation enhancements of metal oxide-based photocatalysts have received considerable interest. By doping and combining semiconductors, it is possible to modify the electronic band. This increases the photocatalytic activity of photocatalysts and changes the visible/UV light absorption range.

6 Modification and Immobilization of Photocatalysts The photocatalysts that are used in the process are generally semiconductor materials, among which titanium dioxide (TiO2 ) is one of the most widely used photocatalysts. For such materials to act as an effective photocatalyst, some of the important properties that define them are stability, chemical reactivity, cost, availability, surface area, number of active sites, non-toxicity, bandgap energy, etc. In order to make use of solar radiation to activate photocatalyst, it is necessary to reduce its bandgap to extend the absorbance wavelength range to visible light region. This can be ensured by adopting various strategies such as doping with metals or non-metals, coupling with noble metals, generating defect structures, constructing heterojunctions, etc. (Table 4) (Fauzi et al. 2022). Table 4 explains a few modifications for the removal of various pollutants in water. The photocatalytic activity for pollutant degradation can be finetuned by increasing the surface area of the photocatalysts, so as to facilitate maximum contact and reaction between the reactive species on the photocatalyst surface and organic pollutant in wastewater. This may be achieved by using them in powder form. However, it later becomes quite difficult to separate the finely powdered photocatalyst from the treated effluent. Therefore, the photocatalyst can be immobilized

Separation of photo-excited electrons and holes is accelerated

Increase the catalytic efficiency of photocatalysis

Photoelectrode

Non-metal-doped: loaded noble metals act as active sites for trapping electrons and protons

Metal doped: narrowing bandgap enhances the photocatalytic activity of photocatalyst under UV irradiation

Coupling

Doping

Type/modification Purpose

Crystal violet

Reduced graphene oxide-ZrO2 composite

Reactive brilliant red X-3B

(Wei et al. 2013)

(Sun et al. 2019)

(Aljeboree and Alkaim 2019)

(Jagannatha et al. 2019)

(Yi et al. 2019)

(Shetty et al. 2017)

(Cardoza-Contreras et al. 2019)

(Raju et al. 2019)

(Bhatia and Dhir 2016)

(Phuong et al. 2019)

Reference

Porous coral-like WO3 /W Perfluorooctanoic acid (Osman et al. 2019) photoelectrode

RuO2 /TiO2 photoelectrode

MFe2 O4 -Ag2 O (M = Zn, Methyl orange Co, Ni)

Benzophenone caffeine

ZnO-zeolite

Diclofenac

Caffeine

Ag-doped ZnO Paracetamol

Organophosphorus pesticide

Cu-doped TiO2

S-doped TiO2

Ibuprofen

N-doped TiO2

Diazinon pesticide

Bi-doped TiO2

Target pollutant

Fe-doped TiO2

Modified photocatalyst

Table 4 Photocatalytic removal of target organic pollutants in water using modified photocatalysts

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or supported on appropriate materials so as to permit simpler recovery of photocatalyst post-treatment and reuse for following cycles. On a variety of support materials, including activated carbon, alumina, glass fibres, silica, ceramics, etc., immobilization can be accomplished (Remya and Swain 2019).

7 Photocatalytic Treatment of SDIW Using Modified Photocatalyst Photocatalytic decolourization of SDIW was tested by making use of two photocatalysts: TiO2 and ZnO along with support periwinkle shell ash (PSA) and snail shell ash (SSA). The type of light source used was visible light or sunlight. It was observed that periwinkle shell ash proved to be an efficient photocatalyst support in the presence of sunlight to give nearly 98% decolourization within 60 min when H2 O2 is added as an oxidant (Aisien et al. 2013). UV lights replaced visible light for more excitation thus increasing photocatalytic activity in TiO2 . The anatase phase of TiO2 has the most potent photocatalytic action among its polymorphs. Photocatalytic breakdown of surface stains in photocatalytic self-cleaning coatings exemplifies the action of photocatalysts (Luna et al. 2019). A SDIW was prepared using sol–gel method with initial observed value of COD, total nitrogen (TP), and total phosphate (TP) as 4780, 598, and 51 mg/L, respectively. The same was treated using microwave-assisted photolysis, with different configurations involving the use of electrodeless discharge lamps (EDLs). The system comprised of microwave and UV light through EDLs. Results showed that within an hour of treatment, there had been rapid mineralization and degradation, with COD removal efficiencies of 88% for microwave-supported photolysis configurations with two EDLs, at 400 W. The equivalent mineralization degrees climbed to 97.3% when the power was raised to 600 W. Additionally, it was shown that microwave systems with EDL designs were capable of producing strong radicals in large quantities; as a result, these systems displayed better efficiency (Swain et al. 2020). A microwave-assisted photocatalytic system was developed for the treatment of same SDIW with two different configurations with having one and two EDLs, along with a simple microwave-assisted photolysis system and photocatalyst. The photocatalyst used in the photocatalysis system was TiO2 supported on granular activated carbon (GAC), and the incident light was UV radiation. It was noted that the microwave photocatalysis system demonstrated the highest COD, TP and, TN removal and its efficiency was nearly 6 times more than that of microwave-assisted photolysis system. To sum up, the fast degradation of contaminants was attributed to the synergistic action of photocatalysis and microwaves (Remya and Swain 2019). Photocatalysis is a promising technology as it can ensure complete mineralization of the organic pollutants in SDIW, since it is highly organic in nature. Additionally, no harmful by-products are produced at the end of the procedure. Solar light-driven photocatalytic systems, for which photocatalysts with reduced band gaps may be

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developed and supported on appropriate support materials, can be used to further reduce the cost of the process. The previously stated modification techniques will assure band gap reduction. Contrary to systems employing electrochemical AOPs, photocatalytic systems do not need elaborate designs and setups of the reactors. The photocatalysts have also demonstrated that they can be recovered easily as well as recyclable for additional treatment cycles with a noticeably smaller loss in treatment efficiency. Consequently, photocatalytic treatment is a potential method for the treatment of wastewater from the soft drink sector.

8 Conclusion SDIW is extremely complex in composition since it comes from a wide range of industrial processes. However, it contains high levels of COD and BOD, and the organic material is often soluble in nature. Since physical or mechanical processes cannot be used to treat SDIW, biological treatment methods naturally have high removal efficiencies but they are constrained by longer treatment durations. Among the few physical and chemical conventional techniques applied for SDIW treatment, a novel combined jet-loop airlift bioreactor achieved COD removal efficiency of 98% and TN removal of 84% with 11 h HRT. Higher removal efficiency was accompanied by secondary pollutants, longer treatment duration and challenging optimal operational conditions. AOPs can, therefore, be thought of as an alternative. Photocatalysis can be classified into two types, i.e., homogenous and heterogeneous photocatalysis, on the basis of appearances of the physical state of reactants. However, homogenous photocatalyst is not very popular since it is difficult to separate photocatalyst posttreatment, low potential for reusability and absorb narrowly light within the limits. One notable approach among various homogeneous AOPs employed for the treatment of wastewater from the SDIW involves electrocoagulation, accompanied by pre-treatment using calcium-modified clinoptilolite zeolite (modified with CaCl2 ). This method has demonstrated remarkable efficiency by achieving complete removal of COD and color within a treatment duration of 6 hours. However, its implementation at an industrial scale has posed significant challenges. Consequently, the focus has shifted towards heterogeneous photocatalysis among AOPs. Heterogeneous photocatalysts have relatively large band gap, with modification like doping and composites of semiconductor are relatively used to overcome this limitation. There are relatively few studies and researches on its use especially for treating SDIW. This SDIW was treated with microwave photolysis and microwave photocatalysis system. Microwave photolysis system used microwave (power 600 W) and EDLs, which achieved 97.3% mineralization. Microwave photolysis system was capable of generating strong radicals in large quantity. The COD removal rate in the microwave photocatalysis system was 5.9 times higher than in the microwave photolysis system. Therefore, advancements in the application of photocatalysis with different modification can be studied as a very promising solution due to various advantages like complete mineralization,

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no toxic end products, cost-effective, simple systems, reusability and highly efficient treatment strategy for industrial effluents such as that of soft drink industry.

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Chemical Nanosensors for Monitoring Environmental Pollution Abel Inobeme, Charles Oluwaseun Adetunji, Alexander Ikechukwu Ajai, Jonathan Inobeme, John Tsado Mathew, Alfred Obar, Munirat Maliki, Nkechi Nwakife, and Chinenye Eziukwu

Abstract The role of industrialization and urbanization in socioeconomic advancement cannot be overstated. This, however, has resulted in a rapid deterioration of the environment due to various anthropogenic activities associated with the trend, resulting in the release of numerous pollutants. Environmental pollution has therefore become an issue of global interest in recent times as a result of its impact on humans as well as the ecosystem. There is, therefore, a pressing need for efficient and reliable strategies in environmental monitoring with a view to ensuring environmental and human safety. There are different categories of organic and inorganic pollutants as well as various microbes that are released into the environment most of which have deleterious effects on humans. Various approaches have been employed in monitoring different contaminants in the environment with some of these methods having their inherent limitations. The use of chemical nanosensor is promising due to its low cost, remarkable selectivity, high reliability, and accuracy in detecting even trace concentrations of contaminants. This chapter, therefore, reviews the application of chemical nanosensors in environmental monitoring. A general overview of the concept of chemical nanosensors in environmental monitoring is provided. The chapter also discusses the classification of chemical nanosensors, sensing principles, advantages, and limitations in environmental monitoring. Finally, most recent reports and future trends in the area of environmental monitoring using chemical nanosensors are also highlighted. A. Inobeme (B) · M. Maliki · N. Nwakife · C. Eziukwu Department of Chemistry, Edo State University Uzairue, Edo State, Nigeria e-mail: [email protected] C. O. Adetunji Applied Microbiology, Biotechnology and Nanotechnology Laboratory, Department of Microbiology, Edo State University Uzairue, PMB 04, Edo State, Nigeria A. I. Ajai · A. Obar Department of Chemistry, Federal University of Technology Minna, Minna, Nigeria J. Inobeme Department of Geography, Ahmadu Bello University Zaria, Zaria, Nigeria J. T. Mathew Department of Chemistry, Ibrahim Badamasi Babangida University Lapai, Niger State, Nigeria © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_6

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Keywords Contaminants · Environment · Monitoring · Nanosensor · Pollution

1 Introduction There is increasing pollution of the environment as a result of the skyrocketing industrialization and rising human population. There are various contaminants present in water, soil, air, and food due to various anthropogenic factors. Pollution has been reported to be responsible for about 9 million deaths on a global scale in 2015. Thus the causalities that have emerged from environmental pollution due to industries have been documented to be thrice greater than that from various pathogenic diseases such as malaria, tuberculosis, and AIDS (Sivaramanan and Kotagama, 2021). There is, therefore, a pressing need for the monitoring of the environment with a view to protecting humans and ecosystems from highly toxic substances and pathogens. The contamination of the environment significantly impacts on human mental and physical health. Also, most of the emerging pollutants from industries and agricultural activities have the tendency of inducing endocrine disruption and cancers. Pathogenic microorganisms have also affected the survival of humans due to the various diseases associated with them (Manisalidis et al. 2020). Several efforts have been put in place with a view to developing simple and reliable sensors for detecting environmental contaminants. The quantity of the contaminants is dependent on the nature of the area and the medium where they are present. There are various analytical techniques that have been adopted for the detection of environmental contaminants with some of them having their inherent limitations (Rasheed et al. 2019). The application of sensors makes it possible for the detection of analytes through the use of recognition elements which are then converted to signals that are understandable making use of a transduction or transducer component. The chemical sensors make use of a chemical component as the recognition element. Nanomaterials make it possible for the improvement of the transduction mechanism with regard to reproducibility, cost effectiveness, durability, sensitivity, and selectivity (Odobaši´c et al. 2019). The emergence of nanotechnology has given rise to novel materials, methods, and concepts that are readily adjustable to environmental application and sustainability. The rapid transition from microsensors to nanosensors is a welcome transformation that is neither effortless nor straightforward. Environmental assessment and monitoring is a complex process that deals with varieties of environmental contaminants, several products of decomposition, and chemical intermediates amongst others (Singh et al. 2017). Nanotechnology and the utilization of advanced nanomaterials is an emerging and highly promising field that involves the usage of nanomaterials for the facilitation of the detection of different chemical and physical parameters such as pH, temperature, relative humidity, presence of anions, metallic ions, inorganic

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and organic molecules, biological molecules, which are responsible for different environmental problems that could be responsible for various diseases. Through the monitoring of environmental samples and the detection of various environmental contaminants, advanced nanomaterials have paved the way for a more reliable sensory technology for the improvement of the quality of the environment and human life (Sharma et al. 2016). Even though there are numerous types of sensors that are available for detecting anions, gases, monovalent ions, and heavy metals amongst others, most of the existing models need reliable power and they lack improved technology for higher sensitivity, quality, and selectivity. Chemical sensors enabled by nanoparticles are reliable technology that makes provision for the accurate detection of nanomolar to picomolar levels of environmental pollutants. The quest for these kinds of sensors emerged from their on-site and facile determination potential, without the need for expensive laboratory equipment (Khan et al. 2019). Nanosensors are sensing devices that have at least a dimension of 100 nm used for the gathering of information at nanoscale and are capable of converting them into analytic data. Nanotechnology is an area that is concerned with the chemical and physical properties of materials at nanoscale and differs from the properties of bulk materials (Wen, 2016). Nanomaterials have unique physicochemical properties such as large surface area, exceptional sensitivity, and fast responses amongst others which are responsible for their applications in chemical sensors (Asadnia et al. 2016). Chemical sensors fabricated from nanomaterials have remarkable potential for usage in monitoring various types of contaminants in soil, water, and air. There are various kinds of nanomaterials (nanorods, nanowires, and nanobelts) that have found relevance in this regard. The larger surface areas of the chemical sensor imply an improved exposure even at low content of the analyte. The fragility in the structural nature of the nanomaterial enhances an extreme extent of determination. The use of nanomaterials in chemical sensors also makes it possible for higher robustness and efficiency. Various types of nanomaterials such as palladium, silver, and platinum nanoparticles have been used in the fabrication of chemical nanosensors. Chemical nanosensors have been utilized extensively as part of human advancement hence their role in environmental monitoring and assessment is paramount. This chapter, therefore, presents the application of chemical nanosensors in environmental monitoring. It discusses the classification of chemical nanosensors, sensing principles, advantages, and limitations in environmental monitoring. Finally, the most recent reports and future trends in the area of environmental monitoring using chemical nanosensors are also discussed (Fig. 1).

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Classification of Chemical

Components of Chemical

Chemical Nanosensors for Environmental Monitorin

Advantages of Chemical Nanosensor

Principles of Chemical Nanosensor Fig. 1 Schematic representation of chemical nanosensors for environmental monitoring

2 Components of a Nanosensor The basic components of a nano chemical sensor include a sensor, analyte, and a transducer whose role is for the conversion of one form of energy to another form as well as a chemical detector. A typical chemical nanosensor device has three primary components in its mechanism of functioning: i. Preparation of sample: This could be a complex mixture or suspension of liquids, gases or solid-state matter. This can also be homogenous. The preparation of samples of environmental specimens is a complex process as a result of the presence of various interfering substances and impurities. The sample must contain specific organisms, molecules, and functional groups, amongst others which the sensor must be able to detect. Such molecules commonly detected in environmental media include dyes, colors, pesticides, toxicants, vitamins, antibiotics, surfactants, and metals. Chemical sensors are also capable of detecting abiotic parameters such as weather, light, temperature, humidity, and volatile organic and inorganic substances. ii. Recognition element: There must be certain molecules that should be able to recognize the presence of the analytes in the samples. Such recognition components include aptamer, enzymes, and antibodies amongst others having remarkable specificity, affinity, and selectivity features to their analytes for efficient quantification at acceptable levels (Malik et al. 2013).

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Sensor

Components of

Analyte

Chemical Nanosensors Transducer

Detector

Fig. 2 Components of chemical nanosensors

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Transduction of signals: There are various methods of signal transduction that have also formed the basis for classifying the chemical nanosensors. The transduction component generally aids the conversion of the recognition event to signals that are detectable and computable and then generate the data (Fig. 2).

3 Principles of Functioning of Chemical Nanosensors Chemical nanosensors function by various processes such as gravimetry, colorimetry or optical phenomenon for the transformation of data obtained from the analyte at various concentrations into signals that are detectable. This is dependent on the analytical performance and chemical selectivity of the nanosensor. Nanomaterials such as nanowires and nanotubes show compatibility with the features of chemical nanosensors. These chemical nanosensors function through the binding of antibody activities to the conductive nanomaterials such as carbon nanotubes and then through the application of variations in the conductivity of the materials once the

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antibody is connected to the nanomaterials. The electrochemical sensors are basically immunosensors that are made of cerium oxide nanoparticles together with chitosan for the detection of contaminants that are foodborne. The chemical nanosensor has the potential of measuring up to the extent of unit molecule level. The nanosensor functions through the tracking of electrical variations in the sensing material. The analyte diffuses to the surface of the sensor making it possible for its detection. This change within the physicochemical parameters of the surface of the transducer brings about a change in the electronic or optical properties of the transducer’s surface; the change is then converted to an electrical signal that is detected (Willner et al. 2018). Various kinds of chemical nanosensors follow varying detection principles. For example, the electrochemical nanosensor detects the changes in the electrical distribution; the optical nanosensor focuses on the measurement of the variation in the intensity of light. The calorimetric nanosensors are based on the measurement of variation in heat intensity. In the carbon nanomaterial that uses a nanotube, if a particular molecule such as ammonia is present, it reacts with the vapor of water thereby making the carbon nanotube more conducive through the donation of a single electron. If, on the other hand, the molecule that is present is nitrogen dioxide, the carbon nanotube becomes less conductive through the stripping of an electron from the nanotube (Abdel-Karim et al. 2020). Therefore, a good chemical nanosensor must possess certain features which include: remarkably high environmental stability, fast dynamism, and high specificity for an analyte of interest in the presence of various interferents.

4 Classification of Chemical Nanosensors Classification of nanosensors is based on their application and structure. Based on structure, they are grouped into optical and electrochemical nanosensors. On the basis of their application, nanosensors are grouped into biosensors, nanosensors, chemical sensors, and others discussed below. There are other kinds of chemical nanosensors that have found relevance in various areas of environmental pollution monitoring which include photoacoustic-based nanosensors, magnetic resonancebased nanosensors, Plasmon coupling type nanosensors, quantum dot fluorescentbased nanosensors, the plasmonic-based nanosensors, amongst others.

4.1 Electrochemical Nanosensor In electrochemical sensors, the detection of the signals occurs at the electrode or a static or dynamic interface of the solution. The interface involves oxidations and reduction processes which are then accompanied by the transfer of electrons within

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the voltammetric nanosensors. The utilization of nanoelectrodes makes a provision for a higher charge transfer, surface area, and electrocatalytic activity, thereby providing an improved response of the sensor (Dzulkurmain et al. 2021).

4.2 Nanowired-Based Chemical Sensors There are also chemical nanosensors that are based on nanowires. Their emergence as powerful tools is due to their remarkable ultra selectivity, direct detection potential, ultrasensitivity, and biospecies. Such nanosensors have the potential of detecting various small organic contaminants such as proteins and viruses and are, therefore, employed for detecting various environmental contaminants.

4.3 Raman Scattering Chemical Nanosensors These have the potential of detecting analytes up to a single molecular level through a nondestructive and ultrasensitive spectroscopic approach.

4.4 Piezoelectric Nanosensors They measure the variation in mass due to the vibration within the influence of electric field on exposure of the substance to crystal or light. These sensors are able to detect the particular angle at which the waves of electrons are released. It changes the variation in mass from chemical adsorption into electrical signals. The alteration in frequency is directly proportional to the quantity of the absorbed analyte.

4.5 Immunochromatographic Strip Nanosensors They are found in numerous point-of-care devices employed for analytical purposes. They have also been widely employed in environmental monitoring. Their sensitivity is usually improved through the augmentation of the intensity of their detection signals and optimization of the technique of labeling.

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5 Advantages of Chemical Nanosensors Over Conventional Approaches in Environmental Monitoring Chemical nanosensors play an indispensable role in various areas of environmental pollution monitoring and testing. They have unlimited advantages when compared to the traditional approaches and also make provision for the need for portable and highly sensitive analytical tools with unique features of stability and selectivity. The prominent advantage of chemical nanosensors is their provision of a significantly large surface area to volume ratio, thereby making them gain higher sensitivity in the detection of atoms, single molecules, and other environmental analytes at trace level. The fabrication of a reliable chemical nanosensor is projected with vital realistic requirements and pragmatic value in the field of environmental contaminant detection and monitoring. The unique structural properties of the sensing device critically account for the efficiency of the overall device. The chemical nanosensor provides outstanding performances that outmatched the conventional sensing techniques (Shah 2020, 2021a, 2021b). They show outstanding reproducibility of signals, selectivity, sensitivity, and stability. They are also suitable for on-site accurate detection of the analyte.

5.1 Reports on the Use of Chemical Nanosensors in Environmental Monitoring Julkapli and Bagheri (2018) in their review work highlighted those there highly flammable and malodourous gases that are generated from the petroleum industries which are readily absorbed into the respiratory systems. They, therefore, highlight the need for constant monitoring of numerous gases found in the environment due to their toxicity to humans and possible alteration of various ecological processes. They also emphasized the promising prospects of nanomaterials in the efficient monitoring of various kinds of gases released into the environment through anthropogenic activities. Amongst the different groups of environmental pollutants, heavy metals have attracted serious attention due to their persistence in the environment as well as their deleterious effects on humans and other organisms. Various studies have reported the use of chemical nanosensors for the detection of heavy metals. VitoFrancesc et al. (2022) developed an integrated nanosensing system for the real time detection of heavy metals in river catchment. The mechanism of detection was based on semiautonomous driving that was integrated with a microfluidic component for high sensitivity to the metals. The finding from their study showed the suitability of the system for the on-site determination of copper and lead from the rural and urban areas releasing effluents in water bodies. Xiang et al. (2020) collected data based on the available literature on the application of chemical nanosensors for the detection of heavy metals and pesticide residues in water. They gave special attention to the reports on the sensitivity of the sensors applied, the nature of the sensors,

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and the compositions of the water samples. The findings from their study showed that most of the available sensors could be employed for river and stream water. The mean detection limits for the pesticides and heavy metals were 72.53 ng/ml and 65.36 ng/ml, respectively. Hakonen and Stromberg (2018) developed a sensing technique for the detection of lead in water. The detection technique used dye ionophore which increased the sensivity. They also developed a simplified test tube mix. The detection and quantification limits for the measurements were found to be 3 and 10, respectively. Varun and Kiruba (2018) in their study opined the pressing need for the utilization of nanotechnology as a reliable tool for the detection of heavy metals in the environment. They highlighted the recent advancement in the use of chemical nanosensors for the detection of heavy metals in the environment. Potadar et al. (2022) in a related review highlighted some recent advancements in the area of chemical nanosensors in the detection of the presence of heavy metals such as arsenic, iron, lead, copper, palladium, cadmium, and rhodium in soil samples. They also discussed the ideal features of fertile soil as well as the toxicity associated with soils that are contaminated with heavy metals. Omowunmi and Joseph (2006) employed novel nanomaterials for detecting, identifying, and quantifying heavy metals. They used new colloidal nanocomposites that were introduced into a conducting polymer bed for the fabrication of the sensor. They used this device for the detection of selected heavy metals in aqueous media. Li et al. (2013) in another review work documented that environmental pollution due to heavy metals is one of the recent issues that is of more concern. They also emphasized various efforts that have been put forward in the development of portable sensors for environmental monitoring. They also observed that the integration of nanomaterials into sensing technology would further increase various features sucha s selectivity, sensitivity, and multianalyte detection. Rasheed et al. (2022) reviewed the recent advances in the application of colorimetric in the detection of heavy metals in environmental samples. They also discussed the synthesis of nanomaterials for sensing technology using environmentally friendly approaches. Zamora-Sequeira et al. (2019) in their review work observed that there has been a rapid increase in the application of pesticides for enhancing agricultural productivity which has consequently resulted in environmental contamination. They highlighted that the most recent advances in this area involve the utilization of nanomaterial in the area of chemical sensing for higher sensitivity, selectivity, and accuracy. They also outlined the various kinds of sensors that have been used for the detection of different classes of pesticides. Umapathi et al. (2022) reported their work on the development of a highly portable electrochemical technique of sensing for the real-time determining of pesticide residues in vegetables and fruits. They highlighted sensing technology as significant tools suitable for the detection of various types of pesticides. They also emphasized their suitability for on-site pointof-care determination. The advantages, challenges as well as future trends were also presented.

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6 Conclusion The most remarkable advantages of chemical nanosensors are their provision of remarkably large surface area that makes it possible for them to gain high sensitivity in detecting a single atom or molecule at a trace level. For these reasons, chemical nanosensors are being employed in various areas of environmental monitoring.

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Nanotechnology for Bioremediation of Industrial Wastewater Treatment Manisha Kumari, Jutishna Bora, Archna Dhasmana, Sweta Sinha, and Sumira Malik

Abstract The current decade has the primary concern of providing affordable and safe water to meet the requirements of human beings. Adequate wastewater treatment is essential for economic growth in the current era of water and water resources scarcity. Wastewater treatment is gaining more importance in this world full of industries. Among numerous treatment techniques, recent advancement in the field of nanotechnology has gained the interest of scientists. Nanotechnology has immense potential to improve water and wastewater treatment efficiency and augment water supply by safely utilizing unconventional water sources. The unique characteristic of nanomaterials possessing a high surface area can be used effectively to remove toxic metal ions and inorganic and organic solutes from the water. This paper includes a discussion on the utilization of nanotechnology and recent development in the field of nanotechnology for the bioremediation of wastewater treatment. On both small and large scales, nanotechnology has shown a variety of practical techniques for wastewater treatment in a more accurate and precise way. Keywords Wastewater treatment · Nanotechnology · Nanomaterials · Bioremediation

M. Kumari · J. Bora · S. Malik (B) Amity Institute of Biotechnology, Amity University Jharkhand, Ranchi, Jharkhand, India e-mail: [email protected] A. Dhasmana Himalayan School of Biosciences, Swami Rama Himalayan University, Dehradun, UK S. Sinha Department of Chemistry, Amity Institute of Applied Sciences, Amity University Jharkhand, Ranchi, Jharkhand, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_7

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1 Introduction Water is one of the essential substances for all life on earth, and for human civilization, it is the most precious and abundant natural resource. However, the availability of this resource for human consumption is only around 1%. It is estimated that due to the growing population, a variety of environmental and climatic changes, and the rise in the costs of potable water, more than 1.1 billion people lack access to adequate drinking water. In the twenty-first century, the most fundamental goal of humans is access to safe and affordable water; it continues to be a significant challenge globally. The water supply chain’s primary concern is the ongoing contamination of freshwater resources through various industrial, inorganic, and organic pollutants (Schwarzenbach et al. 2006). Due to the enhancement in the production of water, enormous pressure has been put by the industries on its consumption. As a result of increased manufacturing, a large amount of industrial effluent has been produced. For the sustainable development of both environment and the industries, cost-effective and strict treatment of these industrial effluents is essential (Gupta and Shukla 2020). The biological treatment of industrial wastewater can help reduce these issues, although the traditional technologies used for wastewater treatment are insufficient to remove the new contaminants entirely and meet the stringent water quality standards. Different valorization, electrochemical, and advanced oxidation techniques have been used to reduce the toxicity in wastewater effluents generated by industries and to make their use more sustainable. However, these wastewater treatment methods are insufficient and cost-effective in many industries (Gupta and Shukla 2020). Among the different new technologies emerging to overcome this problem, nanotechnology has enormous potential for the bioremediation of industrial wastewater and other environmental issues. Nanotechnology is the branch of nanoscience that deals with the phenomenon applied on a nanometer-scale level. Among humans, nanomaterials are the tiniest structure that has been created, measuring only a few nanometers in size. In various literature, among the various technologies’ nanotechnology has been cited as one of the most advanced technologies for the treatment of industrial wastewater. Because of their small size, advanced chemical characteristics, high surface area to volume ratio, and strong mobility for a solution, nanotechnological pathways are found to be more effective and efficient than their traditional counterparts. Nanomaterials associated with membranes are also effective for removing industrial effluents. Nanomaterials provide innovative functions for pollutant degradation and enhance membrane permeability, stink resistance, and thermal and mechanical strength. In enhancing degradation reactions, nanocatalysts also play an essential role (Dixit and Shukla 2020). Metal–organic frameworks (MOFs) eliminate heavy metals such as Pb, mo, etc., from wastewater, membranes, and nanocatalyst. The coordination of precursors of metal ions and organic ligands is used in the synthesis of these MOFs. The coordination of metals to functional groups compared to organic ligands can improve MOFs’ effectiveness because of the low steric hindrance shown by metals (Deshpande et al. 2020). The production of green nanomaterials from microbes and extracts

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from different species has shown a path to the bioremediation of eco-friendly industrial pollutants. Among the green nanoparticles, iron nanoparticles are mainly used in this remediation because of their magnetic susceptibility, non-toxicity, and redox potential during reaction with water (Dixit and Shukla 2020). The present review focused on removing pollutants from industrial wastewater with the help of various nanotechnologies. Moreover, using microbes and green nanotechnology-based on enzymes is also discussed for the removal and valorization of waste materials in water.

2 Water Pollution: Major Sources The significant sources of water contamination can be broadly divided into two groups: (i) Point sources In point source pollution, the contaminants originate through single sources, arrive in water through identifiable sources, and discharge directly into water or aquatic environments (Rafique et al. 2019). For example, discharge of wastewater from oil refineries, illegally or legally by manufacturers, wastewater treatment facilities, and domestic sewage. This also includes pollutants from chemical and oil spills, leaking septic systems, and illegal dumping. Although the pollutants in point source pollution originate from a single source, it has the potential to contaminate miles of oceans and streams (Wu and Chen 2013). (ii) Nonpoint sources Nonpoint source water pollution occurs when contaminants reach the aquatic ecosystem from different sources. The most common example of nonpoint source pollution is fertilizers and pesticides (Rafique et al. 2019). Agriculture-related nonpoint source pollution is often regarded as the primary cause of quality surface water quality degradation. When irrigation water, rain or snowmelt water runs over land, it deposits and carries pollutants into coastal water, lakes, and rivers, causing nonpoint source pollution (Wu and Chen 2013). The sub-categorization of point and nonpoint source pollution is done as follows.

2.1 Fertilizers and Pesticides Globally, modern agriculture is the primary source of organic chemicals such as fertilizers and pesticides produced by industries widely utilized by most countries and in a wide range of environments. Pesticides have been widely used to eliminate pesticides, pests, bacteria, and microorganisms. Environmental monitoring has increasingly shown that trace levels of pesticides can be found in ground and surface

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water bodies distant from pesticide application locations, thus polluting the water and deteriorating the quality of water (Gambhir et al. 2012). The agriculture ecosystem is harmed when pesticides are used excessively or improperly controlled. It is seen that only 60% of the fertilizers are efficiently utilized in the soil, and the remaining part is absorbed as a contaminant in the water and soil (Rafique et al. 2019). As various fertilizers are not entirely utilized or absorbed by the crops, many fertilizers are still present. The residual fertilizers, which are present in the form of ammonia, nitrates, sulfates, and phosphates, contaminate the water. Moreover, algae can grow in surface water due to fertilizers, leading to eutrophication and posing a threat to the ecosystem. Many algae can contaminate water resources and cause toxicity. Furthermore, some fertilizers also contain heavy metals, leaving heavy metals in soil and water resources, thus contaminating the environment (Greenlee et al. 2009).

2.2 Water Pollution Due to Industries The primary source of water pollution is dumping various untreated industrial effluents into the rivers. Depending on the nature of industries, a pollutant discharge is caused by discharging poisonous and harmful materials, causing contamination in ground and surface water. Industrial water pollution accounts for about 25% of all pollution, resulting in a dangerous situation (Rafique et al. 2019). Many significant industries contribute mainly to water pollution, such as manufacturing, fertilizers and pesticides, power generating, mining and construction, sugar, petrochemical, and food processing (Dash 2015). These industries can generate hundreds of millions of gallons of wastewater, which contains harmful metals such as cadmium, iron, mercury, magnesium, lead, chromium and arsenic, cations, anions, nitrites, and nitrates (Greenlee et al. 2009). Most harmful pollutants, including various heavy metals and organic chemicals, are produced by manufacturing industries such as oil refining, steel, and chemical (Dash 2015). Other industries have lower potential and thus have less impact, yet they are considered highly dangerous when it comes to pollution. Textile, fertilizers and pesticides, leather tanning, pharmaceutical, plastics, pulp, and paint industries are among them (Raja and Venkatesan 2010). The primary source of radiation and heat is the power-generating industries. The significant contributors to thermal pollution are almost all power stations, regardless of fuel type. Nuclear power plant-generated radioactivity can pollute the water in various ways, including groundwater contamination by buried radioactive waste and the discharge of wastewater that is slightly radioactive (Gambhir et al. 2012). Radioactivity can be found in both surface and ground waters. In surface waters, it could be due to effluents from enrichment plants and uranium mining, while in ground waters, it may be because of radioactive substances in subsurface rocks. Acid drainage and sediment are critical contributors to the construction and mining industries. The impact of mining on the quality of water can be divided into four

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main categories: leaching and heavy metal contamination, erosion and sedimentation, acid mine drainage, and processing chemical pollution. The significant environmental challenges in the industries are water discharge and water utilization, trash and food scraps, chemicals used in cleaning and processing, and packing reduction and disposal (Gambhir et al. 2012).

2.3 Polythene and Plastic Bags Commercial plastics and polythene bags are other primary sources of pollutants present in wastewater. The disposal of the waste is done by placing the bags of plastic in the trash. Polythene bags and plastic release hazardous and non-decomposable substances, majorly heavy metals, into the water and air, thus polluting both. Incinerators used to recycle plastics also release poisonous products and gases into the environment, further polluting food resources and the entire food cycle (Rafique et al. 2019).

2.4 Polluted Groundwater Groundwater is the primary source of fresh water for the global population and is mainly used for agricultural, domestic, and industrial uses. A third of the world’s population relies on groundwater as their primary source of drinking water (Li et al. 2021). Groundwater pollution is the introduction of undesired substances into groundwater due to human activities. The significant causes for the reduction of groundwater quality are industries, agriculture, urbanization, and climate change. Toxic contaminants such as heavy metals, organic trace contaminants, hydrocarbons, pesticides and fertilizers, pharmaceutical pollutants, and other toxins put human health and natural ecosystems at risk (Li and Wu 2019; Siddique et al. 2019). Currently, chemical contamination has become the main focus of groundwater investigations. Groundwater pollution can also be caused by chemicals, bacteria, pharmaceuticals, petroleum, and brines. Iron, cadmium, and arsenic are metals that can dissolve in groundwater and be detected in large amounts. These contaminants can pose significant health concerns throughout the food chain if the contaminants in groundwater are at higher levels than the allowed guideline concentration. However, unlike surface water contamination, groundwater contamination is invisible, and recovery of groundwater resources is expensive and difficult for the current level of technology (Al-Hashimi et al. 2021) (Fig. 1).

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Plastics and polythene bags

Organic and Inorganic pollutants

Industrial effluents

Industrial water pollutants

Fertilizers and pesticides

Heavy metals

Fig. 1 Schematic representation of Industrial water pollutants (Rafique et al. 2019)

3 Conventional Method Used in Industrial Wastewater Treatment and Purification In wastewater, different types of inorganic and organic contaminants are found. To reduce the deteriorating properties, present in this wastewater, it is treated using conventional methods, which might adversely affect humans and the ecosystem. Using conventional methods can lower the amount of suspended and floatable materials and treat biodegradable organic matter seen in wastewater. On the other hand, conventional methods cannot remove hazardous substances, suspended solids, nutrients, dissolved solids, and harmful pathogens from the wastewater (Rafique et al. 2019). The use of conventional methods to remove heavy metals is either getting more expensive or cannot meet the stringent regulatory limits of the effluents. Ion exchange, membrane processes or filtration, activated sludge, trickling filters, chemical precipitation, sedimentation, and carbon adsorption are some conventional methods (Fig. 2) used to remove hazardous substances and dissolved heavy metals from the wastewater. All the inorganic and organic contaminants present in the wastewater are discharged using advanced and cost-effective methods (Rajasulochana and Preethy 2016).

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Fig. 2 Schematic representation of technology used for Industrial wastewater treatment

3.1 Filtration by Micro Membrane In wastewater filtration, micro-membrane filters are made of tiny pores (less than 0.1 μm) and porous fibers. The pores on the hollow fiber membranes are the path through which water is driven by exerting pressure. As the size of the water molecules is small enough to flow through this pore, some helpful pollutants also pass through it. Therefore, clean water is accumulated on the membrane’s other side. The arrangement of hollow fibers is made in a unique design of U-shape due to which the clean water is moved toward the open end of the fiber into the mouthpiece of the bottle, which the contaminants are collected on the outside of the fibers and can be easily washed away (Rafique et al. 2019). Some species and pollutants with sizes more significant than a micron that are bigger than the size of the pores are prevented from passing through the membrane in which protozoan cysts, including Cryptosporidium and Giardia lamblia cysts, slits clays, sand, and pathogens such as bacteria are included. In the case of viruses, micro filtration alone is not a complete barrier, but in water, it appears to regulate these microorganisms when micro filtration combines with the disinfection process. As a result, this method is used to eliminate synthetic organic matter, pathogens, chemicals, etc., from the wastewater (Rafique et al. 2019).

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3.2 Sedimentation Sedimentation is one of the most important, old, and widely used methods in effectively treating and purifying industrial wastewater. In the process of sedimentation, turbidity, floating materials, and sediments are removed from the wastewater with the help of settler tanks. Sedimentation, also known as clarification, is a method used for wastewater treatment under gravity, where water velocity is reduced below the velocity of suspended particles, and these particles get separated from the water. The suspended particles that are settled are eliminated as sludge, while the floating particles are eliminated as scum. The performance and effectiveness of this process are influenced by the design of the tank, retention time, temperature, condition, and quality of all the types of equipment (Awaleh and Soubaneh 2014). The most common method used for industrial wastewater treatment is gravitation coagulation. In sedimentation, the significant processes are clarification and gravity coagulation. Wastewater with fewer pollutants is treated under clarification, whereas water with high amounts of pollutants is treated under gravity coagulation (Rafique et al. 2019).

3.3 Filteration by Sand Sand filtration is a type of chemical–physical process which is used for the removal of suspended pollutants and colloidal pollutants from the wastewater by the passage bed made up of granular materials. In this filtration method, pollutants are absorbed on the surface of the grains or caught in the openings and water is filled in the filter medium pores. The sand filtration method is divided into two categories: (i) Slow sand filtration and (ii) Rapid sand filtration (Rafique et al. 2019). (i) Slow Sand Filtration The slow sand filtration method combines biological, chemical, and physical methods in the wastewater purification process. Both the physical and biological filtration processes run parallel to each other inside the same filter bed. At the upper layer of the filter, removal of pollutants from the wastewater takes place with the help of biological processes, which is done by biological activity and then followed by the processes of adsorption, mechanical filtration, and degradation (Rafique et al. 2019). The removal of contaminants mainly depends upon two critical physical factors: slow filtration rate (0.1−0.3 m/h) and fine sands. Predation through protozoa and adsorption onto the surface of sand particles are responsible for the processes of bacterial immobilization. Behind the reduction of viruses in the slow sand filtration, the possible mechanisms are the higher microbes on virus particles and the synthesis of microbial extracellular substances such as grazing of bacteria or some proteolytic enzymes (Elliot et al. 2011). Slow sand filtration can also eliminate the cysts of Cryptosporidium enteroparasites and Giardia. In the process of filtration, a layer of

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inactive grain system and organic matters are present on the sand bed’s top layer, known as Schmutzdecke. In addition, the growth of microorganisms is also seen within the gravel support and the sand bed, which significantly affect the purification system (Verma et al. 2017). (ii) Rapid Sand Filtration The two main principles in operating rapid sand filtration are mechanical straining and physical adsorption. The media used in rapid sand filtration processes are significantly grainer, and the effective range of the grain size lies between 0.6−0.2 mm. The interstices between the grains are large, providing less resistance from the downward flow and permitting faster speed, mainly in the range of 5−15 m 3 /m 2 /h. Rapid sand filtration can usually achieve high rates of hydraulic flow and can be automatically clean through the backwash system to eliminate the aggregated materials. The filtration mechanism of particles mainly depends upon some staring or adsorption, but it is independent of biological filtration (Nassar and Hajjaj 2013). Cleaning is required to restore the quality of contaminants and the capacity of the filters, and it is done at regular intervals. In mechanical agitation, high-pressure water is forced upward, and the entire bed is used to clean the individual grains, allowing the pollutants to be flushed away to their depth (Rafique et al. 2019).

4 Nanotechnology Used for Bioremediation of Industrial Wastewater Treatment In various publications and research, it has been cited that nanotechnology is one of the most critical and advanced technologies used in wastewater treatment. In wastewater treatment, nanomaterials are found to be suitable because of their small size. Nanomaterials have been used in various fields and have a wide range of applications because of their unique biological, physical, and chemical properties (Dixit and Shukla 2020). In eliminating effluents from the wastewater, various nanomaterials (Fig. 2), including metal and their oxide based and carbon-based (i.e., Nanotube and Nanocomposites) nanomaterials, have been used. The practices involved in wastewater management are nanoparticle filtration, adsorption, monitoring of various pollutants and contaminants, and photocatalytic degradation. Various cost-effective, efficient, and eco-friendly nanomaterials with unique capabilities have been produced to potentially decontaminate the drinking water, surface water, groundwater, and industrial effluents in the wastewater treatment program.

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4.1 Nanophotocatalysts Among the methods of treatment and purification of water, photocatalysis is one of the more efficient methods, and it also suppresses the crisis of energy and reduces pollution. In the remediation process of environmental pollution, photocatalysts based on nanomaterials have emerged as a viable candidate; nowadays, they are also used for water purification (Rafique et al. 2019). Photocatalysis is a process in which photocatalysts are activated or stimulated by illuminating them with light, resulting in the generation of electron–hole pairs. The electrons generated during this process are in their excited state and tend to jump from the valence band to the conduction band, generating holes in this process. During this process, an oxidation–reduction reaction takes place, and as a result, hydroxyl radical and superoxide ions are formed, which further react and oxidize the organic pollutants such as dyes in the water and degrade them (Akhavan et al. 2009). Because of their shape-dependent feature and higher surface ratio, nano photocatalysts are extensively used in water purification and treatment because they help increase the catalyst’s reactivity. Catalytic nanoparticles like bimetallic nanoparticles, semiconductor particles, and zero-valence metals are used commonly in the degradation and treatment of pollutants that are present in the environment, such as halogenated herbicides, azo dyes, polychlorinated biphenyls (PCBs), nitro aromatics and organochlorine pesticides (Xin et al. 2011). The most critical and common nano photocatalysts based on metal oxides are TiO2 , ZnO, Al2 O3 , SiO2 , etc. Among various existing nanomaterials, titanium oxide (TiO2 ) is the most widely used and one of the greatest photocatalysts because of its several reasons, such as chemical stability, cost-effective, toxic-free properties, and its high reactivity under UV (ultraviolet) light of less than 387 nm (Akhavan et al. 2009). Similarly, some other nano photocatalysts, such as ZnO, have also been synthesized to reduce pollutants in wastewater and show their efficient, reusable ability (Lin et al. 2014). The efficiency of nano photocatalysts depends on particle size, pollutant concentration, dope, pH, and band gap energy. However, another wellknown semiconductor with a band gap of 2.42 eV and can be operated at a wavelength less than 495 nm, known as CDS as a photocatalyst CDS, has gained much attention for wastewater treatment of industrial dyes.

4.1.1

Application of Nano Photocatalysts in Wastewater Treatment

During the photocatalytic water treatment process, its overall efficiency depends on the photoreactor operation parameters and their configuration. TiO2 immobilized and slurry-based reactors are the two most common configuration types performed. Different catalytic immobilization and recovery techniques are being studied to enhance their efficiency. A large-scale investigation of the operating parameters has been conducted with the help of pilot or lab-scale systems. A recent review discussion on the effects of a wide range of operating parameters such as pH, light intensity and wavelength, pollutants type and its concentration, TiO2 loading, temperature,

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Oxidative Estrification

Reduction reaction

Nanophotocatalysts Applications

Oxidation Reaction

C-H Activation reaction Fig. 3 Schematic representation of nano photocatalysts and their application (Yaqoob et al. 2020)

and water quality is done (Chong et al. 2010). The nanoparticle-based metal oxides serve as excellent photocatalysts in different oxidation–reduction processes. These oxides show high catalytic reactivity toward the polluting substances and convert these contaminants into eco-friendly products. These nanomaterials show several unique characteristics, such as high reactivity, nano size, and large surface area. Among different oxides, photocatalysis by TiO2 plays an essential role in eliminating various impurities present in the surface water (Yaqoob et al. 2020). However, these photocatalysts are well-known for their activity. However, on the other hand, they are only active under UV radiations (l < 387 nm), and this is because of the comprehensive band gap energy, low quantum efficiency, and high rate of charge-carrier recombination, which make them unsuitable for a visible region of the electromagnetic spectrum, and therefore, reduces its photocatalytic effect. As a result, more modifications for the photocatalysts have been studied to enhance their activity in the visible region of the spectra through coupling, doping, and composite formation as they directly affect photocatalysts’ structural and surface morphology, which in turn influence their band gap energy (Dutta et al. 2014). Moreover, using nano photocatalysts to eliminate pollutants from wastewater is an efficient method; some of their applications are shown in Fig. 3 (Yaqoob et al. 2020).

4.2 Nanofilteration Membranes Among the various advanced techniques used in wastewater treatment, nanomembrane filtration is one of the most effective approaches. The fundamental goal of

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wastewater treatment is to eliminate the unwanted chemicals from the polluted water, and these chemicals are a barrier because of their size. The process of membrane filtration provides an excellent level of mechanization, takes less space, uses no chemicals, and allows flexible design due to its modular configuration (Qu et al. 2013). The inherent change between the layer penetrability and selectivity is the major challenge for membrane technology. Besides, using membrane-based technology to clean the layers during the process and pressure-challenging membrane processes requires high energy. The membrane and the membrane unit lifetime can be reduced due to high pressure and energy use. Furthermore, incorporating functional nanomaterials in the membrane technology provides an excellent opportunity to enhance chemical and thermal stability, membrane permeability, and membrane fouling resistance, and exhibit new pollutant-eliminating functions and self-cleaning (Rafique et al. 2019).

4.2.1

Nanofiber Membrane

Electrospinning is a cost-effective, efficient, and simple method to produce ultrafine fibers with the help of different resources such as metals, polymers or ceramics. As a result, the synthesized nanofibers have high porosity and large surface area and form a mat of nanofibers with a complex structure of pores. Manipulation of composition, secondary structure, morphology, spatial alignment, and width of the electrospun fibers can quickly be done for specific applications (Li and Xia 2004). However, the utilization of membrane-based nanofibers is done commercially in the application of air filtration, and the strength of nanofiber membranes in wastewater treatment is still highly inactive. Nanofiber membranes can eliminate micron-sized particles from the aqueous phase with a high rejection rate without any significant fouling (Ramakrishna et al. 2006). Therefore, before the process of osmosis and ultrafiltration, nanofiber membranes are used as a pretreatment method. Because of their tunable properties and unique characteristics, Electrospun fibers are an ideal stage for synthesizing multifunctional membrane/film filters by either presenting the functional materials on the nanofibers or using multifunctional materials directly as TiO2 . For example, incorporating specific confine agents or ceramic nanomaterials on the scaffold of nanofibers can lead to the formation of affinity nanofiber membranes which helps to eliminate organic pollutants and heavy metals during the filtration process (Qu et al. 2013).

4.2.2

Thin Film Nanocomposite Membrane

During the development of thin-film nanocomposite (TFN) membranes, primary attention was given to incorporating nanomaterials in the active layer of thin-film composite (TFC) membranes with the help of modification in structures or by doping in the casting solutions. Nanomaterials incorporated in such processes are nano-Ag, CNTs, nano zeolite, and TiO2 nanoparticles. Based on nanoparticles size, type, and

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concentrations integrated into the membrane, its effect is seen on the membrane selectivity and permeability. The most common dopants used in the thin-film nanocomposite are nano-zeolites, which have shown their potential to improve the membrane’s permeability. Integrating nano-zeolites in the membranes leads to the formation of a thick layer of active polyamide, which is more permeable and has a more negative charge (Lind et al. 2009). The thin-film composite membrane is utilized to achieve an 80% increase in water permeability over the membrane layers with strong salt rejection. It is seen that in comparison to conventional reverse osmosis membranes, nano-zeolites of 250 nm doped in the thin-film composite membrane at 0.2 wt% achieve high salt rejection, i.e., greater than 99.6 percent and higher permeability. The tiny hydrophilic pores present in nano-zeolites allow the free movement of water. Although water permeability increases even with the zeolite filled with pores, at a slower rate than the pore size, which could be assigned to defects at the interface of zeolite polymer (Qu et al. 2013). Nano-zeolites can also be used as a carrier for antimicrobial particles like Ag+ , which provides anti-fouling characteristics to the membrane. Similarly, the integration of nanoparticles of TiO2 into the thin-film composite’s active layer increases the membrane’s rejection ability and maintains the membrane permeability. Under the influence of ultraviolet irradiation, TiO2 can inactivate bacteria and other microorganisms and degrade the organic contaminants. Because of their antimicrobial activity, CNTs also have some specific applications in the thin-film nanocomposite membranes (Rafique et al. 2019).

4.2.3

Nanocomposite Membrane

Multifunctional systems are now synthesized by incorporating the nanomaterials in the polymeric or inorganic membrane using the method of membrane technology. The nanomaterials added in such processes are antimicrobial, catalytic nanomaterials, and hydrophilic metal oxides. Adding nanoparticles such as silica, alumina, and TiO2 to the polymeric ultrafiltration membrane enhances their water permeability through the membrane, fouling resistance, and surface hydrophilicity. Inorganic nanoparticles are used to increase the thermal and mechanical stability of the polymeric membrane (Rafique et al. 2019). Nanoparticles can reduce membrane biofouling with antimicrobial activities such as nano-Ag and CNTs. In order to minimize the inactivate virus infection, bacterial adhesion, and biofilm synthesis, nano-Ag have been surface doped or grafted on the polymeric membrane (Qu et al. 2013). However, due to the short-term efficiency of nano-Ag against the biofouling of membrane, an appropriate substitution of nano-Ag is necessary. The polyvinyl-Ncarbazole SWWNT nanocomposite with three wt% of CNTs has shown the bacteria’s maximum inactivation (Ahmed et al. 2012). On the other hand, conventional methods are employed to inactivate the nanotubes that are single-walled and insoluble in water, and in this procedure, there is no need for substitution. The photocatalytic nanoparticle present within the membranes is linked with their function of physical division and degradation of pollutants through catalyst reactivity. Researchers have devoted their efforts to forming photocatalytic

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inert membranes incorporated with nano photocatalysts such as nanoparticles of modified TiO2 or normal TiO2 (Choi et al. 2006).

4.2.4

Application of Nanomembranes in Wastewater Treatment

Nanofiltration membranes also play an essential role in nutrient recovery from industrial waste. NF50 gives the highest phosphorous rejection of 70% from the paper and pulp industry effluent. However, the difficulty of membrane fouling arises due to high phosphorous content (Leo et al. 2011). Shalaby and coworkers (2020) used the woven polymer blend with gold nanoparticles of the nanofiller membrane to achieve a more remarkable recovery of phosphorous from the wastewater. As a result, they attained 91.6% trivalent phosphate with increased hydrophobicity and membrane fouling resistance (Shalaby et al. 2020). In other research and study, Ceramic-supported graphene oxide (GO) was developed to eliminate heavy metals. The membrane did nearly 100% rejection of metal ions of nickel, cadmium, lead, and copper. Various types of nanomembranes used in the treatment of industrial wastewater with their efficiency are shown in Table 1. It will be advantageous to produce such a membrane due to immense water stability, excellent rejection ability, and increased flux speed (Dixit and Shukla 2020). Table 1 Different nanomembranes with their efficiency in industrial wastewater treatment Nanomembranes

Pollutants

Efficiency

Nanofiltration membranes

Removal of reactive dye Black5 from the effluent of the textile industry

99%

Filtration by nanoporous membrane

Elimination of oil, TSS, grease, TDS, and BOD from oil wastewater

Oil (99%), TSS (100%), grease (80%), TDS (44%), BOD (76%)

Forward osmosis with nanofiltration

Removal of paracetamol and COD Paracetamol (100%), COD from industrial effluents (97%)

Nanofiltration

Removal of remazol fiber reactive dyes from effluents of cottage textile industry

≥ 80%

Carbon nanofiber membrane

Removal of metal oxide and metal nanoparticles

~ 95%

Photocatalysis through nanofiber membrane

Effluents of the dairy industry

75–95%

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4.3 Nanaoadsorbents The membranes of nanoparticles have been researched for their potential application as adsorbents in nanotechnology. Adsorption is a process commonly used as a polishing step to eliminate inorganic and organic pollutants from wastewater. The efficiency of the traditional adsorption method is usually restricted due to less adsorption kinetics, surface area, and lack of sensitivity. These limitations can be overcome with nano adsorbents as they have incredibly high adsorption capacity, high surface area, surface chemistry and variable pore size, and a short distance between intraparticle diffusion (Qu et al. 2013). The use of nanoparticles as an adsorbent is done widely by industries to eliminate harmful pollutants from industrial effluents. Nanoparticles commonly used for the adsorption and elimination of heavy metals are based on carbon nanotubes, activated carbon, metal, and their metal oxides (Dixit and Shukla 2020).

4.3.1

Nano Adsorbents Based on Metal

Nanoadsorbents based on metal oxides such as aluminum oxide, iron oxide, and titanium oxides are efficient and cost-effective for treating radionuclides and heavy metals from industrial wastewater. The process of sorption is majorly run by the complexation of oxygen with dissolved metals in metal oxides. This process is mainly divided into two steps: first, there is rapid adsorption of metal ions on the exterior surface, which is then followed by the intraparticle diffusion along the walls of the micropore, and this is the rate-limiting step (Qu et al. 2013). The counterparts of this technique based on nanotechnology have a high number of sites for surface reaction, short distances for intraparticle diffusion, faster kinetics, and great adsorption capacity due to the large specific surface area. For example, if nano-magnetite particle size can reduce from 300 to 11 nm, the arsenic adsorption capacity of nano-magnetite can rise by more than 100 times (Yean et al. 2005). When moderate pressure is given to metal oxide nanoparticles, they can be compressed into porous pellets without reducing their surface area. By adjusting the consolidation pressure, the size and volume of the pore can be altered. Therefore, they can be used in both forms, such as porous pellet and fine powder, the most common forms used in industries (Lucas et al. 2001). Nanomaterials based on metals have been studied to eliminate various metals such as chromium, arsenic, cadmium, lead, copper, nickel, and mercury. These metalbased nanomaterials have the potential to beat activated carbon (Sharma et al. 2009). Among various metals, arsenic has gained much attention to find various applications required for its removal. However, activated carbon is an effective adsorbent for various inorganic and organic pollutants, but in the case of arsenic, it shows limited capacity, particularly for As (V). Some nanomaterials-based metal oxides such as TiO2 and nano-magnetite have shown high adsorption capacity for arsenic than activated carbon (Qu et al. 2013).

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Nano Adsorbents Based on Carbon

Carbon nanotubes (CNTs) are the most studied material that can eliminate different organic pollutants and heavy metals from wastewater through adsorption. However, some drawbacks exist with using CNTs as an adsorbent, such as problems in separating particles, the small size of the particles, and poor dispersion ability. Researchers have now converted the normal CNTs into modified CNTs like multi-walled carbon nanotubes (MWCNT) to overcome the issues related to normal CNTs (Tang et al. 2012; Tarigh and Shemirani 2013). The modified form of CNTs shows excellent dispersion ability and, with the help of magnets, can be easily extracted from the used media or the wastewater. In some research and studies, it has been reported that multi-walled carbon nanotubes are used for the elimination of heavy metals such as Cu(II) (Tang et al. 2012, Mn(II), and Pb(II) (Tarigh and Shemirani 2013). Carbon nanotubes’ overall adsorption activity can be enhanced by modifying their surface. Various researchers have investigated surface modification methods such as metal impregnation, functional group grafting, and acid treatment. The properties such as surface charge, hydrophobicity, surface area, and dispersion of CNTs surface can be changed using the techniques mentioned earlier. The treatment of CNTs with acids was performed with various types of acids like H2 SO4 , HCL, H2 O2 , H3 PO4, and KMnO4 , and this treatment is used to eliminate the contaminants that are seen on the surface of CNTs. Furthermore, it also adds a functional group to the CNTs surface, and as a result, the wastewater adsorption capacity of CNTs is increased.

4.3.3

Application of Nano Adsorbents in Wastewater Treatment

Nanoadsorbents can be easily integrated into the adsorbers or the slurry reactors of ongoing wastewater treatment processes. Nanoadsorbents in their powder form used in slurry reactors can be highly effective since all the adsorbent’s surface is used, and mass transfer is facilitated by mixing it greatly (Qu et al. 2013). Moreover, an extra separation unit is needed for the recovery of nanoparticles. In fluidized or fixed adsorbers, nano adsorbents can be used as porous granules or beads loaded with nano adsorbents. Fixed-bed reactors are mainly linked with heat loss and mass transfer elimination, although they require no future separation processes. For arsenic removal, nano adsorbent applications have been commercialized, and their comparison with other commercial adsorbents based on efficacy and cost-effectiveness is made through pilot tests (Aragon et al. 2007) Table 2.

4.4 Nanomaterials Nowadays, researchers are gaining much attention to using modified nanomaterials in treating wastewater and other industrial fields. Nanomaterials with antimicrobial properties have potential usage in industrial wastewater treatment (Rafique et al.

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Table 2 Various nanosorbents and their functions (Yaqoob et al. 2020) Nnanoadsorbents

Functions

Nano-metal oxides

Treat various heavy metals

Graphite oxide

Elimination of dyes from polluted water

Carbon-based nano adsorbents

Remove nickel ions present in the wastewater

Polymer fibers

Remove arsenic and various hazardous metals

Polymeric nanosorbents

Remove inorganic and organic contaminants present in the wastewater

2019). In a point-of-use water treatment system, a high potential is shown by nanoAg. Nano-Ag can increase water quality for top-of-the-line use or provide an additional barrier against the pathogens in the water bodies for the population exposed to it. Nano-Ag particles are used in various commercially available devices such as the Marathon water system or Aquapure. Incorporating nano-Ag particles into ceramic micro filters can act as a barrier against pathogens, which could be very useful for purifying drinking waters in developing countries (Peter-Varbanets et al. 2009). Carbon nanotube (CNT) filters, due to their unique properties such as antimicrobial activities, fibrous shape, and high conductivity, have been utilized widely to remove bacteria and viruses from the water system. The elimination of bacteria and viruses can be done efficiently through the thin layers of carbon nanotubes by using depth and size exclusion filtration (Brady-Estevez et al. 2010). The application of nanomaterials that are frequently used for the treatment of wastewater includes photocatalysis (TiO2 ), nano-Ag, CNTs, nanofiltration membranes, and nanotubes (Table 3) (Mansoori et al. 2008).

4.5 Ultrafiltration As global industrialization is rising rapidly, more and more focus has been paise on how to enhance the efficiency and level of industrial wastewater treatment and decrease pollution. Membrane-integrated technology has gained many advantages compared to conventional wastewater treatment, such as requiring a simple operation, low maintenance and operating cost, ideal operating environment, small equipment for wastewater treatment, strong sewage purification capacity, and high treatment efficiency (Li et al. 2018). Thus, the use of membrane-integrated technology is done widely for industrial wastewater treatment. The application and advantages of ultrafiltration technology show its great potential for advanced methods of oily wastewater, food wastewater, heavy metal wastewater, papermaking wastewater, and dyeing and printing wastewater (Li et al. 2018).

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Table 3 Different nanomaterials and treatment methods used in wastewater treatment (Mansoori et al. 2008) Nanomaterials

Sample of interest

Method of treatment

Advantages

Magnetic nanoparticles

Organic compounds, heavy metals

Absorption

No sludge formation can be separated easily

Nanotube

Organic contaminants, anion, heavy metals

Adsorption

High mechanical properties, high chemical stability

TiO2

Organic contaminants

Photocatalysis

Low toxicity, photostability, water-insoluble

Nanoclay

Organic contaminants, heavy metals, anions

Adsorption

Cost-effective, excellent stability, recycle, good sorption capacity

Fe

Organic pollutants, anions

Adsorption and reduction

Cost-effective, less harmful, in-situ water remediation

Carbon nanotubes (CNTs)

Heavy metals

Adsorption

High chemical stability, high surface area and mechanical properties

Nanomembranes and nanofiltration

Inorganic and organic pollutants

Nanofiltration

Low pressure

Debit and coworkers (2010) studied the impact of pretreatment and water quality on ultrafiltration/nanofiltration double-membrane integrated technology used to treat dyeing and printing wastewater. The result shows that the utilization of the technique mentioned above can achieve greater water flux as compared to single nanofiltration technology and treating pollutant indicators of wastewater by ultrafiltration/ nanofiltration double-membrane integrated technology to meet the quality of water that is required for dyeing and printing wastewater (Debik et al. 2010). Membraneintegrated technology was used by Zhou and colleagues for emulsified oil wastewater treatment. According to experimental data, the removal rate of COD from emulsified oil wastewater after treatment is over 95%, and over 95% flux recovery is seen after cleaning the membrane (Xiaotie et al. 2008). For resource utilization and advanced wastewater treatment of industries containing colloidal heavy metals such as Cu2+ , Liguo and coworkers (2005) introduced an ultrafiltration-reverse osmosis-ion exchange membrane integrated technology system (Liguo et al. 2005).

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4.6 Nanomotors and Sensoring In water and wastewater treatment, the main problem is monitoring the quality of water due to the high complexity of water and wastewater matrices, low amount of several pollutants, and lack of rapid pathogen detection. Thus, there is an excellent requirement for innovative sensors with rapid response and high selectivity and sensitivity (Rafique et al. 2019).

4.6.1

Detection of Pathogens

Pathogen detection has potential application as they directly show its effect on public health. The indicator systems that are used traditionally are slow and unable to detect the presence of effective pathogens such as bacteria (Helicobacter and legionella), protozoans (Giardia and Cryptosporidium), and viruses (echoviruses, Norwalk viruses, adenoviruses, coxsackieviruses, and hepatitis E and A) (Theron et al. 2010). Most of these pathogens act as an etiological agents in outbreaks caused by polluted drinking water. Furthermore, the critical part of the water sanitization approach based on diagnosis is pathogen detection, in which sanitization is triggered in the presence of target microorganisms. Nowadays, active research and studies are going on for the development of pathogen sensors enabled by nanomaterials, and these sensors mainly contain three components: signal transduction mechanism, nanomaterial, and sites of recognition (Vikesland and Wigginton 2010). The epitopes and other antigens on the pathogen surface provide selectivity through their interaction with recognition agents. With the help of nanomaterials, rapid selectivity and response was achieved, related to signal transduction during the event of recognition. Carbohydrates, antibodies, aptamers, and antimicrobial peptides all have been utilized as recognition agents. Multiplex target detection can be achieved by nanomaterials which can enhance the speed of detection and selectivity and incorporate their unique optical, magnetic, electrochemical, and physicochemical characteristics. These sensors can detect the biomolecules (Theron et al. 2010) and the complete cell (Vikesland and Wigginton 2010). In pathogen detection, the most frequently used nanomaterials are noble metals, quantum dots (QDs), CNTs, and nanomaterials doped with dyes. CNTs and magnetic nanoparticles are used extensively for sample purification and concentration analysis. Various pathogen detection kits can be developed with the help of commercially available dynabead and magnetic composites. Quantum dots are fluorescent nanocrystals of semiconducting substances like CdSe, whose electronic properties mainly depend on the shape and size of the crystals. Smaller quantum dot particles attain a wider band gap and thus require high energy to emit exciting light of a shorter wavelength. Quantum dots have stable and narrow fluorescent emission spectra but have broad absorption spectra. As a result, quantum dots are the best candidate for multiplex detection with only one excitation light source (Rafique et al. 2019).

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Detection of Trace Contaminants

Nanomaterials can be utilized to detect and trace inorganic and organic contaminants. Among various nanomaterials, carbon nanotubes have the potential to analyze the concentration of trace organic and inorganic contaminants present in the environment as they attain fast kinetics, high recovery rate, and adsorption capacity (Duran et al. 2009). Quantum dots and gold nanoparticles are other types of nanomaterials that have also been used. In colorimetric analysis, gold nanoparticles separated pesticides at part per billion (ppb) levels. With high selectivity and sensitivity properties, modified gold nanoparticles were used to identify CH3 Hg+ and Hg2+ rapidly. By using quantum dots modified TiO2 on fluorescence resonance energy transfer, the detection limits of PAHs were reduced to pica-mole-per liter level (Rafique et al. 2019). CoTe quantum dots-based nanosensor was immobilized on the surface of glassy carbon electrodes and was used to detect Bisphenol A at various concentrations in water as low as ~ 10 nm within 5 s (Yin et al. 2010).

5 Microorganisms Involved in Nanotechnology for the Treatment of Wastewater Simultaneous use of microorganisms and nanoparticle fabrication can make nanotechnology more environmentally beneficial and sustainable. Using self– agglomeration and chemicals in an aqueous solution can be some disadvantages of chemically produced nanoparticles. Thus, green nanoparticle synthesis using fungal, plant extracts, and enzymes associated with bacteria could be a viable solution. They generate metallic nanoparticles by behaving as a reductive agent in the case of metal complex salt. Due to the addition of proteinaceous and bioactive components or co-precipitation on the external face of the provisional nanoparticles, these nanoparticles achieve superior solidity in an aqueous environment (Dixit and Shukla 2020). Mahanty and his colleagues (2020) fabricated the nanoparticles of iron oxides from the Aspergillus tubingenis (STSP 25) organisms isolated from the rhizosphere of Avicennia officinalis found in the Sundarbans, India. Manufactured nanoparticles with the capability of regeneration up to five cycles were able to eliminate more than 90% of heavy metals [Ni (II), Zn (II), Cu (II), and Pb(II)] from the wastewater. In endothermic reactions, metal ions were absorbed chemically on the surface of the nanoparticles (Mahanty et al. 2020). In other research and studies, exopolysaccharides (EPS) isolated from Chlorella Vulgaris were used to co-precipitate with iron oxide nanoparticles. The effective modification of nanoparticles by functional groups of exopolysaccharides was analyzed using Fourier-transform infrared spectroscopy (FT-IR). Furthermore, it was seen that the nanocomposite could remove 3− 85% of N H + 4 and 91% of P O 4 (Govarthanan et al. 2020). Using microbes to synthesize nanoparticles has proven an eco-friendly and costeffective method—Escherichia sp. SINT7, a copper-resistant bacteria, was used

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Table 4 Different microorganism-assisted biogenic nanoparticles used in the treatment of dyes present in wastewater Biogenic nanoparticles

Associated microorganisms

Copper nanoparticles

Escherichia sp. SINT7

Iron-sulphur nanoparticles

Pollutant

References Reduction rate At 25 mg/L (%)

Pseudoalteromonas sp. CF10-13

(Noman At 100 mg/l et al. 2020) (%)

Congo red 97.07

83.90

Malachite green

90.55

31.08

Direct blue-1

88.42

62.32

Reactive black-5

83.61

76.84

Napthol Green B dye

(Cheng et al. 2019)

to synthesize copper nanoparticles. The capability of these biogenic nanoparticles to degrade textile effluent and azo dye was investigated (Table 4). The treatment of industrial effluent was also done, and the treated sample showed a decrease in phosphate and chloride ions and suspended solids. The performance of these biogenic nanoparticles provides an enhancement in sustainable and cost-effective products from the industries (Noman et al. 2020). The endogenous manufacturing of nanoparticles inhibited the production of metal complexes and hazardous gases. Biogenic nanoparticles are a superior technology to use in the remediation of industrial effluents. Apart from directly producing nanoparticles with the help of microbes, microorganisms can also boost nanotechnology in various ways. Microorganisms, for instance, may also produce catalytic enzymes, which in combination with nanoparticles, help in the bioremediation of wastewater. From industrial wastes, microorganisms can also produce valuable products (Dixit and Shukla 2020).

6 Enzyme Technology Assisted with Nanotechnology Combining nanotechnology with enzyme technology shows maximum importance in making nanomaterials less hazardous and less destructive to the environment. The interaction between the nanomaterials cells and enzyme molecule cells gets reduced through steric hindrances when they are present together, resulting in a decrease in surface energy (Dixit and Shukla 2020). The unique catalytic feature of enzymes and their eco-friendly nature make nanomaterials more effective and adaptive in green energy production and bioremediation. On the other hand, immobilized enzymes on nanomaterials are seen to be more stable because of less exposure to diffusional

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provisional restrictions, enhanced kinetic properties, show restriction in unfolding, and can be used in several cycles (Ding et al. 2015). The large surface areas of nanomaterials improve the immobilization efficiency of an enzyme by elevating enzyme loading. The separation of immobilized enzymes from the reaction mixture can be done quickly by using an immobilized matrix containing magnetic nanomaterials (Dixit and Shukla 2020). The immobilization of oxidoreductases, a multimeric enzyme on nanomaterials, can also help stabilize them. Due to the immobilization of enzymes on a solid substrate, changes can occur in the structure of an enzyme, which mainly increases the β-pleated structure and decreases the α-helix structure. In contrast, no such modification can be observed when nanomaterials are utilized in enzyme immobilization. Many kinds of research and studies have shown the importance of combining enzyme technology with nanotechnology (Secundo 2013). Darwesh and his colleagues (2019) demonstrated the effect of an enzyme, immobilized peroxidase, on the bioremediation of wastewater. Where modified iron oxide magnetic nanoparticles provide temperatureand pH-stable immobilized enzymes by glutaraldehyde. Red and green azo dyes were eliminated individually in 4 h with the help of an enzyme, Immobilized peroxidase. When the combination of red and green azo dyes was used simultaneously in lab experiments, it took 6 h to remove all the dyes altogether (Darwesh et al. 2019). The enzyme that is widely used in the treatment of industrial wastewater is known as a laccase. Different enzymes for biodegradation can be immobilized using various magnetic nanoparticle composites (Table 5). Thus, these research and studies make it clear that combining enzyme technology with nanotechnology provides an efficient and stable environment for the bioremediation of industrial wastewater (Dixit and Shukla 2020). Table 5 Immobilization of enzymes by using different magnetic nanoparticles composite for biodegradation (Dixit and Shukla et al. 2020) Immobilized enzyme

Nanoparticle composites

Contaminants

Efficiency (%)

Laccase

Chitosan and Fe3 O4

4-Choloro-phenol

75.5

2,4-Dichloro-phenol

91.4

Reactive blue-19

81

Malachite green

99

Crystal violet

79

Brilliant green

93

Chelated Cu2+ and Fe3 O4

(continued)

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Table 5 (continued) Immobilized enzyme

Nanoparticle composites

Contaminants

Efficiency (%)

Lignin peroxidase

Polydopamine, SiO2 and Fe3 O4

Phenanthrene

79

Fluoranthene

73

Tetracycline

100

5-chlorophenol

100

Cyanate hydratase

Multi-wall Multiwall CNTs filled with iron oxide

Cyanate

≥ 84

Iron

35.53

Copper

29.63

Lead

34.48

Chromium

39.31

7 Conclusion and Futuer Prespective As water pollution increases, the amount of clean water is vanishing rapidly; therefore, due to the high demand for clean water, wastewater purification, and treatment techniques are emerging and becoming famous. Traditional methods have been utilized for industrial wastewater treatment and purification; however, they are ineffective and incapable of removing all the pollutants completely. Currently, many advanced techniques based on nanotechnology are used for the purification and treatment of industrial wastewaters, such as photocatalysis, ultrafiltration, nanomembrane filtration, nono-sensors, nano adsorbents, etc. Nanotechnology is a highly efficient and multifunctional technique for industrial wastewater treatment as it can remove heavy metals, hazardous inorganic and organic matter, metal ions, nitrates, bacteria, viruses, complex compounds, and other natural organic matter in the wastewater. Furthermore, integrating nanotechnology with microorganisms has created a green approach to the bioremediation of various industrial effluents. Nanotechnology assisted with enzymes has also produced highly active, long-lasting, and stable enzymes for various applications. Nanomaterials are efficiently used in wastewater treatment. However, some severe limitations of this technique are needed to be overcome. During the treatment and preparation processes of these nanomaterials, they may be released into the environment and accumulated for a very long time, posing a significant risk. To reduce the risk associated with chemically produced nanomaterials, microorganisms and enzymes assisted nanotechnology can be used. Therefore, the large-scale use of these effective and simple microorganisms-assisted nanotechnology methods will serve as a stepping stone for the industries. In addition, more work is needed on developing synthesizing processes of nanomaterials that are cost-effective and testing their effectiveness on a wide scale for successful field use.

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Nanoadsorbents for Treatment of Wastewater Pratik V. Tawade, Samyabrata Bhattacharjee, and Kailas L. Wasewar

Abstract Domestic and industrial wastewaters have many pollutants, including organic and inorganic compounds. Many of the contaminants present in wastewater are harmful with negative impacts if they exceed permissible limits. To avoid the adverse effect of such pollutants on the environment and human beings, it is essential to treat wastewater to a permissible level before discharging it into water bodies. Several methods are available for wastewater treatment. The commonly used methods are solvent extraction, chemical precipitation, lime coagulation, reverse osmosis, ion exchange, adsorption, cementation, electrodeposition, etc. Adsorption is one of the most convenient and proven techniques for removing and treating many pollutants, including toxic metals from water and wastewater. Nanoparticles represent a promising new wastewater remediation technology because of their high treatment efficiency and cost-effectiveness, as they have the flexibility for in situ and ex-situ applications. The present chapter focused on nanotechnology and nanoparticles, various types of adsorbents for wastewater treatment, and aspects of adsorption using nanoadsorbents.

1 Introduction Potentially toxic elements (PTEs), phenolic compounds, pesticides, and dyes, can all be found in freshwater, apart from emerging micropollutants like endocrine disrupting compounds (EDCs), personal care products, and pharmaceuticals Pratik V. Tawade and Samyabrata Bhattacharjee are Equal Contribution. P. V. Tawade Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, India S. Bhattacharjee Department of Chemical Engineering, Haldia Institute of Technology, Haldia, India K. L. Wasewar (B) Advance Separation and Analytical Laboratory (ASAL), Department of Chemical Engineering, Visvesvaraya National Institute of Technology (VNIT), Nagpur, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_8

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(Shannon et al. 2008; Lapworth et al. 2012). These pollutants have the potential to be bioaccumulative, mutagenic, carcinogenic, and harmful to flora, fauna, as well as human health (“Sick water:” 2022; Chowdhury and Balasubramanian 2014). Different technologies for purifying water and recycling have been published in the literature throughout the last few decades. Physical, thermal, chemical, electrical, and biological principles are involved in these technologies. Screening, oxidation, filtration, ion exchange, coagulation–flocculation, distillation, biological treatment, and adsorption are some of the most common water purification procedures (Barakat 2011; Gupta et al. 2012; Enamul Hoque et al. 2017; Tlili and Alkanhal 2019; Blanco, et al. (n.d); Ali et al. 2020). Under ideal settings of temperature, pH, pollutants concentration, and other testing parameters, some of the most prominent wastewater treatment methods claimed efficacy of 99% or higher. In a realistic wastewater system, efficiency drops to 90% or even lower, implying that one contaminant molecule in every 10 may evade the purification pathway (Gul et al. 2021). Furthermore, the majority of modern wastewater treatment treatments are prohibitively expensive, and those that are cost-effective frequently result in secondary contamination. As a result, wastewater treatment still has certain loopholes in terms of cost-effectiveness and efficiency, to the point where water pollution has caused irreversible harm in a number of impoverished nations. Because of its universality, adaptability, extensive application, economic feasibility, and the simplicity of use, adsorption is the quite extensively used purification technology (Gupta et al. 2012). The capability of adsorption to remove inorganic, organic, and biological contaminants from wastewater can be as high as 99.9% (Ali et al. 2012). The porosity and pore size of adsorbents, as well as their surface area, are factors that influence adsorption effectiveness. Limestone (Aziz et al. 2008) clays (El-Geundi et al. 2016), silica gel (Do 1998), activated alumina (Singh and Pant 2004), zeolites (Ming and Dixon 1987), activated carbon (Aggarwal et al. 1999), and other adsorbents are now employed for wastewater purification. Activated carbon is the most widely utilized adsorbent among all of them (Babel 2003). Activated carbon, however, has a number of drawbacks, despite its versatility. Activated carbon has a low porosity, pore volume, and surface area and its adsorption capability is rapidly depleted. Surface functionalization of traditional adsorbents is, in general, an appealing approach to improving adsorbent performance. These functionalized materials, on the other hand, need a sophisticated, multistep synthesis method that is not suitable for large-scale manufacturing and hence is costly (Bhatnagar et al. 2013) (Tawade 2020). Furthermore, traditional adsorbents have considerable difficulty in separating the adsorbent post-water treatment and removing contaminants at ppb levels (Li et al. 2011; Mohan and Pittman 2006). Recent breakthroughs in nanotechnology have revealed that chemical, mechanical, sonochemical, microwave, combustion, sol-gel, and other methods may be used to generate nanomaterials from a variety of sources, including biomass residues, agricultural wastes, and byproducts (Biswas et al. 2017) (Rangari et al. 2017). Nanotechnology is being studied as a potential technology with impressive results in a variety of disciplines, including wastewater treatment. Nanostructures, with their tiny size, huge surface area, and simplicity of functionalization, provide unrivaled prospects

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for creating more efficient catalysts for wastewater purification. Organic and inorganic solvents, dyes, heavy metals, biological pollutants, and pathogens have all been demonstrated to be efficiently eliminated from wastewater using nanomaterials (Kumar, et al. 2013) (Jain et al. 2021). Researchers developed next-generation adsorbents (nanoadsorbents) for the water treatment system to overcome the shortcomings of conventional adsorbents. Large surface area, selectivity, high chemical reactivity, magnetic, magnetic, and optical features are only a few of the physicochemical properties of nanoadsorbents. Due to the large surface area, there are more active sites for different contaminants to react with the nanoadsorbent. These characteristics enhance the absorbent efficiency than their bulk counterparts (Kalfa et al. 2009; Liu et al. 2005; Hurt et al. 2006) (Ali et al. 2020). Nanoadsorbents have a potential market in both local and international environmental sectors.

2 Wastewater Water is fundamental for all life forms to exist on this planet (Bailey et al. 1999). Even though water is often viewed as the cheapest and most ubiquitous asset in conventional notions, the world’s immediately available freshwater sources are minimal (Liu et al. 2022). In the last 50 years, total freshwater consumption has nearly doubled to over 4 trillion m3 per year (Tao et al. 2022). Water-consuming sectors are anticipated to expand to 4.35 trillion m3 by 2040, leading to an increase in wastewater production. The agricultural industry continues to be the world’s largest consumer of freshwater, accounting for 70% of overall intakes for irrigating 275 million ha of land around the world (Lu et al. 2022). To minimize the water shortage and meet the water requirements’ demand, the best way is to set up a facility for water treatment. Only 20% of the world’s effluent is now treated adequately, allowing it to be reused for other purposes. From the statistics of water usage and wastewater production from industrial and domestic sections, it can be concluded that the wastewater treatment reuse systems are a critical way to relieve strain on freshwater resources. The objective of sewage treatment in the past was to avoid the transmission of pathogens. The focus of wastewater treatment switched to resource recovery as the usage switched from a linear to a circular system in line with ecological sustainability. Advanced wastewater treatment offers substantial economic advantages in terms of conserving water and minimizing excessive water losses (Zhang et al. 2016; Habibi et al. 2018).

3 Major Contaminants in Wastewater When we talk about water treatment, it isn’t easy to talk about it without initially pinpointing the contaminants we would like to get rid of. The effluent discharged from various industries, and domestic sectors contain many impurities that pose a

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severe risk to human health and the environment. This contaminant can be further categorized into multiple domains.

3.1 Heavy Metals Heavy metals are among the most common pollutants in wastewater. Mostly all industrial facilities, such as mining, light industry, energy industry, chemical industry, etc., create heavy metals (Hao et al. 2020). It is a metallic element with a density of more than 5 g/cm3 , and the most frequent harmful metals common in industrial effluent are mercury, cadmium, chromium, lead, and copper (Ghosh et al. 2022). Manganese and Copper are primarily accumulated in the sludge (>70%), while Zinc, Chromium, Lead, Cadmium, Nickel, and Iron are retained in the treated effluent (47– 63%). To improve animals’ health and also protect from several infections, some heavy metals, especially Cu, Zn, As are often supplied as nutrients (Jin and Chang 2011) in poultry farms, but due to overdose, most of the metals are excreted in faces and urine and finally enter in an aquatic ecosystem as heavy metal waste. Excessive deposition of these toxic substances has been shown in numerous studies to have a negative effect on the human brain, lung, kidney, liver, and other organs, as well as the neurological and immunological systems (Tao et al. 2021, Cheng et al. 2019, Jiang et al. 2021). Some of this also has a carcinogenic effect (Maleki and Jari 2021). The Minamata disease and the itai-itai disease that occurred in Japan in the last century occur due to Hg and Cd; respectively, these events are a clear indication to humankind that the disposal of heavy metal caused by various sectors can seriously threaten to health. Consequently, appropriate treatment and permanent elimination of these particles are highly required. Table 1 lists the characteristics of common heavy metals and their permissive limit. Table 1 Characteristics of common heavy metals with permissive limit Heavy metals MCL (mg/L) (maximum concentration levels)

Human health effect

Common sources Maximum contaminant level (mg L−1 ) USEPA WHO

Arsenic As(III)

0.05

Cadmium Cd(II)

0.01

Skin damage circulatory system issues

Naturally occurring electronics production

0.010

Kidney damage carcinogenic

Naturally 0.005 occurring various 0.003 chemical industries

0.010

(continued)

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Table 1 (continued) Heavy metals MCL (mg/L) (maximum concentration levels)

Human health effect

Common sources Maximum contaminant level (mg L−1 ) USEPA WHO

Chromium Cr(III)

0.05

Copper Cu(II)

0.25

Lead Pb(II)

0.006

Mercury HgII 0.00003

Allergic dermatitis diarrhea, nausea, and vomiting

Naturally occurring steel manufacturing

Gastrointestinal liver or kidney damage

Issues with naturally occurring household plumbing systems

Kidney damage reduced neural development

Household plumbing systems

Kidney damage and Fossil fuel nervous system combustion damage electronics industries

0.1 0.05 1.3 2.0

0.0 0.01 0.002 0.006

3.2 Dyestuff Environmental degradation by disposing of toxins in water due to the textile and dyestuff industry’s inability to appropriately dispose of their waste is currently one of the biggest global concerns. Textile industries are substantial contributors to environmental degradation in many countries. This sector discharges a variety of dyes as waste in water, which harms human health and other living organisms (Ali et al. 2022). As per some statistics, 7 × 107 tons of synthetic dyes are produced annually all over the globe (Chandanshive et al. 2020). Depending on the specific like their origin, structure, and application, dyes are frequently categorized into multiple groups (Akpomie and Conradie 2020), depicted in Fig. 1. As per some literature, dyes are also categorized as acidic dyes, basic dyes, dispersed dyes, direct dyes, solvent dyes, sulfur dyes, and fluorescent brighteners (Chakraborty and Ahmad 2022; Teo et al. 2022). Among all other categories, azo dye is the most common one (above 60%). When we talk about the waste caused by the textile industry, the only things that come to our mind are the dyes and the complex organic structure. Still, the textile industry also uses a variety of chemicals in their various processes like sizing, softening, brightening, and finishing agents (Kishor et al. 2021)—this poses serious ecotoxicological threats and harmful effects on living organisms. Textile wastewater rules differ based on the type of product that the facility produces (Table 2). In

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Fig. 1 Classification of dyes (Al-Tohamy et al. 2022)

the past, dye effluent wasn’t given any consideration. Over the last 30 years, the health problems related to the dyes have become more prominent. Since then, it has become a significant concern among researchers and engineers all around the globe (Katheresan et al. 2018). The worldwide benchmark for dye effluent is shown in Table 3.

3.3 Pharmaceutical One of the biggest sectors is the Pharmaceutical sector; its production and usage rate exponentially increase year after year. The worth of the Indian health sector has been projected to jump from 140 billion U.S. dollars in 2016 to 372 billion dollars by 2022 (India: healthcare sector size 2022). Over 50,000 unique types of pharmaceuticals are manufactured, and about 30 million tons of medications are utilized all over the globe (Liu et al. 2020). They include antibiotics, analgesics, steroids, antidepressants, antipyretics, stimulants, antibacterial drugs, hormones, anti-inflammatory drugs, β blockers, lipid regulators, contrast agents, and impotence drugs (Balakrishna et al. 2017). There are many ways this pharmaceutical compound (organic and inorganic compounds) enters the aquatic system, from manufacturing units, hospitals, dispensaries, and residential areas (Alenzi et al. 2021), which lead to a severe threat to

150–10,000 1794 ± 7

480

201

249

425–474

100–4000

1350 ± 13

8–10.5

7.43

8–9.5

6.27–8.80

7.73

8.8

–

6.7–9.3

5.5–10.5

10.9

Algeria

Turkey

Malaysia

Morocco

Pakistan

Pakistan

India

Iraq

India

7.1–85

–

36.5

580–750

755–2490

471

513

1741.66

55–294

700–1250

100–200

1220–2200

2133.8

Indian

366.7

6.5–8.5

Tanzania

COD (mg L−1 )

pH

Country

BOD (mg L−1 )

1800–6000

1500–6000

2300–3200

4569

5251

2311.66

1250–3610

–

–

3580–4670

1250–3610

TDS (mg L−1 )

Table 2 Physical and chemical properties of textile wastewater (Dihom et al. 2022)

100–5000

100–5000

4509–6370

391

324

1433.33

69–205

200–450

36.2

280–430

567.8

TSS (mg L−1 ) Color

–

–

–

35.5

66

–

17–140

500–1250

–

–

1685.9

Turbidity (NTU)

–

–

–

–

–

–

5.89–26.6

–

–

–

165.0

References

(continued)

Rangari et al. 2017)

Biswas et al. 2017)

Mohan and Pittman 2006)

Li et al. 2011)

Tawade 2020)

Bhatnagar et al. 2013)

El-Geundi et al. 2016)

Babel and T. K.-J. 2003)

Aggarwal et al. 1999)

Ming and Dixon 1987)

Singh and Pant 2004)

Nanoadsorbents for Treatment of Wastewater 139

224.6 ± 40.7

100–4000

8.5 ± 1

6–10

Pakistan

India

80–6000

80–6000

6.95–11.8

6–10

Malaysia

India

93.0–188.0

141

8.080–11.21

–

Ethiopia

970

8.66

India

India

BOD (mg L−1 )

pH

Country

Table 2 (continued)

150–10,000

433.7 ± 35

150–12,000

150–30,000

1090

189.6–264.0

3080

COD (mg L−1 )

1800–6000

2570 ± 490

2900–3100

2900–3100

–

277.0–900.4

242,220

TDS (mg L−1 )

100–5000

244 ± 76

15–8000

15–8000

1004

90.50–147.0

7116

TSS (mg L−1 ) Color

–

456 ± 22.6

50–2500

50–2500

–

Blue-black

5200

–

–

–

–

–

–

81.5

Turbidity (NTU)

Liu et al. Mar. 2022)

Bailey et al. 1999)

Hurt et al. 2006)

Liu et al. 2005)

Kalfa et al. 2009)

Jain et al. 2021)

Kumar, et al. 2013)

References

140 P. V. Tawade et al.

Nanoadsorbents for Treatment of Wastewater Table 3 The worldwide benchmark for dye effluent (Katheresan et al. 2018)

141

Factor

Standard allowed

Biological oxygen demand

Below 30 mg/L

Chemical oxygen demand

Below 50 mg/L

Color

Below 1 ppm

pH

Between 6 and 9

Suspended solids

Below 20 mg/L

Temperature

Below 42 °C

Toxic pollutants

Not allowed to be released

the environment and living organisms as well. Because many drugs are persistent or pseudo-persistent, poisonous, and non-biodegradable, they may affect the quality of drinking water and prove to be a threat to living organisms. (Huang et al. 2021).

3.4 Inorganic Pollutants Toxic inorganic pollutants, such as metal cations like Cu(II), Ni(II), Zn(II), Pb(II), Cd(II), Hg(II), Cr(VI), and anionic species such as SO4 , NO3 , F, ClO4 , P4 O3 , etc., are released into the streams, which affect the environment, marine life, and causing a wide range of health problems in humans. Numerous industries like mining and processing of ores, petroleum and chemical activities, polymeric, electroplating, fertilizer plants, leather tanneries, steel fabrication tanneries, glass, and cement production activities discharge these contaminants into water (Banerjee 2012). Different ionic inorganic compounds are resistant to biological and chemical breakdown and have a great tendency to bioaccumulate in the food supply chain. Prolonged exposure to hazardous inorganic pollutants, at even minimal amounts, may result in severe illnesses or even death; some are tabulated in Table 4. Table 4 Consequences of some of the toxic inorganic substances on the human body Compound Consequence on human body

References

Lead

Brain damage, mental deficiency, kidney damage, vomiting, and behavioral disturbances in humans

Iqbal et al. 2002)

Copper

Necrotic changes in the kidney and liver, lung cancer, mucosal and gastrointestinal irritation

Zhou et al. 2014)

Nickel

Allergy problems, cancer of the respiratory tract, and lung fibrosis

Genchi et al. 2020)

Cadmium

Acute and chronic intoxications, and it can replace Zn(II) ions Kazantzis 2004) in some metalloenzymes, thereby affecting the enzyme activity

Perchlorate Anemia, fetal brain damage, and also affect iodide uptake by the thyroid gland

Park et al. 2012)

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3.5 Radioactive Waste World energy consumption and demand are expanding significantly due to population and industrial activity growth, yet conventional fossil fuels remain the primary source of energy. Due to the non-renewable nature of fossil fuels and the restricted availability of renewable energy, nuclear power has been gaining traction as a viable option. Through diverse operations and versatile applications, a considerable amount of radioactive waste has been created as a result of the development of new nuclear technologies across the world, Table 5. It is essential to recognize that such emergent radioactive pollution poses a significant hazard to the environment and human health.

4 Wastewater Treatment Wastewater treatment methods were initially designed to respond towards the negative consequences of effluent released into the environment and human health risks. Moreover, as urbanization became more extensive, there was less area available for effluent processing and recycling, primarily conducted through irrigation and intermittent filtering. Furthermore, as populations grew, the volume of wastewater discharged increased rapidly, as well as the degrading condition of this enormous volume of effluent surpassed its self-purification ability (Rajasulochana and Preethy Table 5 Common sources of radioactive waste (Zhang et al. 2019) Waste category

Common sources of waste

Common radionuclides

High-level radioactive waste (HLRW)

Partially used fuel from nuclear power reactors; liquid waste from the reprocessing of spent fuel

90 Sr,

Transuranic waste

Weapons’ production waste included mixed transuranic waste

238 Pu,

Weapons’ production waste and some research wastes

239 Pu,

Scale buildup on pipe walls that carry petroleum products

226 Ra,

Mixed waste Naturally occurring radioactive material (NORM) waste

Uranium or thorium mill tailings Production exclusively at the waste site of milling for rare earth extraction

half-life: 29.78 y half-life: 30.07 y

137 Cs,

half-life: 87.7 y half-life: 432.7 y

241 Am,

241 Pu,

half-life: 24,100 y half-life: 14.4 y

228 Ra,

half-life: 1599 y half-life: 5.76 y

230 Th,

half-life: 75,400 y

Low-level radioactive waste (LLRW)

3 H, half-life:12.32 y 60 Co, Industrial trash from nuclear power plants; medical, half-life: 5.27 y research, and academic trash such as paper, plastic, and glass

Very low activity waste

Various medical procedures

131 I,

half-life: 8.027 d

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Fig. 2 Techniques for removing dyes and heavy metals from wastewater (Ali et al. 2020)

2016). It is high time for the industry to develop more efficient and cost-effective technologies which require less space. Filtration, flocculation, activated charcoal, and ion exchange are some of the conventional techniques used for wastewater treatment (Karthikeyan et al. 2005). Even though the aforementioned methods are effective and meet discharge regulations, most of them create secondary pollutants. The advancement of new promising techniques for treating effluent has started with a more incredible speed. Physical, biological, and chemical methods for remediation are depicted in Fig. 2. Filtration, ion exchange, coagulation, flocculation, precipitation, oxidation, membrane separation, enzyme, algae, and fungi-derived breakdown techniques are just a few methods used to eliminate contaminants from wastewater (Lee and Hsieh 2019). Most of these conventional techniques contain inherent flaws and shortcomings, like low efficiency, high costs of operation, a complex process, large amounts of sludge formation, and feasibility.

4.1 Physical Treatment of Wastewater Among the many techniques for treating wastewater is the mechanical treatment process. This approach eliminates toxins using automated activities governed by

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natural rules. Physical processes are often straightforward and more efficient than other wastewater treatment methods. Non-biodegradable pollutants that enter a water treatment facility are removed using this method.

4.2 Chemical Treatment of Wastewater Chemical wastewater treatment is another sort of technique for treating wastewater. Various chemicals are employed in this process that entails removing or reducing contaminants as a consequence of a chemical process. However, this procedure is quite expensive. All engineers are looking for innovative ways to decrease the number of processes involved in chemical processing. They expect to get the most remarkable outcomes by utilizing the least quantity of chemicals possible. In industry, using various chemicals for water treatment is termed as chemical dosing.

4.3 Biological Treatment of Wastewater The biological way of treating wastewater is another feasible approach for wastewater treatment. Microorganisms are often used in treating wastewater. There are two types of biological activity-based techniques: aerobic and anaerobic. Biodegradable, soluble, organic, and nutritional compounds and colloids are removed from wastewater using these procedures. Due to the complex interaction of biology and biochemistry, biological wastewater treatment is the least understood phenomenon among others. It uses biological mechanisms to degrade the complex organic structure utilizing bacteria and nematodes (Karri et al. 2021).

5 Adsorption For wastewater treatment, reverse osmosis, ion exchange, and oxidation are popular methods. These technologies deliver hazardous secondary contaminants into the ecosystem, limiting their usage in potable and industrial wastewater treatment (Crini 2005). As a result, there is a need to investigate various alternative strategies that are efficient and cost-effective in eliminating contaminants. The development of the adsorption technology, effective for purification and separation of water and wastewater contaminants, was prompted by scientists’ growing environmental awareness and concern. An adsorption is a prominent approach for wastewater treatment that is believed to be efficient, inexpensive, and environmentally friendly among all the water purification treatment methods (Crini 2006). Adsorption is a mass transfer process in which contaminants from the liquid phase or gaseous environment in contact with the substrate are concentrated or adsorbed on a solid substrate. In this

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145

Fig. 3 Depiction of adsorption mechanism (Ali et al. 2020)

case, pollutants are referred to as adsorbates, and the substrate is referred to as an adsorbent. Kayser was the first to use the term adsorption in the literature, describing the process as a surface accumulation of materials in 1881 (D¸abrowski 2001). If the adsorbate or species is physically connected to the adsorbent surface without any chemical connection, the process is called physisorption. On the other hand, chemical bonding is involved in the adsorption process and is referred to as chemisorption. The adsorption mechanism consisting of mass transfer, adsorption, and transportation in adsorbent is depicted in Fig. 3.

6 Nanotechnology Nanotechnology and nanoscience research have exploded in popularity in recent years. Nanotechnology has grabbed a lot of interest and has grown in popularity over

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time especially in terms of technical developments. Despite the fact that nanotechnology appears to be a young branch of science, its applications are far from new. Natural asbestos nanofibers were used for ceramic matrices 4500 years ago, and nanomaterials have been used in buildings since then. Egyptians, one of the world’s oldest, wealthiest, and most advanced civilizations, recognized the possibilities of nanotechnology 4000 years ago (Khan et al. 2022). Nanoparticles are objects ranging in size from 1 to 100 nm that differ in size from bulk material. The manufacturing of nanoscale materials, notably metallic NPs, has gained enormous attention in the last decade due to their unique features. It is defined as “the synthesis, design, characterization, and use of assemblies, tools, and systems by controlling morphology and size variation at the nanoscale level from 1 to 100 nm” (Yadollahi et al. 2010). Nanomaterials (Fig. 4) have several dimensions of structural elements, crystallites, molecules, and clusters, including zero dimension (nanoparticles, nanoclusters, and quantum dots), one dimension (carbon nanotubes and multiwalled nanotubes), two dimension (graphene layers and ultrathin films), and three dimension (nanostructured materials).

Fig. 4 The different forms of nanomaterials (Fajardo et al. 2022)

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Fig. 5 Structure of a nanoparticle (Khan et al. 2022)

The size and structure of nanoparticles have an enormous impact on their applications. The nanoparticles are synthesized, analyzed, measured, and modified at the nanoscale. Many nanocompounds are now created with the assistance of this emerging nanotechnology, which is gaining traction in scientific study. Figure 4 depicts different structures of nanoparticles. The synthesis process, which is fundamental in the field of nanotechnology, deals with the chemical makeup, size, shape, and appearance of nanoparticles. Nanoparticles often have distinct size-dependent features due to their large surface area. The characteristics of nanoparticles are used to offer a higher surface area than the bulk material due to their size. As a result, such materials will contain atoms that interact more with the exterior environment, whereas bulk materials would keep particles closer to the core (Khan et al. 2022). Nanoparticles are unusual in a way that they have a large surface area, mechanical strength, optical activity, and chemical reactivity, making them excellent for a wide range of applications in science and technology (Fig. 5). Nanoparticles, as well as associated devices and technology, are employed for a wide range of remedial operations based on their specific properties. Few of the applications are heavy metal pollution treatment, wastewater decontamination, hydrocarbon remediation, solid waste cleanup, and radioactive material remediation. Table 6 shows various nanotechnology-mediated water treatment technologies. A wide range of nanoparticles are used in the cleanup. The three types of nanomaterials used in environmental remediation are organic nanoparticles, inorganic nanoparticles, and polymer-based nanomaterials.

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Table 6 Utilization of nanotechnology for water treatment (Ajith et al. 2021) Serial Number

Nanotechnology-mediated water treatment processes

Targeted pollutants

Advantages

Disadvantages

1

Photocatalysis

Organic pollutants such as pesticides, endocrine disruptors, dyes, drugs, glycerol, etc.

Complete degradation of pollutants, no secondary pollution, useful for degradation of non-biodegradable contaminants

Slow rate of reaction, difficulty in separation of NPs employed in photocatalysis, inefficiency in utilizing visible spectrum of light

2

Adsorption

Organic and inorganic (heavy metals, elements) pollutants, microbes

Offers reversibility, low costs, ease of operation, and high efficiency

Low selectivity, exhausted adsorbents generated as waste

3

Nanomembrane

Microbes, particulates, organic and inorganic pollutants

Convenient to adjust, less chemical consumption, high efficiency, less solid waste generated

Membrane fouling, low quality of permeate, low flow rate, high operational cost

4

Antimicrobial activity

Microbes

Low cost compared to conventional antibiotics, broad therapeutic index

Nanotoxicity, difficulty in extraction of NPs after treatment

7 Nanoadsorbent Because of their unique features, nanomaterials hold enormous potential as the best possible approach to remediate organic and inorganic pollutants. Depending on the functionalization of nanomaterials, the interaction between nanoadsorbents and particles might be chemisorption or physisorption. The interaction of inorganic and organic contaminants with nanosorbent materials has been studied in several investigations. The adsorbent’s nature is a critical aspect of the adsorption process, as it impacts the efficiency, adaptability, and economics of the adsorption technique. Traditional sorbents like activated carbons (Kobya et al. 2005), chelating materials (Sun et al. 2006), and chitosan/natural zeolites (Wang et al. 2009) can remove heavy metal cations from water or wastewater. Still, some properties, such as low sorption capacities, can reduce their efficiency in an application. Nanomaterials, or substances with a particle size range of 1 to 100 nm, have been employed to overcome the shortcomings of conventional sorbents in the previous 10 years.

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For wastewater treatment, a considerable variety of nanoadsorbents are utilized. They’ve been proved to be absolutely excellent in removing pollutants from water. However, a direct capacity comparison is impossible due to various factors such as the size and shape of the nanoparticles, the operating circumstances (such as pH, temperature, and reaction time), and the experimental form. The various nanoadsorbents are discussed below.

7.1 Carbon-Based Carbon-based adsorbents such as Carbon Nanotubes (CNTs), Activated Carbon (Gupta et al. 2014), Porous Carbon (Gupta and Saleh 2013), Graphene, and Fullerenes, all of which have excellent thermal stability and adsorption capabilities (Ren et al. 2011) and hence these are widely used in wastewater treatment.

7.1.1

Carbon Nanotubes

Carbon nanotubes (CNTs) are cylindrical carbon nanostructures. CNTs are categorized as single-walled or multi-walled nanotubes depending on the fabrication technique. At the corners of hexagons, carbon atoms are organized in sp2 hybridization. CNTs have a large surface area, several adsorption sites, and a chemically adjustable surface. The hydrophobic surface characteristics of CNTs generate particle aggregation in an aqueous solution, which prevents decline in surface activity (El-sayed 2020). CNTs may be used to clean up polluted areas and detect pre-concentrate levels and disclose toxins. Electrostatic attraction and chemical bonding are used to interact CNTs with metal cations. The SWCNT is made by rolling a single graphene sheet into a cylindrical shape, whereas the MWCNT is made by rolling numerous concentric SWCNTs into a tubular shape (Kadleˇcíková et al. 2022), as depicted in Fig. 6.

7.1.2

Graphene

Graphene is a honeycomb structure of single-atom-thick, two-dimensional (2D) nanosheets of sp2 hybridized carbon atoms. It may be found in the 3D graphite structure as a stack of 2D layers and the fundamental building component of other carbon allotropes. Graphene has attracted a lot of interest from researchers worldwide because of its unique properties, such as excellent mechanical strength, high thermal and electrical conductivities, chemical inertness, high current density, optical transmittance, and so on. It can be used in a variety of applications, including sensors, photovoltaic cells, energy storage, catalysis, lubrication, and membrane separation technology. It is a promising option for the adsorption of organic and inorganic effluents from water due to its high surface-to-weight ratio and chemical

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Fig. 6 CNT structure representations of a a MWCNT and b a SWCNT (Backes and Hirsch 2010)

stability (Zhao et al. 2012). Graphene oxide (GO), reduced graphene oxide (rGO), GO sponges, chemically functionalized GO, and graphene oxide nanocomposites have recently been found to be effective adsorbents in the removal of pollutants from industrial, residential, and agricultural effluents. Several studies have examined the effect of graphene and its derivatives in the dynamic adsorption of organic dyes (e.g., rhodamine (RG), malachite green (MG), methyl orange (MO), methylene blue (MB), Congo red (CR), and medicinal substances (Gusain et al. 2020) (Fig. 7).

7.1.3

Activated Carbon

Activated carbon (AC) can be made from various carbonaceous materials, including wood, coal, lignite, and coconut shell (Wang et al. 2021). Activated carbon is a versatile material with numerous applications in many areas. Still, primarily used in the environmental field, due to its high surface area, large porosity, well-developed internal pore structure consisting of micro, macro, and mesoporous, and a broad spectrum of functional groups present on the surface. The effectiveness of activated carbon as adsorbents for various contaminants has been widely documented. It is generally known that activated carbon is far more effective than metals and other inorganic contaminants at eliminating organic molecules. Efforts are now underway to significantly increase the potential of carbon surfaces by employing various chemicals or appropriate treatment procedures, allowing activated carbon to improve its ability to remove particular pollutants from the aqueous phase (Bhatnagar et al. 2013). Activation circumstances (different agents, temperature, and time of the process), precursors, additives, and other factors can affect activated carbon’s physical and chemical structure (Jana et al. 2021).

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Fig. 7 Graphene: the basic 2D building block of carbon materials (Gusain et al. 2020)

7.2 Metal Oxide Nanoparticles Metal oxide nanoparticles are widely employed in a broad range of applications in food, materials, chemistry, and biology (Aitken et al. 2006). Bulk materials based on TiO2 , SiO2 , aluminum, and iron oxides have been mass-produced for many years, as is widely known. Nanoparticulate versions of these metal oxides have recently been manufactured and introduced in commercial products such as cosmetics and sunscreens (TiO2 , Fe2O3 , and ZnO) (Nowack and Bucheli 2007), dental fillers (SiO2 ) (Balamurugan et al. 2006), catalysis (TiO2 ), and fuel additives (CeO2 ). We will go through a few of the most commercially important nanoparticles. According to a literature review, nanometal oxides (NMOs) have a significant potential to adsorb toxic metals. As a result, NMOs can be used to treat water by eliminating various harmful metal contaminants (Deliyanni et al. 2009). The main disadvantage of NMOs is that when the size is lowered from micro to nano, the surface energy increases to the point where stability is severely compromised. As a result of Van der Waals forces and other interactions, they tend to agglomerate at this size, reducing their adsorption capacity to a bare minimum. The table below compares the adsorption capacities of several NMOs for the adsorption of heavy metals and dyes. On the other hand, the adsorption capacity varies substantially depending on the experimental circumstances (Table 7).

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Table 7 NMO adsorption capabilities for a variety of contaminants (Kumari et al. 2019) Serial number

Adsorbent

Adsorbate

pH

Adsorption capacity (mg g−1 )

Refs.

1

MgO

Reactive blue 19

8

166.7

Sadeghi-Kiakhani et al. (2013)

Reactive red 198 2

y-Fe2 O3

123.5

Cr (IV)

2.5

17

Cu (II)

6.5

26.8

Tomic (1965)

Ni (II)

9.5

23.6

3

Goethite (α-FeOOH)

Cu (II)

6

100%

Younas et al. (2021)

4

Hematite (α-Fe2 O3 )

Cu (II)

5.2 ± 0.1

84.46

Chen et al. (2010)

5

γ-Al2 O3

Ni (II)

−

176.1

Barthelet et al. (2002)

6

ZnO

Pb (II)

−

6.7

Czaja et al. (2009)

7.3 Metal Nanoparticles A variety of metal NPs have been employed as adsorbents for wastewater treatment in the literature. Here are a handful of them that have been discussed.

7.3.1

Zero-Valent Iron Nanoparticles

Zero-valent iron nanoparticles have been widely explored and employed for water cleanup as one of the cheapest transition metals. Because of Fe(0) nanoparticles’ high reactivity due to the ease with which they may be oxidized, their usage and efficiency are primarily reliant on their stabilizing technique and age, both of which differ across the various publications that deal with this type of nanoparticles. Indeed, the use of Fe(0) nanoparticles for water remediation has gotten a lot of attention since the late 1990s (Zhang 2003), thanks to their substantial specific surface area and strong reactivity, which favors organic pollutant adsorption and degradation. Fe(0) nanoparticles have been employed to adsorb and decompose organic pollutants and heavy metals, notably polychlorinated biphenyl (PCBs) and chlorinated organic solvents, as novel promising materials with high reactivity. The catalytic reactivity and effectiveness of Fe(0) nanoparticles for water remediation are highly dependent on particle properties, mainly if the nanoparticle’s Fe(0) oxidation state is maintained. Other zero-valent metal nanoparticles, such as Cu, Ag, and Au nanoparticles, have also been examined for the remediation of organic contaminants and earth-abundant zero-valent iron nanoparticles (Gawande et al. 2016). Various organic polymers have

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153

been used to support Cu nanoparticles for catalytic degradation of organic pollutants (e.g., dendrimers, synthetic/natural organic polymers) (Sinha and Ahmaruzzaman 2016). A study reported the catalytic reduction behavior and activity of zerovalent metal nanoparticles for organic contaminants. Zero-valent metal nanoparticles (Cu0, Co0, Ag0, and Ni0) were loaded onto Chitosan-titanium oxide nanocomposite fibers as supports, with zero-valent metal nanoparticles produced by reducing corresponding CuSO4 , Co(NO3 )2 , AgNO3 , and NiSO4 with NaBH4 . The Cu nanoparticles template on chitosan-TiO2 -15 fibers had the highest catalytic efficiency for reducing organic dyes such as methyl orange, Congo red, methylene blue, and acridine orange, as well as nitrophenols, among the zero-valent metal nanoparticles generated (Ali et al. 2018). In the presence of NaBH4 , a bimetallic Cu/CuO-Ag nanocomposite carrying Ag nanoparticles and CuO nanoparticles on the surface of Cu showed improved catalytic activity for the reduction of 4-nitrophenol. Au nanoparticles have been extensively studied in terms of their synthesis, characterization, characteristics, and applications (Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications Toward Biology, Catalysis, And Nanotechnology | Request PDF. 2022). Despite their effectiveness and recyclability, Au nanoparticles are rarely employed for wastewater cleanup due to their high cost. However, Au nanoparticles have been used to remove pesticides from water (Das et al. 2009). The proposed polyphenolic functionalized Au nanoparticles showed intense photocatalytic activity in reducing organic dyes such as methylene blue, methyl orange, bromophenol blue, bromocresol green, and 4nitrophenol under visible-light irradiation demonstrating an alternative methodology for the preparation of Au nanoparticles using Lagerstroemia speciosa leaf extracts. Pharmaceuticals (e.g., ciprofloxacin (Durán-Álvarez et al. 2016)), industrial organic compounds (e.g., phenol), and organic dyes have all been photocatalyzed with Au nanoparticles and Au-related nanomaterials. 7.3.2

Bimetallic Nanoparticles

For water cleanup, bimetallic nanoparticles and multimetallic nanoparticles have received far less attention than monometallic nanoparticles. As a result, the precise technique for repair has yet to be determined. In other words, the capacity to remediate will be determined by the crucial component of metal nanoparticles. Adsorption and degradation of organic contaminants have been investigated using a variety of bimetallic nanoparticles. The coupling of earth-abundant metal Fe nanoparticles with second metals (e.g., Ni, Cu, Pd, Au) has been widely researched to overcome the shortcomings of solitary Fe nanoparticles and improve the effectiveness of treatment of organic pollutants due to high potential activity at a cheap cost (Fang et al. 2011).

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7.4 Polymeric Adsorbents Polymeric adsorbents have been suggested as an alternative to traditional adsorbents because of their high surface area, adaptive surface chemistry, perfect mechanical stiffness, pore size distribution, and feasible production under particular conditions; polymeric adsorbents have been suggested as an alternative to traditional adsorbents (Zare et al. 2018). Metal oxide/polymer nanocomposites, carbon nanotube/polymer nanocomposites, metal and graphene/polymer nanocomposites, and dendrimer-based nanocomposites are the four basic types of polymeric nanoadsorbents depending on their composition (Wilson et al. 2018). Dendrimers are an excellent example of polymeric nanoadsorbents and their influence on removing organic and inorganic contaminants since they have repetitively branched molecules. Organic molecules can be absorbed through the interior hydrophobic portions, whereas the exterior branches can adsorb heavy metals. Some researchers improved the efficacy of dendrimers by combining two chemicals, such as chitosan and dendrimer nanostructures, to increase their capacity for removing anionic molecules from wastewater, such as dyes (Sadeghi-Kiakhani et al. 2013). They’re biodegradable, biocompatible, and non-toxic materials with a high dye removal efficiency of over 99%.

7.5 Metal Organic Framework Tomic (1965) was the first to develop materials with metal-organic polymers or supramolecular structures, which are now known as metal organic framework (MOF). Figure 1 depicts the historical evolution of MOF synthesis in detail (Tomic 1965). Since the initial publication of both non-flexible and flexible porous metal organic frameworks (i.e., MIL-47 and MIL-53) in 2002 (Barthelet et al. 2002), research has demonstrated that MOF synthesis combined with functionalization (i.e., postsynthetic modification) may be an effective and practical technique for changing their structure and other features. Bi- and trivalent aromatic carboxylic acids have already been used to make frameworks containing Al, Fe, Ni, U, Th, and Zn, yielding intriguing properties including high metal concentration and thermal stability (Czaja et al. 2009). Metal organic frameworks are one of the most frequently investigated materials and are usually called a new category of developing adsorbents. Because of its exceptionally high porosity, with pore sizes ranging from micro to meso, large surface area, customizable form, size, and functionality, MOFs have gotten a lot of interest for their adsorptive uses. The UiO series and ZIFs are the most frequent MILs (Matériaux de l' Institut Lavoisier) and MOFs (Zeolitic imidazolate frameworks) (Nasir et al. 2018) (Table 8). Zr-based MOFs, for example, have promising adsorption features, such as changeable shape, strong chemical and thermal stabilities, water and acid stability throughout a wide pH range, and moisture stability, all of which contribute to high adsorption capacities.

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Table 8 Some common metal organic frameworks (Bhuyan and Ahmaruzzaman 2022) MOF

Crystal formula

Central Structure metal

Refs.

UiO-66

Zr6 O6 (BDC)6

Zr

Das et al. (2009)

UiO-67

Zr6 O6 (BPDC)6

Zr

Durán-Álvarez et al. (2016)

MIL-53

Al(OH)(BDC)

Al

Fang et al. (2011)

MIL-100 FeIII 3 O(H2 O)2 F(BTC)2 .nH2 O Fe

Zare et al. (2018)

ZIF-8

Zn(MIM)2

Zn

Wilson et al. (2018)

ZIF-90

Zn(FIM)2

Zn

Sadeghi-Kiakhani et al. (2013)

7.6 Magnetic Nanoadsorbents At the laboratory and industrial scale, magnetic nanoadsorbents are proving to be very efficient functional materials with excellent micropollutant sequestration capacities and rapid adsorption kinetics. Apart from their redox activity and surface charge properties, high selectivity, binding specificity, and excellent reusability, magnetic nanoadsorbents have the unique ability that the adsorbate sludge can be separated in situ from adsorption-remediated waters (Zaidi et al. 2013). Separating micropollutant(s)-loaded spent magnetic nanoadsorbents from purified water/wastewater to produce clean water represents a huge opportunity for water science and technology research and development. In comparison to traditional procedures, magnetic separation provides several appealing features. These advantages are broadly related to (i) the high throughputs processing, (ii) the ability to

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perform integrated one-step capture and purification of specific species, and (iii) the low energy requirements and associated costs entailed by semi-continuous or continuous processes run at low pressure (Mudhoo and Sillanpää 2021).

8 Future Prospects Due to their outstanding physicochemical features, nanoadsorbent materials play an essential role in addressing environmental challenges such as wastewater remediation. The need for larger-scale wastewater treatment technologies exists, yet the deployment of these nanomaterials is dubious. Scaling up laboratory size studies to bigger scales, enhancing the biocompatibility of nanomaterials, making the process eco-friendly, and making the overall process cost-efficient are the things that need to be worked on. For researchers in this sector, the use of nanoparticles to remove pollutants from wastewater has been a game-changer. However, a few technical issues must be addressed for this technique to become a viable wastewater treatment option in the future. The first issue is the absence of available methods for the desorption of the nanoadsorbents in use. If we want to make this procedure cost-efficient, we need to recycle these adsorbents, which may be done via the desorption method. There has been little study done on this so far, and there is a need to identify effective strategies to return nanoadsorbents to their active state. Furthermore, this approach needs a substantial surface area of nanoparticles for effective adsorption. Optimizing the synthesis technique under optimal circumstances and the type of coating materials and their ultimate physical arrangement on nanoparticles will aid in the production of nanoparticles with the desired size and surface area. Many nanomaterials that have been addressed so far have been created through chemical processes, which might have hazardous consequences on the treated wastewater. Greener procedures for manufacturing these nanoadsorbents might be investigated to prevent such issues. Silica gel, coal, chitosan, clay materials, limestone, (Ali et al. 2020) agricultural wastes such as bagasse, coconut shell, rice husk, and so on (Younas, et al. 2021), cotton wastes, and cellulose-based wastes (Kumari, et al. 2021) have all been utilized to develop nanoadsorbents. These adsorbents are likewise challenging to come by at a reasonable price. However, if there is a rise in market demand for such materials, this issue can be solved. As a result, the broader use of such particles will increase their utilization and make their synthesis more cost-effective. Given the high cost of nanoparticles in comparison to standard materials, future research should focus on efficient procedures that only require modest amounts of nanomaterials. Furthermore, additional effort is required to create cost-effective nanomaterial production processes and evaluate efficiency on a large scale to achieve viable and practical applications.

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9 Conclusion Pollution of water has become a serious global problem in recent decades as a result of the expansion of manufacturing and agricultural operations to fulfill the demand for sustained world population increase. There are various strategies for water/wastewater cleanup, but adsorption is by far the most essential, efficient, and frequently employed. Adsorption may remove a wide spectrum of pollutants without leaving behind any by-products or intermediates. As a result, it has a broader range of applications in terms of eliminating contaminants from a water supply. However, traditional adsorbents have significant drawbacks, such as high adsorbent costs, depletion, low separation effectiveness, and costly regeneration, to name a few. Due to their unique qualities in the adsorption process, such as high selectivity, magnetic and catalytic properties, and most importantly high surface/volume ratio with active sites’ nanoadsorbent materials have recently gained a lot of traction. Nanoadsorbents’ unique qualities, along with their integration with conventional technologies, have expanded their applicability and provided a new aspect to the global revolution in water treatment. As a result, nanoadsorbent materials are regarded as next-generation adsorbents that perform admirably in the cleansing of the environment and the management of contaminants in water and wastewater. Due to their unique qualities such as large surface area, stability, and microbial action, a variety of nanoadsorbent classes can be utilized, including magnetic, nanometals and nanometal oxides, carbon-based and polymeric nanoadsorbents. This diverse group of nanoadsorbents has been effectively employed to remove inorganic, organic, and biological contaminants in the past. In the batch adsorption process, the adsorbents perform well. More pilot and industrial-scale investigations, on the other hand, are critical for determining the overall efficiency of large-volume water treatment. With such great potential, there’s a huge scope of research for developing adequate safety, increasing efficiency, creating cost-effective nanomaterials, and adapting acceptable procedures required to avoid negative effects (e.g., toxicity) of nanoadsorbents in the water treatment process.

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Nanofiltration Technique for the Treatment of Industrial Wastewater Niladri Shekhar Samanta, Piyal Mondal, and Mihir Kumar Purkait

Abstract Throughout the last few decades, membrane technology has played a major role in wastewater treatment and has been widely used to maintain water quality standards. The nanofiltration (NF) membrane technique has attracted researchers due to its unique property which lies between reverse osmosis (RO) and ultrafiltration (UF). While RO membranes are the industry standard for seawater desalination, NF membranes can be utilized to extract heavy metal ions and organic compounds electively from a variety of wastewater types and qualities, as well as for saltwater desalination. This chapter explores various kinds of filtration processes involved in wastewater treatment, mainly concentrating on nanofiltration. The useful utilization of nanofiltration through polymeric membranes, their advantages, and modifications have been discussed in detail in this chapter. Nanomaterials utilization towards preparing NF membranes and their specific applications towards industrial wastewater treatment is also elucidated in this chapter. Furthermore, recent trends of advanced modifications utilizing nanocomposites, biological, and stimuli-responsive materials for enhancing the efficiency of NF membranes have also been illustrated in this chapter. In addition, major challenges and future scope of developments of such NF applications have also been elaborately discussed. Keywords Nanofiltration · Polymeric membranes · Industrial wastewater treatment · Biological NF membranes · Stimuli-responsive NF membranes

N. S. Samanta · M. K. Purkait (B) Centre for the Environment, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India e-mail: [email protected] N. S. Samanta e-mail: [email protected] P. Mondal · M. K. Purkait Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_9

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1 Introduction Clean water is crucial for humanity’s existence and development. It is, after all, a fundamental requirement for all alive things. However, the provision of potable water has recently become a global concern due to widespread water contamination. Polluted water, according to the United Nations, kills more people each year than all types of violence combined, including war (United Nations News Centre 2010). According to the United Nations’ World Water Development Report (2016), more than 8% of the world’s population lives in water-scarce places; however, the global population is expected to reach about 8.1 billion by 2025, with up to 38% of that suffering from freshwater shortages (Sharma et al. 2022). “More than one billion people throughout the world do not have access to safe drinking water, and the situation is becoming worse,” Nature writes in its web emphasis on the coming global water catastrophe. The average amount of water/person will decrease by a third over the next two decades, perhaps causing millions of people to die prematurely” (Das et al. 2022). Water must be cleaned not just for human consumption, but also for a range of other uses. It’s an important raw material for the pharmaceutical, food processing, medical, and chemical sectors. Physical and chemical techniques are the two most common types of water purification technologies. Sedimentation, distillation, filtration, boiling, reverse osmosis, desalination, and UV light irradiation are examples of physical techniques. Flocculation, chlorination, and coagulation are the most extensively employed chemical techniques (Das et al. 2021; Chakraborty et al. 2019; Changmai et al. 2020). Photocatalytic destruction of dissolved water contaminants under irradiance is a type of phsysico-chemical technique that has extensively studied for contaminated water treatment during the last decade. Flocculation, coagulation, sedimentation, chlorination, sand filtration, and adsorption on activated carbon, among other methods for cleaning water, are ineffective in eliminating dissolved organic molecules and heavy metal ions. Alternative methods for removing pollutants from water include ozone treatment, cremation, and UV light irradiation, however, they are not cost-effective for extracting trace chemicals. As a result of revolutionary advancement in the field of nanotechnology and nanoscience over the last couple of decades, the scientific community has been encouraged to investigate this highly promising research fields, where the unique and advantageous properties of novel nanostructured materials could be employed to deliver more effective and sustainable solutions to the manifesting water-related issues. Membrane is an extremely thin semipermeable film of material which enables things to pass through its holes selectively depending on their size and structure. Membrane-based methods have been extensively applied in wastewater treatment in recent times. Membrane prevents pollutants (whose size exceeds the pores) from passing through, resulting in cleaner water during water filtration. Membrane technology has advanced dramatically in recent years, ranging from desalination to antimicrobial filtration. Micropollutants, particulate matter, microorganisms, and another organic elements that give color, taste, and odor to water have been separated using very effective membranes.

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Membranes are categorized as aquaporin-based membranes, nanofiltration membranes, nanofiber membranes, self-assembling membranes, nanocomposite membranes, biological membranes, thin-film composite membranes, and membranes for forward and reverse osmosis based on their composition, porosity, and mode of application. The fabrication of various kinds of membranes and their utilization in water treatment are discussed in the next section. Nanofiltration is a pressure-driven method in which unclean water is forced through a thin polymeric membrane with pores ranging from 1 to 10 nm, separating impurities larger than the pores from the water. The removal of polyvalent cations, dissolved particles, and natural organic matter from water is made easier using this technique. Water softening is the most common use of nanofiltration membranes because they block magnesium and calcium ions while allowing only hydrated monovalent ions to flow through. NF membranes are significantly utilized for the recovery of solvent in the fine chemical and pharmaceutical industries. They’re also employed to refine gas condensates in the petrochemical industry. Nanofiltration membranes are used in the life sciences to extract lipids and amino acids from the blood and another cell cultures (Mohammad et al. 2015). This chapter focused on types of membrane separation involved in water filtration along with a comprehensive discussion on nanofiltration (NF). The present chapter also deals with intrinsic characteristics, benefits, and limitations associated with the nano filtration technique. Moreover, the surface modification, as well as advantages and disadvantages of nanofilter membrane, is also explicitly reported in this chapter. In addition to that, preparation of nanocomposites imprinted flat sheet nano filter membrane, hollow fiber membrane and their utilization to several applications including dye, heavy metal, and organic pollutants removal are comprehensively elucidated here. Despite the synthesis and utilization of nano filter membrane, advanced techniques employed to fabricate the hydrophilic nano filter membrane fabrication are also highlighted in this study.

2 Filtration Using Membrane Membrane filtration is a typical physical separation technique that can be classified into various processes includes RO, UF, and NF. The following approaches are discussed in further detail below.

2.1 Reverse Osmosis The reverse osmosis technique refers to osmosis in reverse. While osmosis takes place naturally without the need for energy, reverse osmosis necessitates the input of energy to the more saline fluid. A reverse osmosis membrane allows the majority of organics, bacteria, dissolved salts, and pyrogens to pass through, but not all dissolved organics,

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Fig. 1 a Reverse osmosis b ultrafiltration c NF membrane filtration system

bacteria, salts, and pyrogens. However, to desalinate (demineralize or deionize) water, a pressure greater than the naturally occurring osmotic pressure is employed to the RO membrane. This allows for the passage of pure water while keeping the majority of impurities out. Figure 1a depicts the simple working principle of a RO process. Typically, RO is used in the desalination of seawater, where a large amount of salt may be removed to produce drinkable water. Numerous research articles have been reported on the utilization of RO membrane for several applications ranging from gas removal to metals rejection. In modern times, RO membrane is utilized effectively in desalination as well as toxic metal elimination. In recent, Santoyo et al. (BódaloSantoyo et al. 2003) employed the RO technique to reduce inorganic heavy metals like cyanide, ammonium, and sulfate from synthetic solutions. The impact of solution pH on metal rejection has been performed and the result suggested that sulfate removal was found to be 99.45% while keeping the feeding solution pH 9. However, at the same pH condition, the removal percent of ammonium and cyanide were estimated to be 72.30 and 28.80% which is very lower as compared with sulfate removal (99.45%). When cyanide and ammonium both are present in industrial wastewater, the study suggests that they cannot be removed in a one-step process.

2.2 Ultrafiltration UF is a membrane purification method similar to RO which applies hydrostatic pressure to push water through a semi-permeable membrane. The UF membrane’s

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pore size is typically between 103 and 106 Daltons. UF is a pressure-driven barrier that extracts viruses, bacteria, suspended particles, endotoxins, and another pathogen from water resulted in water that is highly pure and low in silt density. The membrane allows low molecular mass solutes and water to pass through, but suspended particles and larger molecular mass solutes are retained. Except for the size of the molecules it retains, UF is not fundamentally different from NF or MF. Figure 1b illustrates the filtration mechanism of the UF membrane. The complexation-ultrafiltration approach has recently been demonstrated to be a potential method for removing hazardous metals from the waste effluent. In a recent study, Barakat et al. (2010) employed a polymer-boosted UF technique to examine the removal capacity for objectional elements such as Ni (II), Cr (III), and Cu (II) from industrial effluent. Separation of toxic metals was conducted in an ultrafiltration module facilitated with a polyethersulfone membrane with a pore cut-off of 10,000 Da. The permeate flow rate was measured at 7.5 L/h with a fixed pressure of 1 bar. The removal percentage of toxic metals was investigated with various dependent parameters like the metal concentration and pH. A toxic metal rejection experiment was conducted concurrently to eliminate Cu (II), Cr (III), and Ni (II), from wastewater.

2.3 Nanofiltration NF is the most recently developed pressure-driven membrane technology for liquidphase separations. Because of its reduced energy consumption and greater flux rates, NF has largely supplanted RO in several applications (Gozálvez et al. 2002). It was observed that the characteristics of non-porous RO membranes and ultrafiltration membranes are likely the same as NF membranes. Figure 1c shows the wastewater purification flowchart using the NF membrane module. Surface groups such as carboxyl acids or sulfonated dissociate in commercial nanofiltration membranes, resulting in a fixed charge. As a result of the characteristics of nanofiltration membranes, ions may be segregated utilizing a combination of UF’s size and impact of electrical energy, as well as RO’s ion interaction methods (Bowen and Welfoot 2002). In the wastewater treatment system, the NF membrane is a relatively recent technology. The pores of NF membranes are so tiny (about 1 nm), hence small uncharged solutes are strongly eliminated, but electrostatic characteristics of the surface permit monovalent ions to get through rather efficiently while multivalent ions are mainly trapped. Because of these properties, NF membranes are ideal for fractionating and can effectively remove solutes from complicated process streams. Nowadays, the advancement in NF methodology as a feasible process has resulted in an enhancement in its use in a variety of industries, including the treatment of the textile plant’s effluent, pharmaceuticals extraction from fermentation broths, the dairy industry’s demineralization procedure, metal restoration from contaminated water, and elimination of virus (Bowen et al. 2002). Moreover, natural filtration (NF) is a potential technology for treating real organic compounds and inorganic contaminants in open water.

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Because the surface or open water has miserable osmotic pressure, NF may perform at low pressure. The NF method rejects a large number of organic compounds, likely sterilized by-products precursors. Natural organic chemicals, which are relatively bigger than the pore size of the membrane, may be transferred by NF, but inorganic salts could be extracted by the effect of charge the membranes and heavy metal (Thanuttamavong et al. 2001).

3 Characteristics, Advantages, and Disadvantages of Nanofiltration Membranes 3.1 Characterization The mechanical, chemical and thermal characteristics of the polymeric membrane determine the nanofiltration membrane’s endurance in the operating environment, and their performance is determined by these parameters, which may be evaluated by membrane characterization. Understanding the surface features of synthesized membranes is crucial for technological and scientific advancement in a wide range of commercial and academic study sectors (Rana et al. 2005). The next sections discuss the many methodologies and techniques used to characterize the physical and chemical characteristics of NF membranes. Field Emission Scanning Electron Microscopy (FESEM) Nano-fibrous media with diameters ranging from submicron to a few nanometers have recently piqued interest in a variety of filtering uses due to their high specific surface area, small pore size, low basic weight, high permeability, and strong pore interconnectivity (Purkait et al. 2009). Belwalkar et al. (2008) used scanning electron microscopy (SEM) to estimate pore diameters ranging from 14 to 24 nm and the influence of effecting factors on thickness and pore structure of anodic aluminum oxide tubular membranes. SEM is employed to examine the pore architecture of NF membranes. The Nano-Pro-3012 membrane belongs to a family of acid-resistant nanofiltration membranes used in water treatment. Figure 2a, b depicts the pore diameters of the Nano-Pro-3012 at greater magnification. Transmission Electron Microscopy (TEM) Transmission electron microscopy (TEM) is a surface characterization method for measuring a material by passing an electron beam through it in a high-vacuum environment. The interaction of electrons passed through the specimen creates a picture. TEM generates higher-resolution pictures than SEM, allowing users to analyze thin tiny samples as small as a single atom column. As a result, TEM achieves virtually atomic resolution. In context, Freger et al. (Freger et al. 2002) provided visual proof and analysis of the morphological and structural modifications produced by in situ alterations in the active and supporting layers of NF and RO membranes module. The

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Fig. 2 a and b SEM analysis of a thin film porous NF membrane (Reproduced with permission from Agboola et al. 2014 © Springer Agboola et al. 2014)

support of porous polysulfone with a high fraction of sulfur atoms was significantly darker than the entire polyamide layer in TEM pictures of changed membranes. Polysulfone holes of varying diameters were visible. The original membrane’s TEM micrographs clearly demonstrated variability in the active layer, with a small quantity of uranyl-stained carboxylic groups occurring in the thin outmost portion.

3.2 Advantages Nanofiltration is a relatively modern membrane technique for softening (removal of polyvalent cation) and reducing sterilized end-product precursors such as manufactured organic and natural organic substances dissolved with surface water and fresh groundwater. Nanofiltration has several advantages. Here’s a brief rundown of them: (1) For low-value salts, smaller discharge volumes and lower retentate concentrations as compared to RO. (2) Brackish water contents reduced salt and dissolved solids (TDS). (3) Heavy metals rejection is high. (4) Showed potential removal of sulfates and nitrates. (5) Colour, turbidity, and tannins can effectively remove in this process. (6) Softening membranes are employed to mitigate the concentration of calcium and magnesium carbonate in hard water. (7) No foreign solvent is required during operation. (8) Non-poisonous.

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3.3 Disadvantages (1) Energy squandering more as compared to MF and UF (0.3–1 kWh m−3 ). (2) Heavily polluted water required for Pre-treatment prior to NF (pre-filtration 0.1–20 µm). (3) Lower retention for univalent ions and salts. (4) Expensive technique than other removal processes. (5) Free chlorine is toxic to membranes (life-span of 1000 ppmh). It can be suggested that bi-sulphite or an active carbon filter are acceptable option for highly chlorinated water.

4 Modifications of Nanofiltration Membrane 4.1 Surface Coating In a recent study, Ba et al. (2010) employed crossflow equipment to conduct the surface coating experiments. The P84-PEI NF membrane was first compressed for 10–12 h at 13.8 bar (200 psi) until it reached a steady condition. A greater pressure of 20.7 bar (300 psi) was used for a long period prior to compaction to speed up the process. The feed consisted of 6 L of a 2.0 g L−1 sodium chloride (NaCl) mixture. The membrane’s salt rejection capability and permeation flux were measured. To extract salt, the membrane was washed with large quantities of deionized (DI) water after compression. After then, the precursor feed was changed to a 6 L aqueous solution of 50 mg L−1 polyelectrolyte (PVA, PAA, or PVS). The feed was cycled for a period of 8–12 h until the flux stabilized. At the time, it was considered that the most polyelectrolyte was adsorbed on the membrane surface, forming a protective layer. The desalination performance (permeation flux and salt rejection) of the coated membrane was evaluated at 13.8 bar using 6 L of a 2.0 g L−1 NaCl aqueous solution as feed after being rinsed with distilled water to eliminate any non-sorbed polyelectrolyte. The purpose of this experiment was to determine the durability of the surface coating in a salt solution, as well as the significant impact of coatings on the membrane desalination process.

4.1.1

Polydopamine (PDA) Surface Coating on Nanofiltration Membrane

Dopamine, a mussel-inspired coating material, has lately attracted a lot of attention as a possible candidate for fabricating functional sticky surfaces. Polydopamine (PDA) is formed when dopamine self-polymerizes in the presence of oxygen. The polydopamine coating may adhere sharply to practically any sort of solid surface due to the various interactions between the substrates and the PDA layer, such as covalent

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bonding, coordination bonding, electrostatic contact, and hydrogen bonding (Jiang et al. 2011). There have been numerous attempts to enhance the interfacial compatibility of composite membranes matrix in which a PDA coating serves as a bridge between the inorganic selective layer and the polymer substrates. For instance, Li et al. fabricated nanomaterials implanted composite membrane by depositing PDA coating on the surface of polyvinylidene fluoride substrate. Nanoparticles were firmly linked to the PDA layer, according to the findings (Wu et al. 2015). By dipping a polyethersulfone (PES) membrane in dopamine solution, Li et al. synthesized a flat sheet nanofiltration membrane with higher structural durability. In alcohol, the membrane had better contacts between polyamide active layer and PES substrate. The interaction between the groups from GO and the groups from PDA can generate strong covalent connections to enhance the structural durability of membranes (Hu and Mi 2013), resulting in the production of a highly sticky platform. In recent years, PDA-covalent organic framework (COF) blended NF membrane also successfully installed in a water treatment plant to get better durability and removal efficiency in rejection of inorganic metal from wastewater. Wu and his team (Wu et al. 2019) give a comprehensive study on PDA-COF imprinted NF membrane fabrication and their utilization in desalination experiments. The study revealed that the interfacial polymerization process enhances the porosity and hydrophilicity of membrane surface, and, in contrast, reduces the size of dense polyamide layer from 79 to 11 nm which controlled the salt rejection very selectively. A desalination ratio of 93.4% for Na2 SO4 was estimated over synthesized PA/PDA-COF/PAN membrane. In the same study, the dye (Orange GII) removal study also investigated employing the same fabricated membrane, where, 94% dye rejection was observed. Findings also suggested that solute rejection was three times higher than commercially available NF membrane. Therefore, the results implied that, synthesized membrane was highly effective for salt as well as dye removal.

4.2 Graft Polymerization Graft polymerization is a surface modification technique of the membrane. In modern times, many attempts have been made on graft polymerization of the nano-filter membrane to enhance its surface properties including hydrophilicity, surface durability, etc. Recently, Abu Seman et al. (2010) reformed PES nanofiltration membrane by UV-facilitated graft polymerization method, where acrylic acid (weakly acidic) and immersion technique are successfully utilized. The investigation revealed that modified membranes have greater permeability than the PES NF membrane that had not been changed. When compared to the original membrane, the rejection factor of humic acid was greater for all changed membranes, and the irreversible fouling by humic acid molecules was decreased following UVfacilitated graft polymerization by acrylic acid (Abu Seman et al. 2010). On the contrary, a hollow fiber polysulfone (PSf) membrane was effectively modified via a two-step plasma technique using 2-acrylamido-2-methylpropane sulfonic acid

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(AMPS) as a grafting agent to fabricate a highly negative surface charge density NF membrane, as proposed by Lei Wang et al. (2012). In this treatment technique, the PSf substrate was first plasma pre-treated. The pre-treated membrane was then immersed in AMPS aqueous solution, and the loaded monomer was incorporated onto the membrane via plasma-induced grafting method. On the membrane performances, the impacts of AMPS concentration, pre-treatment time, and grafting reaction time were investigated. Eleminations to mixed salt solutions and single salt solutions were also assessed. The finding also revealed that the PSf substrate’s pre-treatment was crucial in the formation of this nanofiltration membrane. The pre-treatment of the NF membrane was carried out for 30 s followed by grafting for 80 s with a 5% AMPS solution (Lei Wang et al. 2012). Once the preceding process is over then the pretreated membrane was used to separate Na2 SO4 . According to the survey, the highest acid rejection was found to be 80.8 ± 1.2% at 0.2 Mpa and 23 ± 1 °C temperature with a diffusion rate of 6.4 ± 0.2 L m−2 h−1 . The findings also revealed that in a salt solution negatively charged NF membrane exhibited better SO4 − selectivity as compared to Cl− ions.

4.3 Metallic Nanoparticle Impregnated NF Membranes Metallic nanoparticles (MNPs) and MNPs-embedded NF have a potential removal efficiency towards toxic metals, dye, and another micro-pollutants removal from wastewater as well as surface water. A numerous number of investigations have evident that MNPs-incorporated NF membrane showed considerably higher adsorption capacity than simple polymeric or ceramic NF membrane. This section mainly focused on different metal-loaded NF membrane fabrication technique and their utilization in several applications. Zeolite X nanoparticle imprinted PSf membrane was utilized to eleminate the nickel and lead cations from synthetic solutions, combining the adsorption and filtration processes, as demonstrated by Yurekli (2016). The performance of the blended membrane was evaluated under dynamic conditions. The findings also showed that by modifying membrane fabrication parameters like the casting film evaporation time and the zeolite X loading, the sorption capacity and water hydraulic permeability of the membranes significantly enhanced. At a filtration time of 60 min, at 1 bar of transmembrane pressure, the composite membrane’s highest sorption capacity for lead and nickel ions was found to be 122 and 682 mg g−1 , respectively. The coupling mechanism demonstrated that the membrane design may be used to effectively absorb lower concentrations of metal ions with less transmembrane pressures (Yurekli 2016). The phase inversion approach was utilised to fabricate poly (amide–imide) (PAI) and TiO2 nanoparticles impregnated polysulfone (PSf) nanofiltration membranes with an integrated dense layer from a dope solution comprising N-methyl-2pyrrolidone as the solvent and 1,4-dioxane as the co-solvent (Rajesh et al. 2013). After being subjected to the separation of humic acid (HA) from aqueous streams,

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the separation efficacy of composite membranes were considerably boosted. HA was employed as a model foulant to examine the antifouling properties of synthesized membranes. Attempts have been made to link variations in membrane performance to the structure of the membrane. It’s worth noting that low-free-energy membranes made with PAI and TiO2 NPs could be useful for a variety of industrial separations (Rajesh et al. 2013). In a recent investigation, Shalaby et al. (2020) fabricated gold NPs impregnated polymeric NF membrane to separate out trivalent PO4 3− ions from polluted water. The strategy of phosphate recovery and antifouling behavior of prepared membrane was studied. In addition, the impact of gold NPs in hydrophilicity and phosphate elimination were also investigated. The study showed that a rejection of 96.1% was obtained after experiment for 0.1% gold coated polymeric nanofiltration membrane with a permeation flow rate of 4.72 L m−2 h−1 bar−1 . The findings suggested that NPs grafted polymeric membrane was a viable alternative for waste reduction.

5 Wastewater Treatment Using Nanofiltration Membrane 5.1 Dye Removal Membrane separation methods are a low-cost and efficient way of treating dye effluent (Sinha and Purkait 2015; Jana et al. 2010). Many past studies focused on dye removal and wastewater treatment using the same methodology; however, the research is still continuing to reveal the membrane separation technique in modern times. In a recent study, Yang et al. (2020) procured 1,3,5 benzene-tricarbonyl trichloride and diaminodiphenylmethane monomers for making polyamide-based nanofiltration membranes via interfacial polymerization method, for dye rejection. In addition, effects of two monomer concentrations, the carrier soaking time in an aqueous monomer solution, and the polymerization time were investigated over fabricated membrane. The membrane had a flow rate of 36.81 L m−2 h−1 with a Congo red dye extraction efficiency of 99%. The rejection percentage of the other two negatively charged dyes observed in this study was similarly over 95% (Yang et al. 2020). In a comparison study, Abdi et al. (2018) employed PES and magnetic-grapheme incorporated PES membrane for dye removal. The findings demonstrated that dye rejection considerably increased with magnetic-grapheme embedded PSF membrane as compared to unmodified PSM membrane. According to their study, the dye removal of the graphene embedded PES membranes was nearly 99% for varying concentrations of hybrid graphene NPs, while the removal was found to be 91% of bare PES membrane. During repeated filtration, the flux reduction of the graphene incorporated PES membranes was smaller as compared to the bare PES membrane. On the contrary, A˘gtas et al. (2021) employed a commercial nanofiltration membrane to investigate its dye removal efficiency from an aqueous solution of MgSO4 and NaCl. In this typical dye adorption experiment NF 270, desal 5 L, and Toray membranes

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were used and it was observed that Toray membrane showed effective dye removal efficiency as compared to other membranes. The highest salt rejection efficiency for both MgSO4 and NaCl were found to be 94% and 49% respectively. The study also reveals that, surface roughness, mechanical strength, and contact angle values of the fabricated membrane were found to have a substantial impact on membrane performance.

5.2 Heavy Metal Removal The PES/B-Cur membranes were created by inserting boehmite nanoparticles (NPs) functionalized with curcumin (B-Cur) into the PES membrane using the phase inversion approach, as demonstrated by Moradi et al. (2020). The membranes’ performance was further assessed in terms of antifouling behavior, pure water flux, and heavy metal ion removal (Ni2+ , Mn2+ , pb2+ , Zn2+ , Cu2+ , and Fe2+ ). The PES/B-Cur membrane showed a large pure water flow rate (120–140 kg m−2 h−1 ) than the PES membrane due to an increase in hydrophilicity, porosity, and size of pores. Furthermore, heavy metals ions removal capacity of the resulting membranes was significantly improved due to the synthesis of chelated metal ions at the surface of the PES/ B-Cur membrane in the presence of B-Cur nanoparticles. The Ni2+ , pb2+ , Mn2+ , Zn2+ , Cu2+ , and Fe2+ rejection measured 99.51, 99.61, 98.72, 99.31, 99.11, and 99.88% for PES membrane comprising 0.5 wt% B-Cur NPs whereas they were 14.98%, 14.21, 16.43, 14.38, 15.11, and 15.13, for PES. The PES membrane comprising 0.5 wt% B-Cur NPs showed the maximum adsorption capacity of 32.20 mg g−1 for (for Ni2+ ), 35.01 mg g−1 (for Pb2+ ), 25.32 mg g−1 (for Mn2+ ), 27.08 mg g−1 (for Zn2+ ), 31.12 mg g−1 (for Cu2+ ), and 29.08 mg g−1 (for Fe2+ ). In addition to that, the PES/B-Cur0.5 demonstrated higher permeate flow and FRR than other samples throughout the filtration experiment (Yang et al. 2020). It is well known to us that, variables like solution pH, pressure play a significant role in toxic metal removal during the nanofiltration process (Samanta et al. 2021; Ghaedi et al. 2015). Mikulášek and Cuhorka (2016) employed thin-film composite NF membranes to evaluate the rejection efficiency of hazardous Pb (II) metal from wastewater. In their study, the impact of operating conditions namely pH and concentration of the feed solution, and exerted pressure have also been investigated. Results revealed that higher operational pressure results in decreasing lead ions concentration in the aqueous solution. The findings also showed that ion rejection was above 80% over AFC 40 membrane, meanwhile, 98% of Pb (II) removal was found after using AFC 80 NF membrane. It can be also assumed that membrane pore size and the charge may influence the rejection performance.

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5.3 Organic Pollutants Removal In recent research, Kim et al. (2008) applied chemically modified thin-film polyamide NF membrane to enhance the elimination ability for organic hazardous materials such as salicylic acid, ibuprofen, and bisphenol-A (BPA), which are basically endocrine-disrupting chemicals and pharmaceutically active compounds. The surface amendment of the targeted membrane was accomplished by graft polymerization (methacrylic acid (MA)-membrane) followed by cross-linking and substitution of functional groups. The sequence in membrane modification was maintained in order to improve the formation of the amide bond and carboxylic acids group. The distinguish of BPA rejection was examined for both of the membranes (raw and modified membrane). The result showed that a 74% rejection was achieved for raw membrane, where, 95% BPA rejection was obtained over the modified membrane. Nowadays, graphene oxide (GO) NF membrane was also revealed as a notable candidate for wastewater treatment or separation process. To segregate Na2 SO4 and organic molecules from contaminated water Li and his team (Li et al. 2021) developed a metal–organic framework (MOF) NPs imprinted hollow MOF/ GO composite membrane via the one-step etching-facilitated cross-linking technique. The findings reveal that MOF NPs are high hydrophilicity in nature which in turn enhances the hydrophilic property of the modified membrane ((Li et al. 2021; Haldar et al. 2020)). In addition, the study also implied that 86.3% and >99% rejection of Na2 SO4 and organic molecules were found for MOF/GO composite membrane with a removal flux of 16.4 L m−2 h−1 bar−1 and 45.4 L m−2 h−1 bar−1 respectively as compared to bare GO membrane. The reason may be due to interlayer spacing of hollow structural MOF in GO nanosheets which results in the formation of excessive water channel, therefore significantly increasing membrane permeaselectivity and anti-fouling characteristics. These findings imply that novel MOF/GO hybrid membranes could find widespread application in desalination and water treatment. In another investigation, Xu et al. (2020) synthesized TiO2 grafted Ti3 C2 Tx nanosheet NF membrane through the vaccum-filtration technique to examine the removal efficiency of organic molecules from wastewater. From the experiments, the removal efficiency of more than 99% was obtained over the fabricated Ti3 C2 Tx TiO2 membrane. Meanwhile, a less removal capacity was observed for raw Ti3 C2 Tx membrane. The result suggested that Ti3 C2 Tx -TiO2 membrane possesses a greater impact on organic compounds removal with excellent anti-fouling performance than pure Ti3 C2 Tx membrane. Furthermore, the membranes’ remarkable photocatalytic self-cleaning capability under UV light was validated, along with the enhanced capability of extremely proficient recycling, which was attributed to the in situ synthesis of Ti3 C2 Tx /TiO2 heterojunctions. The uses of various kinds of NF membrane towards different organic pollutants and salt extraction are enlisted in Table 1.

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Table 1 Utilisation of various types of NF membranes for different pollutants and salt rejection Types of NF membrane Pollutants removal

Removal capacity (mg g−1 )/removal (%)

References

Polyamide-based NF

Dye removal

95

Yang et al. (2020)

Graphene/PES

Dye removal

99

Abdi et al. (2018)

Commercial NF

MgSO4 and NaCl

94, 49

Agta¸s et al. (2021)

PES/B-Cur

Fe2+ ,

AFC 80 NF

Pb (II)

Cu2+ ,

pb2+

29.08, 31.12, 35.01

Moradi et al. (2020)

98

Mikulášek and Cuhorka (2016)

Polyamide NF

Bisphenol-A (BPA)

95

Kim et al. (2008)

Modified polyamide NF

Bisphenol-A (BPA)

74

Kim et al. (2008)

MOF/GO-NF

Na2 SO4 , organic molecules

86.3, 99

Li et al. (2021)

Ti3 C2 Tx -TiO2 NF

Organic molecules

99

Xu et al. (2020)

PIP-GO NF

MgCl2 , CaCl2

73.08, 63.75

Hu et al. (2017)

AqpZ NF

MgCl2

95

Li et al. (2014)

AqpZ:ABA NF

NaCl

99

Zhong et al. (2012)

NF 270 NF

MgSO4

90

Marshall and Wickramasinghe (2011)

Gold-sNF

PO4 3−

96.1

Shalaby et al. (2020)

6 New Advancement in Nanofiltration Membrane Membrane technology has received a considerable attention because of its superior separation proficiency, energy efficiency, and environmental kindness. As a result, developing a new membrane is an important step toward expanding membrane applications in water treatment (Mondal et al. 2019, 2020; Sharma et al. 2019).

6.1 Nanocomposite Nanofiltration Membrane for Industrial Wastewater Treatment Based on membrane structure and nanoparticle implantation, four kinds of nanocomposite membranes have been identified. In fact, nanocomposite membranes for example thin-film nanocomposite membranes (TFN) and mixed matrix membranes (MMM) are prepared by dispersing nanoparticles in the casting solution and allowing them to self-assemble on the membrane surface (Jhaveri and Murthy 2016).

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Figure 3 depicts typical type of nanocomposite membrane. (i) (ii) (iii) (iv)

Convectional nanocomposites Thin-film nanocomposites (TFN) Thin-film composite (TFC) with nanocomposite substrate Surface-located nanocomposite.

Thin-film composites with nanocomposite substrates have been employed in pressure-retarded osmosis (PRO) and forward osmosis (FO) procedures. These prepared membranes have also been used in RO/NF applications (Pendergast et al. 2010). The majority of organic–inorganic composite membrane production processes rely on mixing and phase inversion. Nanoparticles are scattered in the polymer by blending. However, particle accumulation and non-uniform dispersion of NPs occur

Fig. 3 Typical type of nanocomposite membrane (here red spheres indicate various nanoparticles) (image has been used with permission from Yin et al. 2015 © Elsevier (Yin and Deng 2015))

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as a result of this approach, which can be avoided by decreasing particle size. The interfacial compatibility of polymer and NPs can also be improved by surface modification of nanoparticles. Polymer chain grafting with polyhydroxyethylmethacrylate (PHEMA) and poly (methyl methacrylate) (PMMA) on the NPs surface, for example, can enhance with nanoparticle dispersal because the nanoparticles and polymer are more compatible. Grafting, on the other hand, forms a coating on the nanoparticle surface that prevents nanoparticles from migrating to surface of the membrane (Pendergast et al. 2010). Figure 4 also depicts various approaches for nanomaterials embedded into membranes. The most common way for making organic–inorganic composite membranes is to mix polymers with inorganic species and prepare the membrane using a phase separation method, shown in Fig. 4a. NPs would partially migrate onto the substrate’s surface during the phase inversion process. Figure 4b illustrates another frequent blending procedure in which starting materials are introduced to casting solutions and NPs are formed during membrane fabrication. Figure 4c–f depicts techniques for fabricating membranes with inorganic components adorned on the membrane surfaces to enhance shortcomings of manufactured membranes by mixing techniques, like surface hydrophilicity and adsorption sites, as well as membrane mechanical strength (Yang et al. 2016). However, these TFN membranes have a high water permeation ability, though, due to nanoparticle aggregation and the production of flaws, their rejection increases moderately. The creation of new TFN composite membranes with a nanomaterial interlayer (TFNi) is intriguing since it leads to better water permeability and selectivity. According to various studies, TFNi membranes increase the tradeoff connection between permeability and selectivity (Pendergast et al. 2010). The fabrication of NF and RO membranes applying a thin film composite (TFC) membrane is a typical method (Purkait et al. 2009). TFC membranes are made up of an ultra-thin polyamide (PA) layer and a porous sublayer that supports the top ultra-thin layer. Cadotte was the first to create it in the 1980s. Nanomaterials are distributed into the ultra-thin layer to influence the removal performance of TFC membranes. Nanoparticles are distributed in an organic solvent, either in an aqueous m-phenylenediamine (MPD) solution or in a trimesoyl chloride (TMC) solution, and then in situ interfacial polymerization (IP) (Fig. 5) (Kar and Bindal 2016). Hu et al. (2017) synthesized nanofiltration membranes by depositing graphene oxide (GO) in an aqueous solution of piperazine (PIP), which was subsequently reacted with TMC to produce an ultra-thin layer on a PSf substrate. CaCl2 and MgCl2 demonstrated stronger elemination than MgSO4 , NaCl, and KCl on the membranes, showing an increase in purification performance between monovalent and divalent positive ions with a common counter-ion of Cl− . The decreased electrostatic interaction between membrane and divalent Mg2+ and Ca2+ cations results in enhanced ion selectivity. Because of its large charge density and big size, SO4 2− is rejected by the negatively charged membrane on the PIP membrane without GO additive. Mg2+ is likewise strongly removed to maintain electrical neutrality, resulting in a larger rejection of MgSO4 than CaCl2 .

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Fig. 4 Impregnation of different NPs into the membrane via different methods (Yang et al. 2016)

6.2 Nanocomposite Hollow-Fibre Nanofiltration Membrane for Wastewater Treatment The TFC hollow fibre (HF) and TFC (DOX) membranes were fabricated co-solvent (dioxane) facilitated interfacial polymerization technique. NPs were first diffused in hexane by ultrasonication for a period of 30 min, right before the dissolving of 0.1 wt% TMC, for constructing TFN membranes via the IP technique. The resulting organic mixture was instantly employed to build the TFN membranes due to the

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Fig. 5 Depicts the fabrication of thin-film nanocomposite membranes (Reproduced with permission from Bandehali et al. 2021 © Elsevier Bandehali et al. 2021)

solution’s poor stability (precipitated within 10 min). A certain quantity of NPs was initially distributed in DOX withnin 30 min of ultrasonication at a fixed temperature of 25 °C to fabricate the TFN (DOX) membrane by IP method boosted by DOX. Then, in a 99 g organic TMC/hexane (TMC: 0.1 wt%) solution, 1 g DOX solution comprising dispersed NPs was added. The DOX/hexane solution comprising scattered NPs (0.0050.1 wt%) was kept unchange by Tyndall’s phenomenon and used to produce TFN (DOX) membranes. The DOX supported IP (or IP) technique was carried out using the following approaches: first, the dual-layer (PES/PVDF) hollow fibre substrate was successively submerged in alcohol and the aqueous solution (PIP: 2 wt%) to achieve saturated monomers in the substrate pores; second, using filter paper the wetted substrate was extracted to eliminate the surplus solution from surface; and finally, the hollow fibre substrate was gradually transferred through the filter paper for the rejection of excess solution on the surface and resulted substrate gradually immersed in the NPs to carried out the DOX facilitated IP process for a period of 2 min followed by curing at 70 °C for a treatment period of 8 min. Eventually, membrane was constructed with a thin film layer on the outside surface and kept for testing in a buffer solution (NaHSO3 : 500 ppm at 4 °C), as demonstrated by Liu et al. (2015). In a recent investigation, Samanta et al. (2023) synthesized the TFC HF NF membrane to evaluate its removal capacity in pilot-scale mode using surface water as a feed source. In this study, TFN membranes were created through interfacial polymerization (IP) of a polyamide (PA) layer on the shell side of hollow fibre membrane supports. TiO2 NPs were applied to exaggerate the removal rate and hydrophilicity of the HF NF membrane. The TFN HF NF membrane was conducted

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by IP technique employing TMC and PIP as monomers. To make nanocomposite membranes, TiO2 (0.01% [w/v], 0.05% [w/v], or 0.2% [w/v]) was mixed with a 2% (w/v) aqueous solution of PIP and sonicated at room temperature for 40 min. The organic phase consisted of a 0.13% (v/v) TMC solution in cyclohexane. To confirm that TiO2 and PIP monomers penetrated the porous support, HF membranes were first submerged in a TiO2 suspension for 2.5 min. Using air and cyclohexane, the remaining PIP monomer was extracted from surface of the membrane. The resulting membranes were then submerged in the TMC aqueous solution for 1 min to initiate the polymerization reaction. Third, the obtained membranes were withdrawn from the organic solution and heated at 70 °C as a posttreatment in order to accelerate polymerization. Finally, the resulted NF membranes were dipped in distilled water at 4˚C until needed. They also reported that the fascinating membrane (TiO2 -incorporated TFN HF NF) showed a higher degree of rejection efficiency towards salt and total organic content (TOC) as compared with TiO2 -free TFC membrane.

6.3 Aquaporin Based NF Membranes In a current study, a high surface area (28.26 cm2 ) aquaporin Z (AqpZ) aided biomimetic NF membrane was fabricated by Li et al. (2014). In this technique, the proteoliposome integrated AqpZ was completely embedded into the selective layer via crosslinking a polyelectrolyte with the membrane substrate made of poly (amide-imide) (PAI). In the preliminary stage, for 1.5 h, the extruded polydopamine (PDA) layered proteoliposomes were accumulated on the surface of PAI membrane. After removing the proteoliposome solution, a0.5% (wt%) 15 ml poly(ethyleneimine) (PEI) in Tris buffer solution was added on the membrane surface for cross-linking in a 343 K water bath for a period of 2 h, which resulted in the formation of thick rejection layers with nanometer range. The AqpZ-based membrane showed approximately 50% greater water flux than mutant membrane. Study also demonstrated that highest MgCl2 removal efficiency of 95% was measured over fabricated AqpZ imprinted polymeric membrane having a water flux of 36.6 L m−2 h−1 . Planar biomimetic membranes containing AqpZ were created for the first time on a cellulose acetate membrane substrate functionalized with methacrylate end groups, as reported by Zhong et al. (2012). A selective layer for NF was created on the substrate via UV polymerization and vesicle rupture of triblock copolymer (ABA) vesicles. The AqpZ:ABA ratio was changed from 1:200 to 1:50, and the impacts on NF performance were investigated. It has been discovered that NF membranes with an AqpZ:ABA ratio of 1:50 can provide an magnificent water permeability of 34 LMH bar−1 and NaCl removal beyond 30%. The current study also revealed that biomimetic membranes have such advantages include less energy consumption and high throughput which enhances adaptability and rejection efficiency of membrane. Using the same preparation technique discussed in the previous study, Samanta et al. (2022) prepared AqpZ integrated HF NF membrane with high fouling resistance. The rejection performance of synthesized fascinating membrane was estimated in terms

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of organic matter and salt extraction from wastewater. The findings also agreed that the reinforced membrane exhibits the highest water permeate flux with the highest separation performance. In addition, the permeability capacity conducted for both, pure TFC and AqpZ embedded HF membrane and the highest permeability was found to be 7.95 L m−2 h−1 for AqpZ imprinted NF sheet where relatively a less permeability estimated of 1.69 L m−2 h−1 for unmodified TFC sheet.

6.4 Nanofiltration Membrane Bioreactor In modern times, NF membrane bioreactor (NF-MBR) has been utilized for pharmaceutical waste reduction from contaminated water very effectively. In a recent study, Zaviska et al. (2013) employed NF-MBR for pharmaceutical waste (cyclophosphamide (CYC) and ciprofloxacin (CIP)) remediation. The overall procedure was carried out in the following order: bioreactor, followed by NF treatment. In summary, the reactor comprised contaminated effluent of 2.5 g L−1 of total suspended solids (TSS) in a 6 L feed volume. A bioreactor, an alimentation tank, and an NF membrane system comprised the experimental unit, as illustrated in Fig. 6. A synthetic influent and biomass were fed at a volumetric loading rate of 1 kgCOD m3 d−1 . The COD/N/P ratio was kept constant at 100/10/1, which favored both autotrophic and heterotrophic bacteria. As the main carbon source, glucose was used, and as a consequence di-ammonium hydrogen phosphate and ammonium chloride were included. The synthetic solution was diluted with tap water, the flow rate of which was controlled by a flush system. The concentrations of CYC and CYP at the inlet were set to 100 ppb. The solid retention time (SRT) and the hydraulic retention time (HRT) were then set to 40 days and 15.6 h respectively, allowing the concentration factor to reach 62.3. The findings also revealed that, after 20 days of acclimation, the concentration of CYC dropped to 40 ppb, and membrane fouling slightly increased CYC and CIP rejection.

6.5 Stimuli-Responsive Nanofiltration Membrane Recent research has looked at the manufacturing of membranes that respond to a variety of triggers, including pH, ionic strength, light, temperature, and electric and magnetic fields. In recent study, Xu et al. (2018) demonstrated the preparation of an electric charge responsive polyaniline (PANI) membrane. PANI membrane sheets were prepared by non-solvent induced phase separation (NIPS) and chemical oxidative polymerization at varied polymerization temperatures ranging from 5 to 25 °C. Initially, in a coagulation bath, deionised water was employed as the nonsolvent. Using a funnel, PANI-EB (11.55 g, 20 wt%) was progressively included to the mixture of 4-MP (3.77 g) and NMP (42.43 g) in small amounts over 5 min. To obtain a homogenous solution, the liquid was agitated at 300 rpm for a period

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Fig. 6 Schematic view of NF membrane bioreactor unit (Image has been reproduced with permission from Zaviska et al. 2013 © Elsevier Zaviska et al. 2013)

of 4 h and allowed overnight (12 h) to eliminate air bubbles. The resulting thickening mixture was poured into the doctor blade’s reservoir. Using an adjustable film applicator, the membranes were then cast on the backing layer at a thickness of 250 m. The casted membrane was submerged in a DI water coagulation bath for a minimum period of 24 h and flushed several times to eliminate the additional organic substances. In a final step, the raw membrane was doped in a 1.0 M HCl solution to assess its initial tuneability. During cross-flow filtration, the effect of electrical tuneability on flux and molecular weight cut-off (MWCO) under external potential (0–30 V) was investigated. In modern times several studies also invented the fabrication of stimuli-responsive NF membrane via surface modification technique. Himstedt et al. (Marshall and Wickramasinghe 2011) investigated the production of pH-responsive nanofiltration membranes via the surface modification method. In this study, a commercial flat sheet NF 270 membrane was employed to conduct the surface modification. According to their study, the procured membrane was rinsed with DI water multiple times before use and allowed to dry at 40 °C for overnight. In that experiment, filter paper (0.4 m pore size) was applied to cover the membranes during irradiation with a Hoenle UV irradiation system. At room temperature, benzophenone, a type II photoinitiator, was mixed to saturation in distilled water. The acrylic acid monomer was then mixed, yielding mixture containing 1 or 2 percent acrylic acid by weight. After that, the acrylic acid solution was cleansed for 15 min with nitrogen gas. In a 15 mL Petri dish, the purged benzophenone-saturated monomer solution (5 mL) was applied to membrane discs (45 mm diameter). To drive out air bubbles from the reaction solution, the filter paper was kept on the membrane and the “sandwich” membrane was placed in a UV reactor. Before turning on the UV source, the membranes were placed in the monomer solution to soak for 15 min. Membranes in a 1% acrylic acid solution were agitated for a period of 15 min, while those in a 2% acrylic acid solution were agitated for 15 min. The resulted membrane washed with DI water followed by stirring 30 min in a 100 mL glass

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container comprising 50 mL deionised water. The membrane was flushed more than two times with 10 mL deionised water and allowed to air dry for 15 min at ambient temperature and evaporated at 40 °C for 6 h to achieve the fascinating membrane.

7 Future Outlooks in NF Membrane Technology for Wastewater Treatment The unique capacity of NF membranes to selectively separate the desired separation species has been the key to their success so far. In order to give the best separation, a membrane with appropriate selectivity should be chosen based on the application of interest. Nanofiltration membranes will continue to discover new uses in a variety of fields, including dye removal, organic pollutants, and heavy metals removal from industrial wastewater. In the future, there will undoubtedly be more fascinating uses to investigate. Based on the progress that has been made thus far, the following views are likely to be crucial in terms of NF membrane research and development: • Prognostic modeling of NF membrane techniques: The prolonged Nernst-Planck formula can be employed to simulate the movement of a large number of ions and dissolved substances over the NF membrane. In addition to that, new methodologies must be created to explain the complex correlations and physical occurance in NF systems, like particle-particle-membrane interactions and surface charge of membrane, etc. • Inventive technologies in the fabrication of NF membrane: Nanotechnology advancements have driven the envelope in terms of NF membrane manufacture. Thin-film NF and TFC membranes made by IP will continue to represent the standard enlargement in NF membrane fabrication. In terms of small-scale development in labs, other approaches for instance UV or photo grafting, plasma grafting, electron beam irradiation, and layer-by-layer approaches will find a role. However, when large-scale membrane manufacture is necessary, these processes will have limitations and issues. New nanoparticles and other forms of additives will also be investigated to see how they affect the properties and performance of membranes. Hence, additional research is needed to understand the function of these novel NPs in the solute transport, morphology, and structure of NF membranes. • Another application of NF membrane: NF membranes will continue to be investigated for a variety of other uses due to their wide spectrum of salt selectivity as well as selectivity of organic solute. Nevertheless, new applications in the elimination of developing contaminants such as perfluorinated chemicals, hormones and personal care products (PPCPs) can also be carried out by NF membrane. However, as water resources become scarcer, NF membranes are projected to be employed more for water recycling and reuse. From

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various research, it is evident that recycling of water will be substantially lower expensive than desalination. In such a situation, innovative methods for optimizing the use of NF membranes are needed.

8 Conclusion NF membranes have achieved success in a range of industries as a subset of liquid membrane technology. Modification techniques for NF membranes have also yielded membranes with selectivity, enhanced flow, and hydrophilicity. The principal method for producing nanocomposite or TFC membranes is still based on IP. The fabricated NF Membrane has been utilized in heavy metal, organic pollutants, and dye removal and discussed in text elaborately. Based on the text’s discussion, it is apparent that the NF membrane can be modified by grafting aquaporin Z, which results in a higher degree of water flux. In addition, techniques approached in thin-film NF membrane modification, fabrication procedure, and their uses in several applications have also been comprehensively enlightened in this chapter. Future research should focus on enhancing the capacity to manage, decrease, and alleviate fouling while producing superior membranes and new inventive applications.

References Abdi G, Alizadeh A, Zinadini S, Moradi G (2018) Removal of dye and heavy metal ion using a novel synthetic polyethersulfone nanofiltration membrane modified by magnetic graphene oxide/ metformin hybrid. J Memb Sci 552:326–335. https://doi.org/10.1016/j.memsci.2018.02.018 Abu Seman MN, Khayet M, Bin Ali, Hilal N (2010) Reduction of nanofiltration membrane fouling by UV-initiated graft polymerization technique. J Memb Sci 355:133–141. https://doi.org/10. 1016/j.memsci.2010.03.014 Agboola O, Maree J, Mbaya R (2014) Characterization and performance of nanofiltration membranes. Environ Chem Lett 12:241–255. https://doi.org/10.1007/s10311-014-0457-3 Agta¸s M, Ormancı-Acar T, Keskin B, Türken T, Koyuncu I (2021) Nanofiltration membranes for salt and dye filtration: effect of membrane properties on performances. Water Sci Technol 83:2146–2159. https://doi.org/10.2166/wst.2021.125 Ba C, Ladner DA, Economy J (2010) Using polyelectrolyte coatings to improve fouling resistance of a positively charged nanofiltration membrane. J Memb Sci 347:250–259. https://doi.org/10. 1016/j.memsci.2009.10.031 Bandehali S, Parvizian F, Ruan H, Moghadassi A, Shen J, Figoli A, Adeleye AS, Hilal N, Matsuura T, Drioli E, Hosseini SM (2021) A planned review on designing of high-performance nanocomposite nanofiltration membranes for pollutants removal from water. J Ind Eng Chem 101:78–125. https://doi.org/10.1016/j.jiec.2021.06.022 Barakat MA, Schmidt E (2010) Polymer-enhanced ultrafiltration process for heavy metals removal from industrial wastewater. Desalination 256:90–93. https://doi.org/10.1016/j.desal. 2010.02.008. Belwalkar A, Grasing E, Van Geertruyden W, Huang Z, Misiolek WZ (2008) Effect of processing parameters on pore structure and thickness membramas. J Memb Sci 319:192–198. https://doi. org/10.1016/j.memsci.2008.03.044.Effect

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Technological Advancement in the Synthesis and Application of Nanocatalysts Prangan Duarah, Pranjal P. Das, and Mihir K. Purkait

Abstract Catalysis is an integral part of chemical transformations and is utilized in an extensive range of chemical procedures, from academic research in laboratories to industrial applications. As a revolutionary tool, nanotechnology has been viewed as a possible tool for precision application in a variety of areas. In this context, nanocatalysts are increasingly being used in energy generation, water treatment, drug delivery, and agriculture. This chapter provides a comprehensive introduction to the nanocatalyst. First, the various physical, chemical, and morphological behavior of the nanocatalyst are featured. Various aspects related to the synthesis process of nanocatalysts, as well as the latest technologies used to modify the synthesis process, including green synthesis methods, are explicitly discussed. Further, the applications of nanocatalysts are explored in different fields, including pharmaceuticals, water treatment, biofuel industries, fuel cells, and agriculture. Finally, the chapter discusses numerous difficulties inherent in the synthesis and development of nanocatalysts, with an eye on prospective advances. The chapter will help readers get an in-depth understanding of nanocatalysts and their diverse synthesis techniques, as well as significant contributions for various applications. Keywords Nanocatalysts · Biofuel · Fuel cell · Water-treatment · Agriculture · Drug delivery

P. Duarah · M. K. Purkait (B) Center for the Environment, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India e-mail: [email protected] P. Duarah e-mail: [email protected] P. P. Das · M. K. Purkait Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_10

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1 Introduction It is essential to chemical processes that produce a diverse variety of chemical compounds and synthetic materials to catalyze the reactions. Catalysts are used at many stages of the manufacturing process, as evidenced by the fact that the great majority of synthetic materials contain at least one, if not multiple, catalysts at some point during their manufacture. Consequently, it is reasonable to conclude that the synthesis of countless useful products, ranging from common things to life-saving medications, would have been impossible or impractical in the absence of catalytic activity (Mohan et al. 2020; Chaturvedi et al. 2012). Process development requires a catalyst not only to speed up the chemical reaction but also to improve the overall process by lowering energy consumption, reducing the creation of undesirable compounds, and boosting production (Chaturvedi et al. 2012). Catalyst has gained in popularity over the course of the previous several decades. It is referred to as a homogeneous reaction when the reactants and catalysts are in the same phase, and it is referred to as a heterogeneous reaction when they are in separate phases. Because of the numerous advantages of heterogeneous catalysis, a large number of scholarly publications and patents have been devoted to the development of novel catalytic techniques in recent years. There are, however, some substantial drawbacks to heterogeneous catalysis’s superior performance in comparison to other methods. Because they contain a high number of active centers, porous materials with internal channels and pores, which may be found in a variety of shapes and sizes, are utilized as catalysts. Another limitation associated with the conventional catalyst is that the catalytic reactors are difficult to forecast and set up because of the diffusion phenomena and fluid transport processes that occur as a result of the form of the reactor. A novel technique is required in order to avoid the disadvantages of both kinds of catalysis while still maximizing their remarkable benefits (Liu 2005). Nanoscience is considered to be one of the most significant technical topics in the twenty-first century. The present researchers suggest that nanocatalysts aren’t as cutting-edge as one might expect, given the hype around the technology. The concept of nanotechnology had existed since the 1950s, long before the term “nanotechnology” was developed. While both homogeneous and heterogeneous catalysis has their own set of advantages and limitations, nanocatalysts brings the best of both worlds together in a single device. The production of nanoscale-specifically designed catalysts has the potential to produce large S/V ratios; however, the present definition of nanocatalysts does not allow for this. Beyond the traditional aims of near-100% selectivity, high activity, and high yield in homogeneous and heterogeneous catalysis, the primary goals of nanocatalysis are improved product separation and catalyst recovery, which are all achievable through nanotechnology. Adequate techniques of nanoparticle preparation are required before they may be used in chemical processes. Diverse techniques have been devised to deal with the wide range of shapes and chemical compositions found in these materials (Sontakke and Purkait 2021). Top-down synthesis and bottom-up synthesis are the two primary approaches to synthesis nanocatalysts. A wide range of solid materials may be

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prepared using these cutting-edge nanoparticle production technologies. To prepare nanoparticles in a bottom-up manner, chemical reduction or electrochemical reduction procedures are the most often used methods. However, these methods required either specialized equipment with significant startup costs or pricey, perhaps harmful substances. New nanoparticle manufacturing methods using plant extracts synthesized under various environmental circumstances have arisen in recent years and are referred to as the “green synthesis process of the nanocatalyst.” The use of nanocatalysts in a variety of industries, from agriculture to medicine delivery, is being investigated due to improvements in the production process (Khan and Al-Thabaiti 2018; Mondal et al. 2020; Haldar and Purkait 2020). This chapter presents an in-depth introduction to the nanocatalyst, taking into account these factors. To begin, the chapter will provide a brief introduction to the numerous physical, chemical, and morphological properties. Diverse elements of nanocatalysts synthesis, including green synthesis approaches, are described clearly, along with the latest technology. Nanocatalysts are also being investigated for their potential use in the pharmaceutical, water treatment, biofuel, fuel cell, and agricultural industries. Finally, with an eye toward the future, the chapter concludes with a discussion of the numerous issues connected with the synthesis and development of nanocatalysts. An in-depth look into nanocatalysts and the numerous production methods is provided in this chapter, as well as the major contributions they provide to a wide range of applications.

2 Structural Features of Nanocatalyst Nanoscience’s unique physics and chemical properties make NPs very desirable for an extensive range of applications, including catalysis (Duarah et al. 2020; Singh et al. 2020). When compared to the density and distance of a single atom or a small atomic cluster, the energy level in nanocrystals is unique. As a result, they are often referred to as “quantum points.” The Valance band (VB) of NP contains the highest concentration of atomic interactions. To begin with, the structure of nanoclusters must be established. The structures of NPs cannot be explained by the bulk crystallography of a material in the vast majority of cases. When studying atomic clusters in the nanometer range, they are expected to demonstrate excellent homogeneity and contain atomic shells that match the symmetry of the cluster. As an item grows in size, the surface area of the thing grows smaller in proportion to the volume of the object. Therefore, smaller items have a greater surface area when compared to their volume, and vice versa. This has profound ramifications for the understanding of chemical processes. When it comes to chemical reactions, high surface area-to-volume ratios are advantageous (Ahmed et al. 2016). A system with only a few hundred atoms has high surface energy due to the fact that the surface atoms are coordinately unsaturated. The melting point can be explained by the fact that the fluid surface energy is always lower than solid surface energy. In order to lower the surface area and undesired surface connections, surface

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atoms move in a dynamic fluid state. Solid-state binding geometries with high energy atoms on the edges and corners form sequential surfaces. Melting reduces all surface energy. As the nanocrystal size decreases, so do the surface energy contribution to the system’s total energy. The melting point of nanoparticles is well supported by the correlation between their diameters and melting point. (Kudr et al. 2017). From the literature available, it can be observed that for two reasons, nanomaterials outperform traditional catalysts in terms of effectiveness. In the first place, their incredibly small size (usually 10–80 nm) results in a high surface-area-to-volume ratio, which is particularly useful. Another advantage of nanoscale fabrication is that it allows materials to possess qualities that are not found in their macroscopic equivalents. The adaptability and efficacy of nanocatalysts can be attributed to any of these two factors.

3 Different Types of Nanocatalyst 3.1 Homogeneous Nanocatalyst In the case of NPs, a solution or suspension of NPs in a solvent is often utilized as the catalyst. Nanoparticles are naturally attracted to one another under these conditions and will cluster together to produce bigger particles, which will remove their vast surface area and other advantages if they are not stopped from aggregating. Nanoparticles may be stabilized in solution by attaching long-chain molecules to their surfaces. Using these, it is difficult for the NPs to grow so close together that they form a single particle. However, they have the potential to restrict reacting molecules’ access to the NP surface, reducing the catalyst’s overall activity. Recovery is also a major issue with homogenous nanocatalysts. Removing the nanocatalysts from a solution requires additional processes that might entirely nullify the benefits of utilizing a catalyst. It’s a risk to the environment and the profitability of the process if nanoparticles cannot be retrieved. Nanoparticles can’t be removed by incineration, and the implications of nanoparticle build-up in ecosystems are still entirely unexplained.

3.2 Heterogeneous Nanocatalyst Heterogeneous catalysis is frequently cited as a better alternative in terms of environmental impact. In this case, a catalyst is used that is in a different phase than the reactants. An inert matrix can be used to immobilize the catalyst. As the solid catalyst can usually be filtered away, this avoids the problems of waste and recovery. Various nanoparticle-support systems have been extensively studied for their catalytic potential. Among recent examples are nanoparticles of palladium, iron; gold; nickel; and

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platinum. Silica or aluminum, as well as carbon fibers, are among the most common supports. Nanostructured solids are another area of heterogeneous nanocatalysts that has been studied. The solid material may be grown around a molecular template to produce nanoporous materials. Standard lithography techniques allow for the creation of nanoscale structures on the catalyst surface, which can regulate the flow of reactants and increase the catalyst’s surface area.

3.3 Nanocarbon Catalyst Metal catalysts for the manufacture of diesel by DO have significant drawbacks, including high cost and restricted availability. Carbon-based catalysts for this process were introduced as a result of efforts to find more cost-effective solutions to this challenge. In 1964, Jasinski created Co-phthalocyanines as a new catalyst group for the oxidation of hydrocarbons, which led to a series of experiments experimenting with various unique metal catalysts. To extract green diesel more cheaply, carbon-based catalysts emerged as a less expensive alternative to hydrocarbon DO. Among the various carbon-based nanocatalysts, for years, carbon nanotubes (CNTs) have captivated the scientific community because of their remarkable physical and mechanical qualities. As field emission sources, electric nano-conductors, thermal-conductor, Li-ion secondary batteries, and fuel cells, CNTs have been employed in a variety of applications. Furthermore, CNTs have recently been employed to adsorb hydrogen because of their high porosity, lightweight, stability, and low cost. Their unusual tubular shape makes them particularly well suited for hydrogen absorption (Sontakke and Purkait 2021).

3.4 Bio-derived Nanocatalysts Nanoparticle production methods have evolved over the past several years by using plant extracts in place of the standard chemicals. Many other nanocatalysts, including Ag, Au, Cu, Pd, and Fe3 O4, have been made utilizing plant extracts throughout the years. Bio-derived nanocatalysts have been investigated for an extensive range of applications. A number of reducing agents and proteins that may remove metallic ions from metallic salt solutions have been found in these extracts. Similar to the chemical reduction procedure, capping agents and reducing are introduced at various phases of the NP synthesis. A combination of reduction and capping agents is found in the extract, which can be used instead of chemical molecules in various phases of green synthesis. Green synthesis refers to the use of renewable, biological molecules, which decrease the environmental load on the usage of chemicals. A variety of bacterial, yeast, fungal, and plant extracts are reported in various reviews. Bio-derived nanocatalyst manufacture and use are covered in Sect. 4.2 of the paper.

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4 Progress in Synthesis of Nanocatalysts 4.1 Conventional Approaches for the Synthesis of Nano Catalysts As a catalyst, NPs have been manufactured for several decades. Conventional NP synthesis may be divided into two basic categories: top-down and bottom-up. Nanostructures can be controlled externally through the employment of bigger (macroscopic) structures in the top-down techniques. Thermal breakdown (Pyrolysis), chemical breakdown, and ball milling are examples of typical instances. The ballmilling process has lately gained a lot of attention in chemistry because of its ease of use, speed, cost, and environmental impact. To achieve thermal breakdown of bulk materials, pyrolysis is also a common method of thermal breakdown. Pyrolysis is the process of employing heat to decompose large amounts of material. To begin with, the metallic bulk material is heated to evaporation, and then the nucleation process is carried out in a vacuum chamber. There are also pyrolysis processes that employ different types of energy to heat metals, such as spray flame pyrolysis, laser-induced pyrolysis, and so on. NPs such as metallic and ceramic NPs are typically synthesized this way. Another physical way of creating NPs is vapor deposition, which takes place in a vacuum. There are three stages to this process: To begin, a material or metallic element is heated in an evaporation room and then carried to a deposition chamber where it is solidified. Thin films or nucleated materials are deposited on the surface of the vaporous materials in the deposition chamber. To produce high-purity NPs with diameters ranging from nanometers to micrometers, this is one of the most popular and cleanest processes. For instance, there are several ways to deposit material in the vapor deposition process. These include the use of pulsed lasers and electron beams. Traditional chemical etching uses a strong acid or mordant (liquid with corrosive qualities) to cut through the metal’s exposed surface and create the desired design. Modern nanofabrication relies heavily on chemical etching for complex top-down fabrications of complex device structures. There are several bottom-up methods, including sol–gel, co-precipitation and sonochemical, microemulsions, and electrochemical reduction. Nanostructures can be created by reducing materials components to the atomic level, followed by a selfassembly process in their development. Nanoscale physical forces are employed to assemble basic components into larger, more stable structures during self-assembly. Epitaxial growth and colloidal dispersion of NPs are two instances of quantum dot production. It’s one of the most versatile technologies for making nano-sized materials. This method does not necessitate the use of expensive equipment like chemical vapor deposition. It gives a straightforward way to synthesize nanoscale particles. To achieve catalytic qualities, an active metal must be included in the gel during the gelation step, allowing for direct contact between metal and support (Wu and Chen 2004). In Coprecipitation, a metal–organic precursor undergoes nucleation, which is followed by aggregation or Ostwald ripening to create metal oxides, and then the nanoparticles are formed. Secondary processes, such as Ostwald ripening

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are responsible for determining the size of metallic oxide NPs. NPs of metallic oxide may be quickly synthesized using either microwaves or ultra-sonication. NPs may be synthesized using a variety of ways, including chemical reduction. This approach has been used to synthesize NPs of varying complexity and surface charge utilizing a variety of techniques. There are three steps to the chemical reduction process: reduction of metallic salts, stability of ionic complexes, and capping agent control of size. This approach has been used to create a wide variety of metallic NPs. A reducing agent is mixed with the metallic salt solution before it is heated. These metallic atoms are dissolved in salt solution and precipitated out of solution. The size of NP may be controlled by the stabilizing agent, which is also known as the capping agent. This reaction is carried out in stages, with the reducing agent and capping agent being introduced at distinct times. It is possible for one chemical substance to function as both a capping agent and a reduction agent. Sodium borate, sodium triethyl borohydride, ascorbic acid, or organic molecules like toluene or hydrazine can be used as the reducing agent.

4.2 Green Synthesis Approach for the Synthesis of Nanocatalysts Environmentally friendly design of chemical goods and processes has become more prevalent in recent years. In the chemical industry, the notion of sustainability has a significant influence, with the goal of reducing the use of hazardous compounds and adopting green synthetic processes using renewable, sustainable resources as starting materials. As a result, cellulose has received a lot of interest because of its abundance, biocompatibility, cost-effectiveness, biodegradability, and numerous uses in paper, medicines, textiles, coatings, implants, and tissue engineering. Organic solvents can be avoided using a new top-down strategy called ball milling. Recently, mechanical ball milling (MBM) has been used to produce NPs as a simple and cost-effective alternative to standard techniques of synthesis. It’s also possible to produce vast amounts of NPs at room temperature within a short period of time. As a result, from an economic standpoint, this technology is ideal for large-scale industrial manufacturing. The utilization of plant, microbial, and fungal extracts in the bioreduction process is a novel approach to the production of NPs. Nanocatalysts made from green extracts are shown in Table 1. The production of Ag, Au, Pd, Cu, and CuO, and Fe3 O4 NPs has been described in several scientific studies. For the reduction of Methylene Blue, Vidhu and Philip (2014) described a green approach for the creation of very stable, bio-inspired AgNPs utilizing dried Saraca Indica flower (Vidhu and Philip 2014). Using aqueous Coleus forskohlii root, Naraginti and Sivakumar 2014) made AgNP in a similar fashion. The periodic color shift from brilliant yellow to colorless following the addition of AgNPs showed that they produced AgNPs functioned as an effective green catalyst in reducing anthropogenic pollutant 4-nitrophenol to

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4-aminophenol by sodium borohydride (Naraginti and Sivakumar 2014). Bindhu and Umadevi (2015) have also reported 4-nitrophenol to 4-aminophenol reduction (Bindhu and Umadevi 2015). In a similar vein, the degradation of different dyes from wastewater using nanocatalysts produced from green extract has been reported in the scientific literature (Ahmed et al. 2016; Ajitha et al. 2015; Ghaedi et al. 2016). Table 1 Examples of nanocatalysts prepared via green synthesis route and their applications Nanocatalyst

Raw material

Application

References

Ag

Aqueous Saraca 18–22 nm, indica flowers extract Spherical

Characteristics

Methylene blue reduction

Vidhu and Philip (2014)

Ag

Coleus forskohlii root 35–55 nm and extract 30–40 nm, Triangular and spherical, depends on the amount of extract

4-nitrophenol catalytic reduction

Naraginti and Sivakumar (2014)

Ag

Aqueous beetroot extract

15 nm, Spherical

4-nitrophenol to 4-aminophenol reduction

Bindhu and Umadevi (2015)

Ag

Aqueous Momordica charantia leaves extract

16 nm, Spherical

Methylene blue reduction

Ajitha et al. 2015)

Ag

Aqueous extract of Crotolaria retus leaves

80 nm, Spherical

Cresyl blue reduction

Ahmed et al. (2016)

Ag, Au

Aqueous leaf extract of Mussaenda glabrata

51.32 nm, Ag–spherical 10.59 nm, Au–triangular and spherical

4-nitrophenol, rhodamine B and methyl orange degradation

Topsoe (2021)

Au

Aqueous Gnidia glauca leaves and stem extracts

10–60 nm, Mostly spherical

4-nitrophenol degradation

Ghosh et al. (2016)

Au

Aqueous Sueda fruciotosa extract

2–12 nm, Spherical

Methylene blue degradation

Khan et al. (2017)

Au

Ethanol Artemisia dracunculus extract

Hexagonal, spherical, and triangular shapes

4-nitrophenol reduction

Wacławek et al. (2018)

Pd

Aqueous extract Eucommia ulmoides bark

10–20 nm, Spherical and quasi-spherical

Hydrazine electrocatalytic oxidation and p-aminoazobenzene catalytic degradation

Duan et al. (2015)

(continued)

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Table 1 (continued) Nanocatalyst

Raw material

Characteristics

Application

References

Pd

Aqueous Pimpinella Tirupatiensis leaves extract

12.25 nm, Spherical

Congo red catalytic degradation

Narasaiah et al. (2017)

Fe

Black tea, grape 15–45 nm marc, and vine leaves aqueous extracts

ibuprofen degradation

Machado et al. (2013)

Fe

Hibiscus sabdariffa flower aqueous extract

18–44 nm, Spherical

Rhodamine B degradation

Khan and Al-Thabaiti (2018)

Cu

Aqueous broccoli extract

4.8 nm, Spherical Degradation of methylene blue and methyl red, as well as reduction of 4-nitrophenol

Prasad et al. (2016)

Fe3 O4

Aqueous Ruellia tuberosa leaves extract

20–80 nm, Hexagonal nanorods

Vasantharaj et al. (2019)

Crystal violet degradation

Numerous instances of the use of phytosynthesized gold nanoparticles (AuNP) in catalytic processes can be found in a number of research articles. Degrading 4nitrophenol with the help of phytosynthesized AuNP has been documented by Ghosh et al. (2016) and Wacawek et al. (2018), respectively (Ghosh et al. 2016; Wacławek et al. 2018). For the breakdown of hazardous dyes like methylene blue, few research have described the production of Au nanocatalyst from plant extract (Khan et al. 2017). Phytosynthesis of PdNP from an aqueous extract of Eucommia ulmoides bark yielded spherical and quasi-spherical NPs with an average diameter of 12.2 nm was performed by Duan et al. (2015). Exceptional catalytic activity for the electrocatalytic oxidation of hydrazine and the reduction of p-aminoazobenzene were demonstrated by the produced NPs, which also exhibited high stability in water (Duan et al. 2015). Other groups have created Pd NPs for a variety of purposes, including dye degradation and the removal of hazardous pollutants (Narasaiah et al. 2017). Machado et al. (2013) synthesized FeNP from aqueous extracts of vine leaves, black tea, and grape marc, which they utilized to degrade ibuprofen in both sandy soils and aqueous solutions, achieving degradation efficiencies of up to 66% in aqueous solutions (pH-dependent) and over 95% in soils (Machado et al. 2013). The use of Fe NPs generated by the green approach for dye degradation is also being investigated (Khan and Al-Thabaiti 2018). CuNP with spherical morphologies and an average diameter of 4.8 nm were produced by Prasad et al. (2016) from broccoli extract. Four-nitrophenol reduction with NaBH4 and degradation of methylene blue and methyl red were accomplished using the CuNPs, which were able to complete the reactions within a few minutes with high values of reaction rate constants (32% degradation after 28 h). Even after a fifth cycle of re-use, the authors found that the conversion rates haven’t changed significantly, but the response time required to complete it increased (Prasad et al.

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2016). It has been suggested that Ruellia tuberosa leaves extract can be used to synthesize hexagonal nanorods Fe3 O4 NP by phytosynthesis. Crystal violet dye was degraded by NPs under sun irradiation, with an 80% degradation after 150 min (Vasantharaj et al. 2019). Other applications for nanocatalysts have been developed during the last year, which will be covered in the next section.

5 Emerging Applications of Nanocatalysts 5.1 Application of Nanocatalysts in Biofuel Production Both in the presence and absence of a catalyst, biomass has been used to make biofuels. High-alcohol and FAME-rich compounds such as hydrocarbons (H2 O) have exhibited the best results in addition to the excellent selectivity in the presence of a catalyst. Reduced catalyst performance in fuel generation has been achieved by shrinking the active metals in the catalyst to nanoscale dimensions. The concept of using nanocatalysts prompted researchers to carry out the operations. Nanocatalysts have been used to create a variety of biofuels, including biodiesel, bioethanol, and biogas. Metal oxide NPs, Carbon nanotubes, magnetic nanoparticles (MNPs), and acid-functionalized NPs are the most often employed nanocatalysts in the biofuel production industry. MNPs have become one of the most popular nanocatalysts because of their ease of separation from the reaction mixture. MNPs can be classified into four types, namely, metals-based NPs (Fe, Co, Ni), alloy-based NPs (FePt, FePd), metal oxide-based NPs (FeO, Fe2 O3 , Fe3 O4 ), and iron-based NPs (CoFe2 O4 , CuFe2 O4 ,) (Velusamy et al. 2021). For the transesterification of soybean oil, Alves et al. (2014) employed a co-precipitation approach to combine magnetic iron/cadmium and iron/tin oxide NPs, which exhibited high efficiency for transesterification, hydrolysis, and esterification. It was also discovered that iron/tin oxide NPs had the best efficiency, yielding 84% biodiesel (Alves et al. 2014). To produce biodiesel from waste cooking oil, Wang et al. (2015a) produced acid-functionalized MNP and employed them as heterogeneous nanocatalysts, as demonstrated in Fig. 1. Specifically, crystalline Fe/Fe3 O4 core/shell MNPs with acid-functionalized silica coatings, i.e., sulfamic and sulfonic silica coatings, were produced, and their catalytic performance for transesterification of glyceryl trioleate was proven. The acquired results demonstrated that both acid-functionalized nanocatalysts exhibited remarkable catalytic activity in the laboratory. Sulfonic acidfunctionalized nanocatalysts, on the other hand, demonstrated much greater activity than sulfamic acid-functionalized nanocatalysts in the same experiments (Wang et al. 2015a). For transesterification of recycled cooking oil to make biodiesel, calcium oxide (CaO) NPs and magnesium oxide (MgO) NPs were produced using sol–gel and self-combustion methods, respectively. CaO NPs produced more biodiesel than MgO NPs, according to researchers (Tahvildari et al. 2015). Another group used sol–gel and incipient wetness impregnation techniques to make magnetic Ca/Fe3 O4 @SiO2

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Fig. 1 Methods for the preparation of MNPs with sulfonic acid functionalization and MNPs with sulfamic acid functionalization [Adapted with permission from Wang et al. (2015a). Copyright (2015) American Chemical Society Wang et al. (2015a)]

nanocatalysts for biodiesel production, achieving a 97% yield (Feyzi and Norouzi 2016). An impregnation approach for making transition metal oxides (TMOs) on zeolites Y (Ni, Cu, Co, Zn, and Mn Y) has been used effectively to produce a series of TMOs that may be used to make diesel from triolein. Deoxygenation improved the selectivity towards hydrocarbons in the zeolite Y deoxygenated product, which included hydrocarbons (54.56%), alcohols (10.49%), as well as fatty acids (34.95%).

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A gasoline range (C8–C12), a diesel range (C13–C18), and a heavy hydrocarbons range (C19). The Ni–Y catalyst has the best selectivity (around 92.61%) for diesel because of a synergy effect between the low ratio of Brnsted to Lewis acidities (0.19) and the strong hydrogenolysis potential of Ni, which facilitates decarboxylation, prevents cracking, and reduces coking (Choo et al. 2020). Innumerable uses exist for a variety of metal and metal-oxide NPs (either bare or post-functionalized). The primary stage in the production of bioethanol is the enzymatic breakdown of cellulose and hemicellulose into simpler sugars by hemicelluloses, celluloses, and lipases. The enzyme hydrolysis step’s cost is a major determinant of the process’ economic viability. A decrease in enzyme costs and an increase in stability are both made possible by NPs’ increased surface-to-volume ratios (Sharma et al. 2020). This stable system with high pore diameters (20–40 nm) was used to immobilize cellulose on mesoporous SiO2 NPs via covalent bonding and convert cellulose to glucose by Chang et al. (2011), whereas, A study by Zhang et al. (2015) described the immobilization of cellulose onto functionalized Fe3 O4 magnetic nanospheres, which not only boosted the stability of the enzyme but also preserved its 87% activity (Zhang et al. 2015). Urea was used as a source of urea in the combustion of glycerol and nitrate to produce titanium-doped zinc oxide. Transesterification of palm oil was utilized to make biodiesel using the synthesized TiO2 –ZnO. According to Madhuvilakku et al., the nanocatalyst (TiO2 –ZnO) loading of 200 mg, the reaction duration of 5 h, the temperature of 60 °C, and a methanol/oil ratio of 6:1 were used to optimize the operational conditions for the biodiesel synthesis (Madhuvilakku and Piraman 2013). Reporting in 2015 by Thangaraj et al., by using the co-precipitation and calcination process, a zinc oxide nanocatalyst ranging in size from 5 to 29 nm was produced. ZnO coated with hetero-polyacids was employed as a nanocatalyst for achieving a 95% biodiesel conversion from methanol and madhuca oil at the ideal conditions of 55 °C and 5 h of reaction time (Thangaraj and Piraman 2016). One of the greatest levels of catalytic activity, 98.71%, was reported by Tang et al., who investigated the impact of a nonmagnetic calcium compound made chemically by treating calcium aluminate with Fe3+ oxide in the ratio of 5:1 (Ca: Fe) and then calcining it at 600 °C for six hours (Tang et al. 2012). For the purpose of determining the most efficient nanocatalyst for transesterification of waste cooking oil, Rafati et al. (2019) used seven different types of nanocatalyst, such as MgO–NaOH, MgO–KOH, and CaO–KOH, as well as combinations of all seven. We found that when we upped the MgO–NaOH catalyst concentration from 3 to 5%, the biodiesel output increased by 94–98%. THF as cosolvent was used at 10% w/v in an electrolytic procedure employing graphite as the electrode at 50 V for six hours at ambient temperature with a rotating speed of 500 RPM for the electrolytic reaction (Rafati et al. 2019). Biogas generation relies heavily on nanocatalyst, much as biodiesel does. Prior to anaerobic digestion, the primary method for producing biogas, different organic materials are converted into biogas and its elements (alcohols and VFAs). Hydrolysis, acetogenesis, acidogenesis, and methanogenesis are all critical components of the process. Anaerobic processes have shown encouraging results in the supplementing of nanoparticles, notably in regard to electron donors/acceptors and cofactors of important enzymes like [Fe]- and [Ni–Fe] hydrogenase. The hydrolysis of organic

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materials is increased by the use of NPs. As a result of the huge surface-area-tovolume ratio of NPs, microbes are able to attach to active regions of molecules, which in turn activates their metabolic activities (Sekoai et al. 2019). Sulfate removal from mixed anaerobic digestion sludge is facilitated by ZVI nanoparticles as an electron donor, according to a study published in 2005 by Karri et al. While sulfate production declined significantly, methane production soared. While using ZVI nanoparticles with the smallest particle size feasible (0.01 mm), this resulted in the highest rate of methane synthesis (0.310 mmol CH4 created per mol Fe0.d) and the highest rate of sulfate reduction (0.804 mmol SO4 2− reduced per mol Fe0-d) (Karri et al. 2005). Figure 2 shows the usual core–shell structure of ZVI NPs, where the core consists of ZVI or metallic iron NPs, and the oxide shell consists of iron oxides and hydroxides (FeOOH). Chemical reactions (chemisorption) and electrostatic interactions need active sites in both the core and the shell; the core functions as an electron donor and the shell acts as a site for electrostatic interaction (Yan et al. 2010). NPs’ impact on anaerobic digesting microbial populations has also been the subject of several research. Biogas generation from waste-activated sludge was studied by Wang et al. (2016) utilizing four NPs representatives (Ag, ZVI, Fe2 O3 , and MgO). There was a 120% and a 117% increase in biogas production relative to the control when ZVI nanoparticles (10 mg/g TSS) were used, respectively. According to these findings, it has been shown that methanogenic archaea are more active at low concentrations of ZVI and Fe2 O3 NPs (Wang et al. 2016).

Fig. 2 The nZVI core–shell model includes graphic representations of the chemical processes for Hg2+ , Ni2+ , Zn2+ , and H2 S elimination [Reproduced with permission from Yan et al. (2010)]

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Using photocatalysis, nanocatalysts have a considerable impact on hydrogen generation. Water molecules are divided into H2 and O2 in the presence of an illuminating source in photocatalytic hydrogen generation. Titanium dioxide (TiO2 ) is the most widely researched photocatalyst because of its non-toxic characteristics, low cost, chemical stability, and great photocatalytic efficacy (Arzate Salgado et al. 2016).

5.2 Application of Nanocatalysts in Water Treatment As a rapidly developing field of study, nanotechnology and nanoscience provide several promising solutions for water and wastewater management. Nanostructured materials have become increasingly important in the degradation and remediation of toxic organic and inorganic pollutants due to their unique physicochemical properties, which include excellent catalytic activity, high chemical, physical, and thermal stability, vast specific area, significant chemical reactivity, and strong electron transfer (Samanta et al. 2021; Ardekani et al. 2017). Research on the potential use of noble metal NPs for the cleanup and detection of pesticides at ultra-low concentrations in drinking water has been ongoing for years. For example, transition metal NPs comprise not only Fe, Au, Cu, Ag, and Co; but also Fe/Ni and Fe/ Cu transition metal NPs. Synergistic effects of transition metals can lead to better removal efficiency in bimetallic NPs than monometallic NPs for catalytic degradation (Lu and Astruc 2020). For water cleanup, zero-valent iron NPs, one of the cheapest transition metals, have been widely studied and utilized. It is important to note that the stabilizing technique and age of Fe(0)NPs are extremely reliant on their usage and efficiency because of the strong reactivity of these NPs, which may be attributed to the ease with which they are oxidized (Liu et al. 2005; Zhan et al. 2011). Other zero-valent metal NPs, such as CuNPs, AgNPs, and AuNPs, among others, have been examined for the remediation of contaminants from water, in addition to earth-abundant zero-valent iron NPs. Catalytic reduction of organic pollutants by zero-valent metal NPs was studied by Ali et al. (2018). Zero-valent metal NPs (Cu0 , Ag0 , Co0 , and Ni0 ) were loaded onto chitosan-titanium oxide nanocomposite fibers using NaBH4 to reduce CuSO4 , Co(NO3 )2 , AgNO3 , and NiSO4 . To reduce organic dyes including methyl orange, methylene blue, congo red, and acridine orange, Cu NPs templated on chitosan-TiO2 -15 fibers showed substantial catalytic efficiency, as did nitrophenols, among the zero-valent metal NPs generated (Ali et al. 2018). In the presence of NaBH4 , a bimetallic Cu/CuO-Ag nanocomposite with AgNPs and CuO NPs on the surface of Cu showed better catalytic activity for the reduction of 4-nitrophenol (Liang et al. 2017). In comparison to monometallic NPs, research into bimetallic NPs or multi-metallic NPs for water treatment is restricted. As a result, the precise repair procedure has yet to be determined. Or, to put it another way, the critical component metal NPs will decide the ability to remediate. The capacity of various bimetallic NPs to adsorb and decompose organic pollutants has been explored. It has been thoroughly researched how linking earth abundant metal FeNPs with second

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metals (such as Ni, Cu, Pd, and Au) might overcome the limitations of solo Fe NPs and increase the effectiveness of pollution remediation (Bokare et al. 2008; Nascimento et al. 2016). According to Zhao et al. (2015), a bimetallic heterogeneous Fenton catalyst Cu/Fe NPs may be used to degrade bisphenol A to CO2 and H2 O in the presence of hydrogen peroxide. This approach relied heavily on the use of free radio OH as a catalyst for oxidative degradation. The catalytic reductive hydrochlorination of chlorinated organic compounds (COCs) to degradable non-chlorine products using bimetallic NPs such as Pd/Al, Fe/Pd, and Ni/Fe has also been studied (Wang et al. 2015b). Non-iron zero-valent transition metals for remediation of organic contaminants have been studied and applied very little despite the fact that there are many transition metals on the planet. More advanced catalysts for the treatment of organic contaminants have been developed using a few transition metal NPs and supported transition metal NPs, in addition to the more common and plentiful abundant transition metals (for example, Fe and Cu). An organic dye catalytic reductive ability was demonstrated for porous carbon materials (CPMs) coated with Ni NPs, for example (Veerakumar et al. 2015).

5.3 Application of Nanocatalysts in Agriculture The rising use of agrochemicals in agricultural intensification has resulted in a number of detrimental environmental impacts. Precision agrochemical application is currently advised for increasing agricultural yields and protecting the environment. In order to achieve agricultural sustainability, many precision agriculture methods are being encouraged. Using nanotechnology, agrochemicals can be applied precisely, and agricultural plants can get the most benefit from their effective usage in agroecosystems. These wasted catalysts are now being used extensively in agricultural systems in order to better control these used catalysts. The germination and growth patterns of plants have been demonstrated to be significantly affected by wasted nanocatalysts in several research investigations. It is impossible to cultivate plants without the use of fertilizers. Many agrochemicals are lost to the environment owing to processes such as volatilization, percolation, surface runoff, degradation via hydrolysis, and decomposition; thus crops cannot benefit from them. The slower breakdown rate of chemical fertilizers like herbicides, pesticides, and insecticides results in a longer residence time. There might be serious environmental difficulties globally as a result of the overuse of traditional fertilizers in agricultural fields. A significant man-made element contributing to the global enrichment of freshwater and marine habitats with nutrients is the intensive use of N- and P-based agrochemicals. Due to the need to increase crop yields and productivity while minimizing nutrient loss in agriculture fertilization and reducing environmental concerns, it is vital that systems for developing these goals be developed. Seed dormancy is a crucial issue that reduces agricultural productivity. Multiwalled carbon nanotubes, which generate pores in resistant seed coats, can be used

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to alleviate this issue. This causes the seed coat to soak in water. The chlorophyll index of crops treated with micro crystals is increased (Liu et al. 2008). Shinde et al. (2020) developed green synthesized magnesium hydroxide NPs [Mg(OH)2 NPs] and discovered that they have 100% seed germination efficiency and Zea mays growth in vitro and in vivo (Shinde et al. 2020). Seed germination, nanopore production, ROS/antioxidant system reboot, cell wall loosening by hydroxyl radicals, and starch hydrolysis of seed by nanocatalysts were all induced by AgNPs nanopriming, according to Mahakham et al. (2017). The soil fertility is largely determined by its soil texture for soils with a low density. The use of nanomaterials in soil enhancement provides a clever, unique, environmentally beneficial, and sustainable solution—improvement of the soils. Hydraulic conductivity was increased and soil fractures were minimized by using multiwall carbon nanotube (MWCNT) and carbon nanofiber (CNF) in soil samples from the UKM soil, according to Alsharef et al. (2016). Carbon nanotubes, nano bentonite, colloidal silica, and laponite were also studied by Huang et al. for their potential applications in soil reinforcement, drilling fluid addition, and soil mechanic characteristics (2016) (Huang and Wang 2016). Agricultural ecosystems are concerned with the environmental fate and movement of nanocatalysts, as well as their behavior in diverse abiotic and biotic components such as air and water as well as soil, plants, and animals. There are both positive and negative effects of nanocatalyst translocation in agroecosystems, such as better seed germination, increased plant growth and development, and nano fertilizers, among others. The destiny, mobility, and toxicity evaluation of manufactured nanoparticles in natural ecosystems have been studied in a variety of ways. As a result, NPs have a significant impact on the environment as well as human health. When using nanomaterials, the release of NPs into soil and water, which increases their prevalence in numerous environmental matrices, is becoming an increasing problem. Because of their increased surface area, nanoparticles are capable of adsorbing potentially hazardous compounds (e.g., lipophilic contaminants and heavy metals). Plants can be penetrated by certain nanoparticles through root cell walls with 5–20 nm-sized pores, which allow smaller particles to be mobilized. Since NPs smaller than the holes are able to enter into the plasmalemma, it is possible for them to do so. Studies have shown that NPs may enter cells via ion channels and may be intercalated with various proteins important for mobilization, resulting in significant interference in normal metabolic processes, presumably via the formation of reactive oxygen species (Bhadouria et al. 2020).

5.4 Application of Nanocatalysts in Fuel Cell There has been an increase in research into electrocatalytic energy conversion systems as a result of declining energy supplies and worries about long-term technical breakthroughs like fuel cells. However, the commercialization of fuel cells has been hindered by problems such as high costs, short life expectancies, and low power

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density. Fuel cells rely heavily on heterogeneous electrocatalysts, which improve the pace, efficiency, and selectivity of chemical reactions. Reactive species and active sites on the catalyst surface have a significant impact on the electrocatalytic activity for practically all nanocatalysts (Seh et al. 2017; Duarah et al. 2021). It is therefore important to manage the structure–function relationship of heterogeneous electrocatalysts. Platinum is the most effective electrocatalyst of the single metals used in fuel cell systems, but its high cost and sensitivity to CO poisoning limit its practical usage. As a current technique, adding additional metals to the surface electronic effects and spin density distribution of Pt atoms, boosting CO tolerance and strengthening electrocatalytic performance is successful (Wang et al. 2018). Intermetallic compounds have unique properties such as well-defined atomic ratios and long-range ordered atomic arrangement of the whole NP, with the key to controlling ordered structures often being appropriate high-temperature treatment. Intermetallic complexes based on Pt and Pd exhibit discrete crystalline phases, which may be visually validated by powder X-ray diffraction and transmission electron microscopy (Zhang et al. 2020). For electrocatalytic processes to be effective, they must have a specific surface structure, and this may be directly regulated by metal nanoparticles of varied sizes or shapes, as well as compositions. To maximize surface-to-volume ratio, the particle size of catalysts should be reduced. This will increase the number of reactive sites on a given alloy. Scanning tunneling microscopy and electrochemical experiments were used by Meier et al. (2004) to investigate the connection between particle size and electrochemical proton reduction performance. From 200 to 6 nm in particle size, the catalytic activity of Pd nanoparticles increases by more than two orders of magnitude (Meier et al. 2004). Energy conversion devices such as polymer electrolyte membrane fuel cells are promising since they are capable of directly converting chemical fuels to electricity with high efficiency while still being environmentally friendly. Researchers are working on developing a variety of different types of nanocatalysts in order to maximize the efficiency of the process. Figure 3 depicts the electronic structure of Pt, which is appropriate for the binding energies of oxygen and OH. It is observed that Pt exhibits better ORR activity than other single-element catalysts such as Ir, Pd, Co, Ag, Ni, Au, Ru, and Cu, indicating that Pt has a better electronic structure for the binding energies of oxygen and OH (Nørskov et al. 2004).

5.5 Application of Nanocatalysts in Drug Delivery NPs have found a wide variety of applications in the pharmaceutical and biotechnology industries during the last several decades. This emerging catalytic therapeutic modality has significantly aided advancements in a variety of nanomedical fields, providing effective treatment strategies for a variety of pathological abnormalities, including cancer, bacterial infection, inflammation, and brain injury, among others. On the basis of this therapy approach, a variety of catalytic nanomaterials, including nanozymes, photocatalysts, and even electrocatalysts, have been designed and deployed in diseased areas to initiate/guide catalytic chemical processes against

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Fig. 3 Plots illustrating the oxygen reduction activity as a function of the O and OH binding energies [Adapted with permission from Nørskov et al. (2004)]. Copyright (2015) American Chemical Society Nørskov et al. (2004)]

illness. These nanocatalysts with great activity, selectivity, and stability are capable of transforming intrinsic/delivered chemicals into therapeutic ones, allowing for the controlled regulation of the chemical properties of three-dimensional biological systems. Additionally, due to the rapid advancement of nanodiagnostics, some nanocatalysts have been endowed with diagnostic properties enabling ultrasensitive catalytic imaging of lesion regions. Due to the rapid rise of research into theranostic uses of nanocatalysts, we offer the term “nano catalytic medicine,” which is described herein as “catalytic reaction-based disease detection and therapy utilizing biocompatible nanomaterials,” to describe this growing domain of nanomedicine (Yang et al. 2019). Despite the collaborative efforts of scientists and physicians, cancer remains one of the world’s worst diseases. Conventional cancer chemotherapy has low therapeutic efficacy and a high rate of adverse events, which precludes its continued use as a first-line cancer treatment option. To circumvent this constraint, nano catalytic therapeutic techniques are being brought into cancer treatment to enable the synthesis of harmful chemicals specifically within tumors while leaving normal tissues unharmed (Curigliano et al. 2016). Additionally, nanocatalysts have been investigated for use in a variety of different therapeutic applications, including immunotherapy, sonodynamic therapy, photodynamic therapy, tumor-starving therapy, and controlled drug release (Yang et al. 2019).

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6 Commercial Aspects of Nanocatalysts After hearing about the latest breakthroughs in nanocatalysis research, the issue remains as to how much interest there is from industrial businesses in nanocatalysts. In the next section, we want to throw some light on recent advancements in the sector by an in-depth examination of more than 1,500 patents relating to nanocatalysis technology. Following a search of the United States Patent and Trademark Office Patent Database, these were discovered. Global catalyst market size was USD 12.8 billion in 2009, according to The Freedonia Group, and it is expected to expand at a compound annual rate of 6 percent to USD 18.2 billion by 2015, according to the same source. The three primary categories are chemical processes of various kinds, oil refining, and environmental applications, respectively. It is possible to see the same hopeful trend when narrowing the focus from the catalyst market in general to the market for nanocatalysts (Olveira et al. 2014). Headwaters, Inc., for example, provides the HCAT nanocatalysis technology for heavy oil upgrading, which is available from the company. The extensively scattered catalyst facilitates a more efficient conversion of heavy asphaltene molecules into lighter hydrocarbons in the presence of residue (Headwaters 2021; Shah 2020). Another major competitor in the market, the German company BASF, has a number of nanocatalysts included in its product line as well. Zeolitic nanocatalysts such as the HDXtra and Endurance are employed in the field of fluid catalytic cracking. The former maximizes the generation of light cycle oil from heavy feedstock, whereas the latter increases the selectivity of coke and gas, resulting in better liquid yields from the heavy feedstock. The business Haldor Topsoe has successfully marketed a nanocatalyst for the synthesis of ammonia and hydrogen. The BRIM technology, which makes use of a nickel molybdenum nanocatalyst, is supplied by the same business for the purpose of producing diesel that is almost sulfur-free (Topsoe 2021). ExxonMobil, the second biggest business in the world according to the Standard and Poor’s 500 indexes, has produced a variety of refining catalysts, such as the EBMax technology, which is used in the production of gasoline. It has been demonstrated that this zeolitic nanocatalyst may be utilized to produce ethylbenzene from benzene and ethylene with high selectivity (Shah 2021; Hu et al. 2011; Francis et al. 2017). Additional to these, there are a few other examples of nanocatalysts that are commercially available, including Turbobeads LIC, QIS-Nano copper, and nGimat.

7 Challenges and Future Perspectives The sintering of NPs is the core problem with nanocatalysis, and it must be addressed immediately. Metal atoms are displaced during high-temperature reactions, causing structural changes in the form and size of metal nanoparticles. This leads to undesirable results such as decreased activity and selectivity, inhomogeneity, and catalytic stoppage. As a result, nanocatalysts could not be used in a variety of temperature

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ranges or for an extended period of time due to sintering. Using carbon, silica, polymers, and zeolites as anti-nanoparticle sintering materials has been demonstrated to be successful. Toxicity testing of nanocatalysts, particularly in agriculture, is another challenge. Nanopesticides, nanoherbicides, nanosensors, and nanocarriers, all of which have appeared in the last decade, offer great promise for improving nutrient delivery, protecting crops from pests and weeds, and providing accurate sensing systems for agricultural plants. However, due to the unknown dangers of nanotechnology, we must exercise caution while using it. Metal nanoparticles have the potential to penetrate deep into the cells and tissues of plants, where they can trigger a cascade of physiological events such as senescence, stunt growth, and diminish crop production and yield.

8 Conclusions In this chapter, we have provided a thorough introduction to nanocatalyst technology. First, the numerous physical, chemical, and morphological properties of the nanocatalyst are discussed in further detail. There is an in-depth discussion of several elements of the synthesis process of nanocatalysts, as well as recent technologies that have been developed to change the synthesis process, including green synthesis approaches. Nanocatalysts are also being investigated for use in a variety of disciplines, including medicines, water treatment, biofuel industries, fuel cells, and agriculture, as well as in other fields. The remaining issues, such as sintering of NPs, toxicity, and market compatible price, were identified through the literature review. Because nanocatalysis is a compelling example of a business-to-business market for nanotechnology, recent market figures were provided to highlight the existing position of the market, as well as growth predictions to demonstrate the market’s future potential. Our findings indicate that nanocatalysis continues to provide a varied variety of options for researchers in both academia and industry to increase catalyst performance while also generating innovative and environmentally friendly chemical processes.

References Ahmed S, Manzoor K, Ikram S (2016) Synthesis of silver nanoparticles using leaf extract of Crotolaria retusa as antimicrobial green catalyst. J Bionanosci 10(4):282–287 Ajitha B, Reddy YAK, Reddy PS (2015) Biosynthesis of silver nanoparticles using Momordica charantia leaf broth: Evaluation of their innate antimicrobial and catalytic activities. J Photochem Photobiol, B 146:1–9 Ali F, Khan SB, Kamal T, Alamry KA, Asiri AM (2018) Chitosan-titanium oxide fibers supported zero-valent nanoparticles: highly efficient and easily retrievable catalyst for the removal of organic pollutants. Sci Rep 8(1):6260

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Metallic Nanoparticles and Bioremediation for Wastewater Treatment Elham M. Ali

and Ahlam S. El-Shehawy

Abstract Water critically influences the standard of society living and affects the availability of equal development opportunities. It is hence important to secure safe and clean water supplies for all societies and this requires planned sustainable management of water and wastewater. Bioremediation approaches have recently emerged as one effective low-cost alternative compared to other conventional remediation technologies. Nanotechnology is a potentially good approach for developing the next generation of this field. Nano-bioremediation is the new concept that integrates the use of nanoparticles for sustainable remediation of environmental pollutants. Metallic nanoparticles have almost specific characteristics such as their very small size and large surface-to-volume ratio. Metal nanoparticles possess large surface energy and so have the ability to adsorb small molecules. Iron oxide nanoparticles have extensive applications throughout contemporary science and technological innovation. Ag-nanoparticles have successfully been applied in water and wastewater disinfection. Bimetallic nanoparticles which have core–shell morphology provide some more enhanced properties if compared with their monometallic. There is a new approach is suggested to benefit from the bimetallic nanoparticles, as nanoadsorbents. It is developed by the generation of granular particles with mastered dimensions by the encapsulation of nano-adsorbents in sodium alginate (SA) beads. Keywords Bioremediation · Metallic nanoparticles · Non-metallic nanoparticles · Iron NPs · Ag NPs · Bimetallic NPs · Algae · Water treatment

E. M. Ali (B) The National Authority for Remote Sensing and Space Sciences, Cairo, Egypt e-mail: [email protected] Department of Aquatic Environmental Sciences, Faculty of Fish Resources, Suez University, Assalam City, Egypt A. S. El-Shehawy Mansoura Joint Laboratory, Central Department of Laboratories, Ministry of Health, Cairo, Egypt Department of Botany, Mansoura University, Mansoura, Egypt © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_11

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Preface With no doubts, water is the necessary element for all creatures’ life. Water resources comprise more than 70% of the earth’s surface, of which freshwater constitutes only 0.5%. Egypt is determined among the top vulnerable countries to water scarcity at the global level, and particularly in the northern belt of Africa (Sebri 2017), a problem that might be worse if the proposed worming occurred. In the meantime, the rapid growth of population and the accelerated development and industrialization greatly enhance the national demand for freshwater (Ramakrishniah et al. 2009). This would create a pronounced gap in water availability with a potential water deficit ratio, mainly in Africa with about 28–47% by 2030 (Sebri 2017). The scarcity of clean water influenced society’s living standard and affect the availability of equal development opportunities (Qadir et al. 2007). Water-related problems are becoming a persistent global issue and securing the required quantities of clean freshwater and overcoming the lack of water is becoming the challenge of the twenty-first century worldwide (Saxena and Bharagava 2019). The scarcity of clean water has become a major global risk over the past 5 years based on the UN World Water Development Report (WWAP 2017). The capacity of water treatment processes is sometimes not sufficiently covering the populations’ needs; for example, water consumption in some areas (e.g., China, Australia, Western South America, India, Central, and WN America) is nearly double the available resources of treated water (Mekonnen and Hoekstra 2016). There is hence a critical need for new approaches and advanced techniques to maximize the capacity, quality, and quantity of water treatment.

1 Issues of Water Resources Pollution, Water Treatment, and Management The problem of water pollution is increasing and its impact is expanding day by day affecting all life, for example, >80% of diseases affecting human beings are waterborne (Vigneswaran et al. 2009). Water pollution is mainly caused by solutes of either organic or inorganic nature, by heavy metals (e.g., Hg, Cu, As, Cr, Zn, Pb, Cd, etc.) or from human activities, industrial processes, and hence, it becomes a today’s big global issue. Water parameters and characterization attributes are changed consequently, depending on the original sources and the type of pollutants. A sufficient treatment technique is crucially needed before supplying to the community. This increases the demand for immediate better development and advanced technologies for sustainable use and management of water resources. Nanoscience and the derived Nanotechnologies offer many advantages to improve environmentally friendly technologies for water pollution control (Lande et al. 2020).

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2 Sources and Impacts of Water Pollutants Water pollutants could be received from two main sources; point (the directly identifiable sources) and non-point sources (arrive from different origins) (Singh and Gupta 2017) and enter into either surface or groundwater water arriving at the surrounding environments and impacting all living creatures. Wastewater, residential and/or nonresidential is a common source for pollution of water worldwide but with more focus on developing countries (Bora and Dutta 2014) in addition, waterborne wasters are the biggest pollutant that is discharged untreated into freshwater bodies negatively affecting the floral and faunal communities with increasing their death rates by suffocation (Tudge 1991). Water pollution mainly emerged from sewage and wastewater disposal, industrial by-products, fertilizers leaked from agriculture, pesticides and herbicides, radioactive waste, and urban development with excessive combustion and extraction of fossil fuels, etc. (Krantzberg et al. 2010). Urbanization-related activities such as agriculture (Singh and Gupta 2017), excessive use of fertilizers (Secretariat 2016) and detergent (Owa 2014), as well as industry (Goutam et al. 2018) are other major factors contributing vigorously to eutrophication levels along rivers and lead to serious danger to all life forms. In addition to the previously mentioned sources of water pollution, hot water discharge, from industries is another harmful source that creates a level of thermal pollution, oxygen reduction disturbing the reproductive cycles, respiration, and digestion rates of most living organisms (Owa 2014). Human being is also impacted by water pollution, since around 14,000 cases of deaths/day were estimated by Owa (2014) due to water-related reasons, e.g., drinking contaminant water of untreated sewage. In developing countries (see Fig. 1), around 90% of detected diseases are mainly raised from using contaminated water for drinking purposes (UNICEF, Organization et al. 2012), since it contains types of dangerous chemicals; such as heavy metals; in higher concentration, (Friberg et al. 1974; Singh and Gupta 2017). These metals and contaminants can also reach the human body through eating fish from contaminated water bodies. For example, about 2000 capita were poisoned of which hundreds have died (Mishima 1992) infected by the “Minamata disease” which causes serious chromosomal aberrations and neurological damage to humans. Children are obviously more vulnerable to such impacts; a number of about 1.1 million children are dying every year due to diarrhoeal diseases (Steiner et al. 2006) that are mainly received through groundwater contamination with more than 14,000 daily death cases Larry (2006). Some microscopic organisms (e.g., Salmonella sp., Escherichia coli Vibrio cholera, and Shigella sp.,) also alter water quality (Adetunde and Glover 2010), causing several waterborne diseases such as typhoid fever, diarrhea, dysentery, gastroenteritis, and cholera through the existence of feces in water supplies they use. Therefore, the presence of fecal coliforms (e.g., E. coli) is used as an indicative sign for the presence of such pathogens (Adetunde and Glover 2010). Several nutrients including nitrogen, phosphorus that are used to support the growth of aquatic plants could be a reason for the existence of those unwanted microorganisms (i.e.,

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Fig. 1 Examples of water-related problems/facts in developing countries (Kanchi 2014)

algal gloom and weeds), causing an unpleasant odor, taste, and color to the water (Owa 2014).

3 Current Methods and Techniques for Water Pollution Management To secure clean and safe supplies of water for living creatures, a well-planned and sustainable procedure should be adopted for treating water and wastewater. The misor poor management of wastewater, as well as the lack of public policies, amplifies the problem (Corcoran et al. 2010). Several water treatment methods were established early in the twentieth century and are still used today. These include mechanical separation, chemical purification, coagulation, biological treatments, disinfection, aeration, and boiling (Hazen 1914). In addition to physical, chemical, and biological methods are used to remove insoluble particles and soluble contaminants from effluents (Crini and Lichtfouse 2019). The major disadvantages of those methods are mainly attributed to their high cost that initially for operation, maintenance, and energy in addition to equipment handling engineering expertise and difficulties related to transport and storage (Xin et al. 2012; Berefield et al. 1982). The conventional method is a robust system that was developed and optimized during the twentieth century, it involves processes of coagulation, flocculation, sedimentation, filtration, and chlorine disinfection (Fuller 1933). Since then, other

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several methodologies and technologies were developed to meet the complex goals of end-users. Technologies of membrane filtration and advanced oxidation processes (AOPs) were the most significant editions to the water treatment approaches at the end of the twentieth century: ● Membrane technologies enabling the complete removal of particles and pathogens via filtration membrane size exclusion using the scale required by the application and/or the end-user. ● Advanced oxidation processes = AOPs are potentially effective for oxidizing several types of pollutants to other products (Hu and Apblett 2014), but not for dyes, pharmaceuticals products, and other difficult pollutants (Suárez et al. 2008; Malato et al. 2009; Naddeo et al. 2011), in addition to its high cost (especially for maintenance and energy supply) and operative conditions (Baruah et al. 2012; Bora and Dutta 2014). Early in the twentieth century, the biological treatment method was developed and becomes the worldwide basis of wastewater treatment nowadays and there are several studies conducted to evaluate it (e.g., activated sludge and biological trickling filters). These studies determined its lack and insufficiency to remove some contaminants (Servos et al. 2005; Urase and Kikuta 2005; Vieno et al. 2006). Anaerobic membrane bioreactors (AnMBRs), for example, attract recent global attention as a potent solution for water reusing with regards to renewable energy and fewer emissions of greenhouse gas. AnMBRs are largely used in treating toxic and concentrated wastewater (El-Sheekh et al. 2021). Recent technologies, such as bioremediation and NPs, can provide valuable approaches for the removal of pollutants from the environment.

4 Bioremediation Approach for Polluted Waters Bioremediation is an environmentally benign remediation method that makes use of the natural capacity of various microbes, including bacteria, fungi, and algae, to break down and detoxify organic and inorganic contaminants from industrial wastewaters (Bharagava et al. 2019). As a low-cost substitute for traditional remediation processes, bioremediation has gained popularity. The ability of bacteria to breakdown, detoxify, or transform pollutants through metabolic processes, as well as the accessibility of contaminants and their bioavailability, are all important factors in bioremediation (Antizar-Ladislao 2010). Using bioremediation process, waste is transformed into inorganic substances like carbon dioxide, water, and methane, which aid in contaminants mineralization and detoxification (Reshma et al. 2011). There are several types of approaches for bioremediation including bio-attenuation (a natural process of degradation with a gradual decline in pollutant concentration over time), bio-stimulation (pollutant degradation through adding simulating elements,

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and bio-augmentation (through the addition of microbes with degradation potential) (Maszenan et al. 2011). The use of algae in bioremediation has become more significant because of its capacity to absorb hazardous metals from contaminated environments or to accumulate those metals. (Mitra et al. 2012). Toxic chemical cleanup from wastewater using algae was researched (Zeraatkar et al. 2016). In a water system using microalgae, metal-removal capacity was observed (Gosavi et al. 2004). Many microalga members, including Phormidium ambiguum, Scenedesmus quadricauda, and Pseudochlorococcum typicum, demonstrated efficient removal of Hg, Pb, and Cd (Shanab et al. 2012). Moreover, algal biomass was used to remove waste from water (Romera et al. 2006). The best outcomes for bio-recovery are found in the most researched and productive phylum, Phaeophyta (Bhatt et al. 2021). Bioremediation may be restricted by a number of factors (Saxena and Bharagava 2019) such as ● ● ● ● ●

low or no bioavailability of pollutants to microbes, Toxicity of contaminants to microbes and plants used, Absence of necessary enzymes for detoxification, The remediating plants’ low biomass and slow growth, Lastly, the stringent restrictions placed on the use of these organisms in the USA and other Western nations further limit their potential in field applications.

The novel concept known as “nano-bioremediation” combines the use of nanoparticles and bioremediation to remediate environmental pollutants in polluted matrixes in a sustainable manner (Cecchin et al. 2017). Recently, this method for cleaning up contaminated places has drawn a lot of attention (Lin et al. 2021; Zhou et al. 2021). Algal bioremediation and the production of nanoparticles are complementary components of the same process (Dahoumane et al. 2016).

5 Nanoscience and Derived Applications Nanoscience and nanotechnologies are significant and potential approaches for water and wastewater treatment in this century, they can effectively replace the conventional technologies (Goutam et al. 2018). It strongly supports the global intension towards water reuse of industrial and municipal wastewaters, especially in arid and semiarid countries (Bharti et al. 2022; Di Natale et al. 2020; Elboughdiri 2020; Hussain et al. 2022; Janani et al. 2021; Sajjadi et al. 2021). In the field of water treatment, of application of nanotechnology can be classified into three types based on the aim; (1) to detect pollution, (2) to restore and purify water, or (3) to prevent pollution (Yunus et al. 2012).

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6 Nanotechnology as an Advanced Technique (NTs) The word “nano” comes from the Greek noun “Nanos,” which means little, and Taniguchi first used the term “nanotechnology” in 1974 (Taniguchi 1974), as a field of technology involving processes of material separation, consolidation, and deformation (Iqbal et al. 2012). The scale of one nanometer is 10–9 m. This method therefore relies on a nanoscale of about 1 × 10–9 , where the resulting nanomaterials react and behave differently from their original procurers (Goutam et al. 2018). Measurement and manipulation of objects at the nanoscale are the goals of nanotechnology, which has a size scale of 1–100 nm (Mansoori and Soelaiman 2005) as well as to research nanomaterials (nanoscale) with crucial and particular characteristics and functionalities (Khan et al. 2019). At the nano-level, the material exhibits distinct chemical, physical, and biological properties because the surface area and size are inversely proportion (El Saliby et al. 2008). NPs are made up of three layers and are not just basic molecules themselves; see Table 1. Because of their extraordinary structure, NPs are materials with unique properties that have piqued the curiosity of researchers across a wide range of fields. By changing the chemical concentrations and/or reaction circumstances (e.g., temperature and pH), it is possible to modify the morphological properties of nanoparticles (i.e., size and shape). Nevertheless, the application of the synthesized nanomaterials may have might suffer from some limitations or challenges, such as (i) (ii) (iii) (iv) (v) (vi) (vii)

Stability in the harsh environment, Insufficient comprehension, Bio-accumulation and toxicity features, Need for Expensive analysis, Need for skilled operators, Problems in devices assembling, and Recycle/reuse.

Green synthesis of nanomaterials is a promising trend that enabling to counter the limitations of the method. Some basic principles of “green synthesis” can thus help in wastewater prevention/minimization using safer (or nontoxic) solvent/auxiliaries and renewable feedstock. NPs can be employed for drug delivery (Lee et al. 2011), chemical and biological sensing (Barrak et al. 2019), gas sensing (Rawal and Kaur 2013; Mansha et al. 2016; Khan et al. 2017a), CO2 capturing (Ramacharyulu et al. 2015; Table 1 Different layers on nanoparticles (Shin et al. 2016) Layers on nanoparticles Surface layer

Shell layer

Core layer

Various small molecules, metal ions, surfactants, and polymers have been used to functionalize them

A layer having many chemical components and functions

Essentially, the NP’s core, and frequently used to describe the NP as a whole

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Ganesh et al. 2017), and other related applications (Shaalan et al. 2016). Nanoparticles (NPs) are in high demand on the global market, and by 2025, it is anticipated that this demand would amount to 98 billion USD. (Jeyaraj et al. 2019). Due to their specific characterization relevant to size and area, in addition to the unique catalysis and adsorption properties, nanoparticles (NPs) are frequently used in wastewater treatment and purification (Gawande et al. 2011; Guo et al. 2013). Zerovalent metal nanoparticles (silver nanoparticles, iron nanoparticles, zinc nanoparticles), metal oxide nanoparticles, carbon nanotubes, and nanocomposites (Mueller and Nowack 2009) are examples of nanoparticles that have been successfully reported for water and wastewater treatment and photocatalytic treatment of industrial wastewaters (Filipponi et al. 2010). Methods that exist for NPs fabrication can be broadly categorized into two major types, namely, the bottom-up and the top-down approaches (Fig. 2) (Shimomura and Sawadaishi 2001).

Fig. 2 Different approaches and methods for synthesizing nanoparticles

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● In The top-down process, large metal is used for the synthesis of NPs through mechanical breakdown. It is an expensive, time-consuming, and energy-intensive process. ● The top-down method starts with the bulk component, which gradually leaches away bit by bit, producing fine NPs. In general, there are three categories into which NP synthesis methods can be divided: (1) physical, (2) chemical, and (3) biological, also referred to as constructive methods. Laser ablation, arc discharge, vapor deposition, melt mixing, ball milling sputter deposition, and flame pyrolysis are among the available physical methods are available (Dhand et al. 2015). These methods are characterized by high speed, no use of toxic chemicals, purity, uniform size and shape, and low cost. However, there are some limitations such as low productivity, high cost, radiation exposure, high energy, temperature, and pressure requirements, low thermal stability, high amounts of waste, high dilution, and low stability possibility. It alters the surface and physicochemical chemistry of nanoparticles, making it ineffective for creating nanoparticles in common forms and sizes (Jeyaraj et al. 2019). Chemical synthesis techniques include the sol–gel process, pyrolysis, CVD, micro emulsion, hydrothermal, polyol synthesis, and plasma-enhanced chemical vapor deposition are advantageous as they are economical, have a wide range of surface chemistry possibilities, produce high yields, are size-controlled, thermally stable, and have reduced dispersity. The low purity and the use of toxic chemicals and organic solvents, which can be harmful to people and the environment, are drawbacks of these chemical processes (Jeyaraj et al. 2019). As a result, recent research has focused on exploiting the biological method to synthesize nanoparticles. They are often affordable, nontoxic, scalable, and environmentally friendly (Thakkar et al. 2010). So far, several plant extracts (Gilaki 2010), bacteria (Saifuddin et al. 2009), fungi (Balaji et al. 2009), enzymes (Schneidewind et al. 2012), and algae (Ali et al. 2011) have been used for the synthesis of NPs. In recent years, there has been a growing trend toward employing algae to synthesize NPs (LewisOscar et al. 2016). Algae are referred to as “bio-nano-factories” among biological materials since both live and dead dried biomasses were employed to create metallic nanoparticles (Davis et al. 1998). Algae are a significant group of photosynthetic organisms both economically and environmentally. They are unicellular or multicellular organisms that live in a variety of environments, such as freshwater, marine water, or the surface of damp rocks (Oscar et al. 2014). There are two types of algae: microalgae (microscopic) and macroalgae (macroscopic). They are crucial in applications for medicine, pharmaceuticals, agriculture, aquaculture, and cosmetics. Algae are an important source for many industrial goods, including biofuels and natural pigments (Borowitzka 2013). Algae-mediated nanomaterial production might be regarded as a more recent branch, phyco-nano-technology. Various types of algae have been positively indicated as a potential tool for green biosynthesis and bio-production of metal NPs.

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Algae are adventurous by their ease of harvesting, cell disruption; high accumulation potential; quick rate of cell division; low risk, cost, and toxicity; increased energy; and ease scaling (Sharma et al. 2015). Different groups of algae are currently determined for the synthesis of metallic NPs, including Chlorophyceae (green algae), Phaeophyceae (brown algae), Cyanophyceae (blue-green agae—BGA) Rhodophyceae (red algae), as well as diatoms and euglenoids (Sharma et al. 2016). Numerous species of brown algae (such as Cystophora moniliformis, Sargassum polycystum, Padina pavonica, and Gelidiella acerosa) were used for silver nanoparticles production (AgNPs) (Azizi et al. 2014). Some other species (such as Cystoseira baccata, Fucus vesiculosus, Ecklonia cava, Dictyota bartayresianna, and Sargassum wightii) showed their contribution to the biosynthesis of AuNPs. The production of AuNPs by S. platensis and Phormidium valderianum is well-known (Iravani et al. 2018). Many studies were conducted on the biosynthesis of AgNPs by a variety of red alga strains such as Kappaphycus alvarezii, Gelidiella acerosa, and Kappaphycus sp., and gold nanoparticles by Chondrus crispus, K. alvarezii, and Galaxaura elongata (Castro-Longoria et al. 2012). The synthesis of AgNPs with different morphologies can be obtained by using various BGA species such as Oscillato riawillei, Spirulina platensis, Microchaete diplosiphon, Plectonema boryanum, and Cylindrospermum stagnale (Husain et al. 2015). There are also several strains of cyanobacteria (Singh et al. 2014), and other microalgae (Subramaniyam et al. 2015) showed the reductive transformation of many metals into nanometals (Mahdavi et al. 2013).

7 Classification of Nanoparticles (NPs) NPs are commonly classified according to their morphological features, dimensions, configuration, constituents, uniformity, and combination. Nanoparticles exhibit diversity in terms of their size, shape, and architecture, which can be spherical, cylindrical, tubular, conical, hollow-core, spiral, flat, and so on, or may even be irregular in shape. They may have a surface that is either smooth and uniform or uneven with irregularities. They can also exist in either a crystalline or amorphous state, with some having one or multiple crystal solids that can be either loosely dispersed or agglomerated (Machado et al. 2015). Based on the dimension of electron transport, NPs are further divided into four categories: 0 dimensions, such as nanodots, in which the length, breadth, and height are fixed at a single location; 1D, which contains thin films used mostly in sensor mechanisms for electrical devices; 2D that consist of second-generation nanoparticles like carbon nanotubes, known for their excellent absorption capacity and stability. Additionally, 3D nanoparticles include dendrimers and quantum dots (Pokropivny and Skorokhod 2007). Generally speaking, the nanoparticles are divided into carbon-based, organic, and inorganic NPs depending on their chemical structures (Tiwari et al. 2012). Allcarbon nanoparticles are known as carbon-based nanoparticles (Bhaviripudi et al. 2007). They can be divided into fullerenes, graphene, carbon nanotubes (CNT),

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carbon nanofibers, carbon black, and occasionally nanosized activated carbon (Ealias and Saravanakumar 2017). Dendrimers, micelles, liposomes, ferritin, and others are examples of organic nanoparticles or polymers (Fig. 3). These nanoparticles are safe and biodegradable, and some of them, such as micelles and liposomes, include hollow centers known as nanocapsules. These nanocapsules are sensitive to electromagnetic and thermal radiation, such as heat and light (Tiwari et al. 2008). Inorganic nanoparticles are those that do not contain carbon. Typically, inorganic nanoparticles are comprised of metal or metal oxide. By using either destructive or constructive processes, Metals are reduced to nanometric sizes to create metal-based nanoparticles. Aluminum (Al), cadmium (Cd), cobalt (Co), copper (Cu), gold (Au), iron (Fe), lead (Pb), silver (Ag), and zinc (Zn) are the most often employed metals for the creation of nanoparticles. Nanoparticles possess distinctive properties that make them different from bulk materials. These properties include their small size, typically ranging from 10 to 100 nm, high surface area to volume ratios, varying pore sizes, unique surface charge and charge densities, crystalline or amorphous structures, and shapes that can be spherical or cylindrical. Nanoparticles may also exhibit coloration, reactivity, and sensitivity to environmental factors such as air, moisture, heat, and sunlight (Ealias and Saravanakumar 2017). Metal oxide nanoparticles are synthesized to modify the properties of metal-based nanoparticles. One example is the oxidation of iron nanoparticles (Fe) to iron oxide (Fe2 O3 ) at room temperature, which enhances their reactivity compared to bare iron nanoparticles. Metal oxide nanoparticles are synthesized to improve their reactivity and effectiveness in various applications (Tai et al. 2007).

Fig. 3 Nanoparticles’ classification based on their chemical composition

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8 Metallic Nanoparticle: Ag and Fe Metallic nanoparticles are distinguished by their surface Plasmon resonance, incredibly small size, and high surface-to-volume ratio, among other distinctive properties (Sharma et al. 2016). Metallic nanoparticles are also characterized by magnetic and optical polarizability, and electrical and thermal conductivity (Khan et al. 2017b). These qualities gave rise to numerous applications that had a significant industrial and scientific impact (Yaqoob et al. 2020a, b, c). Noble metal nanoparticles have garnered considerable attention due to exceptional optical properties, surface plasmon resonance, and photothermal properties (Yaqoob et al. 2020a, b, c; Khan et al. 2017a). Due to their ability to integrate into the biological system with nontoxicity, noble metal nanoparticles have impacted significantly in medicinal and biological research (Yaqoob et al. 2020a, b, c). Several industries, including clinical diagnostics and treatments, cosmetics, textiles, food processing and packaging, electronics, wastwastewateratment, environmental remediation, and agriculture, all benefit greatly from the use of noble metallic nanoparticles (Jain 2005; Sanguansri and Augustin 2006; Tiwari et al. 2008; Shan et al. 2009; Pérez-de-Luque et al. 2012; Tiwari et al. 2012; Gurav et al. 2019; Yaqoob et al. 2020a, b, c, Yaqoob et al. 2020a, b, c). The scientific community is particularly interested in silver nanoparticles among all noble metal nanoparticles because of their unique qualities, which include strong conductivity, chemical stability, catalysis, and good antibacterial, antiviral, antifungal, as well as anti-inflammatory actions (Ahmad et al. 2003; Frattini et al. 2005; Hasan 2015; Yaqoob et al. 2020a, b, c). Silver nanoparticles have been demonstrated to be highly effective due to their excellent antimicrobial properties against various types of microorganisms, including lethal viruses, germs, and other nucleuscontaining microbes (Yaqoob et al. 2020a, b, c). Silver nanoparticles have shown promise in the diagnosis and treatment of cancer (Jeyaraj et al. 2013; Ratan et al. 2020). Silver has been found to have antiseptic properties and a broad-spectrum biocidal effect against microorganisms. It achieves this by disrupting the unicellular membrane of microorganisms, which results in the disturbance of their enzymatic activities (Ahmad et al. 2016). Magnetic nanoparticles are popular among researchers because they possess many unique properties such as low cost, Low toxicity, superparamagnetic, high coercivity, low Curie temperature, and other magnetic qualities (Herlekar et al. 2014). They have been effectively utilized in a variety of fields, including catalysts, sensors, wastewater treatment, pigments, magnetic data storage devices, adsorbents, magnetic resonance imaging, semiconductors, bio-separations, and therapeutic applications (Murray et al. 1993; Lv et al. 2008; Zou et al. 2010; Baikousi et al. 2012; Baghayeri 2015, Ma; Damborska et al. 2017; Kuznetsova and Timerbaev 2022). Among the different magnetic nanoparticles, Fe nanoparticles have a strong magnetic field, a large surface area, and good electrical and thermal conductivity. They also provide outstanding dimensional stability and a unique form of magnetism called superparamagnetism which is found only in iron nanoparticles (Fahmy et al.

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2018). Fe nanoparticles are also characterized by their low toxicity and simple separation methodology (Ali et al. 2016). Due to their unique properties, Fe NPs have been used as contrast agents for magnetic resonance imaging (MRI). In biomedical applications, Fe NPs have shown promising results for directed drug delivery. Fe NPs are also used for the labeling and magnetic separation of biological materials and hyperthermia treatment (Pankhurst et al. 2003; Naseem and Farrukh 2015; Kudr et al. 2017; Vallabani and 2018; Gu et al. 2022). Several neurodegenerative illnesses, including Alzheimer’s disease and amyotrophic lateral sclerosis, are diagnosed and treated with iron oxide nanoparticles (Luo et al. 2020; Serio et al. 2022). Iron oxide nanomaterial has been used widely in environmental water treatment remediation (Yantasee et al. 2007; Dong et al. 2009; Shabani et al. 2021; Krok et al. 2022). This remediation includes effective adsorbents for organic dyes and heavy metal ions and good photocatalytic activity for the breakdown of organic contaminants (Liu et al. 2014; Kim et al. 2020; Sarojini et al. 2022). This is attributed to the magnetic nature of the iron oxide material that allows fast magnetic separation after the adsorption process (Khosravi and Azizian 2014; Santhosh et al. 2019). Moreover, they have been used to remove a variety of pollutants, including halogenated organic compounds, with success (Liang et al. 2014), organic dyes (Hoag et al. 2009), nitroaromatic compounds (Xiong et al. 2015), phenols (Wang et al. 2013), inorganic anions such as phosphates (Markova et al. 2013) and nitrates (Muradova et al. 2016), metalloids (Ling et al. 2015), and radio elements (Ling and Zhang 2015).

9 Bimetallic Ag/Fe Core–Shell Nanoparticle for Water Treatment Ag and Fe nanoparticles have numerous significant benefits in the treatment of water contamination in recent years (Prema et al. 2022; Venkateshaiah et al. 2022). Ag nanoparticles are distinguished by their chemical stability, strong surface plasmon resonance (SPR) absorption, flexibility, biological activity, and high electron capture efficiency in the visible range (Ma, Zhang et al. 2019; Xu et al. 2019). With regard to Fe nanoparticles, they exhibit good adsorption, precipitation, and oxidation capabilities as well as a potent reducing capacity (Santhosh et al. 2019). Unfortunately, applying AgNPs directly can have several issues, namely, their propensity to aggregate in aqueous conditions, which gradually lowers their effectiveness over time (Li et al. 2012). Also, Fe NBs provide several benefits, but they can have drawbacks such as aggregation, oxidation, and difficulties separating from the damaged system (Lu et al. 2016). The ability to create novel nanostructures by mixing noble metals and magnetic nanoparticles provides many favorable reciprocal and supportive effects (Figueroa et al. 2011). In comparison to their bulk and monometallic equivalents, bimetallic nanoparticles with a core/shell shape offer higher flexibility and improved characteristics (Lee et al. 2006). Frey et al. found that when these two nanomaterials are united across a nanoscale interface to create

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heterodimeric nanoparticles, their optical, magnetic, and electronic properties can be altered (Frey et al. 2009). The design of Ag/Fe core/shell nanoparticles has recently drawn more attention for a variety of reasons (Carroll et al. 2010; Yazdanparast et al. 2020): ● A substantially higher surface plasmon band extinction coefficient. ● The Ag/Fe core–shell configuration enables the addition of magnetic functionality to silver characteristics. Serious environmental and health issues could result from the release of nanomaterials into the environment throughout the preparation and purification process. This drawback reduces the efficiency of nanomaterials employed in water filtration (Bundschuh et al. 2018). A novel technique for fixing such nano-adsorbents in a rigid form involves encasing them in a rigid support, such as a synthetic or natural polymer (Aziz et al. 2017). This method offers numerous benefits (Aziz et al. 2019). ● It ensured that nanoparticles would be trapped, making it exceedingly difficult for them to be released into the environment. We can regulate this by regenerating the nanocomposites as a whole. This additionally offers the chance to save the adsorbate for future use. ● The technique makes it easier to switch from a batch adsorption process to a fixed-bed column as continuous flow treatment pilots are required for large-scale applications. Alginate is a natural biopolymer and is regarded as an environmentally benign substance due to its excellent biocompatibility, biodegradability, the potential for chemical modification, chelating ability, and high hydrophilicity (Mohamed and Borik 2013). Alginate beads are frequently used as backing materials in many different technologies, and they have lately been used for environmental cleanup (Matricardi et al. 2008; Bahrami et al. 2020). As sodium alginate is a copolymer of two epimer uronic acids, it differs from many other biopolymers in this regard: 1,4(b-D)-mannuronic acid (M), and 1,4-(a-L)-guluronic acid (G) (Painter 1983). This polymer has numerous advantages over other biopolymers since it is biocompatible, inexpensive, abundant, biodegradable, easily processed into different shapes, has an effective encapsulating technique, and is sensitive to temperature and pH (Scott et al. 1989). The wastewater treatment operation at the real scale requires continuous flow. A novel method for utilizing Ag/Fe bimetallic nanoparticles as nano-adsorbents in an applied system for purification was created by creating granular particles of mastered dimension and encapsulating nano-adsorbents in sodium alginate beads. (Aziz et al. 2019; Kong et al. 2020). This will result in the availability of inexpensive, effective, and environmentally benign adsorbents with the ability to bind harmful pollutant molecules.

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10 Uses of Nanomaterials in the Remediation of Pollutants and Water Purification ● Nano-adsorbents: Nano-adsorption is a technique or behavior of the nanoparticles that are used to remove pollutants (e.g., bio-contaminants, organic and inorganic pollutants) from water bodies; including surface water, groundwater, and industrial runoff water (Kumar et al. 2017). For example, Carbon nanotubes and graphene are among the created carbon-based nanomaterials’ that are efficient adsorbents for adsorbing pollutants based on their specific layered nanostructure with tuneable pore size and different functionalities (Kukovecz et al. 2013; Kumar et al. 2017). ● Nano-catalyst and catalytic membrane: Nano-catalysts are other specific functions that can are used for wastewater treatment. For instance, photocatalysts could break down a range of organic contaminants in wastewater, such as dyes, pesticides, volatile organic compounds (VOCs), and detergents (Lin et al. 2014). Among various nano-photocatalysts, TiO2 and ZnO are based on their high reactivity and chemical stability (Akhavan 2009). Nanostructured TiO2 films and membranes are employed in the catalytic membrane, which may also inactivate microorganisms and break down organic contaminants (Choi et al. 2009). ● Nanomembrane: Nanoparticles are used as nanofibers in membrane formation and then could be applied for micro-size removal as a pre-treater method used proceeding to ultrafiltration or reverse osmosis (Sushma and Richa 2015). It can be used to increase surface water permeability, hydrophobicity, or fouling resistance (Maximous et al. 2010). The elimination of different types of contaminants, such as bacteria or viruses, heavy metals and ions, as well as different kinds of complex chemical compounds, etc., is the only use for these nanofibrous composite membranes. ● Bioactive nanoparticle: The bioactive nature of some nanoparticle materials is characterized by their massive potential for wastewater treatment. For example, bacillus cereus was used at a wide range to biosynthesize silver nanoparticles that are of high antibacterial potential. Similarly, Ag nanoparticles embedded in cellulose acetate fibers and MgO nanoparticles work incredibly well to eliminate both positive and negative spores (Prakash et al. 2011). ● Biomimetic membrane: The biomimetic membranes exhibit a high degree of salt removal property and have high permeability and selectivity (Kaufman and Freger 2011), and are chemically stable.

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11 Future Potential Application Nanoscience is a new area in which science and engineering work together to assess how well nanoscale materials can be controlled, worked with, and applied in a variety of different useful ways. The nanoscale-featured synthetic particles exhibit unusual and unexpected characteristics that set them apart from their original percussive material counterparts (Perez 2007). As a result, nanoparticles offer very effective, selective, and biodegradable ligands for a variety of hazardous pollutants in wastewater. It should be noted here that the application of nanotechnology is not limited to wastewater treatment and remediation, but also incorporates agribusiness, health and medical devices, materials and manufacturing, electronics, information and communication technologies, and energy storage, production, and conversion (Smith 2006). In addition, it is simple to integrate nanotechnology with existing technologies and enhance it to solve many problems using the virtue of the nano-synthesized particles, components, and/or systems that perform better (EC 2004). Nanoscience and hence, nanoparticles are representing a promising revolution in wastewater remediation, this is mainly due to their high efficiency as well as their cost–effectiveness. This technology is far more flexible to apply either in or exsitu in which it can be used directly to synthesize the adsorbents nanoparticles that remove the toxic pollutants or catalytic particles that oxidize the noxious wastewater contaminants and break them down, or indirectly by integrating the nanoparticles into the conventional treatment technologies. This means that nanoparticles could be used to degrade organic contaminants and remove salts and heavy metals through adsorptive removal. The application of nanotechnology in wastewater remediation can be simplified in the following two steps, based on Smith (2006) definitions: 1. Application of the used nanoparticles as nano-adsorbents that adsorb the existent pollutants (e.g., metals) by sequestration; then 2. Application of the nanoparticles as nano-catalysts that oxidize the existent contaminants and break them down. Nanoscience with its emerged technology is becoming one of the potential and efficient technological tools that might be used to address issues with energy, water, and health (EC 2004; Tratnyek and Johnson 2006; Perez 2007; Savage and Wentsel 2008). Following are examples of the major benefits of nanotechnology that are potentially expected in the field of environmental cleaning up according to Nassar (2012); Tratnyek and Johnson (2006); Perez (2007) and Savage and Diallo (2005) ● ● ● ● ●

The ability for applying in early treatment (saving time for remediation), The use of stronger, lighter, and more effective nanomaterials, The small size of the used particles enables accurate and more sensible results, The Simplicity of the technique and its space saving, The possibility of in situ application (i.e., less energy need), meaning it is a cost-effective tool.

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Nanoparticles offer a great opportunity to mitigate fouling impacts and improve the filter membrane performance, by incorporating them in the membrane structure and hence, improve the membrane surface nanostructure and enhance its adhesion property. Nanoparticles can be used also as nano-sensors when merged with membrane filtration techniques and effectively enable the early detection and identification of viruses and diseases and identification of other waterborne biological threat contaminants.

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Phytonanoremediation of Metals and Organic Waste in Wastewater Treatment Garima and Navneeta Bharadvaja

Abstract Due to increased anthropogenic activities pollutants in water have become a major concern. Today, when we are facing scarcity of water a systematic, ecofriendly, and cost-effective treatment of wastewater are pre-requisite for the growth of the economy. Nanotechnology and phytoremediation are a hand-full of emerging technology for the efficient elimination of pollutants like heavy metals and organic pollutants from wastewater. Plant species used in nano-phytoremediation are hyperaccumulators and metal tolerant, for example, Cynodon dactylon (Bermuda grass), Eichhornia crassipes (water hyacinth), Helianthus annus (sunflower), etc. Some organic pollutants, for example, long chain hydrocarbons and organohalides, become resistant to previously used degradation methods. Nano-phytoremediation can overcome this disadvantage using nanoencapsulated enzymes which assist rapid and enhanced degradation. This chapter focuses on the adsorption of pollutant on nanoparticles, different plant species used in nanophytoremediation and their mechanism to alleviate pollutant from water, harmful effect of wastewater pollutant on human health, and the future aspect of this approach of combining nanotechnology and phytoremediation. Keywords Nanoparticles · Phytoremediation · Nanophytoremediation · Contaminants

1 Introduction Fresh water is essential for human health, plants, animals, and also for agricultural activities like irrigation, household work, and other crucial activities. Today with the increase in the global warming the temperature of earth is also increasing and adversely affecting the climate. The change in climate may bring drought conditions and can influence the water reservoirs. Therefore, now it becomes more important to Garima · N. Bharadvaja (B) Plant Biotechnology Laboratory, Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Main Bawana Road, Delhi 110042, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_12

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decontaminate wastewater. Wastewater is generally contaminated with heavy metals, microorganisms, and organic pollutants. Heavy metal pollutants are carcinogenic in nature and are mostly generated from industries (like mining, chemical, battery, tannery, nuclear, and metallurgical), soil erosion, volcanic activities, and weathering of rocks. On the other hand, organic pollutants in wastewater are generally produced from agriculture, domestic, urban runoff, and industrial effluents (Ivanova et al. 2016). During the past few decades, several wastewater treatment approaches were developed but there are certain drawbacks in every method. Plants are autotrophic and utilize sunlight and carbon dioxide as an energy and carbon source, respectively. Plants also absorb many compounds from the surrounding that are toxic and detoxify the environment. Therefore, this approach is applied for detoxifying the environment and a new emerging technique comes under consideration which is phytonanoremediation. “Phytonanoremediation is a process that combines bioremediation with phytonanoparticles and recruits higher plants to stabilize, degrade or remove pollutants from the environment.” Plant-derived nanoparticles were first described by Gardea-torresdey et al. (2003) in alfalfa plants. Now numerous types of nanoparticles have been synthesized using different varieties of plants (Zhang et al. 2020). Nanoparticles are small in size with dimension in a range of 1–100 nm and of varied shapes (Materac et al. 2015; Parvin et al. 2018). The phytonanoparticle can be synthesized intracellularly or extracellularly. In the synthesis of intracellular nanoparticle, the selected plant species should be grown in metal-rich organic media, hydroponic solution, or soil. Synthesizing nanoparticle intracellularly is difficult and takes a lot of effort in culturing, monitoring, tracking, and harvesting, whereas extracellular nanoparticle synthesis require the extract of selected plant part like leaves, fruits, shoots, roots, etc. and are added to a boiling salt solution of metals and thereby promote the reduction in metal ions (Augustine and Hasan 2020). Biological method is the favored one as they are safe, eco-friendly, simple, economical with high yield, and good quality. The use of hazardous and toxic materials is also limited and there is no requirement of such high pressure and temperature in green synthesis of nanoparticles. Removal of pollutant with the help of nanoparticle is based on the adsorption capacity. The adsorption of pollutant on nanoparticles depends on the surface area, shape, and charge. The charge, surface area, and shape of nanoparticles decide their optical, mechanical, chemical, and magnetic properties (Salem and Fouda 2021). Phytonanoparticles, for example, ZnO, Ag, and TiO2 possess a great potential in purifying wastewater (Nguyen et al. 2018). Phytonanoremediation is one of the ecofriendly and sustainable methods mediated by nanoparticles (Tripathi et al. 2019). Hence nanotechnology enhances the efficiency of phytoremediation (Ansari et al. 2019).

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2 Impact of Water Pollution Treatment of wastewater should be highly concerned because it affects the health of human being and also pollutes the environment. Due to growing industries like food, textile, agriculture, iron, steel, tannery, pharmaceutical, mining, and iron, the water-borne infections found to be increased (Kumar et al. 2021). The presence of constant heavy metals, organic waste, dyes plastics, etc. affects the ecosystem adversely. Every year around 1.8 million children are diagnosed with diarrhea due to poor quality water consumption only (Jain et al. 2021). The synthetic organic dyes are resistant to natural degration and can lead to detrimental effects (Chauhan et al. 2020). Heavy metals are carcinogenic in nature and are nonbiodegradable (Parvin et al. 2018). Copper and cobalt can affect kidney, heart, and liver in human beings (Khaligh and Johan 2018). The wastewater includes 99.9% water and the rest 0.1% consists of organic substances, heavy metals, nutrients, and micropollutants. Although there are some conventional and biological methods for treating wastewater, such as ion-exchange method, flocculation, electrodialysis membrane separation, anoxic oxidation methods, precipitation, and adsorption, these utilizes chemicals like ammonia, ozone, ferric ions, etc. are not sufficient to eliminate heavy metals and some toxic organic compounds as shown in Fig. 1. Alongwith less efficiency they took a lot of time, costly and have their own limitations and advantage of each method to remove pollutants to a certain extent (Kumar et al. 2021; Jain et al. 2021). Therefore if all the limitations are considered there is an urgent requirement for an eco-friendly method to treat wastewater. It has been reported that by 2050 the world will face difficulties in assessing water every year. Nanotechnology is a highly advanced and promising approach to the remediation of pollutant from environment (Kumar et al. 2021). Nanoparticle found to have application in various field, it comes out as versatile tool in biosensors, medications, cell labeling, and fuel cell and now holds promise in eradicating pollutants from environment (Joglekar et al. 2011). The

METHODS

Physical 1.Ion Exhange 2.Precipitation 3.electrocoagulation 4.Cementation 5.MembraneFilteration 6.Electrodialysis

Chemical 1.Chemical washing 2.Reduction 3.Chelate Flushing

Fig. 1 Current methods used for removing heavy metal from wastewater

Biological 1.Bioremediation 2. Bioremediation 3.Biofilteration 4.Biosorbents 5.Bioaugmentation 6.Phytoremediation

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removal of contaminant is based on the greater surface area and adsorption capacity of nanoparticles (Verma et al. 2021). Plants can be a major source of nanoparticles because of their high production rate as compared to other organisms which will be discussed in further sections of this chapter.

3 Biosynthesis of Green Nanoparticles Many efforts have also been done in synthesizing nanoparticles by microbes like bacteria, fungi, yeast, and viruses. But in comparison to microbes, plants perform photosynthesis and make use of whole parts of the plants as green factories to produce metallic nanoparticles. Also using the plant for the biosynthesis of nanoparticle devoid of complex processes such as isolation of microbes, maintenance, and culturing (Akhtar et al. 2013). Also the rate of synthesizing nanomaterials in plants is higher than microorganisms. Plants possess a number of metabolites and they

Bulk Fine particles

Nanoparticles

Nanoparticles

Nuclei Atoms /molecules

Bottom to top approach Spinning Supercritical fluid synthesis Sol gel process Laser pyrolysis Molecular condensation Green synthesis (non toxic)

Top to bottom approach

All are toxic methods except Green synthesis

Fig. 2 Different approaches used in the biosynthesis of nanoparticles

Etching Mechanical milling Sputtering Electro- explosion Laser Ablation

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are yet to be fully utilized in synthesizing nanoparticles. There are various conventional, rapid, and easy methods for synthesizing nanomaterial. The enzymes which are secreted extracellularly provide an edge for the production of more amount of nanoparticles of 100–200 nm in size free from other proteins and then further recovered by the filteration process (Augustine and Hasan 2020). Nanomaterials have capacity to absorb a good amount of contaminants and assist in catalyzing the reaction rapidly. There are two approaches for synthesizing nanoparticles. a. Top to bottom/Top down—this approach consists of the conversion of bulk into nanoparticles as shown in Fig. 2. It includes physicochemical methods which may result in imperfection in the conformation or surface of nanomaterial and impact their properties (algae based), for example, sputtering, thermal/laser ablation, mechanical/ball milling, and chemical etching. b. Bottom to top/Bottom up—it consists of the clustering of nanoparticles from smaller entity as shown in Fig. 2, for example, plant extract, fungus, bacteria, spray pyrolysis, laser pyrolysis, etc. There are basically three methods to synthesize nanoparticles that are biological, physical, and chemical process. The chemical method has certain limitations as it makes use of toxic organic solvents and produced nanoparticles have narrow size distribution. In the case of physical methods, there is a single step process that

Collection of desired part of the plant ,wash it in running water to remove epiphytes and necrotic plant .Then wash it one more time in sterile distilled water to eliminate any remaining associated debris. These fresh part of plants are now shade dried for around 12-15 days .Once dried now blended to form powder Powder is now boiled with deionized distilled water this process is percolation

The resultant solution is now filtered properly till the nonsoluble substance is observed in the broth.

The plant broth is added to metal salt solution ,it result in the production of nanoparticles.

Qualitative analysis of nanoparticles is done by monitoring UV visible spectra, zeta potention ,FTIR,DLS, TEM,SEM,EDAX, XPS etc.

Fig. 3 Flowchart for bio-synthesizing nanoparticle from the desired plant in laboratories

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leads to massive production in a short period of time but these methods lead to irregular morphology and distribution of NPs. These limitations were overcome by biological green methods, as these utilize nonhazardous molecules like enzymes, proteins, carbohydrates, DNA, and plant extracts (Ocsoy et al. 2018) (Fig. 3).

4 Sources of Green Nanoparticles 4.1 Algae-Assisted Nano-particle Synthesis Algae can be unicellular or multicellular present on the moist surfaces. These are the least classified as a primitive class of plants that holds a promise to produce nanoparticle (Rahman et al. 2019). Furthermore they have a good capacity to uptake metal and contain an enormous amount of reducing agent that assists in reducing metal salts to their corresponding nanoparticle without any toxic by-product. There are four ways of synthesizing nanoparticles from algae (1) Algal cells are disrupted and based on the exploitation of isolated biomolecule, (2) depends on the supernatant from which cells are removed but without being undergone into any process except centrifugation, filtration for recovery, (3) the third way involves harvesting microalgal cells isolated from the culture and again suspended in distilled water to stimulate the synthesis of nanoparticles of various kind, and (4) this last way is based on using live cell of algae survived under normal culture media parameters. Few example of such algal species used for producing Ag nanoparticles are Sargassum wightii (Singaravelu et al. 2007), Chlorella (Annamalai and Nallamuthu 2015), Gleocapsa, and Turbinaria conoides (Mukherjee et al. 2021; Smitha et al. 2020). Some more examples are given in Table 1.

4.2 Plant Synthesized Nanoparticles Plants assisted synthesis is more advantageous than lower organism because of their higher yield. Plants also have biomolecule which can help in stabilizing and reducing green NPs (Singh et al. 2020). Different parts of the plants such as leaf, stem, fruit, and seeds can synthesize different types of nanoparticles (Venkat Kumar and Rajeshkumar 2018). Plant extracts have ample amount of polyphenols, sugars, flavonoids, enzymes, and proteins and can assist as stabilizing and reducing agents for synthesizing metallic NPs (Ocsoy et al. 2018) (Table 2).

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Table 1 Algae synthesized nanoparticles and their characteristics Nanoparticle

Source

Shape

Characterization

References

Ag

Chlorococcum humicola, Spirullina plantenesis, Sargassum muticum,Padinia pavania

Triangle, Quasi-spherical, spherical

UV–Vis spectroscopy, SEM, XRD TEM, FT-IR,

Xie et al. (2007)

Au

T.conoides,Sargassum wightii,Galuxara elongate

Spherical

SEM, FT-IR, UV–Vis

Singaravelu et al. (2007); Xie et al. (2007)

CuO

Bifurcuria bifurcata

Spherical and elongated

UV–Vis, FT-IR, XRD, TEM

Shankar et al. (2004)

CdS

Phormidium tenue

Spherical

FT-IR., TEM UV–Vis EDAX,

MubarakAli et al. (2013)

ZnO

S.muticum

Hexagonal, cubic

UV–Vis, FESEM XRD,

Mahdavi et al. (2013)

Fe

Chlorococcum

Sphere

DLS, TEM, FT-IR, EDA, UV–Vis

Subramaniyam et al. (2015)

Fe3O4

S.muticum

Cubic

EDXRF, XRD, VSM, FT-IR, TEM

Mahdavi et al. (2013)

Pd

Chlorella vulgaris

Spherical monodisperse crystalline

FT-IR, UV–Vis, TEM, XRD,

Arsiya et al. (2017)

Abbreviations used—FT-IR—Fourier transform infrared spectroscopy, TEM—transmission electron microscopy, UV–vis—ultraviolets visible, FESEM—field emission electron microscopy, XRD—X-ray diffraction, EDAX—energy dispersive X-ray spectroscopy

5 Application of Nano-phytoremediation in Wastewater Treatment The emerging nanotechnology will increase industrialization in developing country like India (Verma et al. 2021). Nano-phytoremediation is basically the green fabrication of nanoparticles using plants for remediation (Chauhan et al. 2020) As Sects. 2 and 3 have discussed a number of nanoparticles and their green synthesis, now the chapter will focus on the mechanism for heavy metals and organic waste removal from wastewater. This process is based on adsorption, the liquid or gas molecule will attach to the solid support and result in the formation of layer. The different functional group, dosage, and time of contact play a crucial part in the adsorption method. The elimination of heavy metal depends on its diffusion potential. Diffusion potential varies according to the amount of heavy metals and exposed external surface area on the nanoparticle Because when nanoadsorbent is placed into the wastewater possessing heavy metals pollutants, the metals diffuse on the external surface

Hygrophila

Hibiscus

G.jasminoides

Au

ZnO

Iron Leaves

Leaf

All parts

Root

Leaf

Euphorbia heterophylla

Chromolaena odorata

MnO2

Fruit

Myristica fragrans

CuO

Magnetite

Peel Root

Annona squamosa

Asparagus racemosus

Pd

Leaves

Pt

Aloe vera

Indium oxide

Latex

Fruit

Rosa canina

Jatropha curcas

Spherical Many shapes and Dispersed

Hexagonal

Spongy shape

Spherical, rods, Triangular, polygonal

Spherical

Irregular

Spherical

Spherical

Spherical

Spherical

Spherical, Mono disperse

Spherical

Hexagonal, spherical, Nano-rods

Spherical and hexagonal

Fruit Leaves

Hovenia dulcis

ZnO

Spherical Nanotriangles and spherical

Cubic

Pongamia pinnata

Pb

Morphology Spherical

Seed

Au

Abelmoschchus esculentus

Au

Flower Flower

ZnO

N.arbortristis

Mirabilis jalapa

Au

Au

Seeds Leaves

Macrotyloma uniflorum

A.nilagarica

Ag

Ag

Extract Stem

Plant

Cissus quadrangularis

Nanoparticle

Ag

Table 2 Plant synthesized nanoparticles and their morphology Size

References

Das et al. (2011)

21 nm

30–35 nm

26–35 nm

56.68 nm

10–50 nm

1–6 nm

3–6 nm

5–50 nm

10–12.5 nm

27.7 nm

30.2 nm

20 nm

62 nm

(continued)

Padilla-Cruz et al. 2021)

Devi and Gayathri 2014)

Bharathi et al. 2018)

Nnadozie and Ajibade 2020)

Dewi and Yulizar 2020)

Sasidharan et al. 2020)

Raut et al. (2013)

Anila et al. (2021)

Phokha et al. (2008)

Joglekar et al. (2011)

Jafarirad et al. (2016)

Malaikozhundan et al. (2017)

Basavegowda et al. (2014)

Jayaseelan et al. (2013)

Vankar and Bajpa i(2010)

19.8 + −5 nm 100–159.2 nm

Salehi et al. (2016)

Vidhu et al. (2011)

Santhoshkumar et al. (2012)

150 nm

120.16 nm

30–40 nm

248 Garima and N. Bharadvaja

Jatropha curcas

Eucalyptus macrocarpa

Moringa olifera

Pb

Ag

Fe Leaf

Leaf

Latex

Leaf Air dried seed

Aloe barbadensis

Sambucus nigra

Indium oxide

Latex

Calotropis procera

ZnO

Ag

Leaf Leaf

Ocimum sanctum

Spherical

Cubic

Spherical

NA

Spherical

Spherical

Spherical

Rectangular and triangular

Spherical Plate and spherical

Peel

Irregular, spherical

Cubic crystals

Spherical

Spherical

–

Nanotriangles

Triangular,hexagonal, spherical

Spherical

Distorted Spherical

Morphology

Leaf

Rhizophora mucronata

Citrus sinesis

Dipyros kaki

Ag

Pt

Seeds

Pt

Alfalfa

Au

Leaf

Leaf

Leaf

Ag

Camellia sinesis

Coffe arabica

Pd

Pd

Coleus aromaticus

Ag

Leaf

Cymbopogon flexosus

Azadirichta indica

Au

Phyllanthin

Coccina colocynthis

Phyllanthus amarus

Ag

Au

Bimettalic Ag-Au

Pod

Acacia nilotica Fresh leaf

Extract

Plant

Nanoparticle

Ag

Table 2 (continued)

2.6–6.2 nm

10–12.5 nm

47 nn

5–50 nm

17–19 nm

25–40 nm

23 nm

2–20 nm

15–80 nm

8–48 nm

Lebaschi et al. (2017)

5–8 nm

2–100 nm

Zn (II) > Cd (II) > Cu (II). Mystrioti et al. (2016) develop a phyto-nanoparticle for Cr(VI) degradation using five extracts and juices of plants and they are Syzygium aromaticum (clove), Camellia sinesis (green tea), Mentha spicata (spearmint),

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Punica granatum (pomegranate), and red wine. Lisha et al (Yang et al. 2019) studied the gold nanoparticles for the removal of Hg (II) (heavy metal). Titanate nanoflowers are developed by Huang et.al with a greater surface area and illustrated the heavy metal eliminating ability of these titanate nanoflowers which possess high selectivity for toxic metal ions (Kumar and Gopinath 2016). C. latifolium has an enormous amount of glucoside, flavonoid, and alkaloids that can be a good source to biosynthesize silver and gold nanoparticles. Gold nanoparticle is an outstanding choice for adsorbing heavy metals and was studied for Hg2 + removal (Vo et al. 2019; Skudai 2010). Ce-based nanoparticles were also studied and they assist in the removal of Pb (II) and are more effective than FE3O4 and TiO2 but show more phytotoxicity. Arsenic present in water is also hazardous and can be carcinogenic, and iron nanoparticles synthesized from mint leaves show a 94.47 mg/g adsorption capacity for arsenic removal (Kim et al. 2019).

5.2 Nano Bioremediation of Organic Compounds Magnetic nanoadsorbent based on silica was prepared by Peralta et al. and observed the removal of organic pollutants, aliphatic hydrocarbons, and polyaromatic hydrocarbons. For increasing the efficiency the silica-based nanoadsorbant was further modified by trimethoxyphenylsaline. Furthermore the iron nanoparticle synthesizes from Mangifera-indica, Azadiracta indica, Magnolia chapaca, and Murraya koenigii examined using domestic wastewater treatment resulted in the removal of nitrogen, ammonia, COD, and phosphates simultaneously (Goutam and Saxena 2021). Devi et.al reported the degradation of methylene blue dye by silver phytonanoparticles and characterization was done using TEM (Palani et al. 2021). Removal of Dyes Dyes are the organic contaminants made up of chromophores and auxochromes generated from different industries such as textile and tannery industries. Dyes like methylene blue (MB), Rhodamine B (RB), methyl violet (MV), crystal violet (CV), and congo red (CR) are nonbiodegradable and a serious threat for the survival of living organisms. Most of the dyes are carcinogenic and they also resist sunlight to enter into water affecting the aquatic life (Tara et al. 2019). Kadirvelu et al. (2003) reported that most of the colored compounds are mutagenic, carcinogenic, teratogenic and also have a negative impact on different organs of the human body like lungs, liver, kidney, CNS, and reproductive system. There are many chemical processes that have been used for the removal of dyes but the adsorption method, the surface phenomenon is the best and most economic method. Super paramagnetic FE304 nanoparticles are used for cationic dyes from water. The nanospheric nanoparticles are dispersed in wastewater, and the adsorption power for CR and MB taking the amount of 11.22 mg/ g and 44.38 mg/g, respectively, are studied by Zhang et al. The water is purified using nanomagnetite particles and it is safe and clean for environment. Furthermore

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Jatropha curcas latex extract is used to synthesize Fe3O4 used for reducing MB dye with an adsorbing capacity of 466.6 mg /g. Magnetic nanoadsorbent based on Silica was prepared by Peralta et al. and observed the removal of organic pollutants, aliphatic hydrocarbons, and polyaromatic hydrocarbons. For increasing the efficiency the silica-based nanoadsorbant was further modified by trimethoxyphenylsaline. Furthermore the iron nanoparticle synthesize from Mangifera-indica, Azadiracta indica, Magnolia chapaca, and Murrayakoenigii examined using domestic wastewater treatment result in removal of nitrogen, ammonia, COD, and phosphates simultaneously (Goutam and Saxena 2021). Devi et.al explained the degradation of methylene blue dye by silver phytonanoparticles and characterization was done using TEM (Palani et al. 2021). Falah et al. (2016) modified the hybrid nanoparticle Cu2O/TiO2 by cetyltrimethylammonium bromide (CTAB) and it leads to the removal of methylene blue. Removal of phenols. Phenol is also one of the threats generated by industrial effluent such as olive oil production, petrochemical, and kraft pulp mills. It is dangerous even if present in low amount and tough to degrade biologically. ZnO synthesized through many processes and is coated by glass beads and ceramic rings and it was concluded that the maximum adsorption dosage of 16 g/l and 8 g/l eliminate phenol amount with the efficiency of 100 mg/l and 50 mg/l (Dineshkumar et al. 2015). Removal of pesticides Ahmed et al. (Romeh and Ibrahim Saber 2020) investigated a new group of insecticides used for protecting crops that is Chlorfenapyr (4 bromo-2-(4 chlorophenyl)1-ethoxymethyl-5 (trifluoromethyl)pyrrole-3carbonnitrile). It is the least soluble in water and persists for a long time and resists biodegradation. They synthesized circular iron NP with diameter of 2.46–11.49 nm and brassica and ipomoea silver nanoparticles ranging from 6.05–15.02 nm and 6.27–21.23 nm, respectively, using Plantago major supported by activated charcoal. They conclude that when these were added to the aqueous solution after 24 h the chlorfenapyr reduced to 93.7,92.2, and 92.92%. Photocatalytic degradation of organic pollutants Phytocatalysis is an in situ light-induced reaction driven by a catalyst-advanced oxidation process (AOP) used to produce chemical oxidants (Palani et al. 2021). It is mainly used for degrading organic pollutants in an efficient way. Nanoparticles are modified by catalysts which aid in increasing deterioration efficiency. The nanosized semiconductor substances such as ZnO, TiO2 , and CdS are classified in several methods, for example, photochemical activity, conjugated adsorption along electrical bilayer, and high adsorption surface area. Phytocatalysis by titanium oxide has been reported to have many applications in the remediation of wastewater pollution (Kumar and Gopinath 2016, Shah 2020, 2021). Chaudhary et al. (2017) synthesized AuNP using Lagerstroemia speciosa leaf extract, this green synthesis took 30 min at 25 °C and even can be achieved within 2 min only at 80 °C. Characterization was

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Table 3 Different nanomaterials along with their targeted heavy metals and organic pollutants Source

Nanomaterial/ NP

Targeted pollutant

Mechanism

References

Citrus limon

CuO

Cr(vi)

Adsorption

Mohan et al. (2015)

Black tea, vine leaves

Zv-INP

Ibuprofen

Adsorption

Machado et al. (2014)

Tea polyphenols

Ag

Phenolic compounds

Catalysis

Wang et al. (2015)

Spinach

Ag

Organic compounds

Electrocatalysis

Megarajan et al. (2016)

Citrus grandis Cu

Methylene blue dye

Photocatalysis

Das et al. (2018)

P. pavonica

Fe3O4

Pb

Adsorption

Augustine and Hasan (2020)

Plants

Pd

Nitroanelene, nitrophenol, nitroaromatics

Catalytic reduction

Liu et al. (2019)

Burdock root

Ag-Au

Bactericidal

Catalysis

Nguyen et al. (2018)

TiO2

As

Photo-oxidation

Lata and Samadder (2016)

Convolvulus arvensis

Ag

Azo dyes

Catalytic reduction

Nguyen et al. (2018)

Psidium guajava (flavonoids)

Ag

Methyl orange and Coomassie Brilliant Blue

Catalysis under solar or UV irradiation

Venugopal (2017)

Prosopis farcta

Ag

Methylene blue

Degradation under Visible light

Khatami et al. (2019)

P. guajava

SnO2

Reactive yellow dye

Photocatalytic activity under sunlight

Kumar et al. (2018)

Myristica fragrans

CuO

As

Adsorption

Lata and Samadder (2016)

Dandelion extract

Ag

Rhodamine B and methyl orange

Catalytic degradation

Kumar (2021)

Starch

Bimettalic Fe/ Pd

Chlorinated hydrocarbon

Degradation

Wang et al. (2009)

Thymus vulgaris

CuO

Organic compounds

Catalyst

Nasrollahzadeh et al. (2016)

Rhizophora mucronata

Ag

Larvicidal

Ulothrix cylindricum (green algae)

As(III)

Gnanadesigan et al. (2011) Biosorption

Lata and Samadder (2016) (continued)

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Table 3 (continued) Source

Nanomaterial/ NP

Targeted pollutant

Mechanism

References

Moringa oleifera

Fe2O3

Methylene blue dye, Cu(II),Pb(II),Cd(II), Zn

Photocatalytic (dye degradation) and heavy metal adsorption

Shipley et al. (2013; Archana et al. 2021)

done by both UV visible spectroscopy and TEM. It was concluded that AuNP shows strong phytocatalytic degradation under visible light with NaBH4 in reducing dyes such as bromophenol blue, methylene blue, bromocresol green, 4 nitrophenols, and methyl orange (Table 3).

6 Conclusion This eco-friendly advanced technology of combining nanomaterials with plants holds a strong potential for environmental pollution remediation. The green synthesis of nanomaterial is an economically efficient process. The integration of these nanomaterials in wastewater can make it clean and safe for drinking in the era when saving drinking water is highly needed. The phytogenic nanomaterials are not only used for the remediation of heavy metals and organic pollutant but also possess antilarval, antibacterial, antiviral, and cytotoxic activities. The study of morphology can be studied easily using many techniques such as FT-IR, DLS, SEM, TEM, and EDS. This chapter also discussed the different parts of a plant synthesize various biomolecules which result in the formation of nanoparticles. The phytonanoparticles are greatly accomplished in the removal and recycling of heavy metal and organic contaminants in the purification of wastewater. Plants synthesize nanoparticles naturally therefore nano-phytoremediation is an innovative technique and a significant topic for further research. More studies should be done on physiological conditions for the green synthesis of nanoparticles for enhanced yield. Also, several cellular pathways for the biosynthesis of metal oxides and their impact are still unknown.

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Production and Application of Porous Ceramic Membrane for Water and Wastewater Treatment—A Case Study in Vietnam Khac-Uan Do, Xuan-Quang Chu, and Hung-Thuan Tran

Abstract Water pollution, scarcity and lack of clean water are directly affecting people’s lives, especially in rural, remote and isolated areas. Statistical results show that about 20% of the population in our country does not have access to clean water, mainly using water from untested or untreated wells, ponds and lakes. This work was carried out to manufacture porous ceramic materials used for water purification, ensuring the quality of domestic water for rural and mountainous areas. Research results on manufacturing porous ceramics using agricultural by-products mixed with kaolin at different ratios show that porous ceramics are made from the ratio of 50:50 for a mixture between kaolin and rice husk (size 1–1.5 mm) for the best filterability. The calcination temperature and calcination time greatly affect the durability and filtration yield of porous ceramics. The research results contribute to providing more choices for people in the application of simple porous ceramic materials to filter domestic water. Keywords Ceramic membrane · Production · Purification · Membrane fouling · Water · Wastewater

1 Introduction Clean water supply network in Vietnam has not been fully constructed (Bank 2014). Therefore, many rural and mountainous areas were still lack of freshwater (Van Huynh et al. 2019). In rural areas, water from bore wells and open wells was used for daily activities. Besides, rain water, or surface water from rivers, lakes or ponds were K.-U. Do (B) School of Environmental Science and Technology, Hanoi University of Science and Technology, Ha Noi, Vietnam e-mail: [email protected] X.-Q. Chu · H.-T. Tran Center for Advanced Materials Technology, National Center for Technological Progress, Ha Noi, Vietnam © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_13

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also used. However, groundwater is very scarce in mountainous areas while surface water is often depleted in the dry season (Somers and McKenzie 2020). In addition, in the rainy season, water sources are normally polluted. Therefore, using surface water could face many difficulties. Because of low quality of water sources, several simple methods such as filtration, settling, and then boiling were used in rural and mountainous areas. In fact, many wells are built but closed to the polluted sources. At that areas, water sources are contaminated with ammonium, iron, nitrate, nitrite (Zhao et al. 2013). Therefore, filtration with gravel, coarse sand, fine sand, charcoal, and activated carbon were normally used. It should be noted that many small-scale water filtration equipments were sold in the market (Siwila and Brink 2018). These systems contain many filter media layers, such as sand, gravel, activated carbon, and materials for removing manganese and iron (Pooi and Ng 2018). Recently, advanced water purification technologies (i.e. RO, NF) have been used (Ahmad and Azam 2019). Those systems could purify groundwater effectively. There are many core columns (i.e. coarse filter, activated carbon filter, fine filter, RO or Nano membrane) in a RO purifier (Yang et al. 2019). Water in the final stage of filtration could be irradiated with UV to kill bacteria. Those systems could ensure high water quality. However, those systems are costly. So far, ceramic filters have been applied to provide drinking water in small communities in developing countries (Naddafi et al. 2005). Ceramic filters could be made from combustible materials mixed with clay. They are then furnaced to create the surface pores. Ceramic filters could be a solution to reduce turbidity and bacteria. Ceramic filters are also used as a good solution for both water purification and disinfection Lantagne 2001; Oyanedel-Craver and Smith 2008; Rivera-Sánchez et al. 2020). Porous ceramic filters were produced by three common processes, i.e. pressing, extrusion and casting (van Halem et al. 2007). Porous ceramic filter products were characterized by a range of pore sizes, porosity, and cohesion between pores. In addition, it has high specific area, high permeability, small pore size (Zereffa and Bekalo 2017). Therefore, porous ceramic filters are capable to remove suspended solids, pathogenic bacteria and other organisms in drinking water (Bulta and Micheal 2019b; Mustapha et al. 2021; Yang et al. 2020a). It has been reported that the porous ceramic filters are normal lightweight, flexibility, low cost. More important, it could be operated as self-flowing, which could save operational energy (Chen et al. 2021; Yakub et al. 2013). So far, clay has been mixed with saws at a ratio of 50:50. It was furnaced at 900 °C to form the porous ceramic filters (Abubakar et al. 2013; Aliabdo et al. 2014; Elinwa 2006; Ramasamy et al. 2020). Porous ceramic filters are good at removing coliform bacteria. Porous ceramic filters with silver coating could remove 99.9% of bacteria (Jackson and Smith 2018; Ngoc Dung et al. 2019; Simonis et al. 2013). In case of ceramic filter made from a mixture of clay and sawdust at a ratio of 50:50, it could remove coliform bacteria up to 98.2% (Yang et al. 2020b). These ceramic filters could also remove TDS, hardness, nitrate, color and turbidity effectively. For example, it could remove turbidity (90%) and colors (60%). In addition, silver coating was used ceramic filters to increase the ability of disinfection. Besides, silver coating could reduce pore size which could reduce flowrate and increase fouling (Viet Quang et al. 2011; Wang et al.

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2017). Silver coating could combine with the ceramic matrix. As a result, the pore structure was created during the furnace process. Clay and sawdust were mixed with a ratio of 60:40, then it was furnaced at 887 °C. It was cooled before silver coating on the material surface. Ceramic filter has a pore size from 0.6 to 3 µm. The filtration rate was obtained from 0.13 to 3.5 L/hr. During the filtration process, the silver concentration on the porous ceramic could be dissolved and decreased gradually over time (Fu et al. 2022; Naslain 2005). So far, chloramine B or lime chloride has been used for disinfection in the form of tablets or prepackaged solutions (Shaibu-Imodagbe 2013). Granular filter materials based on bentonite or activated carbon powder have been developed (Jjagwe et al. 2021; Saeidi and Lotfollahi 2015). There have been two trends for the clean water problem, i.e. (i) development of advanced non-electrical filtration equipment with membrane filtration and activated carbon; and (ii) development of ceramic filters and biocides. The disadvantage if the first method is expensive. The second method works simply and cheaply in providing clean water. It is essential and meaningful to ensure a sustainable development for the people in rural and mountainous areas by providing high water quality. Therefore, development of a technological solution that is adaptable, simple and suitable to actual conditions is a potential development direction. This is not only in terms of science and technology but also has social significance. In particular, production of porous inorganic materials, i.e. ceramic filters, for water filtration has a great potential. This could provide more choices for people in treating water safely and hygienically before using.

2 Procedures for Making Porous Ceramic Filter Several raw materials from agricultural by-products (rice husk, coir, corn cob…) were mixed with kaolin to make ceramic filter. This procedure includes the following steps, (1) Kaolin is soaked in water to create a smooth consistency. Based on this step, the adhesion of the kaolin was increased. (ii) Raw materials (i.e. rice husks, or coir,…) are sieved through a sieve of size 1–1.5 mm. (iii) Mixture of raw material and kaolin at a selected ratio is poured it into a mold. (iv) The product is taken out of the mold and dry at 40 °C for 6–8 h. (v) After drying, the product is now put into a kiln. The kiln is operated at a temperature-increasing rate of 10 °C in every 5 min. It is gradually increased to 950 °C. The product was kept stable for 4 h. (vi) The product is then taken out of the oven to cool. Schematic diagram of producing porous ceramic filter is presented in Fig. 1. The manufacturing process diagram (Fig. 1) is used to investigate the conditions for making porous ceramic filter by using kaolin with raw materials from agricultural wastes (i.e. rice husk, corn cob, coconut pulp, bagasse). Porous ceramic products from different ratios of kaolin with agricultural wastes (i.e. rice husk, cob, copra, bagasse) were evaluated. In particular, mixture of kaolin and agricultural wastes was prepared at a ratio of 90:10; 80:20; 70:30; 85:15; 75:25; and 65:25. It was mixed 30 mL of water. It was tightly pressed into a mold (with diameter of 7.1 cm, thickness

266 Fig. 1 Schematic diagram of steps to make porous ceramic filter

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Raw material and kaoling Drying, sieving Smooth material with kaolin Water

Flexible material

Pouring into a mold Furnacing at 950oC, 4 hr Porous material

Products

of 0.8 cm). It was then dried in room temperature. The samples were heated at 950 °C for 4 h. After that it was cooled and carried out for further experiments. The conditions of manufacturing porous ceramic filter materials such as furnacing temperature, furnacing time and some other factors were investigated. The technical characteristic of fabricated porous ceramic filter material was determined. In the manufacturing process, several suitable methods such as differential method, X-ray diffraction method were used to investigate the characteristics of porous ceramic filter (Lorente-Ayza et al. 2017; Nighojkara et al. 2019; Shivaraju et al. 2019). Besides, the curve and continuous expansion through high-temperature microscopy or dilatometers and petrographic methods using different types of microscopes were used to observe the structural changes of calcined samples (Ghitulica et al. 2008; Latella et al. 2006). Scanning electron microscopy (SEM, Jeol 5410 LV instrument at Hanoi University of Science and Technology) was used to study the

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surface morphology of the samples. Magnifications of conventional scanning electron microscopes range from a few tens of thousands to several hundred thousand times, the resolution capacity depends on the diameter of the beam focusing on the sample. In addition, the filtration capacity of the product was determined as follows (Bulta and Micheal 2019a; Do and Chu 2022). F=

 V  L/m2 hr A×t

where V is the volume of water passing through (L); A is the area of filter material (m2 ); t is the filter time (hr).

3 Porous Ceramic Filter Produced from Kaolin and Rice Husks Table 1 shows the production of porous ceramic filter from kaolin and rice husks. It is found from Table 1 that the higher kaolin component in the material, the compressive strength is higher. The results of the ratio of husk and kaolin of 10:90 showed the highest compressive strength reached 14.56 MPa. Due to the high compressive strength, the porosity is low, and the ability to filter water is poor. With the material sample with the ratio of rice husk and kaolin 10:90, the filtration yield was very low, only about 0.24 L/m2 hr. The compressive strength of samples with husk size of 1–1.5 mm is much lower than that of samples with husk size of 0.5–1 mm. However, the filtration capacity is still very low. Sample at 35:65 ratio showed a much higher filtration compared to other samples. The filtration capacity was reached 1.59 L/m2 hr at the compressive strength of 2.09 MPa. Table 1 Porous ceramic filter produced from kaolin and rice husks Ratio of kaolin and rice husks

Effective area (m2 )

Flux (L/m2 hr)

Compressive strength (MPa)

10:90

35.24 × 10–4

0.24

14.56

15:85

39.57 ×

10–4

0.93

10.16

20:80

36.30 × 10–4

0.28

8.63

25:75

38.47 × 10–4

0.78

11.40

30:70

38.47 × 10–4

0.65

10.13

35:65

38.47 × 10–4

0.87

11.70

Size of rice husks: 0.5–1 mm

Size of rice husks: 1–1.5 mm (continued)

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Table 1 (continued) Ratio of kaolin and rice husks

Effective area (m2 )

Flux (L/m2 hr)

Compressive strength (MPa)

10:90

38.46 × 10–4

0.04

0.15

15:85

38.46 × 10–4

0.35

0.10

20:80

40.69 × 10–4

0.21

5.58

25:75

41.83 ×

10–4

0.36

0.89

30:70

39.57 × 10–4

0.76

1.60

35:65

41.94 × 10–4

1.59

2.09

10:90

39.57 × 10–4

0.21

6.77

15:85

39.57 × 10–4

0.97

13.12

20:80

39.57 × 10–4

0.42

2.26

25:75

40.69 × 10–4

1.64

6.94

30:70

41.83 × 10–4

1.67

7.03

35:65

39.57 ×

2.86

3.24

Size of rice husks > 1.5 mm

10–4

The filtration rate was greatly improved when ratio of kaolin and rice husks was increased. At the ratio of 35:65, the filtration capacity could reach at 2.86 L/m2 hr and a compressive strength of 3.24 MPa. The filtration rate was low could be due to a reason that at 800 °C, the rice husks have not been completely converted into ash (Foletto et al. 2009; Glushankova et al. 2018; Hossain et al. 2018). As a result, the pores are blocked which prevented water passing (Kennedy et al. 2013). Based on the observations, it was also found that the size of the rice husks has an effect on the filtration rate and the compressive strength of the porous ceramic filter samples.

4 Porous Ceramic Filter Produced from Kaolin Mixed with Corn Cobs The production of porous ceramic filter from kaolin and corn cobs is presented in Table 2. From Table 2, it can be seen that the obtained results are similar to the tests with rice husks and kaolin. At the ratio of 10:90 (corn cobs and kaolin), the obtained results showed that the highest compressive strength was reached 16.58 MPa. Due to high compressive strength, the filtration capacity is very low, only about 0.09 L/m2 hr. The filtration yield of the kaolin sample mixed with the corn cobs size of 0.5–1 mm was lower than that of the kaolin sample mixed with the same size of rice husks. Actually, the compressive strength of samples with rice husks size of 1–1.5 mm is lower than that of samples with husk size of 0.5–1 mm. However, the filtration rate is still very low. A sample at ratio of 35:65 showed that the filtration rate is high compared to other samples. The filtration yield was achieved at 2.39 L/m2 hr with

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Table 2 Porous ceramic filter produced from kaolin and corn cobs Ratio of corn cobs and kaolin

Effective area (m2 )

Flux (L/m2 hr)

Compressive strength (MPa)

Size of corn cobs: 0.5–1 mm 10:90

35.24 × 10–4

0.24

16.58

15:85

37.37 × 10–4

0.09

11.76

20:80

36.30 × 10–4

0.46

16.07

25:75

38.47 × 10–4

0.65

6.17

30:70

36.30 × 10–4

0.51

13.81

35:65

40.69 × 10–4

0.41

1.38

10:90

41.83 × 10–4

0.04

15.19

Size of corn cobs: 1–1.5 mm 15:85

40.69 ×

10–4

0.49

8.59

20:80

41.83 × 10–4

1.00

5.36

25:75

41.83 × 10–4

0.52

4.53

30:70

45.34 ×

10–4

1.84

2.75

35:65

41.83 × 10–4

2.39

1.79

Size of corn cobs > 1.5 mm 10:90

38.47 × 10–4

2.64

6.57

15:85

40.69 × 10–4

0.41

3.29

20:80

39.57 × 10–4

2.53

2.20

25:75

44.16 ×

10–4

3.02

4.71

30:70

40.69 × 10–4

3.07

5.83

35:65

42.99 × 10–4

3.47

4.32

a compressive strength of 1.79 MPa. It means that the filtration yield of the kaolin mixed with the corn cob size of 1–1.5 mm was higher than that of the kaolin mixed with the same size of rice husks. The filtration rate was greatly improved when kaolin was mixed with corn cobs size larger than 1.5 mm. As seen in Table 2, the filtration rates of the samples at ratios of 35:65 and 30:70 were reached at 3.47 and 3.07 L/m2 hr, respectively. It was much higher than that of kaolin mixed with rice husks at the same size (Allen et al. 2010; Atta et al. 2012). However, the pore size of these samples is large. Therefore, it could affect the removal efficiency of SS and bacteria (Abdulwahab et al. 2021; Muhammad et al. 2021).

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5 Porous Ceramic Filter Produced from Kaolin Mixed with Coconut Fiber Table 3 shows the production of porous ceramic filter from kaolin and coconut fiber. As seen from Table 3 that the obtained results are similar to the experiments of kaolin mixed with rice husks. It could be found that the porosity is low due to the high compressive strength of the samples. This resulted in a very low filtration yield, only about 0.09–0.56 L/m2 hr. The sample at the ratio of 35:65 shows that, it has the highest filtration capacity of 0.56 L/m2 hr. The compressive strength of the samples with coconut fiber size of 1–1.5 mm is high. Therefore, the filtration rate is mostly very low. For example, the samples at the ratio of 30:70 and 35:65 showed that the filtration rates are much higher when compared to other samples (Chukwuemeka-Okorie et al. 2018; Hubadillah et al. 2016). The filtration rate could reach 6.89 L/m2 hr, which is higher than that of kaolin mixed with the same size of rice husks and corn cobs (Hubadillah et al. 2022). Table 3 Porous ceramic filter produced from kaolin and coconut fiber Ratio of coconut fiber and kaolin

Effective area (m2 )

Flux (L/m2 hr)

Compressive strength (MPa)

Size of coconut fiber: 0.5–1 mm 10:90

37.37 × 10–4

0.09

11.61

15:85

38.47 ×

10–4

0.35

8.83

20:80

37.37 × 10–4

0.45

8.37

25:75

38.47 × 10–4

0.48

14.25

30:70

38.47 ×

10–4

0.52

8.04

35:65

38.47 × 10–4

0.56

12.82

Size of coconut fiber: 1–1.5 mm 10:90

38.47 × 10–4

0.04

14.90

15:85

37.37 × 10–4

0.04

11.98

20:80

38.47 × 10–4

0.43

6.71

25:75

38.47 ×

10–4

0.78

12.61

30:70

36.30 × 10–4

6.89

11.33

35:65

36.30 × 10–4

6.89

4.25

Size of coconut fiber > 1.5 mm 10:90

36.30 × 10–4

7.71

15.32

15:85

35.24 × 10–4

11.35

10.31

20:80

30.18 × 10–4

10.07

11.41

25:75

35.24 × 10–4

8.63

16.32

30:70

36.30 × 10–4

6.61

10.53

35:65

35.24 ×

11.35

10.49

10–4

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The filtration rate was greatly improved when kaolin was mixed with the coconut fiber size of higher than 1.5 mm. The compressive strength of this test is also higher than that of the samples with rice husks and corn cobs. In this test, the ratio of coconut fiber and kaolin was at 15:85 and 35:65, which could result in a high filtration rate of 11.35 L/m2 hr.

6 Porous Ceramic Filter Produced from Kaolin Mixed with Bagasse The production of porous ceramic filter from kaolin and bagasse is presented in Table 4. It is found from Table 4 that the obtained results are similar to the experimental works of kaolin mixed with rice husks. The samples of kaolin mixed with bagasse at a small size of 0.5–1 mm have high compressive strength and low porosity. This results in a very low filtration rate in the range 0.05–0.45 L/m2 hr. At a ratio of 35:65, the highest filtration rate was reached about 0.45 L/m2 hr. A compressive strength of the samples of kaoline mixed with with bagasse size of 1–1.5 mm is high. Therefore, the filtration rate is mostly very low. The observations show that at this ratio, the bagasse was not burnt completely. Therefore, at the ratio of 35:65, the filtration capacity was reached at high value of 11.02 L/m2 hr and a compressive strength of 8.84 MPa. The filtration capacity of this sample was higher than that of the kaolin mixed with the same size of rice husks and corn cobs (Acchar and Paranhos 2012; Anukam et al. 2017; Riofrio et al. 2022). The filtration rate of the experimental tests was improved when the bagasse size was higher than 1.5 mm. Observations show that, at that condition, the bagasse was completely burnt. In this experiment, sample at ratio of 35:65 had also a high filtration rate of about 10.06 L/m2 hr. Based on the observations, it could be seen that the filtration capacity of products from kaolin mixed with agricultural by-products Table 4 Porous ceramic filter produced from kaolin and bagasse Ratio of bagasse and kaolin

Effective area (m2 )

Flux (L/m2 hr)

Compressive strength (MPa)

Size of bagasse: 0.5–1 mm 10:90

36.30 × 10–4

0.06

14.64

15:85

35.24 ×

10–4

0.05

16.33

20:80

35.24 × 10–4

0.18

13.85

25:75

36.30 × 10–4

0.26

13.35

30:70

35.24 ×

10–4

0.24

15.56

35:65

37.37 × 10–4

0.45

11.99

Size of bagasse: 1–1.5 mm (continued)

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Table 4 (continued) Ratio of bagasse and kaolin

Effective area (m2 )

Flux (L/m2 hr)

Compressive strength (MPa)

10:90

34.19 × 10–4

0.24

16.58

15:85

35.24 × 10–4

0.24

12.58

20:80

36.30 × 10–4

0.60

16.07

25:75

36.30 ×

10–4

1.33

3.38

30:70

36.30 × 10–4

1.29

6.41

35:65

36.30 × 10–4

11.02

8.84

10:90

36.30 × 10–4

0.69

15.48

15:85

35.24 × 10–4

0.95

16.07

20:80

37.37 ×

10–4

1.74

14.88

25:75

36.30 × 10–4

2.75

13.44

30:70

37.37 × 10–4

3.52

8.32

35:65

36.30 ×

10.06

8.68

Size of bagasse > 1.5 mm

10–4

(rice husk, corn cob, coir, bagasse) was strongly dependent on the size of agricultural by-products (Figueiredo and Pavía 2020; Torres Agredo et al. 2014; Xu et al. 2018). The agricultural by-product size of higher than 1.5 mm could give the best filter performance. However, the filtration capacity through these tests is still low. It should be improved by further works.

7 Effect of Furnaced Temperature and Time on the Properties of Porous Ceramic Filters The observations from the works show that the ratio of 50:50 between kaolin and agricultural by-products could give a good filtration capacity (Abdulwahab et al. 2021; Atta et al. 2012). Therefore, this ratio of 50:50 was used to evaluate the effect of furnaced temperature and time on the properties of porous ceramic filters. In this test, a mixture ratio of 50:50 between kaolin and rice husks (with size 1–1.5 mm) was used. It was then calcined at different temperature ranges of 750, 800, 850, 900, 950, 1000 °C for 2 to 8 h. The obtained results are presented in Table 5. It could be seen from Table 5 that the calcination temperature has a great influence on the filtering ability of porous ceramic filters. Rice husks could be converted completely into ash at the calcination temperature of higher than 900 °C. It could help to form transparent pores (Allen et al. 2010; Hubadillah et al. 2016). As a result, the filtration rate was much higher than the samples which were fired at lower temperatures. Besides, it was also found that the compressive strength of the samples which was fired at 950 °C was the lowest (just about 5.88 MPa). Therefore,

Production and Application of Porous Ceramic Membrane for Water … Table 5 Effect of furnaced temperature and time on the properties of porous ceramic filters

Factors

Effective area (m2 )

Flux (L/m2 hr)

273

Compressive strength (MPa)

Furnaced temperature (o C) 750

36.29 × 10–4

37.73

11.41

800

36.29 × 10–4

43.54

11.89

850

36.29 × 10–4

88.18

16.07

900

31.15 × 10–4

160.51

15.46

950

32.15 × 10–4

174.96

5.88

1000

31.21 ×

10–4

115.35

15.57

32.15 × 10–4

41.78

1.9

Furnaced time (hr) 2 3

32.15 × 10–4

155.99

5.80

4

32.15 × 10–4

226.21

0.88

6

33.16 × 10–4

150.78

2.32

8

31.15 × 10–4

180.58

2.49

the filtration capacity was reached the largest value of about 174.96 L/m2 hr which was corresponded to at the highest porosity. After that, a mixture ratio of 50:50 between kaolin and rice husks with the size of 1–1.5 mm was calcined at 950 °C at different times of 2, 3, 4, 6, 8 h. As seen from Table 5, the filtration rate has a large difference when the heating time of the material was increased from 2 to 8 h. The rice husks were not converted into ash completely at a short burning time. This could be a reason to seal the voids and obstruct the flow. It was found that the calcination time of 4 h could give the lowest compressive strength (about 0.88 MPa). It means that the materials could have the best porosity (Naddafi et al. 2005). This observation is very consistent with the theory (Yang et al. 2020b). At such condition, the filtration rate was reached at the highest value of 226.21 L/m2 hr.

8 Surface Properties of Porous Ceramic Filter Figure 2 shows the photos of the porous ceramic filter before and after furnacing. The porous ceramic filter has a pot shape. The characteristics of the product include an outside diameter of 12 cm; inside diameter of 4 cm; wall thickness of 1.3 cm; and its height of 16 cm. The material sample was imaged and tested by SEM to see the surface characteristics of the material (Fig. 3). As seen from Fig. 3, it was found that the material formed a lot of voids. The porosity of the materials was quite high. The average pore size of the porous ceramic material sample is about 0.46–1.2 µm. This result could be compared with the results of ceramic filter from other works (Mustapha et al. 2021;

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Fig. 2 Samples of porous ceramic filter materials before heating (left) and after heating (right)

Fig. 3 SEM of porous ceramic material surface

Nighojkara et al. 2019; Yang et al. 2020b). The porous ceramic filter (with surface are of 0.11 m2 ) was used to test with surface water samples. The obtained results show that the water quality after filtration was improved. The average filtration capacity is about 14.03 L/m2 hr, which could produce about 1.5 L/h of clean water. Turbidity of the sample was lower than 2 NTU. Coliform in the samples was removed at high efficiency of 99.54%. The quality of the water after filtration was met a drinking water standard of the Ministry of Health.

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9 Conclusions and Remarks Based on the obtained results, it could be concluded that it is possible to make porous ceramic filter from a mixture of kaolin with agricultural by-products. The proportion of kaolin and by-products with different sizes has been investigated. The heating time and heating temperature were investigated. Those factors have a greatly affect the durability and filtration yield of the porous ceramic filter. A ratio of 50:50 between kaolin and rice husk (with size 1–1.5 mm) could give high filtration capacity when it was furnacing at 950 °C for 4 h. The porous ceramic materials could be used for water purification, ensuring the quality of domestic water for rural and mountainous areas. The obtained results could contribute to provide more choices for people in the application of simple porous ceramic materials to filter domestic water. Further work should be focused on improvement of the filtration efficiency. The aesthetics of the porous ceramic samples should be improved as well. In addition, an impregnation of nanosilver and Biopag-D biocide on porous ceramic filters could be tested to enhance the disinfection efficiency. Acknowledgements The authors would like to thank the support of the Hanoi University of Science and Technology. The supports by Center for Advanced Materials Technology, National Center for Technological Progress were sincerely grateful.

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Nanomaterials in Wastewater Management Lavaniya Nagrath, Hina Bansal , and M S Smitha

Abstract The challenge of providing safe and clean water to humans and the environment is a global issue. Water is the most indispensable element essential for the survival and development of life on Earth. Expeditious rises in populations, extensive agriculture practices, and expanding industrialization and urbanization have enormously contributed to wastewater generation, which has made water more polluted and unfit as well as deadly to drink. Innumerable individuals die annually as a result of ailments caused by drinking contaminated water. Efficacious purification of polluted water is thus the matter of greatest importance, and the development of a cheaper and efficient polluted water purification technology is the need of the hour. The most pertinent methodology that is exceptionally effective is the utilization of nanomaterials in wastewater management. Nanomaterials are one of the paramount aspects of the complex field of nanotechnology. Nanomaterials incorporate a high surfaceto-volume proportion, simplicity of functionalization, a high affectability and reactivity, and a high adsorption limit, which makes them compatible for application in wastewater management. The utilization of metal nanoadsorbents such as iron oxide, titanium oxide, and manganese oxide, carbon nanotubes, and antimicrobial nanomaterials has received so much attention due to their unique properties. This chapter focuses on the development and utilization of different nanomaterials that would contribute towards wastewater management. Keywords Antimicrobial nanomaterials · Carbon nanotubes · Metal nanoadsorbents · Nanomaterials · Nanotechnology · Wastewater management

L. Nagrath · M. S. Smitha (B) Amity Institute of Microbial Technology, Amity University, Uttar Pradesh, Sector-125, Noida, U.P 201313, India e-mail: [email protected] H. Bansal (B) Amity Institute of Biotechnology, Amity University, Uttar Pradesh, Sector-125, Noida, U.P 201313, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_14

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1 Introduction Water is the most essential natural element for the existence and survival of life on, in, and above the earth as the human body is mostly made up of water, on an average around 60% (Definition of Freshwater Resources 2021). Contamination of water is one of the prime concerns faced by people in their day-to-day life; the challenge of providing safe and clean water to humans and the environment is a global issue (Kurniawan et al. 2012). Water bodies are drying day-to-day because they are utilized to the hilt, and the hazardous and toxic industrial, residential, and other wastes are causing various maladies. Individuals die every year due to maladies induced by drinking polluted water. Thus, it is necessary to decontaminate the water bodies by treating the wastewater efficiently (Olvera et al. 2017; Singha and Mishrab 2020; Kamali et al. 2019). The conventional or physicochemical techniques to address wastewater treatment include adsorption, coagulation, accumulation, flocculation, precipitation, electro dialysis, membrane separation, and aerobic and anaerobic oxidation techniques. Physicochemical wastewater treatment techniques generally include substances like Cl compounds, NH3 , NaOH, permanganate, alum, HCl acid, ozone (O3 ), and ferric complexes, coagulation and filtration aids, ion exchange resins, and intensive mechanical methods. These conventional techniques are not adequate to remove the harmful toxins from the contaminated wastewater (Kumar et al. 2014; Qu et al. 2013; Rajasulochana and Preethy 2016; Zinicovscaia 2016). Nanotechnology is the best and the highly developed approach for wastewater treatment. Nanotechnology includes the refinement of the substance at the atomic as well as molecular levels to create improved techniques and systems with different essential properties (Sreedharan et al. 2019a; Khan et al. 2019; Jana et al. 2017; Jain 2019). Nanotechnology is a promising technology; it is remarkably used in a variety of areas including wastewater treatment. Due to their large surface area, bigger size, and ease of functioning, the nanostructures provide exceptional opportunities to create tremendously effective catalysts and redox-active media for wastewater purification, Nanomaterials have been very effective in eliminating the pollutants from wastewater such as organic solvents; biological toxins; inorganic solvents; heavy metals; and pathogens that induce maladies such as typhoid and cholera (Kumar et al. 2014).

2 Wastewater Composition and Source Composition Wastewater is composed of innumerable toxins, dangerous salts, pathogens, and metals (Fig. 1). It is a mixture of 99.9% water and 0.1% of numerous substances such as suspended solids and organic waste; this includes kitchen waste, body waste, paper waste, dried leaves, etc. Biodegradable dissolvable organics such as lipids, proteins, and carbohydrates; inorganic solids such as salts, sediments, and heavy

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Fig. 1 Composition of wastewater

metals, particulate stuff, numerous microorganisms, micro-pollutants, and nutrients. Around 63% of phosphate compounds are found to be linked as a soluble fraction in wastewater (Warwick et al. 2013; Templeton and Butler 2011). Sources: Wastewater emanates from different sources, which involves three major sectors; domestic, industrial, and agricultural sectors (Fig. 2) (Ahmad et al. 2016). The

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Fig. 2 Sources of wastewater

domestic sector comprises general waste and wastewater from day-to-day household activities. The industrial sector comprises wastewater from numerous industries like pharmaceutics, chemical, metal, food and beverage, paper and pulp, mines, and thermal power. Although these wastewaters are rich in both organic and inorganic nutrients, their excess amounts will increase the nutrient and mineral content in the water bodies, which will increase the growth of the plant and other microorganisms resulting in a decrease in oxygen level in the water bodies (Rajasekhar et al. 2018). Mostly, all water sources require pure and fresh quality water, especially industries, but in return, large volumes of polluted, dirty, and contaminated water are generated and flown into large water bodies, polluting them (Jassby et al. 2018; Deshpande et al. 2020).

3 Nanomaterials in Wastewater Treatment Nanomaterials are one of the essential aspects of the field of nanotechnology. Nanotechnology is the best and the highly developed approach for wastewater treatment (Deshpande et al. 2020). There are different explanations for the accomplishment of nanotechnology, and researchers are still dealing with an additional upgrade

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of its utilization. Nanomaterials are substances that fall in the size range of 1–100 nm; around 50% of these substances fall in the above-mentioned range (Singh et al. 2018). Depending upon their charges, sizes, shape, solubility, and surface area, they have distinctive physical, biological, and chemical properties. Nanomaterials have a great capacity for absorbing, interacting, and reacting because of their minute size and a large fraction of atoms at the surface (Khin et al. 2012). They offer a significant advantage when it comes to treating deep water bodies and areas that are typically overlooked by other wastewater treatment methods.

3.1 Metal Nanoparticles Metal nanoparticles are economical nanoparticles with excellent adsorptive characteristics. These are primarily used to get rid of heavy metal contaminants in water. Ferric oxide (F2O3), titanium oxide (TiO2 ), manganese dioxide (MnO2 ), magnesium oxide (MgO2), and aluminium oxide (Al2O3) are among the metal-based nanoparticles that have been researched and discovered to be effective to get rid of heavy metal contaminants from sewage sludge (Hua et al. 2012). Nanosized metal oxides are thought to be more effective and useful than ordinary sorbents because of their high surface-to-volume ratio. The chemical interaction between the adsorbent and the adsorbate is improved as a result of this. The pH of the solutions has an impact on the surface chemistry of the nanoparticles and changes the rate of heavy metal adsorption significantly. Metal-based nanoadsorbents have a number of advantages. They are, for instance, simple to synthesize, less hazardous, have a huge surface area for interactions, and are chemically inert. In comparison to other adsorbents, these features distinguish and appeal to metal oxide nanoadsorbents (Kumar and Chawla 2014). Single or combinations of metal oxides can be utilized for wastewater treatment depending on the type of pollutant.

3.1.1

Metal Oxides Nanoparticles

i. Iron Oxides Nanoparticles Over the past few years, iron oxide nanoparticles have become increasingly popular to get rid of heavy metals, because of their efficiency and accessibility. Nanoparticles include magnetic magnetite (Fe3 O4 ), magnetic maghemite (-Fe2 O4 ), and nonmagnetic hematite (-Fe2 O3 ). Sorting and retrieving, nanosorbent compounds from untreated wastewater are a key challenge for sewage treatment due to their small size. With the use of an external magnetic field, magnetic magnetite (Fe3 O4 ), and magnetic maghemite (-Fe2 O4 ), they may be easily sorted and retrieved from the sludge (Lei et al. 2014). As a result, they’ve proved successful in removing heavy metals from various water systems as sorbent materials (Tan et al. 2014).

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Iron oxide nanoparticles have made some significant improvements in their engineering in order to improve adsorption efficiency and eliminate interference from other metal ions. Numerous different ligands such as ethylene diamine tetra acetic acid (EDTA), L-glutathione (GSH), mercaptobutyric acid (MBA), propionic acid, hepta(ethylene glycol) (PEG-SH), and meso-2,3-dimercaptosuccinic acid (DMSA) or polymers have been added to modify their adsorption (e.g., copolymers of acrylic acid and crotonic acid) (Ge et al. 2012). The insertion of a wide range of functional molecules into a variable ligand shell has been reported to allow for the introduction of a wide range of functional molecules into the shell while maintaining the Fe3O4 nanoparticle properties. Furthermore, a polymer shell has been discovered to be capable of preventing particle aggregation and improving nanostructure dispersion stability (Khaydarov et al. 2010). ii. Titanium Oxide Nanoparticles Titanium dioxide nanoparticles are rapidly being utilized in commercial products, and there’s a good chance they’ll end up in municipal sewage flowing to centralized wastewater treatment plants (WWTPs). CBD was used to make TiO2 nanosheets. Such tools’ maximal resistivity and low optical transmission limit their use as optical constituents in thermoelectric materials, necessitating the development of both optical and electrical behaviours. Furthermore, there is a scarcity of data on the characteristics of TiO2 nanoparticles in a chemical environment. Alkaline nanosheet preparation pollutes the environment; typically, it produces hydroxides, which might degrade the quality of the nanosheet. It would be difficult to deposit TiO2 nanoparticles of the highest quality in an alkaline chemical immersion environment until the obstacle of the preparation of TiO2 is overcome (Abel et al. 2021). Since 1972, when Fujishima and Honda detected electrochemical photolysis of water on a TiO2 semiconductor electrode; photocatalytic activity has piqued interest as a possible new technique. The photocatalytic degradation technique has been effectively utilized for the breakdown of contaminants in water and wastewater in recent years (Guesh et al. 2016). Contaminants can be gradually oxidized into low molecular weight intermediate products and subsequently changed into CO2 , H2 O, and anions such as NO3 - , PO4 3- , and Cl- in the presence of catalyst and light (Rawal et al. 2013). Metal oxide or sulphide semi-conductors make up the majority of typical photocatalysts, with TiO2 being the most studied in recent decades. TiO2 is the most outstanding photocatalyst to date due to its strong photocatalytic activity, low price, photostability, and chemical and biological stability (Imamura et al. 2013). To generate charge separation within the particles, TiO2 ’s significant band gap energy (3.2 eV) necessitates UV irradiation. TiO2 produces reactive oxygen species (ROS) in response to UV irradiation, which can totally destroy pollutants in a short reaction time. Furthermore, TiO2 NPs have a low selectivity, making them ideal for degrading a wide range of pollutants, including chlorinated organic chemicals, polycyclic aromatic hydrocarbons, phenols, pesticides, dyes, arsenic, cyanide, and other heavy metals (Lu et al. 2016).

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Furthermore, hydroxyl radicals produced by UV irradiation (400 nm) enable TiO2 NPs to harm the function and structure of a variety of cells. TiO2 NPs’ photocatalytic characteristics can destroy a wide range of microorganisms, including Gramnegative and Gram-positive bacteria, fungus, algae, protozoa, and viruses. TiO2 is the most outstanding photocatalyst to date, with photocatalytic activity, a fair price, photostability, and chemical and biological stability (Foster et al. 2011). iii. Zinc Oxide Nanoparticles Zinc oxide, a vital component used in the rubber and pharmaceutical industries, is being explored as an antibacterial agent (Rajeswari and Venckatesh 2021). Zinc oxide exhibits antibacterial characteristics at the nanoscale, making it ideally fit for a variety of applications (Fatemeh Elmi et al. 2014). Apart from TiO2 NPs, ZnO NPs have emerged as another efficient nanoparticle in the field of photocatalysis for water and wastewater treatment due to their special distinctive characteristics, such as a direct and wide band gap in the near-UV spectral region, strong oxidation ability, and good photocatalytic property (Lu et al. 2016). ZnO NPs are environmentally beneficial since they are compatible with organisms, making them ideal for water and wastewater treatment. Furthermore, because their band gap energies are nearly identical, ZnO NPs have similar photocatalytic capabilities to TiO2 NPs. ZnO NPs, on the other hand, have a lower cost than TiO2 NPs. Furthermore, compared to some semiconducting metal oxides, ZnO NPs can absorb a larger range of solar spectrum and more light quanta (Gomez-Solís et al. 2015). The light absorption of ZnO NPs, like that of TiO2 NPs, is limited in the ultraviolet light range due to their large band gap energy. Furthermore, photocorrosion impedes the utilization of ZnO NPs, resulting in rapid recombination of photogenerated charges and consequently limited photocatalytic efficacy. Metal doping is a typical approach for improving the photodegradation efficiency of ZnO NPs. A variety of metal dopants, including anionic dopants, cationic dopants, and co-dopants, have been tested (Lee et al. 2016). Furthermore, several research have demonstrated that combining ZnO NPs with other semiconductors such as CdO, CeO2 , SnO2 , TiO2 , graphene oxide (GO), and reduced graphene oxide (RGO) is a viable way to improve photodegradation efficiency (Lu et al. 2016).

3.1.2

Zero-Valent Metal Nanoparticles

i. Iron Nanoparticles In recent years, researchers have shown interest in various zero-valent metal particles such as Fe, Zn, Al, and Ni, in wastewater treatment. In the presence of water, nanozero-valent AI is thermodynamically unstable because of its exceptional reducing ability. It also favours the formation of oxides and hydroxides on the surface, obstructing the electron transport from the metal surface to the impurities. When

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compared to Fe, Ni has a lower standard reduction potential, reflecting a weaker reducing capacity. Despite its lower reduction ability, Fe has a number of distinct advantages over Zn for its use in wastewater treatment, including enhanced precipitation and oxidation absorption capabilities and a low cost. As a result, zero-valent Fe nanoparticles have received the most attention among other zero-valent metal nanoparticles. Nano zerovalent iron (nZVI) very large specific surface area because of their extremely small size as a result deposit good absorption properties as strong reducing abilities (Wang et al. 2014). They show excellent performance in the removal of contaminants because of these characteristics. Fe0 can be oxidized by H2 O or H + under anaerobic circumstances to produce Fe2+ . Fe2+ will be oxidized to Fe3+ in the oxidation–reduction process between nZVI and impurities, which can create Fe(OH)3 when the pH rises. As a popular and effective flocculant, Fe(OH)3 aids in the removal of pollutants such as Cr (VI). Furthermore, because ZVI donates two electrons to O2 to form H2 O2 , it may break down and oxidize a wide range of organic molecules in the presence of dissolved oxygen (DO). ZVI can decrease the resulting H2 O2 to H2 O. Furthermore, the interaction of H2 O2 with Fe2+ (known as the Fenton reaction) can produce hydroxyl radicals (HO) with a high oxidizing capacity for a wide spectrum of organic compounds (Fu et al. 2014). nZVI has been successfully used in the removal of a wide range of contaminants, including halogenated organic compounds, nitroaromatic compounds, organic dyes, phenols, heavy metals, inorganic anions such as phosphates and nitrates, metalloids, and radio elements, using the effects of adsorption, reduction, precipitation, and oxidation (Lu et al. 2016). Furthermore, studies on the use of nZVI in water and wastewater treatment are not restricted to water or laboratory experiments. nZVI has also been used in soil remediation in recent years, including pilot-scale and full-scale treatments at genuine water-polluted field locations (Chen et al. 2020). ii. Silver Nanoparticles As silver nanoparticles (Ag NPs) are very poisonous to microorganisms, they offer a variety of antibacterial properties against a wide spectrum of bacteria, viruses, and fungi. Silver nanoparticles have been widely employed for water disinfection because they are a good antibacterial agent (Lu et al. 2016). The mechanism of Ag NPs’ antibacterial activities is not well understood and is still being researched. Recently, it has been revealed that it can stick to the bacterial cell wall and then penetrate it, causing structural changes in the cell membrane and enhancing its permeability. Furthermore, when Ag NPs come into touch with bacteria, free radicals might form. They have the potential to disrupt cell membranes and are thought to be responsible for cell death. Furthermore, because DNA is genetic material, Ag NPs can interact with it and hence destroy it because it contains rich sulphur and phosphorus elements. This is yet another explanation for cell death caused by Ag NPs (Dhanalekshmi and Meena 2016). Furthermore, dissolving Ag NPs release antimicrobial Ag + ions, which can bind with the thiol groups of several important enzymes, inactivate them, and disturb normal cell activities (Prabhu and Poulose 2012). In recent years, with the advancement of nanotechnology, Ag NPs

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have been successfully used in water and wastewater treatment. Direct application of Ag NPs may result in various issues, such as their proclivity to aggregate in aqueous conditions, which gradually diminishes their efficiency over time (Li et al. 2012). Because of their high antibacterial activity and attachment to filter materials, Ag NPs connected to filter materials have been regarded as promising for water disinfection cost-effectiveness (Quang et al. 2013). Ag NPs have been deposited on the cellulose fibres of an absorbent blotting paper sheet via in situ silver nitrate reduction. During filtering through the sheet, the Ag NP sheets exhibited antimicrobial potential towards not only E. coli and Enterococcus faecalis suspensions but also inactivated bacteria. Moreover, the silver loss from the Ag NP sheets was lower than the Environmental Protection Agency (EPA) and World Health Organization (WHO) standards for silver in drinking water (WHO). Filtration through paper coated with Ag NPs could therefore be an effective emergency water treatment for water contaminated by microbes. Moreover, chemically decreased Ag NPs have been incorporated into polyethersulfone (PES) microfiltration membranes. The activity of bacteria near the membranes was found to be strongly suppressed (Ferreira et al. 2015). iii. Zinc Nanoparticles Zinc nanoparticles are a type of nanoparticles that are made up of zinc. Even though iron has been the main focus of most research on pollutant degradation in water and wastewater treatment by zero-valent metal nanoparticles, Zn has also been taken into account. In comparison to Fe, Zn is a stronger reductant due to its lower standard reduction potential. As a result, zinc nanoparticles may degrade contaminants more quickly than nZVI. The dehalogenation reaction has been the basis of most research on nano-zero-valent zinc (nZVZ). Instead of the size of the particle or the surface morphology, solution chemistry was found to have a greater impact on nZVZ’s CCl4 reduction rates. When the reactivity of various types of nZVI and nZVZ was compared, it was shown that under favourable conditions, nZVZ may degrade CCl4 faster and more thoroughly than nZVI (Mohseni-Bandpi et al. 2016). Despite the fact that various studies have shown that nZVZ can reduce pollutant levels, its use is primarily limited to the breakdown of halogenated organic chemicals, particularly CCl4. Until now, nZVZ has only been used to remediate a few different types of pollutants (Mohseni-Bandpi et al. 2016).

3.2 Zeolites Zeolites are 3D, crystalline microporous materials having well-defined voids and channels of various sizes that are freely reachable via openings with very well molecular dimensions that preserve Al, silicon, and O2 in their original structure (Ali et al. 2020). Zeolites are silicate minerals that can be found in nature but can also be produced as magnetically modified zeolite, bio-zeolite, and other materials (Nassar et al. 2017). Because of their water stability, low manufacturing costs, large surface area, selectivity, and natural environment compatibility, zeolitic nanoparticles

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as adsorbents have gained a lot of interest in environmental applications. Numerous investigations have proven their exceptional efficacy in removing metal cations from wastewater (Pandey et al. 2015). Zeolite has a variety of industrial research applications, but its adsorbent property is the most studied because of its capacity to regenerate and reuse, making it a good choice for wastewater treatment. Zhao et al. created cubic zeolite, a microporous crystalline aluminosilicate zeolite made up of Na2 O and Al2 O3 . It is made from natural halloysite minerals using nanotubular structures as a source material for ammonium ions (NH4 + ) adsorption from wastewater. The maximal adsorption capacity for NH4 + ions in prepared Na. A zeolite was determined to be 44.3 mg/g. The developed adsorbent system was reusable, and it demonstrated that it could be used to remove NH4 + contaminants from wastewater (Mohseni-Bandpi et al. 2016).

3.3 Carbon Nanotubes Carbon nanomaterials include carbon nanotubes (CNTs), carbon beads, carbon fibres, and nanoporous carbon (Khin et al. 2012). Carbon nanoparticles are a fascinating class of materials with unique physical as well as electrical properties that make them intriguing for both basic study and certain potential applications, specifically in adsorption studies. Their advantages in water and wastewater treatment are the following: (1) their high capacity to adsorb a wide spectrum of pollutants, (2) their quick kinetics, (3) their huge specific surface area, and (4) their selectivity for aromatics (Khin et al. 2012). Carbon nanotubes (CNTs), carbon beads, carbon fibres, and nanoporous carbon are examples of CNMs. CNTs have received the most interest and have made significant progress in recent times. Graphene sheets that are coiled into cylinders as thin as 1 nm in diameter are used to make carbon nanotubes (Chatterjee and Deopura 2002). Carbon nanotubes (CNTs) have aroused interest as a promising material due to their unique properties. Due to their unusually large specific surface area and abundant porous structures, CNTs exhibit outstanding adsorption capacities and high adsorption efficiencies for a variety of contaminants, including dichlorobenzene (Peng et al. 2003), ethyl benzene (Lu et al. 2008), Zn2 + (Cho et al. 2010), Pb2+, Cu2+, and Cd2+ (Li et al. 2003), as well as dyes (Madrakian et al. 2011). CNTs can be further divided into two types based on their super structures, (1) multiwalled carbon nanotubes (MWCNTs), which are made up of concentric cylinders with multiple layers having a spacing of about 0.34 nm between them, and (2) single-walled carbon nanotubes (SWCNTs), which are made up of single layers of graphene sheets that are seamlessly rolled into cylindrical tubes (Zhao and Stoddart 2009). MWCNTs and SWCNTs have both been used to remove pollutants from water in recent years. To boost their adsorption, tensile, refractive, and thermal capabilities, carbon nanotubes are routinely combined with other elements or types of support (Ray and Shipley 2015). The functionalization of CNTs increases the amount of N, O2 , or other groups

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on their surface, improves their dispersibility, and hence boosts specific surface area (Adeleye et al. 2016). Gupta et al., for example, published a study employing carbon nanotubes as a support for magnetic iron oxide (Gupta et al. 2011). A “composite” adsorbent was created by combining the adsorption capabilities of CNTs with the magnetic properties of iron oxide to extract chromium from water. The “composite” adsorbent, in addition to having outstanding adsorption capabilities, may be conveniently water is separated using an external magnetic field. Despite their exceptional properties, carbon nanotubes (CNTs) are primarily limited in their development and applications due to their production of lower volume and high cost. Furthermore, CNTs cannot be employed to construct structural components without the aid of a supporting medium or matrix (Chatterjee and Deopura 2002).

3.4 Nano-membranes One of the most common methods for removing contaminants from water is membrane filtration. Membranes provide a physical barrier for pollutants, depending on their pore size and molecule size. It is now regular practise to filter water and make it drinkable using the RO (reverse osmosis) process (Cheriyamundath and Vavilala 2021). In the same way, nano-based membranes are employed in industry to remove inorganic substances from water, such as industrial contaminants. The benefits of nano-membrane-based water treatment are ease of use, high efficiency, and little space requirements. Furthermore, the filtering capacity can be improved by utilizing the right chemicals, nanoparticles, or a mix of the two (Pendergast and Hoek 2011). Nano-membranes with anti-fouling, antibacterial, improved permeability, selectivity, photocatalytic, and other features can be manufactured depending on the application (Munnawar et al. 2017). Following that, we’ll go over several nanoengineered membrane-based filters. Membrane filters with nanofibres fall under the first type. They have a lot of surface area, a high surface-to-volume ratio, porosity, and interconnectivity, and they’re easy to make with electro-spin. Nanofibre pore size and form, unlike other porous materials, can be changed or controlled to suit the needs of the application (Ramakrishna et al. 2006). These membranes are capable of effectively filtering micron-sized particles. Even germs and viruses can be filtered out, thanks to the improved composite nanofibre membrane with ultra-fine cellulose (Sato et al. 2011). Nanomaterials with a high specific surface area, paired with nanofibres created by electrospinning, can be used to create excellent absorbents (Min et al. 2016). Chitosan electrospun nanofibre, for example, can be used to eliminate arsenate traces from water. The adsorption mechanism of these nanofibres was boosted by the inclusion of functional groups such as –NH, –OH, and C–O. This is easily reconstituted with NaOH solution and can be reused (Min et al. 2016). Another form of membranebased filter with significant pollutant purification process capability is nanocomposite membranes. The nanoparticles are integrated into a matrix of macroscopic elements

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in this case. Membrane qualities like permeability, selectivity, and antifouling can all be improved using these combinations (Ursino et al. 2018). A blend of adsorption and filtration can be utilized to enhance the wastewater treatment. Zeolite nanoparticles were infused into a polysulphone membrane, which increased the membrane’s adsorption and filtration efficiency. It was also demonstrated that this blend was effective in eliminating heavy metals such as lead and nickel from liquids (Ursino et al. 2018).

4 Nano-informatics for Wastewater Treatment The application of bioinformatics to nanotechnology is known as nano-informatics. It’s a multidisciplinary discipline that focuses on developing methodologies and computational tools and servers for better comprehension of nanomaterials, their interactions, and properties, with living organisms, as well as more effectively applying that knowledge. The infrastructure of nano-informatics includes various file formats, data repositories, and ontologies for nanomaterials (Hoover et al. 2018). It can be used to improve roadmaps in central research, health, and manufacturing by providing high-throughput data-driven methodologies to be used to examine large sets of experimental results (Fig. 3). Nanoparticles have various distinctive features that are essential to be quantified for a comprehensive explanation, like shape, size, properties, surface, dispersion

Fig. 3 Nano-informatics at the nexus of central research, ecological strength, and manufacturing

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state, and crystallinity, along with their biochemical conformation and concentration. Furthermore, nanoparticle preparations are frequently non-uniform, requiring distributions of these attributes to be defined (Singh et al. 2014; Sreedharan et al. 2019b). Their molecular scale properties impact their macroscopic physical and chemical characteristics, also their living sequels. Nano-informatics is defined as the utilization of knowledge at the junction of health and welfare and burgeoning nanotechnology for the effective development and execution of possible nanotechnology applications. It provides high-throughput data-driven strategies to examine and improve investigational outcomes with respect to central research, ecological strength, and manufacturing (Iglesia et al. 2011). Although numerous tactics have been used to promote nanotechnology, a novel strategy centred on the organization, assembly, elucidation, and projection of nanoparticle and physicochemical composition is gaining traction. The use of computer technologies, information science, and molecular simulations as an essential methodology in nanobiotechnology and Nano-informatics research has been gaining traction; these approaches are capable of producing qualitative notions, insights, and design proposals. Nano-informatics is used to characterize elements and materials with applications in nano- and biotechnology by modelling and simulating them, in various cases at the atomic level, using computational chemistry methodologies (Thierry 2009). However, introducing alien substances into the complicated system of the human body is a difficult task. Computer-assisted technologies are a logical choice for accelerating the development of life science innovation. To evaluate the limitations of computational approaches used in this sector, novel strategies should be created and evaluated for simulation, annotation and nanoparticle. The application of modern information approaches to nanobiotechnology challenges could, among other things, speed up the advancement of highly precise biomedical therapies, boost their efficacy, and reduce their side effects (Sreedharan and Singh 2019). The lack of a common language as a means of exchanging knowledge is a major roadblock, particularly in new fields. This highlights the importance of governmental and other databases organizing and/or developing common vocabularies and ontologies in order to collect data more meaningfully. The nature and volume of new data generated by nanotechnology activities, on the other hand, necessitate the use of GRID technologies for quick analysis. Multi-scale datasets are massive, and analyses combining data from multiple sources can only be done in a distributed environment, such as GRID systems, which is the only realistic way to work with this massive amount of data that will be combined with genomics in the near future (Hoover et al. 2018). Further, we can examine futuristic nanobiotechnology informatics by classifying it into four distinct groups: societal characteristics, new extensions to standard bioinformatics approaches, novel modelling trials, and the emerging appearance of collaborative atmospheres, the latter being a hallmark of almost each novel Nano-informatics inventiveness.

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At the nanoscale level, a computational approach is critical in the initial phases of project expansion. Computer molecular design has become a more important topic in exploring novel nanomaterials in recent years, owing to increased computational capacity and the consolidation of several computational chemistry approaches. Design, model, simulate, and envisage nanomaterials and nanoparticles such as dendrimers, metallic nanoparticles, nano-capsules, nanospheres, and quantum dots using computational chemistry. These nanoparticles have applications in both wastewater treatment and nanomedicine. The main benefit of computational nano-design is that it allows for a low-cost and quick exploration of numerous structural ideas, including the research of stability and property prediction. The application of modelling methods and nanoscale simulation to nano-design necessitates the development of novel methodologies or the adaption of computational chemistry techniques such as classical molecular dynamics simulations, molecular mechanics, and quantum mechanics. Aside from using these computational tools at the atomic level, new approaches to using quantitative structure–activity relationship (QSAR) investigations in this sector are required (Bewick et al. 2009). To achieve reliable simulation findings about the structural and dynamic features of nano-systems at the atomic level, computational chemistry employing molecular dynamics (MD) in nanostructures requires a good characterization of physical and chemical properties. The Collaboratory for Structural Nanobiology (CNS) is the world’s first endeavour to integrate a nanoparticle structural database. More than 120 dendrimer models were created utilizing advanced molecular simulation techniques in the first stage of this endeavour. CNS is a joint project of SAIC-NCI in the United States and CBSMUTalca in Chile. The optimal structure of nanoparticles or nanomaterials can be determined using computational chemistry and molecular mechanics (MM). In molecular models, atoms are represented by spheres and their interactions are represented by springs. The total energies executed in a given force field is determined as the overall energy of the molecule. As a result, modelling at the nanoscale necessitates force fields that are adequately correct together for inorganic and organic nanostructure components. These qualities are critical in defining the 3D structural properties of nanostructures. Quantum mechanics (QM) are also used in computational chemistry to envisage the molecular structure of nanomaterials at the atomic level and to calculate various molecular signifiers that depend on the electronic configuration. These approaches are constrained through the number of degrees of freedom and the time scale that such computations need. As a result, applying QM methods to nanoscale simulation for nano-design necessitates the development of new methods or the adaption of existing techniques. A series based on theoretical and investigational training has been used in several studies with the goal of improving system comprehension (Fermeglia and Pricl 2009). Different methodologies developed during the last 40 years in computational chemistry are used in theoretical models for nanoparticle design. It has produced a theoretic education about the shape, size, and surface of nanoparticles utilizing

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modelling tools. When used as transporters and sensor systems in the intravascular trip, such characteristics appear to be relevant. As a result, the demand for precision and speed in nanostructure design necessitates the creation of new computational chemistry approaches or the adaption of current ones to build processes and protocols for designing appropriate nanomaterial. Nanomaterials have been successfully used in wastewater treatment since they can effectively eliminate various contaminants in water. Nanotechnology could be used in combination with physical, chemical, biological, and combined treatment methods to provide many opportunities to reuse water. It paves the path for these systems to improve the quality of wastewater treatment and overcome their shortcomings. Nano-membranes in MBR technology are one of the most appropriate treatment technologies, with the ability to postpone water scarcity for several years.

5 Conclusions and Future Prospects The most intensively investigated nanomaterials, such as metal oxide nanoparticles, zero-valent metal nanoparticles, carbon nanotubes (CNTs), and nanocomposites, were illustrated in this article. In addition, their implications in treating wastewater have been thoroughly discussed. Nanomaterials appear to be extensively promising for environmental remediation, specifically in wastewater treatment, given the present rate of progress and utilization. With the fast growth in population, increased industry, urbanization, and vast agriculture techniques, the need for hygienic and harmless water is increasing over the world. Water is now being decontaminated and purified using a variety of procedures. These procedures, on the other hand, frequently include chemicals and are energetically and operationally intensive, necessitating engineering skills and infrastructure. The step-up of innovative wastewater treatment procedures for the removal of pollutants from water sludge is now required for the upscaling and enhancing of the sewage treatment system. Water contamination problems can be handled more effectively and efficiently with nanotechnologies and will see further improvements in the near future. Nanotechnology-based solutions are more durable, efficient, cost-effective, and provide more environmentally friendly options. The effectiveness, productivity, energy efficiency, and low waste generation of these methods are superior to the earlier bulk materials-based techniques. However, some safety measures need to be acquired to ensure that nanoparticles do not pose any kind of danger to the human health, the environment, or human life. Because of the properties of nanotechnology, they possess the power to tackle the issues associated with traditional approaches due to these qualities. Another facet of nanotechnology, however, is the danger it entails. Many difficulties have been documented by many experts in relation to a variety of nanomaterial’s uses and features. Because of their tiny size, they can be passed into the bodies of humans and other aquatic animals, causing poisoning. The amount of toxicity is also influenced by environmental factors like concentration, pH, and contact duration. Although

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scientists have done a lot of research on nanomaterials, more work is required to fully understand this emerging technology. Using nanotechnology to manage wastewater appears to be highly promising and can have a very bright future prospect in this area. However, a dedicated and sincere attempt through the governmental bodies and the science community will be necessary to make this a reality.

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Cyclodextrin-Based Material for Industrial Wastewater Treatments Amara Lakshmi Lasita, Pallavi Pradhan, Nilesh S. Wagh, and Jaya Lakkakula

Abstract Water pollution from a wide range of pollutants is a serious environmental problem. Conventional water treatments are not effective for the removal of various organic or inorganic pollutants. Cyclodextrins are cyclic oligosaccharides composed of glucose monomer units linked with 1–4 glycosidic linkage and are abundant in nature. Cyclodextrins are biological polymer compounds which are extensively exploited in various research fields. They also depict environment-friendly properties and also have an opportunity to modify cyclodextrins using different functional groups. CD’s hydrophobic cavity forms an inclusion complex with various organic molecules, toxic compounds, heavy metals, etc. through host–guest interaction which leads to the efficient removal of contaminants from industrial wastewater. The unique property of cyclodextrin and its composites allow the removal of dyes, textile waste, pharmaceutical waste, and heavy metals simultaneously through inclusion and absorption. Cyclodextrins are also studded with several metal nanoparticles, biological compounds, etc. to synthesize cyclodextrin composites which enhance its efficacy of adsorption. Different metal nanoparticles are used depending upon the type of effluent which needs to be treated. This chapter provides an updated discussion on cyclodextrin and its composites as a sorbent material for removal of toxic pollutants from industrial wastewater. Keywords Cyclodextrin · Dyes · Heavy metal · Pharmaceutical waste

A. L. Lasita · P. Pradhan · N. S. Wagh (B) · J. Lakkakula (B) Amity Institute of Biotechnology, Amity University Maharashtra, Mumbai-Pune Expressway, Bhatan, Panvel, Mumbai, Maharashtra 410206, India e-mail: [email protected] J. Lakkakula e-mail: [email protected]

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_15

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List of Abbreviations BET BHJ CHN DTA DTG TGA TG-DTG EDX/EDAX NMR 13 C MAS NMR H1 NMR FTIR FT-IR-ATR HPLC SEM TEM FE-SEM HR-TEM UV-Vis VSM XRD XPS EDAX DSC FCC CTS SPR BG CV MB MG MO NR RhB R6G ST GO PVA TEMED TFPPN

Brunauer–Emmett–Teller Barrett–Joyner–Halenda Carbon–hydrogen–nitrogen elemental analysis Differential Thermal Analysis Derivative thermogravimetric Thermogravimetric analysis Thermogravimetry-derivative thermogravimetric Energy Dispersive X-Ray Analysis Nuclear magnetic resonance Carbon-13 (C13) magic-angle number nuclear magnetic resonance Proton nuclear magnetic resonance Fourier transform infrared spectroscopy Fourier transform infrared spectroscopy-attenuated total reflectance High-performance liquid chromatography Scanning Electron Microscopy Transmission Electron Microscopy Field emission scanning electron microscopy High-resolution transmission electron microscopy UV–visible spectrophotometry Vibrating-sample magnetometer X-ray powder diffraction X-ray Photoelectron Spectroscopy Energy dispersive X-ray analysis Differential Scanning Calorimetry Face-centered cubic Chitosan Surface Plasmon Resonance Brilliant green Crystal violet dye Methylene blue Malachite green Methyl orange Neutral red Rhodamine B Rhodamine 6 G Safranine T Graphene oxide Poly (vinyl alcohol) Tetramethylethylenediamine Tetrafluoroterephthalonitrile

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1 Introduction The increase of toxic components in industrial wastewater due to enhanced production rates raised the concern about wastewater treatment. The existence of these compounds is hazardous to human health, posing a severe threat to aquatic ecosystems and the environment (Utzeri et al. 2021). Endocrine disruptors, estrogens, pesticides, detergents, hormones, and dyes are some of the most found pollutants in industrial effluents which lead to various neurological, hepatic, gastrointestinal, and cardiovascular diseases, and cancers. Some of them lead to infertility and genetic abnormalities in bioaccumulation (Sharma and Rajesh 2017). Besides, water scarcity can be met by reusing the purified water for other purposes. Filtration of wastewater involves huge investment and sophisticated instruments which is time taking and unfavorable to treat large volumes of liquid. Various conventional methods like chemical precipitation, ion exchange, solvent extraction, oxidation–reduction, electrochemical treatment, etc. were used for the purification of wastewater from the pollutants, but due to low efficiency, high cost, and secondary pollution, those techniques remained limited (Liu et al. 2020a). Cyclodextrins are cyclic oligosaccharides containing 6–8 glucose units—(6 units in alpha, 7 units in beta, and 8 units in gamma) which are obtained from hydrolyzing starch. These have a torus shape with a hydrophilic outer side and a hydrophobic inner side (Zong et al. 2021; Shah 2020). This property of the cyclodextrin helps to trap the hydrophobic pollutants forming inclusion complexes. This is due to the host–guest interaction and the binding between the pollutants and the cyclodextrin and depends on the polarity and steric compatibility (Sirajudheen et al. 2020). Additionally, the surface hydroxyl groups and carboxyl groups bind with the micropollutants and eliminate them from the aqueous solution. The use of cyclodextrin is inexpensive, eco-friendly, easy to use, biodegradable, and has great recyclability (Badmus et al. 2021). To increase the insolubility of the cyclodextrin, it is often coupled with mineral beads, membranes, etc. via coprecipitation and cross-polymerization techniques to facilitate the removal of organic micropollutants. The wastes from textile industries, pharmaceutical industries, plastic manufacturing, paper industries, mining, chemical industries, petroleum, etc. release a wide range of toxic components which disturb the ecological balance (Chen et al. 2018). A novel approach for the removal of unwanted contaminants like metal ions, BPA, dyes, drugs, etc. from this aqueous solution is the synthesis of a cyclodextrin-based polymer coupled with metallic nanoparticles as an adsorbent (Eibagi et al. 2020). Hydrogels, magnetic adsorbents, and nanocomposites are prepared to utilize βcyclodextrin for the eco-friendly removal of organic and inorganic pollutants from wastewater (Yuan et al. 2014). Microwave-assisted synthesis, one-pot fabrication method, cross-polymerization, etc. are being used to synthesize these eco-friendly adsorbents. In the present chapter, various β-cyclodextrin-modified membranes are

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synthesized using diverse methods and applied for the elimination of a broad spectrum of toxic components from various industrial effluents and their potential is tested (Li et al. 2020).

2 Cyclodextrin-Based Polymers This chapter focuses on the use of β-cyclodextrin-based membranes, nanoparticles, ultrathin fibers, and hydrogels as effective adsorbents for the removal of target pollutants like plastics, heavy metals, dyes, and drugs from industrial wastewater and its purification.

2.1 Removal of Organic Pollutants In this study, pine sawdust modified (CD-PS) by β-CD was used for the adsorption of BPA followed by its photo-degradation. It was carried out to test the ability of the adsorbent to remove organic pollutants from an aqueous environment. The β-CD was embedded on the surface of CD-PS which acted as a catalyst for the removal of BPA and its degradation due to the formation of inclusion complexes with BPA. The thermal behavior of CD-PS, B-PS (pine saw dust), and β-CD (β-cyclodextrin) was studied by the TG-DTG method. The morphological characters were studied by SEM analysis, and the images revealed the micro-porous, rough surface of CD-PS and BPS. The adsorption kinetics followed a pseudo-second-order model and fitted with the Langmuir isotherm of adsorption. The maximum adsorption capacity of CD-PS toward BPA was 0.0319 mmol g− 1 at a neutral pH and 25 °C conditions. CD-PS exhibited better adsorption efficiency than B-PS. The reusability tests confirmed that CD-PS exhibited a minute variation in adsorption performance after the first use, but it can be employed up to 5 repetitive cycles with no major damage. The CDPS membrane can be regenerated by the UV-irradiation method. Photo-degradation kinetic study results show that CD-PS enhanced photo-degradation of the adsorbed BPA compared to BPS under UV-illumination. The above results indicate the possibility of CD-PS commercial use in the purification of contaminated water (Zhou et al. 2017; Shah 2021). Another research was based on the facile precipitation method to synthesize superparamagnetic iron-oxide nanoparticles (SPION) with β-cyclodextrin to make a composite (SPION/β-CD) for removal of organic pollutants and oil spill remediation. The (SPION/β-CD) was characterized by FT-IR and the bands obtained at 3300– 3500 cm−1 (O–H stretching), 2924 cm−1 (C–H stretching vibration), 1159 cm−1 and 1026 cm−1 (C–C/C–O stretch vibration) 946 cm −1 , and 534 cm−1 (Fe–O–Fe band) confirm the synthesis of composite nanostructures. XRD study was conducted for both the prepared SPION and (SPION/β-CD), and there was a slight difference in values observed. The results showed (SPION/β-CD) had an average crystallite size

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of 10–15 nm and the d-spacings (220), (311), (222), (400), (422), (511), and (440) are corresponding to 2.93, 2.63, 2.40, 2.09, 1.79, 1.61, and 1.48 Å, respectively. Mossbauer spectroscopy results showed that saturation magnetization of (SPION/ β-CD) was 39.21 emu/g and confirmed its superparamagnetic nature. Photocatalytic degradation and solar illumination experiments suggest proof that pollutants like BPA can be efficiently removed after 30 min of illumination. The recovery and reusability studies showed that the (SPION/β-CD) are magnetically recoverable with good potential and stable even after 6 cycles. The further developments of this prepared nanocomposite can be used in various applications for the treatment of industrial effluents (Kumar et al. 2015). Further, a composite of β-CD-modified cellulose nanofiber membrane (CA-PCDP) was used as an adsorbent to eliminate bisphenol A (BPA), bisphenol S (BPS), and bisphenol F (BPF) from industrial wastewater. Hydrogen-bonding interactions, synergism of hydrophobic effects, and π–π stacking interactions between the pollutants and the membrane were the actual mechanism of adsorption. FT-IR analysis of the modified β-CD showed bands at 3450 cm−1 , 2894 cm−1 , 2252 cm−1 , and 1481 cm−1 which indicated the stretching of the functional groups resulting in the effective modification of the nanomembrane. C solid-phase NMR showed vibrations at 183 ppm, 98 ppm, and 137 ppm indicating the β-CD and TF cross-linking polymerization. The TG and DTG curves showed that the fabricated (CA-P-CDP) was thermally stable at high temperatures. A series of experiments were carried out and Adsorbent dosage (0.10 g L−1 ), neutral pH (7), temperature (25 °C), and contact time (15 min) were determined as optimal conditions for the maximum adsorption of the bisphenol pollutants. The maximum adsorption concentration was 50.37, 48.52, and 47.25 mg g− 1 for BPA/BPF/BPS, respectively. Reusability test results showed that the CA-P-CDP has great adsorption properties even after 5 adsorption–desorption cycles. The overall result from this research makes it evident that CA-P-CDP can be exploited to a great extent for practical use (Lv et al. 2021). Also in another study, HP-β-CD polymer was synthesized using cross-linking agent tetrafluoroterephthalonitrile (TFPPN) to form a porous membrane for the removal of bisphenols (BPA, BPS, and BPF) from aqueous solutions. FT-IR spectra of HP-β-CD polymer show the characteristic bands of TFPPN (2252 cm−1 and 1260 cm−1 ), and HP-β-CD (3386 cm−1 , 2929 cm−1 , 1033 cm−1 ) indicating their interactions and successful synthesis of the polymer. TGA analysis shows the thermal stability of the membrane at 518.15 K. Furthermore, the SEM analysis shows the irregular shape of the surface and particle size range (10–50 μM). N2 adsorption– desorption isotherm method reveals the porosity of the membrane with 2–4 nm pore diameter, thus confirming its mesoporous morphology. Adsorption kinetics that followed pseudo-first-order, pseudo-second-order model, and Freundlich isotherm well fitted the adsorption pattern indicating the heterogenous chemi-adsorption of bisphenol pollutants on the polymer. Factors affecting the adsorption process were studied and their optimal conditions are noted. The adsorption of BPA increased with temperature while that of BPS, BPF decreased. 0.02 g of adsorbent dosage was the optimum concentration and neutral pH resulted in good performance of the polymer. BPA, BPS, and BPF attained equilibrium for 95%, 90%, and 90% in 1 min, 10 min,

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and 10 min, respectively. The reusability test results show that the polymer can be regenerated and reused for 3 cycles with no change in its performance (Cai et al. 2020). During this project, a trifunctional cellulose-epichlorohydrin-β-cyclodextrin (BAN-EPI-CDP) adsorbent membrane was synthesized using copolymerization reaction for the treatment of non-ionic organic pollutants like BPA and anionic and cationic dyes like CV from aqueous solutions. FT-IR analyses were used for the characterization of the composite membrane and bands formed in the raw materials (B-CD and EPI-CDP) matched with the bands in the product (BAN-EPI-CDP) confirming the successful syntheses. SEM showed that the particles of the sorbent were shapeless, irregular with dense homogeneous surface, and pore size of 2–50 nm. Adsorption studies revealed that the sorption is directly proportional to the adsorbent dosage which attributes to the increased surface area and binding sites for the model pollutants. Langmuir isotherm equation best described the adsorption mechanism, and the maximum adsorption concentration was 113.6 mg g− 1 and 43.1 mg g− 1 for BPA and CV respectively with optimum adsorption pH range of 4–10. The regeneration experiment results showed that the material can be used at least 5 times without compromising its efficiency. The prepared (BAN-EPI-CDP) adsorbent was used for the elimination of pollutants from real wastewater, and the results were highly satisfactory having significant potential for the treatment of effluents. Based on the test results, (BAN-EPI-CDP) was proven to have great regeneration performance, high adsorption properties, and inexpensive and easy synthesis promoting its commercial use (Hemine et al. 2021). Apart from the organic pollutants, β-CD carbon-sphere-based nanocomposite (CS/SiO2@ β-CD) adsorbent was fabricated for the removal of CV and BPA by the process of hydrothermal synthesis and sedimentation–azeotropic distillation. FT-IR spectrum of the adsorbent showed bands at 1097 and 465 cm–1 , 1640 cm–1 , 3428 cm–1 which indicated that the β-CD was successfully deposited on the membrane. Adsorption kinetic studies show that the adsorption process matches with different models like pseudo-first-order, pseudo-second-order, and the equations were listed. The adsorption pattern is well fitted in Langmuir isotherm which suggests it was mainly monolayer adsorption. The maximum adsorption capacity was 87.873 mg g–1 and 165.095 mg g–1 for CV and BPA at 303 K, respectively. BPA showed better adsorption at pH range 3–9 and slightly reduced at 11, as it was not possible to form a stable host–guest interaction in alkaline pH. The adsorption rate was influenced by factors like the concentration of the adsorbent, temperature, pH, contact time, and concentration of dye present in the effluents. Thermodynamic studies were carried out to calculate the parameters like enthalpy (–ΔH0 ), free energy (–ΔG0 ), and entropy change (–ΔS0 ), and the results showed that adsorption of BPA was an exothermic, spontaneous, and physical process. The desorption–regeneration studies prove that the prepared composite can be used effectively for up to five cycles. From this study, the results suggest that CS/SiO2@ β-CD exhibits great potential as an adsorbent and can be used in industry treatment (Tian et al. 2022). In another interesting study, benzylated β-CD was involved in Friedel–Crafts alkylation with 4,4' -bis(chloromethyl)-1,1' -biphenyl as the cross-linking agent to prepare

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a phenyl-rich polymer (PCD-PCP) with micropores for adsorption of aromatic pollutants like BPA and 2,4,6-trichlorophenyl. FT-IR spectra displayed the characteristic peaks of β-CD and BnCD in the PCD-PCP polymer confirming successful synthesis. The chemical environment of the polymer surface was studied by XPS analyses. CP/ MAS 13 C NMR was used to study the chemical structures of both high and low crosslinked PCD-PCPs. N2 adsorption–desorption was used to measure the porous features and nanostructures of the PCD-PCPs, and the results showed that PCD-PCP(H) has a higher micropore volume and is an ideal adsorbent for pollutants. Host–guest interactions and π–π interactions are the underlying mechanism of adsorption. The pseudo-second-order model describes the adsorption kinetics, and the adsorption isotherm studies showed that 2,4,6-TCP is strongly adsorbed when compared to BPA and high temperature did not favor the binding between the adsorbates and the adsorbent. Freundlich model best described the adsorption equilibrium and showed that the pollutants are adsorbed on the heterogeneous surface of PCD-PCP polymer. TGA analysis was done to study the thermal behavior of the polymer and the results showed that the higher thermal stability was due to higher cross-linking. Adsorption–desorption studies were conducted to study the reusability of the adsorbent, and the results confirmed that the PCD-PCP(H) can be reused for 6 cycles with a slight decrease in adsorption efficiency (Huang et al. 2020). Additionally, a green method was employed to cross-link β-CD on the surface of poly (chloromethyl styrene) resin using terephthalonitrile nitrile (TPN) for the removal of BPA and heavy metal ions from water. SEM images displayed that this modified porous resin has an enormous surface area and large holes which leads to higher adsorption. PS@CM-CDP exhibited honeycomb structures that were randomly scattered on the surface. FT-IR spectra of the PS@CM-CDP confirmed that it is a copolymer of TPN, PS-Cl, chloroacetic acid, and β-CD. BET method was used to determine the specific surface area and the pore volume of PS@CDP PS-Cl, and PS@CM-CDP, and the results confirmed that PS@CM-CDP spheres have a much larger surface area and have strong adsorption properties. The effect of pH, adsorbent concentration, and contact time were studied and optimized. Freundlich and Langmuir isotherm best described the adsorption process. The maximum adsorption capacity of the resin toward BPA and Cu(II) was 8.25 mg g−1 and 121.88 mg g−1 , respectively. The multifunctional resin was tested using real wastewater in the column experiment and exhibited 99% adsorption capacity. Due to its high mechanical strength and spherical nature, the PS@CM-CDP resin can be regenerated and reused for 6 consecutive cycles without compromising its performance. From the overall observations of this research, PS@CM-CDP can be suggested for the purification of wastewater in practical applications (Zhang et al. 2021). To enhance the activity (β-CD), branched polyethyleneimine (b-PEI) and polyethylene glycol (PEG) were cross-linked to form a stable, water-soluble adsorbent (X-CD or b-PEI-PEG-β-CD) for removal of heavy metals (Cu(II)), and bisphenols (BPA) from aqueous solutions. FT-IR spectra of the 3 raw materials and the XCD polymer (branched polyethyleneimine, polyethylene glycol, and β-Cyclodextrin polymer) were analyzed, and the results confirmed the successful cross-linking and preparation of the adsorbent. FE-SEM images revealed that the X-CD polymer had

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a non-porous and smooth surface. Further, DSC and TGA method results showed that X-CD has good thermal stability, amorphous nature, and a 3.84 °C glass transition temperature. The effect of pH was studied and pH 6 was determined to be the optimum for the maximum adsorption of Cu(II) and BPA. The adsorption kinetics was well suited to the pseudo-second-order model, and the Langmuir isotherm model exhibited a good correlation with the adsorption data of the pollutants. X-CD polymer can be treated with DI water or ethanol for regeneration and recycling. The experiment has proved that the polymer can be used efficiently for 4 repetitive cycles, and their recovery was 79.2% for BPA and 87.3% for Cu(II) after the fourth adsorption–desorption cycle. Additionally, the simultaneous adsorption studies showed that the co-existing organic pollutants did not greatly affect the adsorption capability of X-CD polymers. Thus, X-CD proves to be an ideal, eco-friendly adsorbent for the purification of heavy metals and endocrine disruptors from industrial effluents (Lee and Kwak 2020). This study involves the esterification of β-CD and citric acid (CA) for the green synthesis of CA-β-CD adsorbent to purify wastewater from contaminants like heavy metals (Cu2+ ), dyes (MB), and endocrine disruptors (BPA). FT-IR spectra of CA-βCD show characteristic bands of β-CD confirming that the structure is not disrupted and maintained well. BET study revealed that CA-β-CD had 0.81 m2 g− 1 surface area. The effect of pH was studied as it influences the surface functional groups which are the active binding sites, and results showed that the adsorption of Cu2+ and MB was pH-dependent. The non-polar BPA were entangled in the hydrophobic cavity of the β-CD, while Cu2+ and MB reacted with the surface carboxyl groups of the membrane. The pattern of adsorption can be attributed to the pseudo-secondorder model. The adsorption isotherm of BPA well suited the Langmuir isotherm, and the equilibrium adsorption data of Cu2+ and MB followed the Sips isotherm model. The maximum adsorption capacity of CA-β-CD toward BPA in a monocomponent system was 0.3636 mmol g− 1 and for Cu2+ , MB it was 0.9155 and 0.9229 mmol g− 1 , respectively. CA-β-CD exhibited excellent anti-jamming properties as its adsorption performance was not affected by the existence of Humic acid. The outstanding adsorption capability, green synthesis, recyclability, and anti-jamming property of CA-β-CD suggest that it is a promising candidate for practical application in water purification systems (Huang et al. 2018). In another fascinating project, a nucleophilic substitution reaction was employed between β-CD and tetrafluoroterephthalonitrile (TFPPN) to synthesize β-CDP polymer for removal of 3 organic pollutants—chloroxylenol (PCMX), carbamazepine (CBZ), and bisphenol A (BPA) from aqueous solutions. FT-IR spectra of β-CDP exhibited the characteristic bands of the raw materials TFPPN and β-CD which confirms the successful preparation of the adsorbent. BET algorithm revealed the surface area of the β-CDP was 21.1 m2 g− 1 , and its isotherm curve was very similar to the type III model. The logKow value was directly proportional to the removal efficiency of the pollutants. Also, from observations of different adsorption systems, it was concluded that the modal organic pollutants only slightly interfered with the competitive adsorption. Besides, the factors like pH, the presence of fumic acid, and ionic strength were studied, and the results showed that they did not

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affect the performance of the β-CD polymer. The adsorption kinetics followed the pseudo-second-order model, and the Langmuir isotherm well described the adsorption progress. The maximum adsorption capacity of the polymer toward CBZ, BPA, and PCMX are 136.4, 164.4, and 144.1 mg g− 1 , respectively. The β-CD polymer can be regenerated by methanol treatment and reused for at least 5 consecutive cycles with no significant decrease in the adsorption capacity of the polymer (Zhou et al. 2019). Several attempts were made to eliminate a wide range of organic pollutants efficiently, in which a mesoporous polymer was prepared by cross-linking of β-CD and 4,4’-difluorodiphenylsulfone (DFPS) by nucleophilic substitution reaction which was used for the removal of organic micropollutants like BPA, BPS, 2-NO, and 2,4DCP from wastewater. Different molar ratios of β-CD and DFPS were used for the experiment, and 1–2 β-CDP was chosen the best as it has a rapid adsorption rate and a very high yield. SEM analyses reveal granular and irregular shapes of 1–2 β-CDP. The powder X-ray diffraction pattern shows the amorphous nature of the β-CDPs and the high granular and irregular shape of 1–2 β-CDPs (Fig. 1a). Moreover, the FT-IR analysis shows bands at 3400 cm−1 , 1600 cm−1 , and 1500 cm−1 which are attributed to the hydroxyl group and benzene skeleton confirming the presence of β-CDP and DFPS in the polymer (Fig. 1b). Further characterization was done using solid-state 13 C NMR spectra, and the peak at 162 ppm in the spectrum represents the C-n’ which was formed due to the nucleophilic substitution (Fig. 1c). The Mercury porosity method was used to find the pore width of 1–2 β-CDPs (Fig. 1d). The covalent bonds between both components were confirmed by TGA. The adsorption process was in line with quasi-second-order kinetics, and the Langmuir isotherm model shows the maximum adsorption capacity at 113.0 mg g− 1 which was homogeneous monolayer adsorption. Ethanol treatment was used for reproducing the polymer, and the β-CDPs show great adsorption even after 5 cycles of regeneration with 99% removal efficiency. Thus, β-CDPs can be exploited for the removal of a broad spectrum of organic pollutants like plastics, pharmaceuticals, pesticides, dye intermediates, etc. from aqueous solutions (Wang et al. 2017). In another interesting work, a quaternary multifunctional β-CDP polymer was synthesized using Tetrafluoroterephthalonitrile (TFTPN) and Epichlorohydrin (EPI) as cross-linking agents and ETA as a quaternizing agent for the removal of natural organic matter (NOM) and organic micropollutants (OMP) from water. Humic acid, fulvic acid for NOM and bisphenol A (BPA), and bisphenol S (BPS), 2-naphthol (2NO), 3-phenylphenol (3-PH), and 2,4,6-trichlorophenol (2,4,6-TCP), for OMP are chosen as model pollutants, and commercial adsorbents such as resins and activated carbon were used to evaluate and then compare the performance of the polymer, respectively. Freundlich model best fitted the adsorption isotherm which indicated heterogeneous adsorption of pollutants, and the Langmuir isotherm model showed maximum adsorption capacity of the β-CDP membrane for HA, FA, 2-NO, 3-PH, 2,4,6-TCP, BPA, and BPS are 40, 166, 74, 101, 108, 103, and 117 mg g− 1 , respectively. Additionally, the polymer also exhibited antibacterial properties due to the presence of quaternary ammonium groups. The β-CDP membrane was easily regenerated with 10% NaCl treatment at room temperature and showed no decrease in its

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Fig. 1 a Powder X-ray diffraction pattern of β-CD, DFPS, and 1–2 β-CDP (inset displays scanning electron microscopy image of 1–2 β-CDP), b FTIR spectra of β-CD, DFPS, and various β-CDPs, c Solid-state 13 C NMR spectra of β-CD, DFPS, and 1–2 β-CDP, and d Pore structure of 1–2 β-CDP calculated by mercury porosimetry method. Reprinted with permission from Wang Z, Zhang P, Hu F, et al. (2017) A cross-linked β-cyclodextrin polymer used for rapid removal of a broad-spectrum of organic micropollutants from water. Carbohydr Polym 177:224–231. https://doi.org/10.1016/j. carbpol.2017.08.059

performance even after 5 adsorption/desorption cycles. The overall findings indicate that the β-CDP polymer exhibits outstanding potential in disinfection and wastewater treatment (Hu et al. 2020b). Another study suggests that β-CD was reacted with methacryloyl chloride to form β-CD-methacrylate, with an average of 3 methacrylate groups/β-CD which was copolymerized with acrylamide to synthesize β-CD-polyacrylamide (β-CD-PAAm) hydrogel by free-radical copolymerization for the elimination of organic pollutants from aqueous solutions. FT-IR spectra of β-CD and β-CD-MA were obtained which showed the characteristic peaks of C = O stretching and C = C stretching, thus confirming the conjugation of the methacrylate groups on β-CD. SEM analysis was performed on the cross-section of the polymer, and the images revealed the larger pore size of the β-CD-PAAm gel which may be related to its higher swelling ratio. Phenolphthalein, propranolol hydrochloride, BPA, and 2-naphthol were selected

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from different classes as modal pollutants. The pseudo-second-order model best described the adsorption kinetics of the hydrogel, and adsorption isotherms well fitted the Langmuir model indicating the homogeneous adsorption pattern. Thermodynamic studies indicated that the adsorption increases with the initial concentration of the pollutants for β-CD-PAAm. The (β-CD-PAAm) hydrogel can be recycled with methanol treatment and reused for up to five consecutive cycles with no compromise in adsorption capacity. Therefore, β-CD-PAAm proves to be a promising adsorbent for commercial wastewater treatment with outstanding adsorption capability and great recyclability (Song et al. 2021).

2.2 Removal of Heavy Metals In this study, the chemical reduction method was used to synthesize gold nanoparticles (AuNPs) and functionalized β-CD/AuNPs for the detection of copper and photocatalytic degradation of textile dyes from wastewater. Optical studies were done using UV-Vis spectroscopy, and the results showed a red shift in the peak which was reduced as the AuNPs were coated with β-CD and formation of stable nanoparticles (NPs). TEM studies showed the spherical shape of the NPs which are monodispersed and self-assembled. XRD pattern of AuNPs showed 38.29°, 44.52°, 64.62°, and 77.76° 2θ angle diffraction peaks corresponding to (111), (200), (220), and (311) Bragg’s reflections which revealed their FCC structure (Fig. 2a). β-CD/ AuNP pattern showed extra peaks at 26.82° and 31.78° which confirmed the presence of β-CD (Fig. 2b). The band shift of the AuNPs before and after functionalization with β-CD in FT-IR analyses indicates the successful formation of β-CD/AuNPs. EDAX spectrum showed Au signals at 2.30 keV, 8.5 keV, 9.10 keV, 11.30 keV, and 13.5 keV which again confirmed the synthesis of β-CD/AuNPs. The antibacterial activity of AuNPs and β-CD/AuNPs was measured by the well disk diffusion method, against E. coli and S. aureus. The results showed that β-CD/AuNPs created a maximum zone of inhibition (ZOI) due to their smaller size which leads to better penetrating power and larger surface area. Based on the SPR property of AuNPs, a copper sensor is constructed for the detection of Cu concentration in water. Photocatalytic degradation of textile dye wastewater (TDWW) showed that AuNPs and β-CD/AuNPs are excellent photocatalysts and can degrade metal-containing dyes (Bindhu et al. 2021). Also in another research, one-pot polymerization followed by an ammonolysis reaction was used to prepare a hydrogel functionalized with β-CD, triethylenetetramine, and graphene to yield a magnetic adsorbent (P(AA-MMA)/MGO/CA-CD/ NH2) for the elimination of pollutants from water. FT-IR spectra of MGO, β-CD, CA-CD, and GO revealed their characteristic bands which were also found in the spectra of the hydrogel confirming the synthesis of polyampholyte adsorbent gel. Heavy metal ions like (Cu2+ ) and cationic/anionic dyes like Malachite green (MG), Congo red (CR), and Methylene blue (MB) were selected as modal pollutants to test the adsorption efficiency of the prepared hydrogel. The pseudo-second-order model well described the adsorption kinetics of the adsorbent. The adsorption pattern of the

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Fig. 2 XRD pattern for solid a AuNPs and b β-CD/AuNPs. Reprinted with permission from Bindhu MR, Saranya P, Sheeba M, et al. (2021). Functionalization of gold nanoparticles by β-cyclodextrin as a probe for the detection of heavy metals in water and photocatalytic degradation of textile dye. Environ Res 201:111,628. https://doi.org/10.1016/j.envres.2021.111628

hydrogel best fitted in the Langmuir isotherm model. Electrostatic interaction, π–π conjugation interaction, hydrogen bonding, and complexation were found to be the mechanism of adsorption. The maximum adsorption capacity of the hydrogel toward Cu2+ , CR, MG, and MB are 140.50 mg g− 1 , 1058.18 mg g− 1 , 3315.00 mg g− 1 , and 3185.16 mg g− 1 , respectively. Also, the factors influencing adsorption like pH, Ionic strength, and temperature were studied to define the optimum conditions for maximum adsorption. Additionally, the (P(AA-MMA)/MGO/CA-CD/NH2) adsorbent exhibited good stability with no reduction in its performance even after 8 regeneration cycles stating its outstanding reusability (Yan and Li 2021). Also, a new approach was followed for the synthesis of Poly-βCD/PVA fibers by electro-spinning method followed by thermal treatment for cross-linking of the fibers for enhancing mechanical strength and water insolubility. SEM images revealed the morphology of the electrospun fibers based on their compositions. DSC analysis was carried out to understand the curing reaction and cross-linking. Cured and uncured fibers were analyzed by ATR, and it confirmed there was no damage in Poly-βCD/ PVA fibers due to thermal treatment. UV-Vis spectroscopy results showed at 160 °C it is optimum for complete curing to yield the insoluble fibers. Poly-βCD/PVA fibers

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exhibited homogeneous and large surface area which increased their contact area with the solutions. The adsorption efficiency of these fibers was tested against Cu2+ and Cd2+ metal ions. All the Poly-βCD/PVA fibers can form metal complexes with both the ions and with a good adsorption rate. The adsorption rate was 50% after 1 h of contact time which increased to 85% after incubation for 6 h. This was analyzed by ICP-OES which detects the remaining ion concentration in the solution after filtration. The fibers can be regenerated by soaking them with HCl for 2 h. The Poly-βCD/PVA fibers did not show any change in their stability and performance after reuse. Therefore, the Electrospun poly βCD/PVA fibers can be exploited for the purification of water in industries (Anceschi et al. 2020). Apart from the β-CD composites, poly (urethane-imide) was cross-linked with β-CD and diisocyanate as the cross-linking agent to prepare a magnetic (β-CDPUImMNPs) composite for adsorption of heavy metal ions like Pb(II) and Cd(II). A coprecipitation reaction was carried out to incorporate Fe3 O4 nanoparticles on (βCDPUIm) to yield β-CDPUIm-MNPs. FT-IR spectra, 1 H-NMR spectrum, and Hdecoupled 13 C NMR spectrum revealed the chemical structures of imide-diacid. BET analysis determined the surface area of β-CDPUIm and β-CDPUIm-MNPs, and the results showed an increase in the surface area of β-CDPUIm from 0.8336 to 1.9705 m2 g− 1 after the addition of Fe3 O4 . The synthesized composite showed maximum adsorption in neutral pH, 20 min contact time, and temperature. The adsorption kinetics followed the pseudo-second-order model and Langmuir isotherm which indicates the homogenous adsorption. 344.830 and 303.030 mg g− 1 were found to be the maximum adsorption capacities of (β-CDPUIm-MNPs) for Pb(II) and Cd(II) ions, respectively. The desorption of metal ions can be done by using a magnet and thorough washing of the composite with water. (β-CDPUIm-MNPs) composite can be used for five consecutive cycles without any changes in adsorption performance. After 5 cycles, the efficiency was reduced by 7.6% and 11.1% for Pb(II) and Cd(II), respectively (Eibagi and Faghihi 2020). In another interesting project, rice-husk biochar was successfully grafted with β-CD by microwave-assisted one-pot synthesis, and BCMW-β-CD (rice husk biochar modified with β-CD adsorbent) was synthesized for the elimination of BPA (Bisphenol A) and plumbum (Pb). SEM images of BCMW-β-CD showed that it was composed of mesopores, and pore diameter was in the range of 2.3– 11.9 nm. FT-IR spectra showed bands at 3398 cm− 1 , 1641 cm−1 , 996 cm−1 , and 1050−1150 cm−1 corresponding to stretching and vibration of functional groups present in the composite. The effect of pH was negligible on the adsorption of BPA but greatly influenced the adsorption of Pb onto BCMW-β-CD. Adsorption equilibrium studies showed that Pb(II) attained equilibrium in 20 min following the pseudo-second-order model and BPA attained equilibrium in 30 min and fits into the pseudo-first-order kinetic model of adsorption. The maximum adsorption capacity was 209.20 mg g− 1 for BPA and 240.13 mg g− 1 for Pb(II), respectively. Adsorption isotherm analyses showed Langmuir and Sips isotherms were best fitted and indicated monolayer adsorption. The mechanism of adsorption for Pb(II) was mainly electrostatic interactions and complexation, whereas π–π stacking interactions and

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host–guest supramolecular interactions for BPA. The adsorption–desorption experiments suggested that BPA and Pb(II) adsorbed can be eluted with the mild treatment of HCl and ethanol. BCMW-β-CD exhibited high adsorption abilities even after five repetitive cycles which indicate its reusability. This study’s results confirm that the synthesized BCMW-β-CD can be efficiently used for the simultaneous elimination of heavy metals, and inorganic and organic pollutants in practical applications (Qu et al. 2020). Additionally, micropollutants were also targeted with the simultaneous removal of the heavy metals. In this study, a (β-Cyclodextrin/ZrO2 ) nanocomposite was synthesized using cross-linking agent citric acid (CA) for the elimination of heavy metal (Pb(II)) and endocrine disruptors (BPA) from complex wastewater. SEM analysis showed the porous and rough surface of the adsorbent due to the presence of a polymer matrix. Additionally, the composite was characterized by FT-IR, TEM, etc. which revealed the properties, functional groups, and crystalline size (9–14) of the ZrO2 nanoparticles, respectively. Adsorption kinetics showed that BPA and Pb(II) adsorption followed the pseudo-second-order model and attained equilibrium within 80–130 min. The isotherm studies indicated that Langmuir and Freundlich isotherms best described the adsorption of BPA and Pb(II). The maximum adsorption was found to be 274.5 mg g− 1 and 174.9 mg g− 1 at 25 °C for Pb(II) and BPA, respectively. The mechanism of adsorption was host–guest interaction for BPA, whereas Pb(II) was removed by oxygen-containing groups. Due to the different mechanisms involved, βCD/ZrO2 facilitated simultaneous removal without interference. Stepwise recovery and recyclability showed that the adsorbed BPA and Pb(II) can be recovered with ethanol and HCl treatment, respectively. Also, the adsorbent showed a slight decrease in its potential after 4 regeneration cycles which indicates its effective reusability. The remarkable adsorption rate, and very stable adsorption–desorption process suggest that β-Cyclodextrin/ZrO2 can be exploited for commercial purposes (Usman et al. 2021a). Another innovative experiment includes β-CD/CS/PVA(β-CD)/chitosan (CS)/ polyvinyl alcohol (PVA) nanofiber membrane synthesized by the electrospinning method and cross-linking with epichlorohydrin for the removal of heavy metals (Pb2+ ) and organic pollutants (BPA) by static and dynamic adsorption from aqueous solutions. FT-IR spectra showed the characteristic functional groups of PVA membrane (1720 cm−1 , 1631 cm−1 , 1095 cm−1 ), β-CD membrane (1157 and 1029 cm−1 ), and CS membrane (1610 and 1366 cm−1 ) in the cross-linked β-CD/CS/ PVA membrane confirming successful synthesis of the adsorbent. The heavy metal ions formed complexes with the hydroxy groups, whereas the organic pollutants are trapped inside the hydrophobic cavity of β-CD. As the mechanism of adsorption was different for both pollutants, it facilitated the simultaneous elimination of the pollutants. The adsorption kinetics indicates that the adsorption followed pseudofirst-order, pseudo-second-order, and intraparticle diffusion models. BPA and Pb2+ adsorption on β-CD/CS/PVA attained equilibrium in 1 min and 10 min, respectively. Langmuir and Freundlich isotherms well fitted the adsorption data. Reusability studies show the membrane can be effectively used up to 5 cycles of adsorption– desorption indicating its recyclability and stability. The overall result of this study

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suggests that β-CD/CS/PVA membrane has a great adsorption capability and can be used for the treatment of wastewater, drinking water, and sewage water (Fan et al. 2019). In this work, superparamagnetic nanoparticles Fe3 O4 were modified with β-CD to synthesize adsorbent (CM-β-CD) for the selective removal of metal ions like Cd2+ , Ni2+ , and Pb2+ from industrial wastewater. The CM-β-CD polymer enhances the adsorption capability of the nanoparticles by forming complexes with the target metal ions with strong affinity. The adsorbent was analyzed by FT-IR, and the bands obtained confirmed the successful synthesis of the adsorbent. The maximum adsorption capacity of the adsorbent toward the metal ions was 27.70, 13.20, and 64.50 mg g−1 for Cd2+ , Ni2+ , and Pb2+ , respectively. The equilibrium was achieved in just 45 min at 25 °C, and the adsorption data well suited the Langmuir isotherm model. Pseudo-second-order kinetics best describe the adsorption rate and mechanism of the metal ions on the adsorbent. In a solution with multi-metal ions, the adsorption followed Pb2+ > > Cd2+ > Ni2+ order. The factors influencing the rate of adsorption were studied and their optimum values were recorded. pH (5.5–6), 25 °C temperature, and lower ionic strength favored the adsorption process. Reusability studies revealed that the adsorbent showed no significant decrease in its performance for 4 repetitive cycles, and there were only negligible differences. Overall results suggest that the β-CD coated Fe3 O4 nanocomposites can be exploited for commercial use in industrial wastewater treatment (Badruddoza et al. 2013). Besides the heavy metals, several adsorbents could effectively remove certain dyes from the aqueous solutions. One such study involves the synthesis of antibacterial βCD nanoparticles (E-β-CDN) using a one-pot fabrication method for the adsorption of heavy metals and organic pollutants from aqueous solutions. FT-IR spectra and 31P and 13C MAS NMR spectra revealed the functional groups and chemical structures of (E-β-CDN). The E-β-CDN had rough surface morphology with an average diameter range of 420 to 480 nm. Methylene blue (MB), Methyl orange (MO), and plumbum Pb(II) were selected as modal pollutants. The NPs exhibited quick adsorption with 95% removal in just 10 s The maximum adsorption capacity of Pb(II) and MO were 970.8 mg g−1 and 3289.6 mg g−1 , respectively. XPS spectra confirmed the adsorption of metal ions on the surface of E-β-CDN by detecting the shifts in binding energy. β-CDN showed no compromise in performance for 10 regeneration cycles which is an added advantage. Besides, E-β-CDN had outstanding antibacterial properties and showed 99% inhibition against gram +ve (S. aureus) and gram-ve bacteria (E. coli) by damaging their cell walls and leading to cell lysis. E-β-CDN showed better adsorption than other commercially used adsorbents, high antibacterial activity, and good adsorption capacity against toxic dyes and metal ions which prove its potential to be utilized in bioremediation (Liu et al. 2020c). In this paper, β-CD-based epichlorohydrin and graphene oxide composite (RGOβCD-ECH) was prepared for removing Cr(VI) from wastewater. SEM images showed the morphological features of βCD, βCD-ECH, GO, RGO, and RGO-βCD-ECH and confirmed the dispersion of RGO on the composite surface resulting in successful synthesis of the adsorbent. The adsorption rate was explained by the Langmuir model,

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and the kinetic data well-fitted in the pseudo-second-order model. The factors influencing adsorption were studied; their optimum conditions were determined as 75 min contact time, 30 °C temperature, pH 1, and 0.2 g/L. Adsorbent dosage will help in maximum adsorption rate. Boyd’s plot showed that intraparticle diffusion influences the rate-limiting step. The ions like Ni2+ , Cl− , Cu2+ , Co2+ , SO2− 4 , and NO− 3 did not show any effect on Cr(VI) adsorption. Besides, RGO-βCD-ECH can be regenerated using NaOH solution and can be utilized for 5 consecutive cycles with good performance. Therefore, RGO-βCD-ECH can be suggested as a cost-effective and good adsorbent for commercial use (Ranjan Rout and Mohan Jena 2022). Another study used the electrospinning technique to transform cyclodextrin into ultra-thin fibers to synthesize Electrospun cyclodextrin fiber (CD-F) which can be used as a matrix for the encapsulation of bacteria for the treatment of wastewater. Besides, CD-F is also a feeding source for the bacteria which forms a composite with CD-F for efficient removal of heavy metal ions (Nickel(II) and Chromium(VI)) and textile dye (Reactive Black 5, RB5). SEM studies revealed that 1% (w/w) of bacteria (Lysinibacillus sp. NOSK) was the optimal concentration for encapsulation and electrospinning to get a homogenous bacteria/CD-F composite. Raman spectroscopy showed peaks at 851 cm−1 , 1650 cm−1 , 1420 cm−1 1005 cm−1 , ∼1048, and ∼995 cm−1 corresponding to functional groups in CD-F, Bacteria, and bacteria/CDF composite confirming the formation of the composite with encapsulated bacteria. Viability studies showed that the encapsulated bacteria can be viable for 7 days at 4 °C conditions. The removal of the pollutants and bioremediation experiments showed the bacteria/CD-F has the efficiency to remove 70 ± 0.2%, 58 ± 1.4%, and 82 ± 0.8 of Ni(II), Cr(VI), and RB5, respectively. The removal efficiency was optimum at neutral pH for metal ions. Langmuir isotherm was best fitted for the removal of Ni(II). The results obtained in this research indicate that CD-F bio-composite can be utilized for the bioremediation of metals and dyes in commercial wastewater treatment (San Keskin et al. 2018). Several pollutants can be adsorbed simultaneously with the use of a magnetic polymer. In the present study, a porous magnetic β-CD-based polymer (MNP-CMCDP) was synthesized in a green route for the effective adsorption of heavy metal ions and dyes in textile wastewater. Cr(III), Pb(II), Zn(II), and Cu(II) BPA, MB, BO2, and RhB were selected as modal pollutants to evaluate the adsorption performance of the polymer. FT-IR spectra of (MNP-CM-CDP) displayed the characteristic bands of –COOH groups and Fe3 O4 . Magnetic polarization analyses revealed that the polymer exhibited superparamagnetism, which was also supported by SEM. The adsorption efficiency of (MNP-CM-CDP) was well described by pseudo-first-order and pseudosecond-order model kinetics and adsorption mechanism well-fitted with Langmuir and Freundlich isotherms. The carboxyl groups formed complexes with the metal ions, whereas the BPA and dyes bound with the inner hydrophobic cavity of the β-CD. Heavy metal ions adsorption attained equilibrium in 5 min and BPA, MB, BO2, and RhB in 5–10 min. The effect of pH, ionic strength, and Humic acid was studied to analyze the optimum condition for the adsorption of pollutants by the polymer. (MNP-CM-CDP) can be regenerated by treating with methanol consisting of 5% acetic acid. Adsorption–desorption experiment suggests that (MNP-CM-CDP)

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can be reused for up to 5 cycles and later its performance was reduced by 5.79%. (MNP-CM-CDP) was tested using actual wastewater, and it has exhibited outstanding adsorption efficiency and stability which proves its use in the commercial treatment of aqueous solutions (Hu et al. 2020a). In the following research, a β-CD/MCM-48 composite was prepared for the adsorption of As(V) and Hg(II) ions from industrial wastewater in batch and column studies. Characterization was done using XRD analysis, and the results showed peaks at 6.81°, 10.85°, 12.57°, 12.63°, 13°, 15.56°, 18.94°, 19.78°, 27.33°, and 34.9° corresponding to the integrated β-CD. Additionally, FT-IR analysis was carried out for MCM-48, β-cyclodextrin/MCM-48 and the obtained bands imply the strong interactions between the functional groups of both components. SEM and HRTEM images showed the highly porous nature of the composite and the MCM-48 grains completely enclosed in β-CD leading to an increase in the particle size. Adsorption studies revealed the effect of various parameters like pH, temperature, and contact time for optimal adsorption capacity. The maximum adsorption capacities for As(V) and Hg(II) were found to be 265.6 mg g− 1 and 207.9 mg g− 1 , respectively. Adsorption of these heavy metals followed pseudo-second-order, pseudo-First order, and Elovich model kinetics. The Gaussian energy values (6.45 kJ/mol for As(V) and 3.95 kJ/mol for Hg(II) ions) obtained indicate the physical nature of uptake. Thermodynamic study results showed that the adsorption process was an exothermic, spontaneous, and favorable reaction. The recyclability tests ensured that the composite can be regenerated and reused for five consecutive cycles by treating it with dilute NaOH solution at 50 °C for 120 min. Therefore, β-cyclodextrin/MCM-48 was proven to exhibit excellent adsorption properties and can be used in the decontamination of aqueous solutions (Bin Jumah et al. 2021). Biological compounds can be exploited for the treatment of cyclodextrins to enhance their performance. In this study, β-CD was treated with citric acid followed by cross-linking with chitosan to prepare a CTS/β-CDP composite for the adsorption of heavy metal ions such as Zn2+ from industrial wastewater. The membrane was characterized by FT-IR analyses, in which the characteristic peaks of chitosan and β-CD were found confirming the synthesis of CTS/β-CDP. The morphology of the membrane was found in SEM images which showed a rough surface that increased the number of adsorption sites and leads to high adsorption efficiency. Further, the XRD pattern of CTS/β-CDP revealed its amorphous structure which was due to the disruption of hydrogen bonds in CTS after incorporation of β-CDP. UV-Vis analysis proved that CTS/β-CDP was more efficient for Zn2+ removal when compared to the CTS membrane. 2% acetic acid, 50 °C temperature, 1 h soaking in NaOH, and 30 ml water dosage of β-CDP were identified as the optimal conditions for the fabrication of the CTS/β-CDP composite. The maximum adsorption capacity was 123.7 μg g− 1 and the adsorption rate was approximately 94.14%. CTS/β-CDP showed less swelling than the CTS membrane due to the incorporation of β-CDP and glutaraldehyde. The CTS/β-CDP membrane surface had holes and depressions which trapped the metal ions. The simple synthesis process, good mechanical strength, and high adsorption rate indicate that the CTS/β-CDP membrane can be applied in large-scale wastewater treatments (Liu et al. 2020b).

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2.3 Removal of Textile Waste Selective elimination of methyl orange from a mixture of dyes (MB and RhB) was achieved by synthesizing chitosan-β-cyclodextrin (CSCD) complexed using glutaraldehyde as a cross-linking agent to form CRCSCD nanocomposite. The stability of these synthesized nanocomposites was increased by mixing a 10 mg adsorbent with a 50 mL MO aqueous solution. For validating successful crosslinking of polymer, FT-IR and 1 H NMR spectrum analysis of CS, CD, CSCD, and CRCSCD were done. Results of FT-IR spectra analysis showed absorption bands in the range of 4000−600 cm−1 , for different stretching vibrations present between different bonds concluding successful linkage between CS and CD. Apart from this, FT-IR spectra before and after the MO adsorption was analyzed, and the range in which adsorption peaks were observed concluded the successful adsorption of MO by CRCSCD. Further, 1 H NMR spectrum analysis showed peaks in the range of 2.0–6.2 ppm for different bonds present, indicating successful linkage between CS and CD via maleic anhydride. Thermal stability analysis done using TGA validated that CRCSCD has good thermal stability at low temperatures. A series of experiments with different parameters were carried out with different initial concentrations, and pH (low to neutral), contact time (600 min), and temperature (298 K) were determined as optimal conditions for maximum adsorption of MO. The adsorption behavior fitted the pseudo-second-order kinetics, and the Langmuir isotherm model shows maximum adsorption by homogeneous monolayer adsorption. As modified adsorbents resulted in excellent MO removal efficiency with CRCSCD showing the maximum adsorption capacity of 392 mg g−1 even with the small adsorbent dosage of 10 mg/50 mL, they make a good potential candidate for the purification and removal of dye pollutants from industrial wastewater, due to its selectivity and biodegradable nature (Jiang et al. 2018). In another study, the removal of MO from an aqueous solution was achieved by synthesizing ethanolamine and amine-functionalized porous-cyclodextrin polymers (P-CD-EA and P-CD-AM). For validating successful cross-linking of P-CDP, FT-IR spectrum analysis of P-CD-EA and P-CD-AM showed absorption peaks at 1081 cm−1 (stretching vibration of C–O bonds), 1275 cm−1 (stretching vibration of C–F bonds), 1606 cm−1 (stretching vibration of N–H bonds), and 2248 cm−1 (nitrile stretching signal) (Fig. 3a). 13 C solid-state NMR spectrum analysis showed vibrations at 55 ppm and 21 ppm for P-CD-EA and P-CD-AM respectively, and elemental analysis indicated the percentage of carbon, nitrogen, and hydrogen present in PCD, P-CD-EA, and P-CD-AM (Fig. 3b). Results of FE-SEM image analysis showed that functionalized P-CDPs had non-porous and smooth surfaces. Thermal stability analysis done using the TGA experiment validated that P-CD-AM has good thermal stability at high temperatures. The effect of pH on adsorption capacity was studied and pH 3 was determined to be the optimum pH for maximum adsorption of MO. The adsorption behavior fitted the pseudo-second-order kinetics, and the Langmuir isotherm model shows maximum adsorption by homogeneous monolayer adsorption. Results of adsorption selectivity showed that modified adsorbents have good

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Fig. 3 a IR spectrum displayed stretching vibrations for different bonds in P-CDP, P-CD-EA, and PCD-AM and b 13 C solid-state NMR spectrum for P-CDP, P-CD-EA, and P-CD-AM. Reprinted with permission from Duan HL, Deng X, Wang J, et al. (2020) Ethanolamine- and amine-functionalized porous cyclodextrin polymers for efficient removal of anionic dyes from water. Eur Polym J 133:109,762. https://doi.org/10.1016/j.eurpolymj.2020.109762

anionic dye adsorption. Modified P-CDPs with adsorbed pollutants are desorbed and regenerated using sodium hydroxide ethanol solution and water for enhanced recycling. As modified adsorbents resulted in 80% anionic dye removal efficiency with P-CD-AM showing the maximum adsorption capacity of 625 mg g−1 for 6 regeneration cycles, hence they make a good potential candidate for the purification and removal of acidic or negatively charged pollutants from industrial wastewater (Duan et al. 2020). Apart from methyl orange, other dyes like methylene blue were also eliminated from industrial wastewater. This study involves the removal of MB from an aqueous solution was achieved by synthesizing water-insoluble nanofibers using sericin, β-cyclodextrin, poly (vinyl alcohol) (PVA) along a cross-linking agent citric acid to form novel sericin/β-cyclodextrin/poly (vinyl alcohol) (PVA-SS-CD). FTIR spectrum analysis of PVA-C, PVA-CD, and PVA-SS-CD were done showing absorption peaks at 1731 cm−1 , 1200 cm−1 , 1665 cm−1 , 1532 cm−1 , 427 cm−1 , 928 cm−1 , 846 cm−1 , 719 cm−1 , and 590 cm−1 for different stretching vibrations present between different bonds concluding successful cross-linking and incorporation of sericin and β-CD onto nanofibers. Thermal stability analysis done using the TGA experiment validated good chemical adsorption of MB on PVA-SS-CD. The adsorption kinetic studies showed electrostatic interactions, and host–guest supramolecular interactions between PVA-SS-CD and MB followed pseudo-secondorder kinetics, and the Langmuir isotherm model for all temperatures showed maximum adsorption by homogeneous monolayer adsorption. Functionalized PVASS-CD with adsorbed pollutants is desorbed and regenerated using an ethanol solution containing 5% HCl for enhanced recycling. As functionalized nanofibers resulted in 92.60% removal efficiency with PVA-SS-CD showing the maximum adsorption capacity of 187.97 mg g−1 at 293 K even for 5 regeneration cycles, they make a good

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potential candidate for the removal of dye molecules from industrial wastewater (Zhao et al. 2015). Additionally, another research was carried out for the removal of MB from aqueous solution that was achieved by modifying polysaccharide β-cyclodextrin using modified graphene-oxide (GO) to form polysaccharide-modified β-cyclodextrin graphene oxide (β-CD/GO) nanocomposites. FT-IR spectrum analysis, which was obtained using the KBr pellet method, was done to understand changes in functional groups on GO and β-C/GO, showing absorption peaks in the range of 4000–400 cm−1 . Additionally, Raman analysis result interpretation concluded β-CD/GO has more structural defects than GO. Results of FE-SEM image analysis showed that β-CD/GO had good adsorption capacity. Additionally, the results of the XRD experiment concluded successful modification of nanocomposites. Thermal stability analysis done using the TGA experiment validated good thermal stability at high temperatures. A series of experiments with different parameters were carried out with different initial concentrations, and dosages of absorbent (0.04 g/L), pH (neutral), reaction time (60 min), and reaction temperature (70 °C) were determined as optimal conditions for increased adsorption of MB by 20%. The adsorption behavior well fitted the pseudo-secondorder kinetics, and the Langmuir isotherm model shows a difference in the adsorption capacity from parent nanocomposites under the same adsorption conditions. Modified β-CD/GO with adsorbed pollutants are desorbed and regenerated using absolute alcohol for enhanced recycling. As modified adsorbents resulted in an increase of removal efficiency of 20% with β-C/GO showing the maximum adsorption capacity of 76.4 mg g−1 for 9 regeneration cycles, from this research result interpretation, it is clear along with MB that it can be further exploited and used for elimination of organic dyes from industrial effluents (Yang et al. 2021). In another study, the removal of MB from an aqueous solution was achieved by synthesizing nanospheres done using cross-linking agent tetrafluoroterephthalonitrile (TFPPN) along with immobilized β-cyclodextrin on magnetic nanoparticles (Fe3 O4 @β-CD) to form magnetic β-cyclodextrin porous polymer nanospheres (PMCD). FT-IR spectrum analysis of Fe3 O4 , Fe3 O4 @β-CD, and P-MCD was done showing absorption peaks at 584 cm−1 , 3340 cm−1 , 2932 cm−1 , 1033 cm−1 , 1648 cm−1 , 1433 cm−1 , and 1267 cm−1 , validating successful polymerization of β-cyclodextrin porous polymer on magnetic nanoparticles. Results of SEM image analysis showed that functionalized β-CD had non-porous and smooth surfaces. For understanding the different characteristics of functionalized nanospheres, different analyses like UV-Vis, TGA, XPS, XRD, and BET were conducted. Thermal stability analysis done using TGA validated the good thermal stability of MB at higher temperatures. The effect of pH on maximum adsorption of MB was studied and pH 7 was determined to be the optimum pH. The adsorption kinetic studies were done, where it was found hydrogen-bond interactions, π–π conjugate interaction, and host–guest supramolecular interactions between P-MCD and MB followed pseudo-second-order kinetics, and Langmuir isotherm model shows maximum adsorption by homogeneous monolayer adsorption. Functionalized P-MCD with adsorbed pollutants is desorbed and regenerated using an ethanol solution containing 5% acetic acid for

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enhanced recycling. As functionalized adsorbents resulted in 86.35% removal efficiency with P-MCD showing the maximum adsorption capacity of 305.8 mg g−1 even for 7 regeneration cycles, they make a good potential candidate for the removal of organic pollutants from industrial wastewater (Liu et al. 2019). Now, in further studies along with MO and MB, simultaneous elimination of other pollutants was also carried out; as seen in this study, simultaneous removal of metal (boron), dyes (MB, MO), and organic pollutant (phenol) from aqueous solution was achieved by incorporating N-Methyl-D-glucamine and glycidol-functionalized polyol groups with maximum adsorption capacity of nanosponges achieved by adding 5 ml GPA (β-CD-9PGMA-MG and β-CD-9PGMA-EN-PG). The adsorption capacity of these pollutants (dyes and organic pollutants) before and after the addition of nanosponge was deducted using UV-Vis spectroscopy. Characterization of synthesized nanosponges, done using 1 H NMR, showed adsorption peaks attributing successful synthesis of β-CD-9PGMA. Further, the results of FT-IR spectra analysis, which showed adsorption peaks corresponding to different stretching and vibration bonds, validated the successful synthesis of β-CD-9PGMA-MG and β-CD-9PGMAEN-PG. The adsorption capacity of boron and chemical characteristics of synthesized nanosponges were studied using XRD, which showed adsorption peaks at 2θ = 18° and 2θ = 11.4°, validating successful boron adsorption and amorphous nature of adsorbent. Additionally, the surface and chemical composition of synthesized nanosponges before and after boron adsorption was studied using XPS analysis showing the presence of other elements (oxygen, chlorine, carbon, nitrogen, and bromine) along with boron. Results of SEM image analysis showed that functionalized β-CD-9PGMA-MG had a 3D network structure having a smooth surface. Thermal stability analysis done using TGA validated that boron has good thermal stability at low temperatures. A series of experiments with different parameters were carried out and contact angle, pH (below 8), initial concentration of boron, and adsorption time were determined for maximum adsorption of boron, MB, MO, and phenol. The adsorption behavior fitted the pseudo-second-order kinetics, and the Langmuir isotherm model shows maximum adsorption by single-layer adsorption. Modified nanosponges with adsorbed pollutants are desorbed and regenerated using dilute acid (H2 SO4 and HCl) and alkali solution (NH3 ·H2 O and NaOH) for enhanced recycling. To conclude, modified adsorbents resulted in excellent boron removal efficiency with β-CD-9PGMA-MG and β-CD-9PGMA-EN-PG showing the maximum adsorption capacity of 31.05 mg g−1 and 20.45 mg g−1 even after 5 successive cycles. Results of the experiments conducted for calculating the adsorption efficiency of boron showed very less influence of inorganic salts. Therefore, these can be potentially good candidates which can be used to eliminate metals, dyes, and organic pollutants simultaneously, due to their selectivity and biodegradable nature (Luo et al. 2020). In another study, simultaneous removal of metal (Hg(II)) and dyes (MB and MO) from aqueous solution was achieved by synthesizing β-CD-based nano adsorbents using cross-linking agent nitrilotriacetic acid (NTA) along with potassium dihydrogen phosphate (KH2 PO4 ) at 25 °C to form NTA-β-CD. Further, modification of the NTA-β-CD cross-linked polymer was done by dissolving it in chitosan (CD),

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4 g in 1 M HCl solution at 85 °C along with glutaraldehyde used as cross-linking agent yielding NTA-β-CD-C. For validating successful cross-linking between CS and glutaraldehyde, FT-IR spectrum analysis was done. Results of SEM image analysis showed that NTA-β-CD-C had a smooth surface. EDAX and BET analysis, wherein NTA-β-CD-C showed an increase in carbon and nitrogen content with a bigger BET surface area in comparison to NTA-β-CD, further validating successful cross-linkage between CS and glutaraldehyde. Additionally, studies on proposed adsorption mechanisms were validated by XPS analysis. A series of experiments with different parameters were carried out and pH (6), pollutant concentration, and contact time (90 min) were determined as optimal conditions for maximum adsorption of metals and dyes. The adsorption behavior well fitted the pseudo-second-order kinetics and multiple isotherm models (Sips and Langmuir isotherm models) showing maximum adsorption by monolayer adsorption. Modified NTA-β-CD with adsorbed pollutants is desorbed and regenerated using ethanol with 1% HCl for enhanced recycling. Removal efficiency after using NTA-β-CD-C yielded a maximum adsorption capacity of 178.3 mg g−1 (Hg(II)), 162.6 mg g−1 (MB), and 132.5 mg g−1 (MO) for 4 regeneration cycles. When the same nano adsorbent was used to eliminate dyes from textile sewage waste, maximum adsorption of MO and MB was 125.0 mg g−1 and 155.2 mg g−1 , respectively. So, to conclude due to their stability and reusable property, they have the potential for simultaneous elimination of pollutants from industrial effluents (Usman et al. 2021b). Apart from the elimination of desired dye from a mixture of dyes, the elimination of dyes from a mixture of micropollutants was also conducted. Here, the removal of micropollutants (BPA, MB, and NR) from the aqueous solution was achieved by synthesizing novel nano adsorbents done by cross-linking β-CD with sugarcane bagasse with cross-linking agent citric acid and sodium dihydrogen phosphate (NaH2 PO4 ) to form sugarcane bagasse-β-cyclodextrin polymer (SB-β-CD). For validating the successful modification of nano adsorbent, FT-IR spectrum analysis was done. For understanding morphological characteristics and validating cross-linking of synthesized nano adsorbent, different experiments like XRD and BET analysis were conducted, respectively. A series of experiments with different parameters were carried out for BPA, MB, and NR and pH (7, 9, and 6 respectively), contact time (300 min, 300 min, and 240 min respectively), absorbent concentration (directly proportional to pollutant adsorption), SB-β-CD dosage (inversely proportional to binding affinity with adsorbent), and salts were determined for maximum adsorption of micropollutants. The adsorption behavior well fitted the pseudo-second-order kinetics and multiple isotherm models (Langmuir isotherm model for BPA, and Freundlich model for MB and NR). Results of adsorption mechanisms showed that adsorption of BPA is slowest, compared to MB and NR, and results of adsorption thermodynamics confirmed physical adsorption. Modified SB-β-CD with adsorbed pollutants are desorbed and regenerated using 75% ethanol, 0.1 mol L−1 (HCl, NaCl, NaOH), and distilled H2 O for enhanced recycling, as modified adsorbents resulted in excellent removal efficiency with SB-β-CD showing the maximum adsorption capacity of 121 mg g−1 (BPA), 963 mg g−1 (MB), and 685 mg g−1 (NR) for 4 regeneration cycles. To conclude, with fairly good adsorption (BPA (92%), MB (96%),

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and NR (95%)) and desorption efficiency (BPA (88%), MB (86%), and NR (90%)), they serve as the best candidate for the elimination of micropollutants from industrial wastewater (Mpatani et al. 2020). Additionally, studies were conducted for understanding the removal of hydrophobic, and hydrophilic dyes from aqueous solution were achieved by synthesizing eco-friendly nanosorbent for eliminating hydrophilic (MG, MB) and hydrophobic dyes (R6G) from aqueous solution. Synthesis of super magnetic nano adsorbents (SPNA) was achieved by using cross-linked β-Cyclodextrin with maleic anhydride (CD-MA) along with covalently conjugated magnetic nanoparticles (MNPs) via ester linkages. A series of experiments were conducted to understand the efficiency of synthesized nano adsorbents. Results of TGA analysis were done for assessing the thermal stability, which showed 3 stages of synthesized nano adsorbent degradation. Further, the magnetic properties of MNPs and SPNA were analyzed using VSM, where SPNA showed decreased magnetic properties as compared to MNPs. A series of experiments carried out in pH 7 at 25°C, for accessing different parameter-cavity of cyclodextrin (MG having highest and R6G having lowest removal efficiency), super magnetic nano adsorbents dosage (inversely proportional to removal efficiency), contact time (30 min), initial concentration (MG-30 mg/L and MB, R6B-20 mg/L), and reaction temperature was determined as optimal conditions for increased adsorption. The adsorption behavior well fitted the pseudo-second-order kinetics and Langmuir isotherm model. Modified nanocomposites with adsorbed pollutants are desorbed and regenerated using ethanol solution for enhanced recycling. To conclude, modified nano adsorbents had excellent dye removal efficiency, maximum being 85.1%, 97.2%, and 37.3% for MG, MB, and R6G respectively, for 5 regeneration cycles. An added advantage of using these nano adsorbents for treating industrial wastewater is that elimination of hydrophobic and hydrophilic dyes can be achieved simultaneously. Being environmentally friendly, low-cost, and feasible, with higher removal efficiency compared to other used nano adsorbents, makes it one of the potential candidates for removal of dyes, especially MG from industrial wastewater (Yadav et al. 2019). Another research conducted on removal of cationic dyes (methylene blue, safranin T, rhodamine B, and malachite green) and anionic dye (methyl orange) was achieved by synthesizing β-cyclodextrin-based nanosorbents which was done using crosslinking agent glutaraldehyde aided by cross-linker accelerator tetramethylethylenediamine to form β-cyclodextrin and graphene oxide functionalized porous superabsorbent composite hydrogel (β-CD/MGO/PAA) via the simple-one-pot method. Results of FE-SEM image analysis concluded that β-C/GO had good adsorption capacity. Results of the TGA and VSM analysis showed successful incorporation of β-CD/MGO into β-CD/MGO/PAA hydrogel. Apart from this, results of adsorption performance tests showed higher removal efficiency for cationic dyes-MB, ST, RhB, and MG (99.1%, 98.5%, 95%, and 97.1%, respectively) but no adsorption for anionic dye. A series of experiments with different parameters were carried out and pH, ionic strength, adsorbent dosage (40 and 60 gms for MB and ST respectively), and contact (180 min), initial concentration, and temperature were determined for

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increased adsorption of cationic dyes. The adsorption behavior well fitted the pseudosecond-order kinetics for MB and ST and Langmuir isotherm model via single monolayer adsorption. Further results of adsorption thermodynamics conducted at different temperatures (298 K, 308 K, and 318 K) indicate spontaneous and exothermic adsorption reactions. Modified β-CD/MGO/PAA where adsorbed pollutants are desorbed and regenerated using anhydrous ethanol and an appropriate 0.1 mol/L HCl for enhanced recycling. As modified adsorbents resulted in an increase of removal efficiency of 95% (MB) and 85% (ST) with β-CD/MGO/PAA showing the maximum adsorption capacity of 802.67 mg g−1 (MB) and 1470.33 mg g−1 (ST) for 8 regeneration cycles at 298 K, from this research result interpretation, it is clear along these hydrogels are highly selective, fast, convenient, and capable for adsorbing cationic dyes from a mixture of cationic/anionic dyes mixture, under the influence of the external magnetic field. This research can be a steppingstone for using these adsorbents for purifying industrial wastewater. Apart from this, another application includes utilizing β-CD/MGO/PAA hydrogel as column packing for the elimination of cationic dyes through filtration (Li et al. 2021). Additionally, research was carried for understanding the removal of toxic dyes from the aqueous solution which was achieved by synthesizing nano adsorbents using super magnetic iron oxide to produce iron oxide, N-heterocyclic palladium complex [Fe3 O4 @CM-β-CDP@Ted-Pd] adsorbents. Along with these, magnetic nanoparticles (Fe3 O4 ), carboxymethyl-β-CD polymers (CM-β-CDP) were synthesized for preparation of Fe3 O4 @CM-β-CDP@Ted-Pd. FT-IR spectrum analysis showed absorption peaks at 1031 cm−1 , 1155 cm−1 , 1720 cm−1 , 1423 cm−1 , and broader peaks at 3300–3500 cm−1 and 2925 cm−1 , 1045, and 883 cm−1 , validated successful modification of nano adsorbents. Results of FE-SEM and TEM image analysis described the morphological characteristics of synthesized nano adsorbents, which have a homogeneous sphere of diameter 20 nm, with iron oxide present in the inner core, forming a core–shell structure. Additionally, XRD and EDAX spectra analysis was done to get the detailed information regarding the morphological characteristics of prepared nano adsorbents. Results of TGA/DTA, VSM, and magnetization curve analysis provided information regarding thermal stability and magnetic property of the synthesized nanocomposites. To understand the catalytic activity of nano adsorbents, the reduction of 5 dyes—MB, RhB, Eosin Y, Metanil yellow, and 4-nitrophenol—in aqueous solution was monitored using UV-Vis. Modified nanocomposites with adsorbed pollutants are desorbed and regenerated using deionized water and ethanol for enhanced recycling. Modified nanocomposites displayed higher catalytic activities (5 s, 9 min, 21 min, 10 s, and 19 s) for MB, RhB, Eosin Y, Metanil yellow, and 4-nitrophenol respectively, in the presence of reducing agent, sodium borohydride (NaBH4 ) even after 6 regeneration cycles. This property along with the added benefit of reusability and stability makes it one of the excellent candidates for eliminating dyes from industrial wastewater (Lighvan et al. 2021). Though many kinds of adsorbents have been synthesized for the elimination of pollutants from industrial wastewater, the synthesis of novel adsorbents was successfully prepared for eliminating crystal violet, heavy metal ions, anionic, cationic, and

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neutral dyes from aqueous solution. For this synthesis of thin-walled, multiple cavities (150 nm), β-C polymer (Hβ-CDs) absorbent was prepared using synthesized silver nanoparticles (SiO2 ) along with functionalized β-C with acryloyl chloride. To validate the successful synthesis of Hβ-CDs, FT-IR absorption peaks were obtained using the KBr pellet method at 468 cm−1 and 804 cm−1 (SiO2 ), 760 cm−1 , and 532 cm−1 (β-C), 1458 cm−1 , and 1157 cm−1 (Hβ-CDs) were analyzed. Results of SEM and TEM image analysis showed the successful synthesis of Hβ-CDs, whereas results of BET analysis gave dimensions of surface area (19.35 m2 g−1 ) and total pore volume (0.065 cm3 g−1 ) for Hβ-CDs. A series of experiments were carried out for understanding the adsorption of CV on Hβ-CDs, and it was concluded that adsorption efficiency can be increased by increasing the pH and ionic strength of the aqueous solution. Results of adsorption mechanisms demonstrated improved adsorption efficiency after using Hβ-CDs. Modified Hβ-CDs with adsorbed pollutants are desorbed and regenerated using ethanol solution for enhanced recycling. The adsorption behavior fitted the pseudo-second-order kinetics, and the Langmuir isotherm model shows maximum adsorption by monolayer adsorption. Modified adsorbents showed 89% removal efficiency for 4 regeneration cycles. To conclude, apart from these, results of batch adsorption experiments demonstrated that, while using Hβ-CDs, better adsorption was observed for cationic (RhB, CV) and neutral dye (Bromophenol blue), whereas poor adsorption was observed for anionic dyes (Orange G, Congo Red) and heavy metal ions (Cu2+ , Pb2+ ). Utilizing these properties, these nanosorbents can be used for treating industrial wastewater, owing to their renewability, reusability, and efficiency in simultaneously treating cationic as well as neutral dyes (Chen et al. 2019). Apart from dyes discussed in previous sections, here removal of RhB from aqueous solution was achieved by synthesizing nano adsorbent from the encapsulation of Triclosan ((5-chloro-2-(2,4-dichlorophenoxy) phenol)) inside the hydrophobic pocket of HP-β-CD to form triclosan (TR)-2-hydroxypropyl–β–cyclodextrin (HPβ-CD) inclusion complex (TP: HP-β-CD). Results of FT-IR spectrum obtained using KBr pellet showed characteristic peaks at 1596.80 cm−1 , 1576.09 cm−1 , 1504.90 cm−1 , 1471.32 cm−1 , 1417.95 cm−1 , 1391.81 cm−1 (TR), and 1032.13 cm−1 , 1081.89 cm−1 , 1157.64 cm−1 (TP:HP-β-CD), conforming successful synthesis of TP:HP-β-CD. Additionally, XRD, FT-Raman, and MALDI-TOF analyses were done for understanding the characteristics of the inclusive complex. Results of SEM image analysis demonstrated the formation of solid-state inclusion complex, whereas results of H1 NMR analysis predicted encapsulation of TR into the pocket of HP-β-CD. A series of experiments were carried out in pH 7 at 30 °C for understanding the effect of adsorbent dosage, initial concentration, contact time on absorption efficiency. The adsorption behavior fitted pseudo-second-order kinetics and the Langmuir isotherm model shows maximum adsorption by monolayer adsorption. To conclude, apart from these, results of batch adsorption experiments demonstrated that TP: HP-β-CD efficiently adsorbs RhB from aqueous solutions, with maximum adsorption efficiency as 261.78 mg g−1 . Utilizing these properties, these nanosorbents can be used for simultaneously treating dye toxicity and microorganism, as Triclosan is a broad-spectrum

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antibacterial agent, it would be capable of eliminating a wide range of microorganisms. Further research can be done regarding the thermal stability and reusability of these encapsulated complexes (Maniyazagan et al. 2019). Summing up our discussion, here removal of toxic dyes from aqueous solution was achieved by synthesizing nano by encapsulation of hydrophilic azo dye (Oil orange SS (OOSS)) inside the hydrophobic pocket of β-CD using co-precipitation method. For carrying out a comparative study, another nano adsorbent was synthesized wherein encapsulation of both OOSS and crystal violet (CV) inside the hydrophobic pocket of β-CD was done. Further, FT-IR spectra obtained using the KBr pellet method showed absorption peaks in the range of 4000–400 cm−1 , resembling stretching frequencies of various bonds present in the nano adsorbents structure were analyzed, and results supported successful encapsulation. Results of the TGA experiment also resulted in successful encapsulation with the good thermal stability of the parent inclusive complex. Results of the DSC experiment also resulted in successful encapsulation. A series of other experiments were carried out for understanding crystal formation (XRD) and binding affinity between dye and hydrophobic pocket of β-CD (UV-Vis). Finally, to conclude results of different experiments conducted at different concentrations of inclusion complex prepared, resulted in higher removal efficiency by OOSS-β-CD than OOSS-CV-β-CD, making the former one of the best potential candidates not only for OOSS but can be used in the elimination of other azo dyes from industrial wastewater (Saifi et al. 2021).

2.4 Removal of Pharmaceutical Waste Elimination of toxic and non-biodegradable pimavanserin (PMV) drug molecules from pharmaceutical wastewater were achieved by synthesizing water-insoluble nanosponges. Synthesis of nanosponge was done using β and G-cyclodextrin (β-CD and G-CD) which was cross-linked with 1,10-carbonyldiimidazole (CDI) via condensation–polymerization reaction to form β and G-nanosorbents (β-NS and G-NS). While conducting this research, biological degradation and toxicity of pimavanserin from activated sludge were determined using high-performance liquid chromatography (HPLC) and microtox bioassay, respectively. Further, SEM image analysis supported the presence of adsorption sites on the surface of β-NS and G-NS. A series of batch experiments for different parameters were carried out, and pH (7), contact time (30 min), and temperature (25 °C) were determined as optimal conditions for maximum adsorption of PMV drug. Apart from this, the effect of adsorbent mass on adsorption capacity was studied, and the removal efficiency of PMV is directly proportional to the adsorbent dosage. Moreover, the effects of adsorbent types were also studied to have a better knowledge about adsorption efficiency. N2 adsorption–desorption at 77 K was used to understand adsorption behavior which fitted the Freundlich isotherms model. Modified nanosorbents with adsorbed pollutants are desorbed and regenerated with methanol for enhanced recycling. Modified NSs eliminated 93% and 83% PMV from model wastewater showing the maximum

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adsorption capacity of 52.08 mg g−1 and 23.26 mg g−1 for β and G-NS respectively for 3 regeneration cycles. Moreover, the adsorption efficiency of these synthesized nanosponges was compared with activated carbon nano adsorbents, and fast and efficient removal of PMV was done by β-CD and G-CD (93% and 81% respectively) in 60 s. Apart from this, adsorption efficiency was observed in model post-reaction raffinates. As the research conducted provides fair enough information regarding the advantages of using this nanosponge (NSs), apart from drugs they serve as a potential candidate for eliminating organic pollutants from industrial wastewater (Hemine et al. 2020). Not just drugs, studies on removal of hormones were also studied; here, elimination of synthetic hormone (17A-methyltestosterone) from aqueous solution was conducted using β-CD covalently bonded to silica. While synthesizing functionalized β-CD covalently bonded to silica, citric acid was used as binders (organic–inorganic hybrid nanocomposite). FT-IR spectra obtained using the KBr pellet method showed characteristic peaks in the range of 4000 to 400 cm−1 . Additionally, TGA, DTA, BET, BJH, and solid-state CP/MAS 13 C NMR analyses were done for understanding the characteristics of the nano adsorbents. Further, results of TGA and DTA analysis concluded that at low temperature, 62.6% of functionalized β-CD remained attached to the inorganic matrix. Moreover, the results of BET and BHJ results concluded that BET surface area and pore volume decrease with the functionalization of β-CD. Additionally, solid-state CP/MAS 13 C NMR results concluded that the mechanism of functionalized β-CD occurs by the esterification method. The adsorption behavior well fitted the pseudo-second-order kinetic model and Langmuir and Sips isotherm models show maximum adsorption by monolayer adsorption. Further results of adsorption thermodynamics concluded successful coating of MT molecules to composite surface. Additionally, studies on adsorption mechanisms showed successful entrapment of MT into the hydrophobic cavity of β-CD in the ratio of 2:1. Modified Hβ-CDs with adsorbed pollutants are desorbed and regenerated using ethanol solution for enhanced recycling. Modified adsorbents showed 62.6% removal efficiency. To conclude, apart from these, results of adsorption assay indicate adsorption efficiency, with a maximum adsorption capacity of 11 mg g−1 at 25o C. Further column assay was done with 98% ethanol, showing a subsequent decrease in adsorption efficiency, with several adsorption cycles. Utilizing these properties, these nanosorbents can be used as filters for eliminating MT in agriculture and livestock farming. Further research can be done regarding the reusability of these organic–inorganic hybrid complexes (Carvalho et al. 2019). To validate the research, elimination of different kinds of drugs were studied, like here removal of diclofenac from 5 sample pharmaceutical wastewater collected from different locations, construction of sensitive sensors was carried out by functionalization of iron nanoparticles was achieved by coating Fe2 O3 on the surface of βcyclodextrin polymer using 0.35 ml dibutyl phthalate (DBP) and 5 ml tetrahydrofuran (THF) solvent. Further, functionalization of sensors was done by combining it with PVC to form MG-Fe (β-CD) and CV-Fe (β-CD) sensors. After calibration of sensors by immersing it in 50 ml standard diclofenac solutions, a series of batch experiments for different parameters were carried out, and pH (7) and sensor sensitivity (CV-Fe

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(β-CD) showed higher sensitivity than MG-Fe (β-CD)) were determined. Functionalized sensors with adsorbed pollutants are desorbed and regenerated by dipping electrodes in diclofenac potassium salt solution (from higher to lower concentration) for enhanced recycling. To conclude, the amount of diclofenac present in pharmaceutical wastewater and dosage form was calculated and compared with the calibration curve. An added benefit of using this method lies in its hush selectivity toward organic and inorganic pollutants without prior sample treatment makes MG-Fe (β-CD) and CV-Fe (β-CD) sensors the best candidate for eliminating diclofenac from industrial raffinates (Elbalkiny et al. 2019). Research for eliminating another drug was studied, wherein for removal of atrazine drug from aqueous solution, synthesis of water-insoluble CD-based polymers was done by cross-linking them with cross-linking agent epichlorohydrin (α-EPI, βEPI, and γ-EPI, respectively) to form α-CD, β-CD, and γ-CD polymers (ECPs). Before proceeding with research, atrazine quantification from an aqueous solution was performed using HPLC and double UV-Vis spectroscopy. Results of FT-IR and DCS confirmed successful adsorption of atrazine drugs from an aqueous solution. The adsorption behavior fitted the pseudo-second-order kinetic model, and the Freundlich isotherm model showed maximum adsorption by heterogeneous adsorption. A series of batch experiments for different parameters were carried out, and adsorbent dosage (directly proportional to removal efficiency), initial concentration (good adsorption at low concentration observed for α-EPI), pH (neutral), temperature (inversely proportional to adsorption efficiency), temperature (35 °C), and ionic strength with α-EPI using NaCl (directly proportional to removal efficiency) were determined for maximum adsorption of atrazine. Further results of adsorption thermodynamics showed that the adsorption process is exothermic, exergonic in nature. Modified ECPs with adsorbed pollutants for α-EPI are initially desorbed and regenerated using water, ethanol, and methanol for enhanced recycling. After a series of tests by keeping all parameters the same, lead to methanol being for maximum adsorption with 5 regeneration cycles. To conclude, having less contact time (1 h) can be an added benefit for using them at an industrial scale; apart from this, the process can be carried out in low concentration. Also, to add regeneration is done using biodegradable solvent, so these have a good practical application for the elimination of atrazine drug from pharmaceutical wastewater (Romita et al. 2019). Another study wherein removal of sulfamethoxazole drug from the water was studied by synthesis of water-insoluble β-CD-based polymers was done by cross-linking them with cross-linking agent epichlorohydrin to form cyclodextrinepichlorohydrin polymer (β-EPI). SEM image analysis gave morphological characteristics of β-EPI. The adsorption behavior fitted the pseudo-second-order kinetic model, and multiple isotherm models (Freundlich and Dubinin–Radushkevich isotherm models) show maximum adsorption by heterogeneous adsorption. A series of batch experiments for adsorption of sulfamethoxazole onto β-EPI were carried out, and the effect of salt (depending on salt; either increases or decreases), and size and charge on anions (inversely proportional to adsorption efficiency) were determined. Further results of adsorption thermodynamics showed that the adsorption process is exothermic in nature. Modified β-EPI with adsorbed pollutants is desorbed and

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regenerated using a 0.5 M solution of sodium bromide for enhanced recycling. Modified β-EPI showed absorption efficiency with maximum adsorption of 61.7% for 5 regeneration cycles. To conclude, these adsorbents can have practical application in the removal of sulfamethoxazole from pharmaceutical wastewater, owing to its ease of handling and reusability. Further research can be done in understanding removal efficiency from the pool of pollutants (Romita et al. 2021). In this study, for removing fluoxetine hydrochloride (FLU) from aqueous solution, synthesis of β-CD-based nanocomposite polymers was carried by cross-linking βCD to form β-cyclodextrin-carboxymethylcellulose (β-CD-CMC) polymer. Results of FT-IR spectrum observed before and after adsorption showed absorption peaks at 1030 cm−1 and 1024.2 cm−1 , indicating 100% sorption of FLU. Additionally, results of UV-Vis spectroscopy also concluded adsorption of FLU by a β-CD-CMC polymer. The adsorption behavior fitted a pseudo-second-order model, and the Freundlich isotherm model showed maximum adsorption by multi-layer heterogeneous adsorption. To conclude, β-CD-CMC polymers showed maximum adsorption at 5.076 mg of FLU/g. Considering all the factors, they can serve as a good candidate for removal of FLU from industrial wastewater owing to its high adsorption capacity and non-toxic nature of the β-CD-based polymer. Further research can be done for understanding the regeneration and reusability of these adsorbents (Bonenfant et al. 2012). In another research for removing ciprofloxacin from an aqueous solution, synthesis of recyclable nanosponges was done using α, β, and γ-cyclodextrin in 0.2 M NaOH sodium hydroxide solution using cross-linking agents 1,4-butanediol diglycidyl ether (BDE), and 1,4-diazabicyclo octane (DABCO). Further, FT-IRATR spectra analysis showed absorption peaks at 900-650 cm−1 , 750 cm−1 , 1080– 1000 cm−1 , 1400–1150 cm−1 , 1640 cm−1 , 2869 cm−1 , 2932 cm−1 , 3354 cm−1 ; these results confirmed successful cross-linking of nanosponges. Additionally, SEM image analysis supported the presence of smooth external surfaces on synthesized nanosponges. Apart from this, EDAX, XRD, and gas-volumetric analyses were also conducted to gather more information about the morphological and chemical characteristics of the synthesized nanosponges. Further, TG and DSC analysis was done for gaining information regarding thermal stability, where maximum decomposition rate temperatures were observed at 320 °C, 328 °C, and 324 °C for α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, respectively. Along with these, UV-Vis analysis was done to have a fair understanding of the adsorption process. The adsorption behavior fitted the pseudo-second-order kinetic model and multiple isotherm models (Freundlich, Temkin, and Dubinin–Radushkevich isotherm models) show maximum adsorption by heterogeneous adsorption. A series of batch experiments for different parameters were carried out, and pH (6), nanosponges amount (directly proportional to adsorption efficiency), and ciprofloxacin concentration (directly proportional to adsorption efficiency) were determined for maximum adsorption of ciprofloxacin drug. Modified nanosponges with adsorbed pollutants are desorbed and regenerated using a 0.1 M NaCl solution for enhanced recycling. Modified nanosponges showed 80% absorption efficiency for 5 regeneration cycles. To conclude, apart from these, results of batch adsorption experiments demonstrated that modified adsorbent resulted in excellent ciprofloxacin removal efficiency (90%) with a maximum

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adsorption capacity of 2 mg g−1 in a few minutes. Apart from these, to have a better understanding of adsorption efficiency, the removal of 4 drugs—Diclofenac, Carbendazim, Furosemide, and Sulfamethoxazole—was achieved in every short span, even if present in the mixture, further validating the adsorption efficiency of this modified nano adsorbent. Utilizing the properties of nano adsorbents, they make a good potential candidate for the purification and removal of drugs from industrial wastewater (Rizzi et al. 2021). Additionally, elimination from a mixture of pollutants was conducted as seen in this study, for removal of 2 dyes—MV, brilliant green (BG), 2 drugs—norfloxacin (NOX), ciprofloxacin (CPX), and 1 metal ion—Cu(II) from aqueous solution; synthesis of the novel gel-based polymer was carried out in 3 steps. First, the synthesis of Fe2 O3 was done by the co-precipitation method. After this, Fe3 O4 :AC nanocomposites were coated onto β-CD in the ratio of 1:1. Finally, synthesis of Fe3 O4 /CD/AC/ SA gel bead polymer was done, with CaCl2 used for bead preparation. Further, FT-IR spectra analysis showed absorption peaks in the range of 4000–500 cm−1 confirming successful incorporation of Fe3 O4 /CD/AC/SA into calcium chloride gel beads. On the further interpretation of results, adsorption peak intensity decreases and shifts were observed before and after adsorbed pollutants. Results of SEM/EDAX image analysis concluded the presence of uneven, porous surface, which can be pointed out as a reason for increased pollutant adsorption after modification of nano adsorbent. To further validate the adsorption of Cu(II) EDAX spectrum was analyzed, which proved the adsorption of Cu(II) by a functionalized gel-bead polymer. Additionally, BET and VSM result analysis concluded successful adsorption by functionalized nano adsorbent. Results of TGA/DTG/DTA analysis showed good thermal stability upon the addition of AC and Fe3 O4 . The adsorption behavior fitted the pseudosecond-order kinetic model, and multiple isotherm models (Langmuir and Temkin isotherm models) show maximum adsorption. A series of batch experiments for different parameters were carried out, and pH (6, drugs 5, and 6), adsorbent dosage (10 g L−1 , 15 g L−1 , and metal ion 10 g L−1 ), contact time (MV (100 min), BG (110 min), drugs (130 min) and metal ion (150 min)), initial concentration (10 g L−1 , 10 g L−1 , and 20 g L−1 ), temperature (35 °C), and ionic strength (order of inhibition by salts: CaCl2 ≥ NaHCO3 > NaCl > NaNO3 ) were determined for dyes, drugs, and Cu(II), respectively. Further results of adsorption thermodynamics showed that the adsorption process is viable, spontaneous, and endothermic. Modified gel bead polymer with adsorbed pollutants is desorbed and regenerated using 20 mL of 0.1 M HCl, 0.005 M NaCl, and 0.01 M EDTA solutions for enhanced recycling. Modified gel bead polymer showed absorption efficiency with maximum adsorption of 5.882 mg g−1 (MV), 2.283 mg g−1 (BG), 2.551 mg g−1 (NOX), 3.125 mg g−1 (CPX), and 10.10 mg g−1 (Cu(II)) for 5 regeneration cycles. To conclude, a comparative study between the synthesized gel bead polymer and commercially available adsorbent was done, which makes it a good candidate for the simultaneous elimination of dyes, drugs, and metal ions from a single aqueous solution. Additionally, owing to its cheap cost and regeneration, it can be used for eliminating different types of toxic pollutants from industrial raffinate (Yadav et al. 2021).

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In this work, for removing acetaminophen from an aqueous solution, synthesis of nanomaterial was carried out in 2 steps. First, the synthesis of chitosan/βcyclodextrin was done using cross-linking agent 5% glutaraldehyde. After this, Ca2+ ions were incorporated into chitosan/β-cyclodextrin to form Ca(II)-doped chitosan/ β-cyclodextrin composite material. Further, FT-IR spectra analysis showed absorption peaks at 159 cm−1 , 1685 cm−1 , 1720 cm−1 , and confirmed successful doping of Ca2+ ions into the chitosan/β-cyclodextrin composite material. Additionally, SEM image analysis showed rough external surfaces with varying sizes of pores on a synthesized nanomaterial, facilitating higher acetaminophen adsorption. Apart from this, EDAX and XRD analyses were done which validated the successful incorporation of Ca2+ ions into the chitosan/β-cyclodextrin composite material. Further, the results of TGA and DTA analysis showed good thermal stability and the formation of calcium oxide at high temperatures. The adsorption behavior fitted the pseudosecond-order kinetic model, and Freundlich isotherm model shows maximum adsorption by heterogeneous adsorption. A series of batch experiments for different parameters were carried out, and contact time (130 min), temperature (300 to 315 K), pH (7.2), and adsorbent dose (0.01 g), and initial concentration of acetaminophen (20 mg/L) were determined for maximum adsorption which increased by 13.58% to 99.88%. Further results of adsorption thermodynamics describe the nature of the adsorption process. Modified nanomaterial with adsorbed pollutants is desorbed and regenerated using 20 mL of 0.3 M HCl solution for enhanced recycling. Modified nanomaterial showed 99.80% absorption efficiency with maximum adsorption capacity at 200.86 mg g−1 for 2 regeneration cycles. To conclude, further validation of this research was done by comparative studies with commercially available nano adsorbents that showed higher removal efficiency for synthesized nanocomposites. Apart from this, adsorption efficiency for tap and municipal water (97.4% and 96.8% respectively) was calculated. Utilizing these properties, the nanocomposite can be used for eliminating acetaminophen from industrial wastewater. Further research can be done for increasing the reusability of these nanocomposites (Rahman and Nasir 2020). Additionally, interesting research involving removal of acetaminophen from aqueous solution, synthesis of β-CD-based nanocomposite super magnetic composite nanomaterial was achieved by using β-CD along with potassium permanganate (KMnO4 ) oxidation, coupled with the incorporation of citric acid-based super magnetic particle (Fe3 O4 ) gives rise to magnetic β-CD polymer (MNPs/β-CDP). Before conducting adsorption experiments, the presence of this acetaminophen in an aqueous solution was deducted using HPLC. Results of FT-IR spectrum of tetrafluoroterephthalonitrile, MNPs, β-CD, and MNPs/β-CDP showed characteristic peaks, indicating successful modification and synthesis of MNPs/β-CDP. Further, results of TEM image analysis showed uniform and regular spheres of diameter (200–250 nm) for synthesized Fe3 O4 , indicating successful incorporation of β-CDP onto MNPs. Additionally, XRD analysis was done for understanding morphological characteristics also interpreting successful modification of successful incorporation of β-CDP onto MNPs. Results of BET and VSM analysis further validate successful incorporation of β-CDP onto MNPs. The adsorption behavior fitted pseudo-second-order

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kinetic model and multiple isotherm models (Freundlich and Langmuir isotherm models) showed maximum adsorption by monolayer adsorption. A series of batch experiments for maximum adsorption of acetaminophen onto MNPs/β-CDP were carried out, and pH (6–8), eluent (methanol), adsorbent dosage (3.33 g L−1 ), and KMnO4 concentration (21.67 μmol L−1 ) were determined. To further validate the research, just as adsorption degradation rate of acetaminophen was calculated to evaluate the amount of adsorbed acetaminophen. Modified MNPs/β-CDP with adsorbed pollutants are desorbed and regenerated for enhanced recycling. It showed absorption efficiency with maximum adsorption of 94.6% for 5 regeneration cycles. To conclude, to understand the practical application of these nanocomposites, removal of pollutants from pharmaceutical wastewater was carried out, so with detailed information about various aspects in both laboratory as well as industry, these can be used for removal of acetaminophen. Further research can be done for calculating adsorption capacity from the mixture of drugs (Shi et al. 2019). Interesting research was conducted where a mixture of drugs was removed from pharmaceutical wastewater as seen here; for removing aspirin and paracetamol from water, synthesis of β-CD-based nanocomposite polymers are carried out in 2 steps. Firstly, the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) and iron-doped carbon nanotubes (Fe-CNTs) are done using chemical vapor deposition (CVD) and microwave-assisted pyrol method, respectively. After this, the prepared raw materials after co-polymerization with β-CD yield Fe/N-CNT/β-CD nanocomposite polymers. Results of FT-IR spectrum observed before and after adsorption showed absorption peaks at 3200 cm−1 , 2938 cm−1 , 1714 cm−1 , 1200 cm−1 , and 1000 cm−1 , indicating sorption of aspirin. Further, results of UV-Vis spectroscopy observed before and after adsorption showed 100% and 63% respectively adsorption of aspirin and paracetamol by Fe/N-CNT/β-CD at 298 K. Further, focused ion beam-scanning electron microscopy (FIB-SEM) image analysis of Fe/N-CNT/β-CD showed a porous and smooth surface, indicating successful sorption of aspirin and paracetamol. The adsorption behavior fitted multiple kinetic models (pseudo-second-order and Elovich kinetic model, and multiple isotherm models (Freundlich and Langmuir isotherm models) for aspirin and paracetamol respectively showed maximum adsorption at 298 K. A series of batch experiments for maximum adsorption of aspirin and paracetamol onto Fe/N-CNT/β-CD were carried out, and pH (2 for aspirin and 7 for paracetamol), temperature, and initial concentration were determined. Further results of adsorption thermodynamics showed that the adsorption process is feasible, spontaneous, and exothermic in nature. To conclude, out of these synthesized green nanocomposite polymers, Fe/N-CNT/β-CD showed maximum adsorption at 298 K for aspirin (71.9 mg g−1 ) and paracetamol (101 mg g−1 ); they can serve as a good candidate for removal of drugs from pharmaceutical wastewater and have many practical applications. Further research can be done for understanding the regeneration and reusability of these adsorbents; being environmental-friendly in nature, treatment with these nanocomposite polymers will cause less harm to the environment (Mphahlele et al. 2015). Continuing with previous sections here removal of drugs was carried out from a mixture containing various pollutants, where removal of IBU, BPA, and caffeine

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(CFN) from aqueous solution was achieved by synthesizing nanomaterial which was carried out in 2 steps. First, synthesis of NaX zeolite was done by mixing fly ash (20 kg) with 0.3 M NaOH for 24 h at 80 °C. After this, NaX was incorporated into β-CD via cross-linking agent 3-Glycidyloxypropyl)trimethoxysilane increased adsorption of selected pollutants to form NaX-CD. Further, FT-IR spectra analysis showed absorption peaks at 2926 cm−1 , 2921 cm−1 , and 2858 cm−1 confirming successful incorporation of NaX zeolite into β-CD. Additionally, CHN, SEM, XRD, BET, and BJH analysis was done for understanding the morphological and texture characteristic of synthesized nano adsorbents. Results of these experiments validated the successful incorporation of NaX into β-CD. Results of TG analysis (Fig. 4) showed weight loss of CD (very rapid up to 300–350 °C), NaX (20% up to 200 °C), and NaX-CD (very rapid up to 400 °C), indicating successful incorporation of zeolite on β-CD. DTA analysis (Fig. 4) was done for understanding the adsorption thermodynamics which showed both exothermic as well as endothermic reactions, due to release of water molecules and combustion reaction, respectively. Further, Nitrogen adsorption/desorption isotherm for NaX and NaX-CD showed the presence of micro and mesopores in NaX, which concluded that not much change in the pore structure of inorganic structure is observed after modification. A series of batch experiments for different parameters were carried out, and adsorbent dosage (inversely proportional to adsorbate uptake), contact time (90 min), and initial concentration (5–200 mg/L) were determined, with BPA having the highest and CFN showing the lowest sorption efficiency. The adsorption behavior fitted the pseudo-second-order kinetic model, and Langmuir isotherm model shows maximum adsorption by monolayer adsorption. Modified nanomaterial showed absorption efficiency with maximum adsorption of 31.3 mg g−1 (IBU), 32.7 mg g−1 (BPA), and 11.8 mg g−1 (CFN) for 5 regeneration cycles. To conclude, as there was a decrease in adsorption efficiency observed for BPA with an increase in the regeneration cycle, more research needs to be done where NaX can be conjugated with other materials for having better and comparative knowledge about its effect on BPA adsorption. Further, it can be a good candidate for eliminating organic pollutants from industrial wastewater (Bandura et al. 2021). For better removal of pharmaceutical waste from pharmaceutical wastewater, combination of 2 techniques yields increased adsorption efficiency, as seen here was achieved by synthesizing β-CD polymer and combining it with a pulsed light system, wherein β-CD was cross-linked with a cross-linking agent, epichlorohydrin to form EPI-β-CD polymer. A comparative study between the adsorption efficiency of EPIβ-CD polymer and EPI-β-CD polymer/pulsed light system concluded that there is a 14% rise in the removal of different classes of drugs present in pharmaceutical wastewater (77% to 91%). Further for desorption studies on modified EPI-β-CD polymer, IBU was used as a model drug; results showed only a significant decrease in removal efficiency from 87 to 74% even after 10 regeneration cycles. To conclude, the combined effect of adsorption and photolytic effect favors increased removal efficiency as seen in different drugs eliminated from pharmaceutical wastewater, so this can be used as a potential candidate in the removal of pollutants especially pharmaceutical waste from industrial effluent (Gómez-Morte et al. 2021).

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Fig. 4 TG and DTA (continuous and dotted lines). Reprinted with permission from Bandura L, Białoszewska M, Malinowski S, Franus W (2021). Adsorptive performance of fly ash-derived zeolite modified by β-cyclodextrin for ibuprofen, bisphenol A, and caffeine removal from aqueous solutions—equilibrium and kinetic study. Appl Surf Sci 562:. https://doi.org/10.1016/j.apsusc.2021. 150160

Another interesting research conducted for removal of IBU from the water was achieved by synthesizing β-CD-based nanofilters and was performed in 2 steps. Firstly, β-CD was cross-linked with cross-linking agent epichlorohydrin to form βcyclodextrin polymer beads (BCPB), then nanofibers are synthesized by sinestiring BCPB with polyethylene for 25 min at 190 °C. Before proceeding with further experiments, pre-treatment and regeneration of BCPB and nanofilters are done. Further, TOC and GC–MS/MS analysis was done for the calculation of the amount of IBU adsorbed by BCPB nanofilters. Modified BCPB and nanofilters with adsorbed pollutants are desorbed and regenerated using ethanol solution for increasing adsorption capacity. To conclude, not only IBU but drugs having the same physiochemical properties as IBU can also be separated from industrial wastewater from these nano filters. Not much information is given regarding the regeneration cycle and absorption efficiency of other micropollutants (Jurecska et al. 2014).

3 Conclusion Nanotechnology as a field has a wide range of applications; through this chapter, we have tried to explore its utilization for treating and purifying industrial wastewater. There are many conventional methods available for treating industrial raffinates: centrifugation, ultra-filtration, evaporation, ion-exchange chromatography, carbon adsorption, and membrane filtration; in this chapter, we have explored adsorption as the method for treating and purifying industrial and pharmaceutical wastewater, owing to the simple use, low-cost, regeneration, and reusability of adsorbent used. There are various ways in which nanomaterials can be classified depending upon the

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practical application and the method employed for preparing nanomaterials. Nanomaterials are often embedded by various chemical or physical methods onto some biological polymer which is used as a base to yield better adsorption capacity; in this chapter, we have described cyclodextrin studded with several different nanomaterials for eliminating toxic and harmful organic and inorganic micropollutants from industrial effluents. Different forms of cyclodextrin are cross-linked with either one or more crosslinking agents for better performance so that particles of various sizes can be entrapped efficiently. Here, we have discussed the adsorption and removal efficiency of plastics, heavy metals, dyes, and drugs. Various methods are discussed wherein either functionalization or combining them with other methods as seen in case of sensors designed for removal of diclofenac from pharmaceutical wastewater or developing a novel nano adsorbent showed increased adsorption and removal efficiency. After modification, different factors which can be modulated for higher adsorption/ removal efficiency are also discussed, with a methodology to improve regeneration and recycling of synthesized nanocomposites.

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Application of Nanomaterials for the Removal of Heavy Metal from Wastewater P. Priya, N. Nirmala, S. S. Dawn, Kanchan Soni, Bagaria Ashima, Syed Ali Abdur Rahman, and J. Arun

Abstract Water treatment technologies are explored around the globe by various research groups for sustainable access to clean water. Water gets polluted by manmade activities mainly through industrial discharge. Heavy metals are one of the primary pollutants that are discharged from tanning, electroplating, etc. Adsorption is the primary most preferred technique for wastewater treatment. Nanomaterials as adsorbents have attained attention in current years for their sustainability and ease of operations. Nanomaterials as composites and tubes are used in many scenarios for the effective removal of heavy metals. Primarily, nanomaterials like graphene oxides, silica, titanium oxide, carbon, and bio-nanomaterials are experimented with different heavy metals. This book chapter focuses on recent advancements in heavy metal removal via nanotechnology. Surface enhancement strategies for enhanced heavy metal removal were consolidated. This book chapter will provide technical insights on the latest research and future directions for academicians in working toward sustainable environmental engineering and wastewater treatment. Keywords Heavy metals · Nanomaterials · Adsorption · Wastewater · Titanium dioxide · Graphene oxide

P. Priya · N. Nirmala · S. S. Dawn · J. Arun (B) Centre for Waste Management, Sathyabama Institute of Science and Technology, Jeppiaar Nagar (OMR), Chennai 600 119, Tamil Nadu, India e-mail: [email protected] K. Soni · B. Ashima Department of Physics, Manipal University Jaipur, Dehmi Kalan, Jaipur, Rajasthan 303 007, India S. A. A. Rahman Department of Biotechnology, Sathyabama Institute of Science and Technology, Jeppiaar Nagar (OMR), Chennai 600 119, Tamil Nadu, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_16

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1 Introduction One of the serious problems which countries are facing is heavy metal pollution in water which affects the environment adversely. Heavy metals being highly toxic even at dilute concentration, non-biodegradable, and also accumulate through the food chain destroying aquatic life and being a serious threat to human life (Razzak et al. 2022). Heavy metals (Cr, Cd, Hg, As, Zn, Cu, Fe, Al, Ba, Ca, Mg, Pb, Mn, Ag, Na, and Se) contaminate drinking and irrigation water which are toxic for organisms that are present in the water environment. Nanomaterials are divided based on their role in adsorption applications which is dependent on their innate surface property (Beni et al. 2022). Broadly categorized, there are two essential approaches for nanoparticle blend: top-down approach and bottom-up approach. The top-down approach includes the breakdown of bulk fabric into little particles. These methods are the extension of those that have been utilized to create micron-sized particles. The top-down approaches is less difficult based on the expulsion of bulk fabric to its craved properties. A downside approach acquires a blemish of surface structure; nano-wires made from lithography contain enormous debasements and basic defects on their surface. The sol–gel amalgamation, and electron beam lithography nuclear drive control gas phase condensation use an amalgamation procedure. The bottomup approach was found to be less squander and more conservative when compared to the top-down approach. Therefore, the present method describes the amalgamation procedure where the material build-up occurs from the foot which focuses on the atomic self-assembly or atomic acknowledgment concepts. The synthesis of homogenous nanostructures with culminated crystallographic and surface structures are the advantages of bottom-up approaches (Maitlo et al. 2019). Anuradha et al. 2010 illustrate the aqueous blend (Darr et al. 2017) format helped sol–gel and electrodeposition (Tonelli et al. 2019). Merits of the bottom-up approach are less surface defects, superior requesting, and homogeneous chemical composition (Pareek et al. 2017). The adsorption process, on the other hand, owing to its ease of operation, is respected as the foremost promising strategy to remove metal particles from effluents. Despite the fact that conventional sorbents are competent in expelling heavy metals from wastewater, their unobtrusive sorption capacities and efficiencies constrain their applications in concentrated arrangements (Haripriyan et al. 2022). Within the past decades, biodegradable polymeric nano adsorbents have been created as a potential differentiating choice to actuated carbon as distant as their boundless surface region, extraordinary mechanical inflexibility, pore measure dispersion, culminate surface chemistry, and regenerative capacity beneath gentle conditions. The transfer of utilized adsorbents containing overwhelming metal(s) may be done after the recuperation of contaminants or straightforwardly without overwhelming metal recuperation, but in both cases there will be auxiliary contamination from the used adsorbents and the chemicals utilized to treat the adsorbents for metal recuperation. However, metal-loaded adsorbents have poisonous impacts on people and the environment.

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Hence, the utilized adsorbents ought to be released into the environment as they were after the recuperation of the heavy metals totally. Considering the requirement of metal desorption and recuperation, this paper summarizes the productivity of different recovering specialists utilized by different authors, the proficiency of the adsorbents for evacuation of heavy metals, and the recuperation of overwhelming metals. Overwhelming metal-induced poisonous quality and carcinogenicity include numerous unthinking viewpoints, a few of which are not clearly illustrated or caught on. In any case, each metal is known to have special highlights and physicochemical properties that bestow to its particular toxicological components of activity. This audit gives an investigation of the natural event, generation and utilization, potential for human presentation, and atomic instruments of poisonous quality, genotoxicity, and carcinogenicity of arsenic, cadmium, chromium, lead, and mercury.

2 Water Pollution Advancements in industries, natural disasters, human population, climate change, and modernization of livelihood have led to scarceness in access to safe drinking water in most of the developing countries. Textile dyes, heavy metals, metalloids, personal and pharmaceutical care products, and organic and inorganic pollutants are the most common pollutants in the water ecosystem. Accumulation, segregation, and storage of industrial waste and household waste near the aquatic system damage the flora and fauna (Wadhawan et al. 2020). In this book chapter, we focus mainly on one of the promising toxic heavy metals. Heavy metals that are commonly reported in aquatic environments are lead (Pb), chromium (Cr), manganese (Mn), nickel (Ni), mercury (Hg), arsenic (As), cadmium (Cd), etc. These many varieties of heavy metals are released into the water system due to the activity of metal fabrication, leather, batteries, electroplating, mining, fertilizers, paints, alloying, etc. (Yari et al. 2015). Continuous exposure to toxic heavy metals led to illness in the nervous system, kidney, brain, liver, and other vital organs (Le et al. 2019). The most important point of this much organ toxicity of heavy metal was due to the carcinogenic activity. Exposure to lead (Pb) in kids, aged below 6, led to lesser IQ levels, retarded growth, impaired hearing, and learning disabilities (Farghali et al. 2013). Considering the toxic nature of heavy metals, it’s the need of the hour to concentrate on the development of cutting-edge techniques for the effective removal and degradation of heavy metals.

3 Heavy Metals: Types, Sources, and Toxicity Heavy metals are described as metallic elements with a massively higher density when compared with water. Heavy metals include metalloids, such as arsenic, that can cause toxicity at even a minimal level of concentration, based on the features of

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heaviness and toxicity (Tchounwou et al. 2012). On the basis of their toxicity, heavy metals were divided into two categories: essential heavy metals and non-essential heavy metals. At low concentrations, essential heavy metals are either nontoxic or less harmful, including cobalt, zinc, iron, and copper. Non-essential heavy metals are harmful even at low concentrations, including chromium, cadmium, arsenic, and mercury (Kim et al. 2019). Heavy metals are naturally occurring components that can be found in the earth’s crust. The majority of heavy metal pollution and exposure is caused by human activities such as mining, smelting, industrial production, and the use of metals and metal-containing compounds at home and in agriculture (He et al. 2005; Herawati et al. 2000). Figure 1 provides a detailed note on the different release points of heavy metals in gas, soil, and water environment. Coal, petroleum, nuclear power, plastics, textiles, microelectronics, paper-processing , and wood preservation factories are all examples of industrial sources of heavy metal pollution (Sträter et al. 2010). Heavy metal contamination has also been correlated to weathering and volcanic eruptions (Nriagu 1989). Natural activities such as volcanic activity, metal corrosion, metal evaporation from soil and water and sediment resuspension, geological weathering, soil erosion, and sediment re-suspension, among others, can contribute to heavy metal contamination (Briffa et al. 2020). Heavy metals are commonly defined as those with a density of more than 5 g per cubic centimeter. The maximum contamination level (MCL) guidelines for the most dangerous heavy metals are listed in Table 1. Heavy metal deposition in the human body causes serious harm to a variety of organs, most notably the respiratory, neurological, and reproductive systems, as well as the digestive tract (Kim et al. 2019). Every metal has distinct physicochemical characteristics that determine its toxicological modes of action. Many studies have shown that arsenic toxicity is affected by the amount of exposure, the frequency and length of exposure, the kind of organism being exposed, the individual’s age and gender, as well as genetic and dietary susceptibilities (Abernathy et al. 1999). Human lymphocytes and mouse leukocytes are both damaged by arsenic trioxide, which has been shown to cause DNA damage. Arsenic chemicals have also been demonstrated to cause gene amplification, cell mitotic arrest, and DNA repair inhibition (Banu et al. 2001). Toxicological effects of exposure to the metal form of chromium range from minimal to high depending on the specific oxidation state (Velma et al. 2009). Inhalation of less soluble or insoluble Cr(VI) compounds appears to be related to carcinogenicity. The elemental form of Cr (VI) has no toxicological properties. It varies substantially across various Cr (VI) complexes (Katz and Salem 1993). According to the results of epidemiological studies, Cr (VI) is a key factor in carcinogenesis. Chromium’s solubility and other properties, including size, surface charge, crystal modification, and phagocytization may be essential in predicting cancer risk (Tchounwou et al. 2012). Lead’s toxic and apoptotic effects on human cancer cells have been shown to involve numerous cell and molecular processes, including the induction of cell death and oxidative stress, DNA damage, the activation of stress genes, the externalization of phosphatidylserine, and activation of caspase 3 (Yedjou and Tchounwou 2007; Yedjou et al. 2010).

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Fig. 1 Release points of heavy metals into gaseous, aqueous, and solid environments

Table 1 The MCL guidelines for the most dangerous heavy metals (Barakat 2011) Heavy metals

Toxicity

MCL (mg/L)

Zinc

Neurological signs, continuous thirst, lethargy, and depression

0.80

Mercury

Nervous system problems, kidneys diseases, circulatory system, and Rheumatoid arthritis

0.00003

Arsenic

Visceral cancers, skin manifestations, and vascular disease

0.050

Chromium

Carcinogenic, diarrhea, headache, vomiting, and nausea

0.05

Cadmium

Carcinogen, kidney damage, and renal disorder

0.01

Lead

Circulatory system problem, fetal brain problem, kidney diseases, and nervous system diseases

0.006

Copper

Wilson disease, liver damage, and insomnia

0.25

The lung is the most conclusive place where people get cancer from cadmium exposure. Other places where cadmium can cause cancer in animals are the injection site, testes, adrenals, and the hemopoietic system (Waalkes 1996). Cadmium, arsenic, chromium, and nickel, among other carcinogenic metals, have all been linked to

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DNA damage caused by mutation, deletion, or oxygen radical damage to DNA. Mercury in all forms is harmful, causing gastrointestinal neurotoxicity, toxicity, and nephrotoxicity (Tchounwou et al. 2003).

4 Nano Adsorbents: Synthesis Routes There are two primary ways to synthesize nano adsorbents: top-down and bottom-up approaches. The top-down approach is the common method in which the process begins with bigger particles (macroscopic) and the size reduction to nano-scale is accomplished by the use of externally controlled energy sources such as sputtering, erosion, high-energy ball milling, mechanical alloying, and reactive milling. However, the fundamental issue with the top-down technique is the potential for crystallographic and surface structure damage during particle size reduction (El-sayed 2020; Singh et al. 2018). Bottom-up is the most recent method. It relies on how a substance is built from the bottom, either molecule by molecule or atom by atom, as in molecular self-assembly, physical/chemical vapor deposition, and sol–gel method. Bottom-up methods have two major challenges: chemical purification is necessary, and large-scale manufacturing is challenging. However, the bottom-up approach is now the suitable technique since it may manufacture materials with precise qualities customized to the remediation needs based on the fabrication pathway chosen (Tulinski and Jurczyk 2017; Nik Abdul Ghani et al. 2021). Figure 2 showcases the various synthesis routes of nano adsorbents.

Fig. 2 Various synthesis routes of nano adsorbents for environmental applications

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Furthermore, chemical and physical methods for the synthesis of nano sorbent materials frequently synthesize nano sorbent materials with a definite shape and size. However, these methods have been proven to be environmentally hazardous due to the use of harmful chemical substances and the elevated heat used during the synthesis methods (El-sayed 2020; Fosso-Kankeu 2019). The microbial production of nanomaterials can be accomplished by extracellular and intracellular methods, as evidenced in the biological entities that are high secretors of proteins and enzymes that are primarily responsible for metal ion reduction and nonabsorbent material control (El-sayed 2020; Tulinski and Jurczyk 2017). Biogenic synthesis method is a sustainable and green technology since it does not need the use of toxic chemicals for production methods (Fosso-Kankeu 2019). Conventional adsorbents have limitations such as poor adsorption capabilities, a lack of functional tunability, recyclability, and reusability. To address such constraints, new nanosized sorbents are being developed and used for water purification (Wadhawan et al. 2020). Nanomaterials have recently received a lot of interest as adsorbents in wastewater decontamination due to their huge specific surface area, lower flocculent generation, and availability of a lot of active groups for attaching heavy metals (Verma et al. 2017).

5 Nano Adsorbents in Heavy Metal Remediation The increasing demand for clean water with low heavy metal concentrations necessitates the efficient removal of harmful heavy metals from industrial runoff prior to its discharge into the ecosystem (Tu et al. 2017). Ion exchange, reverse osmosis, solvent extraction, chemical precipitation, and other standard methods are available for purifying wastewater. Despite the fact that the aforementioned methods are effective and meet discharge criteria, the majority of them produce secondary pollutants. On the other hand, adsorption is seen as a promising option for the removal of toxic metals from wastewater due to its accessibility, adaptability, and high proficiency. It is more suitable than other methods due to its simple design and minimal initial cost and space requirements. Furthermore, if the adsorbent employed is recyclable, the adsorption process becomes extremely cost-effective. Because of these qualities, researchers are paying close attention to the adsorption process in the treatment of industrial wastewater polluted by heavy metals (Wadhawan et al. 2020). There are several types of nano adsorbents used in wastewater treatment, and the most commonly employed nanomaterials are divided into four groups based on their shape, size, and chemical characteristics (Tulinski and Jurczyk 2017). They are carbon-based nano adsorbents, polymer-based nano adsorbents, metal oxide nano adsorbents, and magnetic nano adsorbents.

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5.1 Carbon-Based Nano Adsorbents Carbon-based nano adsorbents such as carbon nanotubes (CNT) and graphene are frequently used in wastewater treatment. These carbon nanotubes are classified into two types: single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWNTs). Nano tubes have unique properties such as surface areas, size, pore volumes, non-corrosiveness, nontoxicity, and electrical conductivity. These nano adsorbents have high removal effectiveness of heavy metals including lead, copper, mercury, chromium, nickel, arsenic, and cadmium from wastewater (Šoli´c et al. 2020; Wadhawan et al. 2020). Several papers discuss the use of carbon nanotubes (CNTs) in heavy metal ion removal from wastewater. In a study, CNTs as adsorptive material showed removal of ions with removal capabilities in the sequence Cu (II) > Pb (II) > Co (II) > Zn (II) > Mn (II) (Stafiej and Pyrzynska 2007). In another study, adsorption of Pb (II) from wastewater on CNTs showed a 70.1 mg/g adsorption capacity (Rahbari and Goharrizi 2009). Another carbon-based nanomaterial, graphene, has received a lot of interest in the field of environmental remediation. The presence of oxygen-containing functional groups on the surface of graphene oxide (GO) gives it a highly hydrophilic character, allowing for fine dispersion in water. Because of its diverse functional groups and large surface area, GO is a promising option for wastewater treatment. It possesses remarkable mechanical, electrical, and thermal properties. These nanoparticles are efficient against a wide range of contaminants found in wastewater (Wadhawan et al. 2020). Zhao et al. reported GO nanosheets for the removal of adsorption of Cd (II) and Co (II). Adsorption capacities of 106.3 and 68.2 mg/g for Cd (II) and Co (II) were achieved (Zhao et al. 2011).

5.2 Polymer Based Nano Adsorbents Conventional adsorbents have inadequate specificity, and adsorption capacity and recyclability are the major disadvantages. In order to address the issues of presently available adsorbents, enormous organic and inorganic hybrid polymers having good adsorption capacity, enhanced thermal stability, more skeletal strength, and vast recyclability should be designed (Khajeh et al. 2013). Polymeric-based nano adsorbents have the capability to bind with organic dyes and heavy metal ions like arsenic, zinc, lead, and cadmium from wastewater. Polymer-based nano adsorbents are further classified as chitosan, cellulose, and dendrimers (Nik Abdul Ghani et al. 2021). Chitosan is a non-toxic, environmentally friendly, biocompatible, and hydrophilic polymer that may form complexes with a variety of metal ions. The existence of amino groups increases chelation interactions with metal ions, and chemical changes of chitosan improve its selectivity and sorption capability. Furthermore, for enhancing the sorption ability of chitosan it can be activated with acidic medium towards enhancement of its mechanical characteristics (Wadhawan et al. 2020; Nik Abdul

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Ghani et al. 2021). In a study, chitosan-alginate nanoparticles were employed for mercury removal. The highest adsorption capacity of 217.39 mg/g was attained under ideal circumstances of pH 5 at 90 min with an initial ion concentration of 4 mg/L (Dubey et al. 2016). Dendrimers are great indicators of polymeric nano adsorbents and their influence on eliminating organic and inorganic contaminants due to their repetitively branched molecules. Organic molecules can be adsorbed through the interior hydrophobic portions, whereas heavy metals can be adsorbed by the exterior branches (Elsayed 2020). To remove copper from the water, researchers used a combination of dendrimers with the addition of ultrafiltration, resulting in the removal of copper ions (Diallo et al. 2005). The absorption of heavy metal ions by biopolymer-based nano adsorbents such as cellulose has been examined. Jamshaid et al. evaluated several cellulose-based nano adsorbents such as cellulose gels, nanocrystalline cellulose, and cellulose composites and derivatives, and the results demonstrated that the adsorption capacity of heavy metals was successfully increased (Jamshaid et al. 2017).

5.3 Metal Oxide Nano Adsorbents Metal oxide nanoparticles have a high removal capacity, a large surface area, and a strong affinity for heavy metal adsorption, making them promising nano adsorbents for wastewater treatment. The range of metal oxide nanoparticles in nanosized materials is 1–100 nm. It includes zinc oxide, manganese oxide, nickel oxide, aluminum oxide, iron oxide, zirconium oxide, titanium oxide, and magnesium oxide (Yang et al. 2019). Due to their high adsorption capacity and huge surface areas, these metal oxide-based nanoparticles are attractive nano adsorbents for heavy metal removal from aqueous systems. Metal oxide adsorption processes were regulated by complexation between dissolved metals and oxygen in two steps: first, metal ion adsorption on the external surface, and, second, rate-restricted intra-particle diffusion along the porosities (El-sayed 2020; Wang et al. 2020).

5.4 Magnetic Nano Adsorbents Magnetic nano adsorbents are extremely non-toxic, highly selective, recyclable, and reusable (Mudhoo and Sillanpää 2021). They have magnetic properties that allow for ease of separation using an electromagnet. Magnetic nanoparticle modification has recently received increased interest as a consequence of magnetic nanoparticles’ capacity to form bonds with various terminal groups of diverse molecules, especially ligands (Zhu et al. 2010). As a result, significant progress has been made in pollutant removal from wastewater using magnetic nanoparticles by reinforcing them onto other nanomaterials. Magnetic nanocomposite materials composed of two or more

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distinct nanoparticles have been used for water and wastewater treatment (Rebuttini 2014). For example, titanium dioxide (TiO2 ) with powerful photocatalytic properties is strengthened into magnetic nanoparticles to boost the latter’s photocatalytic properties for application in the removal of pollutants from wastewater (Lingamdinne et al. 2019; Khan et al. 2020).

6 Nano Adsorbent Recovery and Reutilization Reutilization of spent adsorbent is the main aspect for successful real-time practical applications. The reusability of spent adsorbent helps to reduce the overall cost of the adsorption process as it reduces the need for new adsorbent synthesis and purchase. Reusability of spent adsorbents helps in reduced cost, toxicity, and largescale usability of novel nanomaterials. To date, plenty of research and review articles are published on desorption and utilization of adsorbents to enhance the overall viability of the process. Commonly, nano adsorbents, activated carbon, graphene oxides, and biomaterials are utilized in the adsorption process.

7 Conclusion and Future Directions Nanomaterial, nanoscience, and nanotechnology have come across greater advancements in the last years that have driven the way for synthesis and structuring of novel, economical, eco-friendly nano adsorbents. Higher selectivity and adsorption capacity of the adsorbent define the electability and stand-alone candidate in the wastewater treatment technique. Even though the adsorption of heavy metal is an easier physiochemical technique, in this book chapter we have focused mainly on heavy metal effects, nano adsorbents synthesis, and types. In future, encapsulated and multidimensional nanomaterials can be used for achieving higher removal percentage of heavy metals from an aqueous environment. This helps in achieving a comparative and comprehensive research methodology by identifying the research problem by various scientists and research groups globally. Acknowledgements The authors wish to thank Sathyabama Institute of Science and Technology for their support. Conflict of Interest None.

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Technological Interventions for Wastewater Treatment: Monitoring and Management Anurag Singh, Prekshi Garg, Prachi Srivastava, and V. P. Sharma

Abstract The continuous denouement in the water environment is grounds for the demand of new and innovative technological interventions to achieve sustainable management of urban wastewater systems. There is a continuous increase in the concentration of contaminants like organic/inorganic material, pathogens, heavy metals and other environmental toxicants in the water systems. Various new technologies like the application of nanotechnology, electrochemistry based approaches and other computational technologies are now replacing the obsolete approaches of wastewater treatment, thereby putting forth a futuristic paradigm of wastewater monitoring and management. We have attempted to highlight technologies and approaches that are better suited for efficient removal of toxicants from wastewater. There are various national and international guidelines/Specifications for the establishment, infrastructure development and proper functioning of wastewater treatment plants. In present day scenario these newer ways of wastewater treatment will not only benefit the human health but also have a good impact on the surrounding environment. Keywords Technological · Nanotechnology · Wastewater · Monitoring · Management · Sustainable

A. Singh Department of Biochemistry, University of Lucknow, Lucknow 226007, U.P, India P. Garg · P. Srivastava Amity Institute of Biotechnology, Amity University Uttar Pradesh, Lucknow Campus 226028, U.P, India V. P. Sharma (B) Regulatory Toxicology Group, CSIR–Indian Institute of Toxicology Research, Lucknow 226001, U.P, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 M. P. Shah (ed.), Advanced Application of Nanotechnology to Industrial Wastewater, https://doi.org/10.1007/978-981-99-3292-4_17

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1 Introduction The existence of water is equivalent to existence of life on earth and it is one of the most abundant natural resources, but only approximately a percent of that whole resource is available for human consumption (Adeleye et al. 2016). According to World Health Organization (WHO), almost 785 million people lack safe drinking water and by 2025 half of the world’s population will be living in water-stressed areas (https://www.who.int/news-room/fact-sheets/detail/drinking-water). Now the main reason for this problem is the continuous contamination of fresh water resources by a variety of organic and inorganic contaminants and toxicants. The presence of such toxicants can also lead to a number of problems upon consumption. Every day almost 800 children die due to consuming contaminated water (Schwarzenbach et al. 2006). Now an effective strategy to reduce the contaminations will be treat the wastewater that’s being generated on a daily basis but, the existing technologies of doing it are obsolete and lack efficiency. They are not efficient enough to remove every contaminant, organic or inorganic, from the wastewater. Moreover, the existing technologies require high amount of energy and generate toxic sludge which once again gives rise to a whole new set of problems. Now biological treatment is widely used but it is a slow process and because there is a continuous increase in the usage of non-biodegradable pollutants, it is not enough to solve our problem. Keeping in mind the above-mentioned problems there is only one solution and that is intervention of new technologies into the wastewater treatment procedure and one such intervention is the use of nanomaterials. Among all the newer technologies that have surfaced over the last decade, nanotechnology is the one that has proved to wipe out all our concerns right from remediating wastewater to many other environmental problems associated with it (Ferroudj et al. 2013; Qu et al. 2012; Zelmanov and Semiat 2008; Bali et al. 2003). The challenge of getting access to cleaner water for each individual across globe is highly interdisciplinary thus, the solution to get it must not be stopped by any boundaries. Thus, utilizing our current knowledge of nanomaterials and combining it with already existing technology and technologies like those utilizing electrochemistry, open up a whole new frontier for us to provide solutions to existing problems of water scarcity, death due to consumption of contaminated water and also save energy otherwise being overexploited in obsolete technologies (Burkhard et al. 2000; Crini and Badot 2007; Parsons and Jefferson 2006). With implementing these changes there also will be a need to monitor and manage the whole system as well as make necessary changes in the existing infrastructure so as to incorporate these technologies. In this chapter we are highlighting some technologies which can be of great help with regards to wastewater treatment with special emphasis on nanotechnological based interventions.

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2 Interventions in Wastewater Treatment The development of industries and an exponential rise in industrial activities across the globe has resulted in an increased the release of detrimental pollutants into the environment (Adeleye et al. 2016). Therefore, to attain sustainable development it is crucial to remove these pollutants. There have been a lot of interventions in the paste for the treatment of wastewater like oxidation, electrochemical, biological, hybrid and membrane-based technologies.

2.1 Electrochemical Technologies Electrochemistry based approaches are gaining importance these days because of the fact that electron, which is the main reagent of these technologies is a ‘clean reagent’ and provides high efficiency and cost effectiveness. The electrochemical technologies used in wastewater treatment are listed in Fig. 1.

2.1.1

Electrochemical Oxidation

This technology is capable of breaking the most resistant organic compounds as well. The technology works by both direct and indirect oxidation method. ● Direct Anodic Oxidation: In this method the pollutants are adsorbed on the anode surface and then they are destroyed. The method involves only electrons and no other substance. ● Indirect Anodic Oxidation: In this method total or partial decontamination is carried out at the anode due to physically adsorbed “active oxygen” in the form of OH radicals or chemisorbed “active oxygen” in the form of metal oxide (MO). ● Indirect electro-oxidation: Indirect electro-oxidation is carried out to avoid deactivation of the anode during direct oxidation of chemicals. The method involves destruction of pollutants by indirect oxidation using electrochemical generation of chemical reactants like ozone, hydrogen peroxide and chlorine (https://www.who. int/news-room/fact-sheets/detail/drinking-water, Schwarzenbach et al. 2006) 2.1.2

Electrochemical Reduction

● Electrodeposition: This process is carried out to remove toxic metal ions and recycle valuable materials from effluents of metallurgical and electroplating industries, printed circuit boards, battery manufacturing and electrochemical industries. The approach is based on recovery of metals through cathode deposition. This approach is one of the most efficient ways to remove toxic metals from water without leaving any residues during metal separation. Example, recovery

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Electrochemical Oxidation

Electrochemical Reduction

Sonoelectrolysis

Electrochemical Technologies Photoelectrochemical Method

Electrocoagulation

Electrodialysis

Fig. 1 Electrochemical technologies in wastewater treatment

of gold rich alloys is done using vitreous carbon and titanium cathodes. The metal recovery through electrodeposition can be increased by integrating it with ultrasound. ● Cathode Electrochemical Dechlorination: Chlorinated organic compounds (COCs) such as polychlorophenols, volatile organic compounds (VOCs) and polychlorinated hydrocarbons released from solvent and chemical industries are highly toxic and stable. Therefore, these compounds pose serious threat to human health and should be immediately removed from the environment. Unlike biological, physio-chemical and chemical dehalogenation techniques which have not given satisfactory results, electrochemical dichlorination have emerged as a promising technique for the removal of COCs. This technique uses mild reactive conditions and prevents formation of secondary pollutants (Ferroudj et al. 2013). ● Cathodic electrochemical denitrification:The nitrate and nitrite ions present in ground water and other water sources are treated with electrochemical reduction. Homotopy Analysis Method (HAM) is an analytical method used to develop theoretical model for reduction of nitrate ions. This method provides concentration and current values that can give satisfactory results (Qu et al. 2012).

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Electrocoagulation

Electrocoagulation is a process that causes dissolved contaminants to precipitate as a result of in situ production of coagulated species and metal hydroxides. pH and current density largely affect the performance of electrocoagulation (Zelmanov and Semiat 2008; Bali et al. 2003; Burkhard et al. 2000). The maximum efficacy of pollutant removal is obtained at an optimum pH that depends on the nature of the pollutant. Current density in the process on electrocoagulation is usually set according to parameters like pH, temperature and flow rate. Current density controls the amount of release of iron and aluminium ions from the electrodes. The released ions are responsible for electro coagulant dosage rate. Advantages of electrocoagulation: 1. The process has better removal capabilities than chemical coagulants for certain species. 2. It does not add harmful chemicals to the environment. 3. It produces less sludge thereby minimizing sludge disposal cost (Crini and Badot 2007; Parson and Jefferson 2006). 2.1.4

Electrodialysis

It is the process by which ions are separated by the use of polymeric anion and cation exchange membranes by applying electric potential across alternating series of cation and anion exchange membranes placed between two electrodes. On application of electric difference across the electrode, positive ions migrate to the negative electrode, that is, cathode and negative ions migrate to the positive electrode, that is, anode.

2.1.5

Photoelectrochemical Method

This method involves treatment of toxic recalcitrant organic compounds by integrating photocatalysis with electrocatalysis. The method involves usage of DSA type oxide electrodes that help in generation of highly reactive oxidants due to presence of UV irradiation and generation of chloro-oxidant species (Feng et al. 2016).

2.1.6

Sonoelectrolysis (SECT)

This method involves combination of ultrasound with electrochemical techniques to remove organic pollutants like aromatics, nitro and chlorinated compounds (Mijin et al. 2012) and textile dyes. This approach helps in prevention of electrode poisoning and activating electrode surface along with enhancement of mass transfer efficacy. Similar approach has been used for degradation of progesterone in water, known as, conductive diamond electrochemical oxidation (CDEO) (Tavares et al. 2012).

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3 Nanotechnology in Wastewater Treatment With the advancement in the field of nanotechnology and the increasing benefits of nanoparticles like high reactivity, improved catalysis and adsorption has made this field a key domain in research and development (Li et al. 2012). Nanoparticles are in general the materials made up of structural components having size in the range of 1 and 100 nm. The nanosized dimension of particles give them unique magnetic, mechanical, optical and electrical properties. Researches have concluded that nanomaterials are capable of removing various heavy metals (Loghambal and Rajendran 2011), inorganic anions (Vasudevan and Lakshmi 2012), organic pollutants (Gong et al. 2014) and bacteria (Fouad 2014).

3.1 Application of Nanotechnology in Wastewater Treatment Nanotechnology is largely applied for the treatment of wastewater in the areas of adsorption, biosorption, photocatalysis, wastewater remediation, sensing, monitoring, nanofiltration, disinfection and pathological control (Zhao et al. 2014) (Fig. 2).

Adsorption

Disinfection and Pathological Control

Biosorption

Nanotechnology in Wastewater Treatment

Nanofilters

Photocatalysis

Fig. 2 Integration of nanotechnology in wastewater treatment

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Table 1 Salient Nanosorbents being used for treatment S. No

Nanosorbent

Treatment

1

Carbon based

Used for treatment of nickel ions in water

2

Polymeric

Organic and inorganic contaminants

3

Nanoclays

Phosphorous and hydrocarbon dyes

4

CaptymerTM

For removal of uranium, nitrate, bromide and perchlorate

3.1.1

Adsorption

Adsorption is the process of transfer of an adsorbate phase onto an adsorbent in order to form a monomolecular layer on the surface through chemical or physiochemical interactions. An adsorbate phase is usually a molecule or ion in liquid or gaseous phase. An adsorbent is a solid and sometimes a liquid phase (Isaa et al. 2014; Souza et al. 2014; Esclapez et al. 2011). High specific surface area, mechanical strength, good adsorption capacity and chemical resistance are certain properties that make nanomaterials suitable for adsorption. The list of nanomaterials used for adsorption are given in Table 1 (Vidales et al. 2014).

3.1.2

Biosorption

Biosorption is a kind of adsorption process that exploits the intrinsic property of biological components to exclude out heavy metals from wastewater. Bacteria, fungi and algae are generally used for the process of biosorption. The process of biosorption involves principles of ion-exchange, micro precipitation and cell-surface complexation (Lu et al. 2016; Khin et al. 2012). Example, Aspergillus niger microsphere (ANM) biosorbent was prepared for the removal of thorium (IV) ions from radioactive wastewater (Liu et al. 2014).

3.1.3

Nanofilters

Nanofilters are widely used for the removal of suspended particles, microorganisms, detrimental biological and chemical components from wastewater so that the water is fit for use (Yan et al. 2015). Nanofilters membranes have a pore size of 0.5 to 2.0 nm and pressure ranging from 5–20 bars. These are like an intermediate between ultrafiltration and reverse osmosis. Polymeric and ceramic membranes are usually used as Nanofilters. Ceramic membranes are more chemically, mechanically and thermally stable (Kalhapure et al. 2015) whereas polymeric membrane have low chemical resistance and high fouling rate.

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Properties of Nanofilters: ● ● ● ● ● ● ●

Highly flexible Cost effective Easy to produce Low rejection of monovalent ions High rejection of divalent and higher-valent ions. High flux Lower energy consumption (Jain et al. 2021; Gusian et al. 2020; Crawford and Quinn 2017).

3.1.4

Photocatalysis

Photocatalysis is a recent process of wastewater treatment that utilizes light to alter the rate of a chemical reaction without being involved in the reaction itself. Photocatalyst, that is, a solid material absorbs light (photons) and induces a chemical reaction (Refaat Alawady et al. 2020). It uses UV light, ozone, hydrogen peroxide or catalyst to remove contaminants of emerging concerns (CECs) like strong organic compounds, dyes, crude oil, pesticides, inorganic molecules, metals, viruses and chlorine resistant organisms from wastewater (Prachi et al. 2013; Derco and Vrana 2018).Nanomaterials that are generally used as photocatalysts are zinc sulfide, zirconium dioxide, tungsten trioxide, zinc oxide, titanium oxide and cadmium sulfide (Fard et al. 2011). The various steps involved in the process of photocatalysis are illustrated in Fig. 3 (Ding et al. 2019).

Diffusion of Pollutants Adsorption of Pollutants Reaction of Adsorbed Pollutants Desorption of Pollutants from the Surface Removal of Products from Interface. Fig. 3 Steps in photocatalysis

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Disinfection and Pathological Control

Waterborne diseases are caused due to contamination of water by pathogens like viruses, prions, fungi, bacteria and protozoan (Koyuncu et al. 2015; Parham et al. 2013; Wu et al. 2017). Disinfection is the process by which the micro-organisms are removed from the surface and bulk of the material using chemical or physical methods (Mulyanti and Susanto 2018). Currently used disinfection techniques consume high energy and require expensive equipment, therefore, now nanotechnology is being applied for disinfection of water as well. Large surface area and specific reactivity make nanomaterials suitable for inactivation of pathogens in water (Abdel-Fatah 2018). Most commonly used nanomaterials for disinfection are carbon nanotubes, polymeric nanoparticles, titanium dioxide, silver, zinc and copper oxide (Bethi et al. 2016; Rueda-Marquez et al. 2020; Mehrjouei et al. 2015). These nanomaterials use surface based electrostatic and physiochemical reactions to generate reactive oxygen species that disrupt the cell wall and deliver disinfecting agents to the target, thereby disinfecting wastewater (Mahmoudian-Boroujerd et al. 2019; Bai et al. 2020; Zhang et al. 2018).

4 Conclusion The current methodologies adopted by wastewater treatment plants are not at all sufficient to cater to the needs of millions of people around the globe. The current methodology only deals with organic and inorganic contaminants but is ineffective against a wide range of heavy metals, non-biodegradable pollutants and environmental toxicants. Few approaches may be expensive, energy consuming and inefficient due to its inability to completely purify wastewater. Thus, it is best to intervene in the current process with our latest understanding and knowledge. Currently, nano-science is at a boost and the best shot at saving the world from clean drinking water crisis. When we combine nanotechnology with electrochemistry and other new approaches, it will solve all our problems and we can completely remove every contaminant from the wastewater. The properties of nanomaterials are such that we can easily adjust them as per our needs thus, we can get “personalized wastewater treatment plants” depending upon the wastewater generated in a specific geographical location and solve the problem at hand. Moreover, nanomaterials can also be engineered in a way that they capture solar energy and decontaminate the water reducing the cost of the whole process. Thus, application of nanomaterials, electrochemical approaches and other newer technologies will prove to be a paradigm shift in wastewater treatment. Acknowledgements Authors are thankful to Director, CSIR-IITR for infrastructural support of the prestigious institute. Moreover, the support of Department of Biochemistry, University of Lucknow and Amity University Uttar Pradesh are praiseworthy.

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