Polymer-Based Advanced Functional Materials for Energy and Environmental Applications (Energy, Environment, and Sustainability) [1st ed. 2022] 9789811687549, 9789811687556, 9811687544

Table of contents :
Preface
Contents
Editors and Contributors
Part I General
1 Introduction to Polymer-Based Advanced Functional Materials for Energy and Environmental Applications
References
Part II Energy and Environment Related Applications of Polymer-Based Advanced Functional Materials
2 Sustainable Polymer-Based Materials for Energy and Environmental Applications
2.1 Introduction
2.2 Classification of Sustainable Polymers
2.3 Sustainable Polymers in Water Purification
2.4 Sustainable Polymers in Energy Applications
2.5 Sustainable Polymers for Other Environmental Applications
2.6 Concluding remarks
References
3 Polymer Aerogels for Energy Storage and Water Purification Applications
3.1 Introduction
3.2 History and Fundamentals of Polymer-Based Aerogels
3.3 Polymer-Based Aerogels for Energy Storage Applications
3.4 Polymer-Based Aerogels for Water Purification Applications
3.5 Challenges and Future Scope
3.6 Concluding Remarks
References
4 Polymer Nanocomposites and Metal Halide Perovskites for Luminescent Solar Concentrator Applications—Host Materials Perspective
4.1 Introduction
4.2 Architecture and Working Mechanism of LSC
4.3 Luminescent Host Materials Used in LSC
4.4 Hybrid Perovskites
4.5 Concluding Remarks
References
Part III Environment Related Applications of Polymer-Based Advanced Functional Materials
5 Polymeric Membranes and Hybrid Techniques for Water Purification Applications
5.1 Introduction
5.2 Membrane Filtration
5.3 Reverse Osmosis
5.4 Forward Osmosis
5.5 Hybrid Techniques
5.6 Concluding Remarks
References
6 Environmentally Significant Cellulose Fiber Reinforced Polymer Matrix Composites
6.1 Introduction
6.2 Cellulose Fibers
6.3 Polymer Matrices and Additives
6.4 Cellulose Fiber Surface Modification
6.5 Mechanical Performance of Cellulose Fiber Reinforced Thermoplastic
6.6 Concluding Remarks
References
7 Factors Limiting the Application Window of Acoustically Important Natural Fiber Based Polymer Reinforcements and Their Related Control Strategies
7.1 Introduction
7.2 Natural Fiber
7.3 Factors Limiting the Application Window of Natural Fibers
7.4 Correlation Between Moisture Absorption, Fire Retardancy and Microbial Growth
7.5 Control Strategies
7.6 Concluding Remarks
References
8 Advanced Functional Polymer-Based Porous Composites for CO2 Capture
8.1 Introduction
8.2 Thermo-Kinetic Aspects of CO2 Adsorption
8.3 Gas Transport in Polymeric Membranes
8.4 Liquid Polymers
8.5 Polymers of Intrinsic Microporosity
8.6 Thermally Rearranged Polymers
8.7 Porous Organic Polymers (POPs)
8.8 Concluding Remarks
References
9 Functional Polymer Materials for Environmental Monitoring and Safety Applications
9.1 Introduction
9.2 Synthetic Strategies of Functionalized Polymer Composites
9.2.1 Functionalized Conducting Polymer Composites
9.2.2 Functionalized Molecularly Imprinted Polymer Nanoparticle Composites
9.2.3 Functionalized Biopolymer Composites
9.3 Applications of Functionalized Polymer Composites
9.3.1 Environmental Monitoring
9.3.2 Safety Applications of Functionalized Polymers
9.4 Conclusions
References
10 Progress in Functionalized Polymeric Membranes for Application in Waste Water Treatment
10.1 Introduction
10.1.1 Membrane Classification
10.1.2 Membrane Fabrication Methods
10.2 Functionalization of Polymeric Membrane
10.2.1 Physical Modification Methods
10.2.2 Chemical Modification Methods
10.3 Conclusion
References
11 Fungal Chitin-Glucan: Renewable Nanofibrils for Water Treatment and Structural Materials
11.1 Chitin
11.1.1 Chitosan
11.1.2 Chitin Sources
11.1.3 Fungal Chitin
11.1.4 Mycelium
11.2 Water Treatment
11.2.1 State of the Art
11.2.2 Chitin in Water Treatment
11.3 Fungal Chitin Nanopapers
11.3.1 Chitin-Glucan Nanopapers from Mushroom
11.3.2 Chitosan-Glucan Prepared by Deacetylation of Fungal Chitin
11.3.3 Chitin-Glucan from Mycelium
11.4 Concluding Remarks
References
12 Advanced Functional Materials for the Detection of Perfluorinated Compounds in Water
12.1 Introduction
12.2 Physical and Chemical Properties of PFAS
12.2.1 Physical Properties
12.2.2 Chemical Properties
12.3 Degradation of PFAS
12.4 Future Research Directions and Summary
References

Citation preview

Energy, Environment, and Sustainability Series Editor: Avinash Kumar Agarwal

Nithin Kundachira Subramani S. K. Nataraj Chetankumar Patel Sachhidananda Shivanna   Editors

Polymer-Based Advanced Functional Materials for Energy and Environmental Applications

Energy, Environment, and Sustainability Series Editor Avinash Kumar Agarwal, Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India

AIMS AND SCOPE This books series publishes cutting edge monographs and professional books focused on all aspects of energy and environmental sustainability, especially as it relates to energy concerns. The Series is published in partnership with the International Society for Energy, Environment, and Sustainability. The books in these series are edited or authored by top researchers and professional across the globe. The series aims at publishing state-of-the-art research and development in areas including, but not limited to: • • • • • • • • • •

Renewable Energy Alternative Fuels Engines and Locomotives Combustion and Propulsion Fossil Fuels Carbon Capture Control and Automation for Energy Environmental Pollution Waste Management Transportation Sustainability

Review Process The proposal for each volume is reviewed by the main editor and/or the advisory board. The chapters in each volume are individually reviewed single blind by expert reviewers (at least four reviews per chapter) and the main editor. Ethics Statement for this series can be found in the Springer standard guidelines here https://www.springer.com/us/authors-editors/journal-author/journal-author-hel pdesk/before-you-start/before-you-start/1330#c14214

More information about this series at https://link.springer.com/bookseries/15901

Nithin Kundachira Subramani · S. K. Nataraj · Chetankumar Patel · Sachhidananda Shivanna Editors

Polymer-Based Advanced Functional Materials for Energy and Environmental Applications

Editors Nithin Kundachira Subramani Centre for Research and Development, Department of Chemistry The National Institute of Engineering Mysore, India Chetankumar Patel Department of Mechanical Engineering, Department of Chemistry Sitarambhai Naranjibhai Patel Institute Bardoli, India

S. K. Nataraj Centre for Nano and Material Sciences Jain University Bangalore, India Sachhidananda Shivanna Department of Chemistry The National Institute of Engineering Mysore, India

ISSN 2522-8366 ISSN 2522-8374 (electronic) Energy, Environment, and Sustainability ISBN 978-981-16-8754-9 ISBN 978-981-16-8755-6 (eBook) https://doi.org/10.1007/978-981-16-8755-6 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 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

Preface

Today’s world demands an intimate connection between energy, environment, and sustainable development. That is to say, a learned society seeking sustainable development idealizes the utilization of only those energy resources which cause very less or no environmental impact. Accordingly, The International Society for Energy, Environment and Sustainability (ISEES) was founded at the Indian Institute of Technology Kanpur (IIT Kanpur), India, in January 2014, to spread knowledge/awareness and catalyze research activities in the fields of Energy, Environment, Sustainability, and Combustion. Society’s goal is to contribute to the development of clean, affordable, and secure energy resources and a sustainable environment for society, spread knowledge in the areas mentioned above, and create awareness about the environmental challenges the world is facing today. The unique way adopted by ISEES was to break the conventional silos of specializations (Engineering, science, environment, agriculture, biotechnology, materials, fuels, etc.) to tackle the problems related to energy, environment, and sustainability in a holistic manner. This is quite evident by the participation of experts from all fields to resolve these issues. The ISEES is involved in various activities such as conducting workshops, seminars, conferences, etc., in the domains of its interests. Society also recognizes the outstanding works of young scientists, professionals, and engineers for their contributions in these fields by conferring them awards under various categories. Fifth International Conference on ‘Sustainable Energy and Environmental Challenges’ (V-SEEC) was organized under the auspices of ISEES from December 19–21, 2020, in virtual mode due to restrictions on travel because of the ongoing Covid-19 pandemic situation. This conference provided a platform for discussions between eminent scientists and engineers from various countries including India, Spain, Austria, Bangladesh, Mexico, USA, Malaysia, China, UK, Netherlands, Germany, Israel, and Saudi Arabia. At this conference, eminent international speakers presented their views on energy, combustion, emissions, and alternative energy resources for sustainable development and a cleaner environment. The conference presented two high voltage plenary talks by Dr. V. K. Saraswat, Honorable Member, NITI Ayog, on ‘Technologies for Energy Security and Sustainability’ and Prof. Sandeep Verma, Secretary, SERB, on ‘New and Equitable R&D Funding Opportunities at SERB.’ v

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The conference included nine technical sessions on topics related to energy and environmental sustainability. Each session had 6–7 eminent scientists from all over the world, who shared their opinion and discussed the trends for the future. The technical sessions in the conference included Emerging Contaminants: Monitoring and Degradation Challenges; Advanced Engine Technologies and Alternative Transportation Fuels; Future Fuels for Sustainable Transport; Sustainable Bioprocessing for Biofuel/ Non-biofuel Production by Carbon Emission Reduction; Future of Solar Energy; Desalination and Wastewater Treatment by Membrane Technology; Biotechnology in Sustainable Development; Emerging Solutions for Environmental Applications and Challenges and Opportunities for Electric Vehicle Adoption. 500+ participants and speakers from all over the world attended this three days conference. The conference concluded with a high voltage panel discussion on ‘Challenges and Opportunities for Electric Vehicle Adoption,’ where the panelists were Prof. Gautam Kalghatgi (University of Oxford), Prof. Ashok Jhunjhunwala (IIT Madras), Dr. Kelly Senecal (Convergent Science), Dr. Amir Abdul Manan (Saudi Aramco), and Dr. Sayan Biswas (University of Minnesota, USA). Prof. Avinash K. Agarwal, ISEES, moderated the panel discussion. This conference laid out the roadmap for technology development, opportunities, and challenges in Energy, Environment, and Sustainability domain. All these topics are very relevant for the country and the world in the present context. We acknowledge the support received from various agencies and organizations for the successful conduct of the Fifth ISEES conference V-SEEC, where these books germinated. We want to acknowledge SERB (Special thanks to Dr. Sandeep Verma, Secretary) and our publishing partner Springer (Special thanks to Ms. Swati Meherishi). The editors would like to express their sincere gratitude to a large number of authors from all over the world for submitting their high-quality work on time and revising it appropriately at short notice. We would like to express our special gratitude to our prolific set of reviewers, Mr. Kishen Karumbaiah, Dr. Sandeep S., Dr. Karthik, Mr. Aaqib Javeed, Mr. Jagajeevan Raj B. M., Dr. Aruchamy Kanakaraj, Dr. Haradhan Koyla, Dr. Bharathi Saini, Dr. Anshu Raj, Dr. Manohara Halanur, Dr. Rishi Kant, Dr. Koshal Singh, Dr. Shakil Kagzi, Dr. Arif M. Varsi, and Dr. Ram Chandra Chaurasia, who reviewed various chapters of this monograph and provided their valuable suggestions to improve the manuscripts. The world is in the midst of a multidisciplinary technological revolution, that aims to keep pace with the ever mounting consumer desires. Going forward, these technological revolution have created a swift demand for high performance materials, with advanced end properties. Polymer-based advanced functional materials are one of the most sought-after products, towards satisfying, this global high performance material demand, as these materials guarantee both processing ease and design flexibilities. Also, the material behaviors (optical, electrical, magnetic, mechanical and so forth) and the resultant functionalities of polymer-based systems may be successfully engineered. Either inherently, that is by adopting different synthetic approaches and/or surface functionalization, or by introducing different functional fillers. Consequently, a book/volume, that provides a comprehensive and updated review of major innovations in the field of polymer-based advanced functional

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materials would endow with sufficient number of ways for academicians, scientists, researchers, and students to garner constructive knowledge on advanced multifunctional materials and their resultant techno-commercial applications. Further, to which, and owing to the fact, that the application window of such polymer-based advanced functional materials is sufficiently large. This book aims at restricting the coverage to energy and environment-related applications. As the said two are among the most emerging application domains of polymer-based advanced functional materials. This book aims to present the cutting-edge and recent research findings of polymer-based advanced functional materials in energy and environment sectors, where each chapter will highlight a specific energy and environment related application of polymer-based advanced functional materials, their preparation technique, property enhancement achieved, and allied factors. We hope that this book would greatly interest fellow researchers, academicians, professionals, postgraduate students involved in polymers, chemistry, energy and environmental research, and other allied domains. Mysore, India Bangalore, India Mysore, India Kanpur, India

Nithin Kundachira Subramani S. K. Nataraj Sachhidananda Shivanna Chetankumar Patel

Contents

Part I 1

Introduction to Polymer-Based Advanced Functional Materials for Energy and Environmental Applications . . . . . . . . . . . . Nithin Kundachira Subramani, S. K. Nataraj, Sachhidananda Shivanna, and Chetankumar Patel

Part II 2

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4

General 3

Energy and Environment Related Applications of Polymer-Based Advanced Functional Materials

Sustainable Polymer-Based Materials for Energy and Environmental Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nidhi Maalige R., Manohara Halanur Mruthunjayappa, and S. K. Nataraj Polymer Aerogels for Energy Storage and Water Purification Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manohara Halanur Mruthunjayappa, Dibyendu Mondal, and S. K. Nataraj Polymer Nanocomposites and Metal Halide Perovskites for Luminescent Solar Concentrator Applications—Host Materials Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Sahaya Dennish Babu and B. S. Madhukar

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Part III Environment Related Applications of Polymer-Based Advanced Functional Materials 5

Polymeric Membranes and Hybrid Techniques for Water Purification Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Haradhan Kolya, Vijay K. Singh, and Chun-Won Kang

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Contents

Environmentally Significant Cellulose Fiber Reinforced Polymer Matrix Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yucheng Peng, Sanat Chandra Maiti, and Rajendra Kumar Bordia

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Factors Limiting the Application Window of Acoustically Important Natural Fiber Based Polymer Reinforcements and Their Related Control Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 K. M. Rakesh, Srinidhi Ramachandracharya, and K. S. Nithin

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Advanced Functional Polymer-Based Porous Composites for CO2 Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Ravi Vaghasia, Bharti Saini, and Anirban Dey

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Functional Polymer Materials for Environmental Monitoring and Safety Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Sreeramareddygari Muralikrishna, Sureshkumar Kempahanumakkagari, Ramakrishnappa Thippeswamy, and Werasak Surareungchai

10 Progress in Functionalized Polymeric Membranes for Application in Waste Water Treatment . . . . . . . . . . . . . . . . . . . . . . . 205 Prachi Nilesh Shah, Tanmay Sanghvi, Arya Shah, Bharti Saini, and Anirban Dey 11 Fungal Chitin-Glucan: Renewable Nanofibrils for Water Treatment and Structural Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Andreas Mautner and Ernst Wintner 12 Advanced Functional Materials for the Detection of Perfluorinated Compounds in Water . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Satya Ranjan Jena, Sudesh Yadav, Anchal Yadav, M. B. Bhavya, Ali Altaee, Manav Saxena, and Akshaya K. Samal

Editors and Contributors

About the Editors Dr. Nithin Kundachira Subramani is currently associated with National Institute of Engineering, Mysuru, India and holds an academic position as Assistant Professor and coordinator, NIE-Center for Research and Development. He has authored more than 50 research articles with journals of national and international repute. He has filed 2 Indian and 1 US patent, authored 9 book chapters, edited 2 books, 4 editorials and 1 monograph. He is also the recipient of 2 Project of the Year Award and Certificate of Commendation from Karnataka State Council for Science and Technology, India, IXth National Award for Technology Innovation from the Department of Chemicals and Petrochemicals, Government of India, Young Scientist Award—2020 from ISEES, India. He is also an honorary external R&D advisor for rural science and engineering institutes, and Life Member of Indian Nuclear Society.

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Editors and Contributors

Dr. S. K. Nataraj is currently working as Professor at Centre for Nano and Material Sciences (CNMS), Jain University, India. He obtained his Ph.D. on ‘Membrane Based Separation Processes for Industrial Effluent Treatment’ in 2008 from Centre of Excellence in Polymer Science (CEPS), Karnatak University, India. He pursued his postdoctoral assignment at Alan G MacDiarmid Energy Research Institute (AMERI), Chonnam National University, South Korea on Energy Materials. He was also a postdoctoral scholar at Institute of Atomic Molecular Sciences (IAMS), Academia Sinica, Taiwan to develop ion-exchange membranes for fuel cell applications. Further, he worked as Qatar University visiting fellow at Cambridge University (2010–11) and continued as full time Postdoctoral Research Associate (2011–2013) at Cavendish Laboratory, University of Cambridge, UK. Later, he moved to India to work as DST-INSPIRE Faculty Fellow (2013–2015) at CSIRCSMCRI, Bhavnagar. He has been admitted to the prestigious Fellow of Royal Society of Chemistry (FRSC), UK. He teaches courses in separation and purification technologies, battery-fuel cells and solid-state materials at postgraduate level. He has Published over 90 research articles, 14 US/PCT patents, 15 book chapters, among others. Dr. Chetankumar Patel is currently working as an associate professor at the Mechanical Engineering Department of Sitarambhai Naranji Patel Institute of Technology and Research Centre, India. He pursued his Ph.D. from Indian Institute of Technology (IIT) Kanpur in 2016. He was at PRISME Laboratory, University of Orleans, France as a Postdoctoral fellow (2018-19). He obtained his bachelor’s and master’s degree in Mechanical engineering from L.D. College of Engineering, India in 2002 and 2007 respectively. His primary areas of research include microscopic and macroscopic spray investigations, in-cylinder spray and combustion visualization, in-cylinder combustion investigations, emissions, noise and vibrations investigations, biofuels, composite materials, manufacturing science and engineering. He has 16 peer-reviewed publication in high impact SCI journals and 6 peer-reviewed international

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conference publications. He also authored three book chapters. Dr. Sachhidananda Shivanna is a CSIR-Senior Research Fellow in the Department of Chemistry, National Institute of Engineering, India. His primary research interest is in the area of advanced functional materials which embraces search for polymer-based composite materials for solar energy conversion and storage, mechanically flexible spectral manipulators for UV protection and sensing, and electro-active smart materials for pressure sensing. He is the recipient of IXth National Award for Technology Innovation from the Department of Chemicals and Petrochemicals, Government of India. He has filed 1 Indian and 1 US patent, and has 32 research papers in reputed international journals, and 6 book chapters to his credit.

Contributors Ali Altaee Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, Ultimo, NSW, Australia G. Sahaya Dennish Babu Department of Physics, Chettinad College of Engineering and Technology, Gandhigramam, Tamil Nadu, India M. B. Bhavya Centre for Nano and Material Sciences, Jain University, Ramanagara, Bangalore, Karnataka, India Rajendra Kumar Bordia Department of Materials Science and Engineering, Clemson University, Clemson, SC, USA Anirban Dey Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, Gujarat, India Satya Ranjan Jena Centre for Nano and Material Sciences, Jain University, Ramanagara, Bangalore, Karnataka, India Chun-Won Kang Department of Housing Environmental Design and Research Institute of Human Ecology, College of Human Ecology, Jeonbuk National University, Jeonju, Jeonbuk, Republic of Korea Sureshkumar Kempahanumakkagari Department of Chemistry, BMS Institute of Technology and Management, Bengaluru, Karnataka, India

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Haradhan Kolya Department of Housing Environmental Design and Research Institute of Human Ecology, College of Human Ecology, Jeonbuk National University, Jeonju, Jeonbuk, Republic of Korea B. S. Madhukar Department of Chemistry, Sri Jayachamarajendra College of Engineering JSS Science and Technology University, Mysuru, India Sanat Chandra Maiti Department of Materials Science and Engineering, Clemson University, Clemson, SC, USA Andreas Mautner Institute of Materials Chemistry & Research, University of Vienna, Wien, Austria Dibyendu Mondal Centre for Nano and Material Sciences, Jain University, Bangalore, India Manohara Halanur Mruthunjayappa Centre for Nano and Material Sciences, Jain University, Bangalore, India Sreeramareddygari Muralikrishna Pilot Plant Development and Training Institute, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand S. K. Nataraj Centre for Nano and Material Science, Jain University, Bangalore, India; IMDEA Water Institute, ParqueCientíficoTecnológico de La Universidad de Alcalá, Alcalá de Henares, Spain Nidhi Maalige R. Centre for Nano and Material Sciences, Jain University, Bangalore, India K. S. Nithin Department of Chemistry, The National Institute of Engineering Mysuru, Mysore, India Chetankumar Patel Department of Mechanical Engineering, Sitarambhai Naranji Patel Institute of Technology and Research Centre, Gujarat, India Yucheng Peng School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL, USA K. M. Rakesh Department of Mechanical Engineering, JSS Science and Technology University Mysuru, Mysore, India Srinidhi Ramachandracharya Department of Mechanical Engineering, JSS Science and Technology University Mysuru, Mysore, India Bharti Saini Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, Gujarat, India Akshaya K. Samal Centre for Nano and Material Sciences, Jain University, Ramanagara, Bangalore, Karnataka, India Tanmay Sanghvi Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, Gujarat, India

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Manav Saxena Centre for Nano and Material Sciences, Jain University, Ramanagara, Bangalore, Karnataka, India Arya Shah Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, Gujarat, India Prachi Nilesh Shah Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, Gujarat, India Sachhidananda Shivanna Department of Chemistry, The National Institute of Engineering, Mysuru, India Vijay K. Singh Department of Physics, Indian Institute of Technology Jodhpur, Jodhpur, India Nithin Kundachira Subramani Department of Chemistry, The National Institute of Engineering, Mysuru, India Werasak Surareungchai Pilot Plant Development and Training Institute, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand; School of Bioresources and Technology, Nanoscience and Nanotechnology Graduate Programme, and Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand Ramakrishnappa Thippeswamy Department of Chemistry, BMS Institute of Technology and Management, Bengaluru, Karnataka, India Ravi Vaghasia Department of Chemical Engineering, School of Technology, PanditDeendayal Energy University, Gandhinagar, Gujarat, India Ernst Wintner Photonics Institute, Vienna University of Technology, Wien, Austria Anchal Yadav School of Chemistry, Monash University, Clayton, Australia Sudesh Yadav Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, Ultimo, NSW, Australia

Part I

General

Chapter 1

Introduction to Polymer-Based Advanced Functional Materials for Energy and Environmental Applications Nithin Kundachira Subramani, S. K. Nataraj, Sachhidananda Shivanna, and Chetankumar Patel Abstract The ever mounting demand for speciality materials with superior material behaviours have fast-driven the development and performance evaluation of advanced functional polymers. Further, polymer are those wonder matrices, whose overall material functionalities can be thoughtfully tailored via appropriate surface functionalization and/or using dopants. Accordingly, such functional materials with engineerable material properties can be successfully employed for various commercial applications. And energy and environment applications are no exception. Going forward, this chapter gives a brief introduction to polymer-based advanced functional materials and their energy and environment related applications. Also, this chapter being the introductory chapter of the monograph titled polymer-based advanced functional materials for energy and environmental applications, it furnishes the details pertaining to various chapters covered in the said monograph. Keywords Advanced functional polymers · Energy · Environment · Applications · Sustainability Polymers are those wonder matrices, that are known to exist, ever since the begin of life on earth. Consequently, the human race explored and exploited various naturally occurring molecules for diverse domestic and commercial purposes. Going forward, it was only in the early nineteenth century, that Thomas Hancock, gave an insight of modifying the properties of natural polymer via blending. While, Charles Goodyear bettered the material behaviors of natural rubber by vulcanization. Which was soon N. K. Subramani (B) · S. Shivanna Department of Chemistry, The National Institute of Engineering, Mysuru, India e-mail: [email protected] S. K. Nataraj (B) Centre for Nano and Material Science, Jain University, Jain Global Campus, Bangalore, India e-mail: [email protected] C. Patel Department of Mechanical Engineering, Sitarambhai Naranji Patel Institute of Technology and Research Centre, Gujarat, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_1

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followed by the reporting of first synthetic polymer (Bakelite) in 1909, and first synthetic fiber (rayon) in 1911. However, it was rapid advancement in the field of synthetic organic chemistry and the development of novel material characterization tools and theories, that enabled the human race to perceive further and deeper into the roots of polymer technology. Polymers are unique macromolecular assemblies that are regularly employed in almost every field. The exceptional demand for polymers and their functionalized derivatives, may be owed to their increased adaptability, higher accessibility and ease of processing. Although, the conventional polymers were able to match most of the material requirements of the modern world. The ever mounting human aspirations, demanded materials with special functionalities. Which initiated the search for polymers with advanced functional behaviors and subsequent origin of advanced functional polymers. Though, polymers can be used without any additives/fillers, however, more often they are either surface modified or loaded with organic/inorganic fillers, so as to enable special functionalities. The resulting advanced functional polymers are reported to display improved optical, electrical, thermal and mechanical properties (Nithin et al. 2021; Karumbaiah et al. 2021). Polymer-based advanced functional materials also offer large surface area-to-volume ratio, their by enabling special functionalities, such as high energy conversion efficiency, high permeability, antifouling characteristics, catalytic activity, controlled wettability, antibacterial activity and many more (Ulbricht 2006). The observed material properties and resultant functionalities of polymer-based advanced functional materials may be owed, either to their unique synthetic chemistry, surface treatments resulted improved interfacial behaviours, or filler (inorganic or organic)/matrix (polymer) enabled combinatorial and/or synergistic interactions (Sachhidananda et al. 2021). Further, the ability of polymers to display dopant and/or processing condition dependent material behaviors render them highly desirable for various commercial applications. Accordingly, advanced functional polymers have become an important cornerstone of the modern world, with no exception to energy and environment sectors. Today, topics such as energy, energy security, and global warming are some of the most searched and researched scientific keywords. As the three are very much interrelated and often end up, under the board umbrella of the twinned word energy and environment. Going forward, the United Nations (2016) defined, energy use as one of the most dominant cause of environmental change in general, and climate change in particular. It further added, that the energy use accounts for about 60% of total global greenhouse gas emissions. It is for this reason, reducing fossil fuel intensity is one of the key objective of the long-term climatic targets. And innovations in polymer-based functional material research is opening up newer possibilities in energy and environmental sectors. Accordingly, a number of polymer-based functional materials with a large number of task specific functional groups and/or fillers, size, morphology and large surface areas have been developed and performance evaluated in recent years (Ulbricht 2006). In particular, polymer-based functional materials for energy

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conversion and storage, pollutant adsorption and separation, and other allied applications are gaining prominence globally (Yusuf et al. 2020; Yadav et al. 2021; Garba et al. 2020). Nonetheless, these polymer-based advanced functional materials when used for energy and environmental application, and in various applied conditions and process parameters, often pose regeneration/ recycling problems. In addition to leaching effects, owing to their highly active sites and strong affinity towards the solvent system. This causes overall decrease in device performance or creation of secondary contamination in environmental applications. Which has raised worries among environmental and occupational health specialists. However, to overcome these limitations, the scientific community focused at adopting advanced modification routes and techniques. That is the polymer-based advanced material is being prepared in various forms and dimensions, so as to meet the end user demands. Nonetheless, a thoughtful selection of appropriate raw material or precursor and process parameters, must be taken up to achieve the sustainability goals. Therefore, they are being prepared in the form of composite films, three dimensional (3D) sponges, hydrogels, aerogels, foams, beads, membranes and other forms (Tian et al. 2019; Li et al. 2020). Consequently, this monograph includes considerate compilation of most recent research and innovation advancements in advanced functional materials and processes in energy and environmental application, in general and water treatment in particular. Further, we believe that the said compilation would endow with sufficient number of ways for academicians, scientists, researchers and students to garner constructive knowledge on the said domain. The entire contribution has been divided into three parts that includes; an introductory part to polymer-based advanced functional materials for energy and environmental applications; the second part of the monograph covers energy and environment related applications, while the final part is dedicated to environment related applications. The specific topics covered in the monograph includes; • Introduction to Polymer-Based Advanced Functional Materials for Energy and Environmental Applications • Sustainable Polymer-Based Materials for Energy and Environmental Applications • Polymer Aerogels for Energy Storage and Water Purification Applications • Polymer Nanocomposites and Metal Halide Perovskites for Luminescent Solar Concentrator Applications–Host Materials Perspective • Polymeric Membranes and Hybrid Techniques for Water Purification Applications • Environmentally Significant Cellulose Fiber Reinforced Polymer Matrix Composites • Factors Limiting the Application Window of Acoustically Important Natural Fiber based Polymer Reinforcements and their Related Control Strategies • Advanced Functional Polymer-Based Porous Composites for CO2 Capture • Functional Polymer Materials for Environmental Monitoring and Safety Applications • Progress in Functionalized Polymeric Membranes for Application in Waste Water Treatment

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• Fungal Chitin-Glucan: Renewable Nanofibrils for Water Treatment • Advanced Functional Materials for the Detection of Perfluorinated Compounds in Water

References Garba ZN, Lawan I, Zhou W, Zhang M, Wang L, Yuan Z (2020) Microcrystalline cellulose (MCC) based materials as emerging adsorbents for the removal of dyes and heavy metals-a review. Sci Total Environ 717:135070 Karumbaiah KBJ, Nithin KS, Prakash KR, Ravi Kumar V, Shilpa KN, Basava T, Shruthi P, Sachhidananda S (2021) Nanotechnology-enabled polymer-based flexible electronics and their potential applications. Elsevier, In polymer-based advanced functional composites for optoelectronic and energy applications, pp 321–340 Li B, Zhang Q, Pan Y, Li Y, Huang Z, Li M, Xiao H (2020) Functionalized porous magnetic cellulose/Fe3 O4 beads prepared from ionic liquid for removal of dyes from aqueous solution. Int J Biol Macromol 163:309–316 Nithin KS, Sachhidananda S, Shilpa KN, Sandeep S, Karthik CS, Jagajeevan Raj BM, Siddaramaiah H (2021) Polymer-based smart composites and/or nanocomposites for optical, optoelectronic, and energy applications: a brief introduction. Elsevier, In Polymer-based advanced functional composites for optoelectronic and energy applications, pp 1–29 Sachhidananda S, Sarojini BK, Nithin KS, Shilpa KN, Jagajeevan RBM, Muthappa KA, Siddaramaiah H, Sahaya ANA (2021) Metal oxide nanofillers introduced polymer-based composites with advanced optical, optoelectronic, and electrical energy storage functionalities. Elsevier, In Polymer-based advanced functional composites for optoelectronic and energy applications, pp 51–89 Tian S-Y, Guo J-H, Zhao C, Peng Z, Gong C-H, Yu L-G, Liu X-H, Zhang J-W (2019) Preparation of cellulose/graphene oxide composite membranes and their application in removing organic contaminants in wastewater. J Nanosci Nanotechnol 19(4):2147–2153 Ulbricht (2006) Advanced functional polymer membranes. Polymer 47(7):2217–2262 Yadav P, Ismail N, Essalhi M, Tysklind M, Athanassiadis D, Tavajohi N (2021) Assessment of the environmental impact of polymeric membrane production. J Memb Sci 622:118987 Yusuf A, Sodiq A, Giwa A, Eke J, Pikuda O, De Luca G, Di Salvo JL, Chakraborty S (2020) A review of emerging trends in membrane science and technology for sustainable water treatment. J Clean Prod 121867

Part II

Energy and Environment Related Applications of Polymer-Based Advanced Functional Materials

Chapter 2

Sustainable Polymer-Based Materials for Energy and Environmental Applications Nidhi Maalige R. , Manohara Halanur Mruthunjayappa , and S. K. Nataraj Abstract Polymers are an important class of materials that are providing unparalleled benefits in our daily life. Over the past decade, there is a rapid increase in demand for ecofriendly materials to counter various problems, such as environmental issues, biodegradability, sustainability, and biocompatibility. Thus, sustainable polymers derived from renewable resources is fast growing and evolving research field for energy and environmental applications. The sustainable polymers can be derived from natural sources or synthesized from renewable resources. However, in order to design ecofriendly materials, there is a need for a basic knowledge of sustainable polymers. Therefore, the present book chapter provides discussion on the classification of sustainable polymers and their structures, physical and chemical properties. Further, polymeric materials which exhibit high performance for energy storage and environmental applications are briefly discussed. Keywords Sustainable polymers · Biodegradable · Energy storage · Water purification

2.1 Introduction The incessant progress in technology and living standards has led to increasing awareness to develop sustainable materials for health and environmental sustainability (Miller 2013). Interestingly, polymers are the basic components of health, energy and environment sectors in the modern life. Intensive research and development can be seen in utilization of polymers in cloths, food industry, drug delivery systems, water purifiers, energy storage and conversion devises, to name few (Miller 2013; Zhu et al. 2016). Inevitable extensive use and nonscientific disposal of polymer-based Nidhi Maalige R. · M. H. Mruthunjayappa · S. K. Nataraj (B) Centre for Nano and Material Sciences, Jain University, Bangalore 562112, India e-mail: [email protected] S. K. Nataraj IMDEA Water Institute, ParqueCientíficoTecnológico de La Universidad de Alcalá, Avenida Punto Com, 2, 28805 Alcalá de Henares, Spain © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_2

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materials can possibly potential threat to the environment. Extreme use of polymers which are non-biodegradable poses severe threat to the environment (Schneiderman and Hillmyer 2017). For example, various non-biodegradable polymers such as polyethylene, polystyrene, polypropylene, poly(ethylene terephthalate), poly(vinyl chloride), polyester and polycarbonate are the basic constituents of various necessary products. These polymers releases micro plastics into the environment which are recently categorized as emerging contaminants in aqueous system. According to a survey, use of plastic which are nothing but polymers significantly increased from 1.5 million tons in 1950 to 299 million tons in 2008 with 9% of annual growth rate (Mohapatra et al. 2017; Shukla and Maiti 2019). Therefore, development of recyclable, low-cost, biodegradable polymers are the center of sustainability and has a crucial role in ecosystem survival. On the other hand, with increase in population and rapid urbanization, global demand for energy and potable water is escalating day by day, which lead to the emergency for development of efficient functional materials for water purification, energy storage and conversion applications (Pérez-Madrigal et al. 2016). Water is one of the major constituent of living organisms on Earth. Certainly, cautious utilization of fresh water and purification of wastewater are important aspect of human life. Thus, developing a low-cost and sustainable technology for wastewater purification are important topic of the global research community (Pronk et al. 2019). Similarly, global demand for durable, highly efficient, sustainable energy storage and conversion materials has been increasing at the same time. As a result, intense research efforts were made to develop several synthetic and biopolymer-based materials and explored for their performance (Arunachalam 2018; Srinivasan et al. 2015). Hence, the present book chapter particularly discusses the progress in design and development of sustainable polymer-based materials for water purification, energy storage and conversion applications (Table 2.1). Table 2.1 Overview of the sustainable polymers and their significant properties for the application in energy, environmental and health sector Sectors

Significant features

Applications

Energy

✓ Thermally stable

Batteries Araujo et al. (2017)

✓ High mechanical strength

Supercapacitors Wang et al. (2014)

Environment

Health

✓ Flexibility

Fuel cells Gaur et al. (2017)

✓ Biodegradability

Membrane filters Xie et al. (2019)

✓ Chemically stable

Adsorption Huang et al. (2018)

✓ Scalable & recyclable

Photocatalyst Nawi and Sabar (2012)

✓ Biocompatible

Drug delivery Kouser et al. (2018)

✓ Non-toxic

Biosensors Jiang et al. (2019)

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2.2 Classification of Sustainable Polymers By definition, sustainable polymers are nothing but degradable polymers either derived from natural sources (biomass) or from low-cost precursors which cause no harm to the environment, health and economy (Wang et al. 2020). Biodegradability is one of the important parameter of sustainability. Biodegradability is produced by the ability of microorganisms to modify the structure of a polymers by their metabolic action under natural environmental condition (Kubowicz and Booth 2017). Numerous biodegradable polymers have been developed such as polylactide, poly(hydroxyalkanoate), poly(lactide-co-glycolide), poly(propylene fumarate), poly(butylene succinate), poly(vinyl alcohol), poly(ε-caprolactone), and biopolymers like lignin, chitin, chitosan, cellulose, agarose, alginates, silk, sericin, carrageenan and some other rarely used polymers (Zhu et al. 2016). The better understanding of the structure and property relationship is essential to tune the properties of the polymers for desired applications. In general, the biodegradable polymers can be classified into polyesters, biomass derived polymers (biopolymers) and polyvinyl alcohol (Bandehali et al. 2021). 1.

Polyesters

Poly(lactic acid) (PLA): PLA is natural origin linear polymer derived from the polycondensation of lactic acid or 2-hyfroxypropanoic acid (Fig. 2.1). The first ever PLA was prepared by Carothers in 1932, however, the product had low molecular weight and poor mechanical strength. Further, high molecular weight polymer with completely aliphatic ester was produced and patented in 1972 (Zhu et al. 2016) Within few years pilot scale production and commercialization activities were observed worldwide. PLA generally dissolves in organic solvents such as chloroform, dioxane and possess high crystallinity, elasticity depending on the preparation conditions. Commercially, mechanical properties of PLA is better than polystyrene (Auras et al. 2004) and can be tuned from soft and elastic polymer to stiff and high strength polymer. Most importantly, they are non-toxic, biocompatible and biodegradable polymer (Jalil and Nixon 1990; Lunt 1998).

Fig. 2.1 Chemical structure of polyvinyl alcohol and polyester (Aoki and Saito 2020)

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Poly(butylene succinate) (PBS): PBS is a aliphatic, bio-based polyester obtained by polycondensation reaction of 1,4-butanediol and succinic acid (Fig. 2.1). It is a flexible polymer with chemical resistance, thermoplastic process ability, excellent biodegradability and remarkable mechanical properties depending on the degree of crystallinity (Rafiqah et al. 2021). PBS was introduced in 1990 in Japan, and widely utilized polymer over polyolefin for various applications aims to increase independency on petroleum products since, butanediol and succinic acid can be derived from renewable resources (Mochane et al. 2021). Poly (ε-caprolactone) (PCL): PCL is a biocompatible, slow biodegradable, mechanically compatible and semi crystalline polymer, prepared by ring opening polymerization of seven membered ε-caprolactone using a suitable catalyst (Fig. 2.1) (Sinha et al. 2004). The ring opening polymerization of PCL was first established by Van Natta in 1934 further, used to blend with other polymers to enhance stress crack resistance. PCL is comparatively high cost, possess low glass transition temperature, soluble in organic solvents such as chloroform, dichloromethane. PCL used in a wide range of biomedical applications attributed to its slow biodegradability (Sinha et al. 2004). Poly (lactide-co-glycolide) (PLG): PLG is linear polyester copolymer derived from PLA and poly (glycolic acid) (Fig. 2.1) (Makadia and Siegel 2011). The molar ratio of the two monomers is highly influential in deciding the crystallinity of PLG polymer. It is a biocompatible, biodegradable polymer where, degradation products are lactic acid and glycolic acids (Gentile et al. 2014). Interestingly, it is the best-defined biodegradable polymer available for the drug delivery and biomedical applications. PLG can be to prepare materials of any shape and size due to their plasticity and mechanical strength (Jalil and Nixon 1990). 2.

Polyvinyl alcohol

Physically, polyvinyl alcohol (PVA) is a whitish, odorless, biocompatible, thermostable, semi crystalline, linear synthetic polymer derived from the polymerization of vinyl acetate (Halima 2016). Vinyl acetate is a reactive monomer undergo free radical chain-polymerization to form PVA. However, PVA was first manufactured by Hermann in 1924 via saponifying poly (vinyl ester) using sodium hydroxide solution. It is a low-cost, hydrophilic, environmentally friendly polymer widely used in fuel cell and membrane filtration applications (Marin et al. 2014). Commercially, PVA is synthesized by indirect method such as complete hydrolysis of polyvinyl acetate due to unstable nature of vinyl alcohol. The hydroxyl groups of the PVA are reactive and crosslinks with aldehyde to form thermally stable, hydrophilic polymer with enhanced mechanical stability. Significantly, it is a water soluble polymer, slightly soluble in alcohol and insoluble in organic solvents (Aslam et al. 2018). 3.

Biopolymers

Over the decades, the convenience of synthetic polymers obtained from petroleum and non-renewable sources is significantly diminishing as the scientists are widely exploring the biomass derived polymers. Proteins and carbohydrates being the basic

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fundamental of all living organism significantly possess unique physico-chemical properties and also biocompatible (Yates and Barlow 2013). Various biopolymers have been widely explored due to enriched surface functionalities, natural hetero functionalities, considerable chemical and mechanical stability also, biodegradable (Bandehali et al. 2021). In this section, structure and properties of most studied biopolymers will be discussed. Cellulose: Cellulose contains repeating units of β-D-glucopyranose which are covalently linked through 1, 4-glycosidic linkage (Fig. 2.2). Cellulose is a linear-chain polymer with the production rate of 1012–1013 tons annually by photosynthesis and considered as inexhaustible bio resource for increasing demand for energy and environmental application. Cellulose has flexibility to bend and twist in the direction of the plane and has a ribbon shape (Bandehali et al. 2021). It has excessive hydroxyl functionality which caused inter and intramolecular hydrogen bonding which further lead to high crystallinity and remarkable mechanical strength (Mishra et al. 2018).

Fig. 2.2 Chemical structure of biopolymers (Venkateshaiah et al. 2020)

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Further, it has chirality and hydrophilicity, and the reactive hydroxyl groups for easy modifications. In particular, cellulose has high affinity to adsorb heavy metal ions due to donor or chelating properties of the hydroxyl groups. Moreover, an ideal antifouling membrane with high tensile strength, superior permeability and surface hydrophilicity can be synthesized using cellulose (Lv et al. 2017). However, major disadvantage with cellulose is that insoluble in water and typical organic solvents due to high crystallinity which lead to the use of cellulose fibers in various applications (Nasrollahzadeh et al. 2021). Lignin: Lignin which contains 30% of the organic carbon is the most explored biomass after cellulose. Lignin accounts 20–30% of the plant and derived from phenylpropanoid or phenylalanine (Fig. 2.2). It acts as binder for hemicellulose and cellulose to form lignin-carbohydrate complex (Laurichesse and Avérous 2014). Lignin was first mentioned by a botanist Candolle in 1813 and its structure is typically complex further, monomers vary with the species of the plant thus, yet to exploit. Although, lignin containing both hydrophilic and hydrophobic groups, lignin-based materials exhibit hydrophobic nature which helps to contain water molecules in the cell wall (Kai et al. 2016). Lignin is fundamentally amorphous and soluble only in dimethyl sulfoxide and pyridine, whereas acetylated lignin soluble in most of the organic solvents (Kim and Ralph 2010). Chitin/Chitosan: Chitinis abundantly available biopolymer which are extracted from the crabs and shrimps. Structurally, chitin is an N-acetyl-D-glucosamine monomer linked through β (1, 4)-glycosidic bonds (Fig. 2.2). Whereas, chitosan is deacetylated form of chitin (Nasrollahzadeh et al. 2021; Zhu et al. 2016). From past few decades, chitosan has been extensively studied for numerous application due to their abundancy, biocompatibility and enriched hydroxyl and amine functionalities. Importantly, chitosan is the only polymer which exist in protonated form in nature and only cationic biopolymer which is commercially available (Nechita 2017). They are highly hydrophilic, chemically stable and possess considerable mechanical properties. The chitosan is water soluble in aqueous medium makes it excellent candidate to build functional materials for desired applications. Significantly, hydroxyl and amine functionalities exhibited high adsorption capacity for heavy metal ions and charged organic molecules through metal–ligand chelating effect or by coordination bonds (Nasrollahzadeh et al. 2021; Shaari and Kamarudin 2015). Alginate: Alginate is linear block copolymer of α-L-guluronic acid and β-Dmannuronic acid linked together by β-1, 4-glycosidic linkage (Fig. 2.2). It is low-cost, anionic polysaccharide extracted from the component of the cell walls of brown algae (Fernando et al. 2020). Alginate are water soluble, hydrophilic in nature and possess excellent gelling property attributed to widespread hydroxyl and carboxylic functionalities (Thakur et al. 2016). Thus, widely utilized in adsorption, wastewater remediation due to its structural integrity, biodegradability, robust water permeability, and biocompatibility. Remarkably, several studies showed that the efficacy of alginates

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can be enhanced by developing hybrids with the proper materials for desired applications (Nasrollahzadeh et al. 2021; Shaari and Kamarudin 2015). Commercially alginates are produced by simple alkali treatment of seaweeds such as Laminaria hyperborea, Macrocystis pyrifera, Laminaria digitata, Ascophyllumnodosum, and Laminaria japonica followed by filtration (Yang et al. 2011) (Table 2.2). Table 2.2 Various sustainable polymers, their properties, disadvantages and applications Sl. no

Polymer

Advantages

Disadvantages

Applications

Refs.

01

Cellulose

✓ Naturally occurring substances

Partial regeneration of materials

Water purification, Fuel cell, pervaporation & Gas separation

Nevárez et al. (2011), Abdellah et al. (2018); Gebald et al. (2011)

02

Chitosan

Soluble in water with small amount of acetic acid

Water purification, drug delivery, fuel cell & wound healing applications

Borgohain and Mandal (2019), Bakshi et al. (2020)

03

Alginate

Thermal instability

Tissue engineering, Pervaporation, Water treatment & Gas separation

Wang et al. (2019)

04

Lignocellulose

Pretreatment and fractionation of lignocellulose

Production of fuel alcohol and chemicals, energy storage

Mehta et al. (2020), Chen et al. (2017)

05

Starch

Brittleness

Oil/water separation, Wastewater treatment & Drug delivery

Chen et al. (2020)

06

Collagen

Membranes are swollen when it contacted to water

Pervaporation & Sionkowska Tissue et al. (2017) engineering

07

Lignin

Complex ✓ Biodegradable structure, Low solubility ✓ Hydrophilic

Water treatment

Meng et al. (2019)

✓ Non-toxic ✓ Low cost (continued)

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Table 2.2 (continued) Sl. no

Polymer

Advantages

Disadvantages

Applications

Refs.

08

Poly (ε-caprolactone)

Biocompatible, slow biodegradable, mechanically compatible and semi crystalline polymer

Low solubility

Drug delivery & Abrisham et al. Tissue (2020) engineering

09

Poly (butylene succinate)

High chemical resistance, thermoplastic process ability, slow degradation and biodegradability

Weak strength and poor mechanical resistance

Wastewater treatment & Drug delivery

Rafiqah et al. (2021)

10

Poly (vinyl alcohol)

Hydrophilic, biodegradable, high mechanical strength and thermal stability

High viscosity and swelling affinity

Tissue regeneration, Drug delivery, Pervaporation, Gas separation, Water treatment & Fuel cell

Aslam et al. (2018), Shaari and Kamarudin (2015)

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Poly (lactic acid) Nontoxic, biodegradable, high mechanical strength and biocompatible

Brittleness, low and thermal resistance

Tissue regeneration, Drug delivery, Pervaporation, & Water treatment

Liu et al. (2020), Ma and Sahai (2013)

2.3 Sustainable Polymers in Water Purification Efficient separation processes to obtain clean water which currently account for a significant portion (10–15%) of the world’s energy consumption. Focus on water availability and sustainable recyclability is likely to create businesses, drive the economy, and make the world breathe better (Bolisetty et al. 2019; Le and Nunes 2016). Various technologies have made substantial contribution in providing contaminant-free water to humanity such as decontamination by physicochemical treatment (such as coagulation, flocculation, sedimentation, ion exchange resins, electrochemical treatments, adsorption and membrane filtration for organic and inorganic contaminants), disinfection (chlorine treatment, advanced oxidation processes), and desalination (Bolisetty et al. 2019; Sholl and Lively 2016). In several cases, many contaminants occur simultaneously, whereas some of the separation techniques such as ion exchange resins and electrochemical treatment are designed to target a single type of contaminant hence, limits their applicability. Significantly,

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this issue has led to the development of consolidated and emerging water decontamination technologies such as advanced adsorption, membrane technologies and degradation processes designed based on empirical approaches and molecular-level strategy have attempted to deliberate solutions for organic, inorganic and microbial contamination (Bolisetty et al. 2019). The choosing of suitable technique depends on nature of pollutants, pH of the aqueous medium, concentration of the pollutants in water etc. For example, a drinking water treatment plant involves sedimentation and coagulation as primary treatments, multistep adsorption as secondary and chlorination or advanced oxidation process as tertiary treatment prior to supply as depicted in ‘route a’ in Fig. 2.3. However, in the industry effluents, municipal wastewater treatment the adsorption process will be substituted by membrane technology as shown in ‘route b’ in Fig. 2.3. However, some of the treatment process uses both adsorption and membrane processes during purification based on the nature of pollutants (Pei et al. 2019). 1.

Adsorption: Adsorption is one of the most promising technique widely implemented for the removal of low concentrations of non-degradable organic compounds because it is simple, highly effective an economical. Though adsorption process for water purification was established using charcoal back in 2000 B.C., research attention and widespread application was accomplished in late seventeenth century. In 1733, Robens reported the gas adsorption capacity of carbon (Robens and Jayaweera 2014). However, in 1785, Lowitz observed de-colorization of liquids when interacted with charcoal which further led to widespread application of biochar in wastewater treatment. He established first use of powdered charcoal to remove bad odor and tastes from water in 1790. Since 1960, apart from carbon various other natural and synthetic materials were widely studied for their adoptions capacity (D˛abrowski 2001). Importantly, adsorption processes are usually non-destructive, but the post-treatment of the adsorbent is inevitable and also noneconomic. Various sustainable polymer beads, membranes, hydrogels, aerogels were established for robust and efficient adsorption (Ali 2012). Polymers like, chitosan, cellulose, PVA, alginate

Fig. 2.3 A general practice for wastewater treatment process involves during drinking water treatment, industry effluents and municipal wastewater treatment (Pei et al. 2019)

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were extensively studied for their adsorption property. Due to high surface functionality offers excellent adsorption via chelation or electrostatic or weak Van der Waals force (Lakherwal 2014). Various organic contaminants such as dyes, pharmaceutical drugs, surfactants, pesticides, and inorganic contaminants such as heavy metal ions, fluoride, nitrates, and other charged nutrients were successfully separated by polymer-based beads and bio composites. The porous beads and bio composites can be prepared by using water soluble sacrificial template, or axillary chemicals such as polyglycolic acid, polyethylene glycol etc. via phase inversion technique (Mok et al. 2020). A chemically stable, porous alginate, chitosan and PVA beads were prepared by crosslinking with suitable cross linker. For example, glutaraldehyde crosslinked chitosan, calcium chloride crosslinked alginate and PVA based beads using boric acid and aluminum salts were widely explored for their adsorption capacity. Further, economic point of view, polymerase excellent candidates for preparation of hydrogels (Ngah et al. 2011). For examples, various research groups have developed cellulose nanocrystal/alginate, chitosan/alginate cross linked network based on gelation method was demonstrated as excellent adsorbing agent for organic dyes, heavy metal ions. Most importantly, adsorption is key phenomenon for the separation of heavy metal ions and nutrients in real drinking water purification. And significantly, biopolymer-based adsorbents shows superior adsorption for heavy metal ions through metal ion-ligand interaction (Lakherwal 2014). Aluminium and iron composites immobilized based chitosan beads were successfully demonstrated as drinking water purifiers for separation of arsenic and fluoride in various parts of India (Kumar et al. 2017). Thus, sustainable polymers exhibited as excellent candidates for adsorption basedwater purification. Oxidation and Photo catalysis: In the process of conventional wastewater treatment, physico-chemical treatment involves chlorination/advanced oxidation processes after adsorption/membrane treatment. Biological treatment does not work efficiently due to high resistance of synthetic dyes to aerobic degradation of organic compounds. Hence, advanced oxidation process is significant to reduce COD/BOD levels and to remove remained organic and oxidizable inorganic components. The concept of “advanced oxidation processes” was defined by Glaze and co-workers in 1987 as the processes involving the insitu generation of highly reactive species and degradation of organic substances (Mohajerani et al. 2009). Though, chlorination being technically simple and inexpensive was extensively used as disinfectant against waterborne pathogens. However, involves major drawback such as formation of toxic disinfection byproducts (DBP) for instance trihalomethanes and halo acetic acids by reacting with naturally occurring organic matter present in raw water sources leads to cancer and reproductive defects. To overcome this various powerful disinfectant and a strong oxidants such as ozone, hydrogen peroxide, hypochlorite, and Fenton’s reagent were used in chemical oxidation processes as a primary technique for drinking water treatment prior to chlorination (Zangeneh et al. 2015). Presently, more than 4000 Ozonation plants operation worldwide and more are to be installed in the future.

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Numerous PVA, cellulose, chitosan, alginate based photo catalyst were widely explored for water purification. Since, nanomaterial based heterogeneous photo catalyst showed disadvantages like leaching, complex recyclability, efforts were made to immobilize nanomaterial based photo catalyst in sustainable polymeric network (Crini and Lichtfouse 2019; Wang et al. 2009). This is a promising technique to enhance the photocatalytic activity due to enhanced exposure of active surface of a nanocatalyst. Various metal based photo catalyst such as TiO2 , Fenton catalyst, Fe2 O3 , MgO, ZnO, WO3 , CdS non-metallic photo catalyst like carbon nitride and laccase enzymes were studied for their photocatalytic activity by immobilizing over polymeric network (Melinte et al. 2019). A group of researcher has developed polymer/semiconductor hybrid catalyst using PVA/TiO2 based film for enhanced photocatalytic efficiency for sustainable photocatalytic degradation (Liu et al. 2015). Similarly, chitosan, alginate and other biopolymers are widely applied as support for the active photo catalyst which further enhances the oxidation reactions due to the heteroatom based donor functionality. Recently, polymer-based aerogel system are emerging as promising candidates with excellent degradation capacity attributed to high surface area and easy installation (Gjipalaj and Alessandri 2017; Su et al. 2017). In sum, sustainable polymers can be efficiently used for oxidation processes. Membrane filtration: Membrane separation processes are promising and reliable area of research and are rapidly developing for wastewater treatment due to its significant role in water purification. Membrane separation is a technology that selectively separates materials using the pores of a membrane that acts as a physical barrier (Pronk et al. 2019). Membranes found their significant use in testing drinking water during World War II. Afterwards, the research on membrane filters continued to address the broken down situation in serving drinking water to large community around the world (Bolisetty et al. 2019). Because of easy preparation and simple operation, membrane technology was widely used in various kinds of polluted treatment including drinking water treatment, industrial wastewater, brackish and seawater desalination and does not involve phase changes also, can be made modular for easy scale up. Though, membrane technology is a capableto address severe water scarcity, it has some disadvantages such as fouling (Zhang et al. 2016). Fouling is the undesirable accumulation of solutes either on the surface of the membrane or internally inside the pores or both. Membrane fouling can be caused by pore blocking, cake formation, organic adsorption, inorganic precipitation and biological fouling, leading to blockage of pores, decreases the membrane shelf life, reduction the flow rate, higher energy demanding during processing and decreases the membrane productivity (Rana and Matsuura 2010). When applied to sustainable water purification, almost all membrane processes suffer from fouling problems because of the direct contact with various kinds of foulants in the raw water.

In order to deal with the membrane fouling several methods have been attempted, such as surface modification of membrane using antimicrobial agents, pretreatment of membranes using organic solvents, development of antifouling agents and chemical

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cleaning agents (Kang and Cao 2012). Among these methods, membrane cleaning is still the most effective way to avoid fouling aggravation, quickly restore membrane permeability and considered as the most feasible strategy to regenerate membrane performance. Chemical cleaning agents is the most common cleaning method, especially in reverse osmosis. The most common cleaning agents used are acids, alkalis, metal chelating agents, surfactants and enzymes (Maalige et al. 2021; Zhang et al. 2016) and (Fig. 2.4). Various blended and thin film composite membrane were developed for microfiltration, ultra/nanofiltration and reverse osmosis processes. Researcher have developed various chitosan based membrane for example, glutaraldehyde crosslinked chitosan, catechin-grafted-chitosan based antifouling and antibacterial membrane for water purification. The membranes were assembled over porous polymer support which exhibited high rejection for dyes, and low retention for inorganic salts (Liu et al. 2018; Wang et al. 2010). Further, cellulose based membranes were extensively studies due to their pore forming capability and exceptional mechanical strength. Lignin and cellulose acetate based nanocomposite membrane has showed excellent performance for purification of contaminated groundwater. The membrane exhibited 15–45% rejection for high concentrated fluoride, arsenic, calcium, sodium and magnesium ion contaminated ground water. Interestingly, fluoride and arsenic removal was affected by the ionic and organic matter present in groundwater (Nevárez et al. 2011). Cellulose and modified cellulose based membrane fabricated over polyester films fabricated via non-solvent induced phase separation showed excellent performance for organic dyes separation with high flux up to 600 L/m2 /h. The membrane exhibited excellent antifouling behaviour with 100% flux recovery (Abdellah et al. 2018). Furthermore, aerogels derived from hydrogel are merging as high-performance adsorbents due to high surface area, surface functionality and exceptional mechanical strength. Novel adsorption based membrane derived from chitosan and agarose based aerogels were successfully demonstrated for the adsorption of arsenic, fluoride and Fig. 2.4 Schematic representation of water purification by membrane filtration (Bolisetty et al. 2019)

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organic contaminants with ultrafast permeability which shows potential application in wastewater treatment (Mruthunjayappa et al. 2020). Thus, these studies demonstrated that sustainable polymer-based membranes can be promising alternative for convention non-biodegradable polymers based membrane filtration.

2.4 Sustainable Polymers in Energy Applications 1.

Battery applications: Rechargeable batteries are most promising energy storage devises which are widely used in all sectors. Main constituents of the commercial batteries are cathode, anode, electrolyte, separator and binder. Significantly, various sustainable polymer has been pursued intensively for battery applications. Currently, polypropylene and polyethylene are commercially available separators due to the uniform distribution of pore size and high chemical stability and mechanical strength, unfortunately they are nonbiodegradable and not compatible with some electrolytes (Venugopal et al. 1999). A PVA/cellulose hybrid was reported as an efficient, ecofriendly separator with 60% porosity, enhanced electrolyte uptake and better ionic conductivity (Liu et al. 2016). An electrode in a battery usually comprises of with or without binder loaded on an electrode substrate. Binder plays an important role in enhancing the storage capacity and cyclic stability. The studies were also show that carboxymethyl cellulose, calcium alginate hydrogel based binder which can potentially substitute commercially applied non-biodegradable, toxic poly(vinylidene fluoride) for Si/C based Li-ion, lithium sulfur battery with enhance performance and excellent cyclic performance (Bao et al. 2013; Liu et al. 2014). The enhanced electrochemical performance is due to the highly crosslinked network structure which further increases mechanical stability. Further, chitosan was developed as a significant additive to enhance the performance of cathode and binder (Chen et al. 2015). The chitosan containing numerous hydroxyl and amine functionality acts as an effective polysulfide trap agent in lithium-sulfur batteries. Researchers have also developed PVA/polyimide blend membrane which can potentially substitute costly, commercially used Nafion 117 membrane in vanadium redox flow battery (Xia et al. 2019). The membrane exhibited lower vanadium permeability and enhanced proton selectivity resulted in high performance and cyclic stability. Recently, chitosan and cellulose acetate-based paper like electrode for high performance supercapacitor application have been demonstrated by PANI/MWCNT in the matrix. The significant progress in the flexible electrode is promising advancement for developing sustainable flexible supercapacitor (Aswathy et al. 2021). These results shows that a battery can be completely designed using sustainable polymer-based materials. In case of cathode and

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Fig. 2.5 A schematic illustration of working principles of: a EDLC; b Pseudo Supercapacitor and c three-electrode assembly (Meng et al. 2017)

2.

3.

anode materials, the biopolymer derived carbonaceous materials were demonstrated as excellent choice of materials due to their high energy density and superior specific surface area (Varma 2019). Overall, sustainable polymers can be successfully employed in battery application. Supercapacitor applications: Supercapacitor are gaining remarkable research interest due to high charge density, low thermal heating, fast charge–discharge mechanism, and long-term operational stability. Similar to batteries, they are mainly constituent of electrodes, electrolyte and separator. Significantly, their energy density is several times higher than tradition capacitors. However charge–discharge mechanism involves in two paths i.e., pseudo capacitance and electric double layer capacitor (EDLC) as shown in Fig. 2.5 (Meng et al. 2017). In pseudo capacitor, charges generated due to redox reaction is occurred at the surface of the electrodes and permeate across the double layers. Whereas in EDLC, a charge accumulator is laced in between at the interface of the electrolyte and electrodes. During charging, the electrons moves from cathode to anode and vice versa during discharge (Snook et al. 2011). Commercially, polypropylene was used as separator however, currently cellulose based membrane are used as the state of art separators. Research efforts were made to utilize biopolymer/electroactive polymer composite to enhance the charge density. When poly-anionic lignin is combined with conductive poly(3,4-ethylenedioxythiophene), lignin act as a dopant and surfactant resulting in enhanced specific capacitance however, it is observed that the blending of biopolymer reduces the charge storage capacity due to nonconductive and electric insulation properties (Ajjan et al. 2016; Inganäs and Admassie 2014). Nevertheless, there is rising interest in design and developing conjugated biopolymer and degradable conductive polymers which are promising material for sustainable future (Tropp and Rivnay 2021). Fuel cell applications: Fuel cell is an energy conversion devise which converts chemical energy stored in fuel into electrical energy with ecofriendly byproducts such as electricity, water and heat (Fig. 2.6) (Peighambardoust et al. 2010). Unlike batteries and super capacitor, they don’t need charging where electricity will be produced as long as fuel is supplied. Recently, polymer-based proton or ion exchange membranes, electrolyte and electrodes are widely developed

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Fig. 2.6 Schematic representation of fuel cell (Peighambardoust et al. 2010)

for fuel cell application (Aili et al. 2021; Shaari and Kamarudin 2015). Various sustainable polymers such as chitosan, cellulose, PVA, PBS etc., were used in components of fuel cells. Interestingly, chitosan and alginate were extensively studied in direct methanol fuel cell, polymer electrolyte fuel cell, biofuel cell and alkaline fuel cell due to their abundancy, stability, low-cost and eco friendliness. Although, chitosan possesses low electrical conductivity, lithium salt and ammonium salt solvated chitosan exhibited enhanced ionic conductivity (Ma and Sahai 2013). Interestingly, amorphous nature of chitosan increases the conductivity rather than crystalline phase. Efforts were also made to enhance by blending with PVA, alginate, carrageenan since, they provides more salt complexation sites (Shaari and Kamarudin 2015). Similarly, research efforts were made to incorporate biopolymers or degradable polymers as binder in fuel cells. Interestingly, hydrophilic polymers with excellent water retention properties such as chitosan, alginate, PVA, PLA exhibited superior performance compare to commercial Nafion binder at increased cell temperature (Ma and Sahai 2013). These results motivates research community to develop sustainable polymers based fuel cell devises for sustainable future.

2.5 Sustainable Polymers for Other Environmental Applications 1.

Gas separation: With rapid industrialization, air quality has declined in major cities create necessity for regeneration of air through filtration and other processes. Importantly, purification of gases at the point of emission can greatly contribute to the improved air quality (Sanders et al. 2013). Also, purification of air have immense application such as separation of particulate materials from contaminated environments, for example providing protection to people

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from accidentally or naturally liberated toxic chemicals in the air and high dust loading industrial amenities (Wang et al. 2016). The membrane gas separation industry is more than three decade old and developing at a significant rate. Improvement of higher permeance and higher selectivity membranes is essential to address the existing challenges. In 1831, Kearsley Mitchell has observed that the gas is escaping from hydrogen balloon with time (Rowe et al. 2010). He assumed that the hydrogen gas is passing through pores of the rubber balloon and thus, experimented with mixture of gases of different size. Interestingly, he observed that the various gases have escaped at different time interval. This important observation has motivated the development of polymeric gas separation membrane by 1970s (Baker and Low 2014). Recently, there is increase in attention to develop sustainable polymer-based membranes for gas separation. Currently, cellulose acetate based thin or dense asymmetric films fabricated over porous substrate by phase inversion method has widely used as commercial gas separation membrane in various industries (Nikolaeva et al. 2018). Approximately, these membranes are purifying 50–700 M cubic feet of natural gas per day in various parts of the world. The rate of permeability highly influenced by the nature of polymers. For example, oxygen permeability through PVA is eight times higher than poly (acrylonitrile). Significantly, degradable and low cost polymer such cellulose, PVA are prominently commercialized membrane for air filtration (Sanders et al. 2013) (Fig. 2.7). 2.

CO2 Capture: Separating carbon dioxide from flue gases is essential for environmental prospective and has drawn considerable research attention worldwide. Polymers are excellent candidate for this purpose due totheir tailorable pore structure and tunable physico-chemical properties and achieved up to 90% efficiency (Scholes et al. 2010). The basic principle of CO2 separation using membranes is the size exclusion through porous structure of polymers layers. The polymer thin and selective layer with mechanical support allows CO2 to pass through while separation the other constituents of flue gas, thus achieves CO2 separation and collection (Yuan et al. 2016). However, the efficiency of membrane depending on the concentration of flue gas and the applied pressure. Various single stage and multi stage processes have been demonstrated for the separation of CO2 with efficiency rate achieved up to 95%. Chitosan/PVA

Fig. 2.7 Schematic representation of typical gas separation membrane (Elhenawy et al. 2020)

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hybrid aerogel was reported inexpensive and highly efficient CO2 adsorbent. The CO2 binds to the hydroxide ions and quaternary ammonium groups, reversibly by humidity swing at ambient temperature. The carbon dioxide capture efficiency of 0.18 mmol/g, which is 38% higher than the state-of-the-art commercial membrane was obtained (Song et al. 2018). In another study, Christoph and group have established the amine functionalized nano fibrillated cellulose for the adsorption of CO2 . The aerogel has showed excellent adsorption up to 1.39 mmol CO2 /g for over 20 consecutive cycles (Gebald et al. 2011). Further, PVA/nanocellulose composite membranes also exhibited high permeability (Torstensen et al. 2019). Furthermore, Mandal and group demonstrated the carboxymethyl chitosan based membrane for CO2 separation from mixture. The excellent separation of CO2 is attributed to salting out effect offered by carboxymethyl chitosan matrix proved itself to be a viable candidate for large scale CO2 separation applications (Borgohain and Mandal 2019). Later, the addition of poly(allylamine) with chitosan membrane has enhanced the separation efficiency (Prasad and Mandal 2018). Hence, these studies showed that sustainable polymers are the potential solution for CO2 fixation.

2.6 Concluding remarks In summary, there is increase in research attention to develop sustainable materials because of their usefulness and beneficence for energy and environmental applications. These sustainable polymers are prominent candidates for adsorption, membrane filtration, advanced oxidation processes, gas separation and CO2 capture due to unique properties such as high surface functionalities, film forming ability and easy regeneration of the sustainable polymers based materials. Further, high mechanical strength, excellent chemical and thermal stability favors their utilization in battery fabrication, supercapacitor assembly and fuel cell devises. It is also observed that successful cooperation of high-performance nanomaterials with sustainable polymer can produce excellent multifunctional materials. Thus, green and biodegradable polymer-based materials can exhibit superior performance for energy and environmental application, which suggest a potential substitute to conventional polymer-based material in various sectors for sustainable future. Acknowledgements SKN acknowledges the Department of Science and Technology, Government of India for DST-Nanomission Project (SR/NM/NT-1073/2016), DST-Technology Mission Project (DST/TMD/HFC/2K18/124G)Government of India and Talent Attraction Programmed funded by the Community of Madrid, Spain (2017-T1/AMB5610), and the Government of India for DSTINSPIRE Fellowship, Grant IFA12-CH-84.

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Chapter 3

Polymer Aerogels for Energy Storage and Water Purification Applications Manohara Halanur Mruthunjayappa , Dibyendu Mondal , and S. K. Nataraj

Abstract The increase in energy demand and global water scarcity lead to the extensive research for the development of high performance aerogels. Significantly, aerogel based materials are emerging as a promising candidates for diverse applications such as thermal insulation, filtration, oil–water separation, and energy storage applications. Aerogels have remarkable physical properties such as ultra-low thermal conductivity, extremely low density and high specific surface area. Thus, understanding the chemistry of polymer-based aerogels, so as to tune their physical and chemical properties can deliver high performance materials. Therefore, the present book chapter illustrate the fundamental concepts, comprehensive information and development of polymer-based aerogels and their application in energy storage and water purification. More specifically, material choice for high performance aerogels, their physical and chemical properties, and their application in energy storage and water treatment processes are briefly discussed. Keywords Polymers · Aerogels · Energy storage · Water purification

3.1 Introduction Various crucial problems for instance, rising population, rapid urbanization and industrialization demands massive supply of food, water and energy. This further, lead to a severe shortage of potable water and affordable energy storage devises in the upcoming decades (Bolisetty et al. 2019; Zheng et al. 2018). Eventually, global water M. H. Mruthunjayappa · D. Mondal (B) · S. K. Nataraj (B) Centre for Nano and Material Sciences, Jain University, Bangalore 532112, India e-mail: [email protected] S. K. Nataraj e-mail: [email protected]; [email protected] S. K. Nataraj IMDEA Water Institute, ParqueCientíficoTecnológico de La Universidad de Alcalá, Avenida Punto Com, 2, 28805 Alcalá de HenaresMadrid, Spain © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_3

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scarcity is increasing day by day with the increase in industrial effluent discharge into the water reservoirs and river streams. Approximately two millions tons of waste such as dyes, pharmaceutical drugs, pesticides and heavy metal ions are discharge into the surface water without proper treatment (Manohara et al. 2019). Unfortunately, most of the dyes are non-biodegradable cause severe threat to aquatic organisms. Several metallurgical industries discharge high concentrated heavy metal ions such as Cr (III/VI), Hg(II), Cu(II), Ni(II), Pb(II), Fe(III) and Zn(II) which causes several critical health issues (Bolisetty et al. 2019; Mruthunjayappa et al. 2020). Simultaneously, domestic operations such as toilet, cloth and dish washing, and shower consumes large amount of water and releases various hazardous chemicals such as surfactants into surface water. Unfortunate comprehensive wasteful use of water is drying out rivers, lakes and underground aquifers, there by triggering water scarcity (Peydayesh et al. 2020). Hence water reuse and recycle is becoming important for conservation of water resources. Thus, various techniques such as coagulation, adsorption, chemical oxidation, biological processes and membrane filtration were developed for wastewater treatment (Bolisetty et al. 2019). Among them, adsorption and membrane filtration are widely implemented in industrial and municipal wastewater treatment owing to their high efficiency, comparatively low cost and easy installation (Peydayesh et al. 2020). Therefore, design and development of high performance sustainable materials for adsorption and membrane application is always been one of the important goal of material chemist’s. On the other side, the demand for efficient energy storage devises are extremely high due to rapid increase in energy consumption (Kim et al. 2019). Recently, in an effort to decrease the dependence on fossil fuels, remarkable developments were made towards producing electric motors and vehicles. Thus, according to a survey, the energy requirement for the entire world in 2020 is anticipated to 178 × 109 MWh which will drastically increase upto 193 × 109 MWh in 2030 (Alwin and Sahaya Shajan 2020). In order to promote electrical motors in all sectors, it is necessary to develop high performance energy storage materials with high energy density and excellent cyclic stability (Liu et al. 2014). Also, flexible and portable electronic devises for example, smart watches, television screens, bendable displays have been new generation electronics and attracting huge number of developers and costumers (Lv et al. 2017). Thus, the development of flexible solid state energy storage materials with high energy density and excellent charge–discharge capacity are of main interest. With an unprecedented progression in the demand for clean water and energy storage materials, intensive research efforts were made to develop facile, environmentally friendly, low-cost advanced functional materials that can be commercialized in the near future. Interestingly, various synthetic and natural polymers were widely investigated for water purification and energy storage application (Liu et al. 2014; Gao et al. 2013a). Polymers were extensively used as precursor to produce numerous functional materials in various forms such as thin films, composite beads, membranes, hydrogels and aerogels to name few (Fig. 3.1). Among them, aerogels are emerging as promising materials due to their exceptional physical and chemical properties such as low density and high intrinsic porosity (Salimian et al. 2018).

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Fig. 3.1 Overview of the polymer-based materials in various forms such obtained via physical and chemical methods

Going forward, the present book chapter illustrates the strategies involved in development of polymer-based high performance aerogels for energy storage and water purification applications.

3.2 History and Fundamentals of Polymer-Based Aerogels Aerogels are defined as three dimensional nanostructured materials derived from gels where the liquid component is substituted by air. Aerogels were first reported by Samuel Kistler in 1931. For the first time, he introduced supercritical drying technique by heating gel in a closed system until it exceeds the critical temperature (Tc ) and pressure (Pc ) of the solvent system (Kistler 1931). During this process, formation of liquid–vapour meniscuses was avoided which is responsible for the gel shrinkage. To begin with, Kistler demonstrated aerogel using biopolymers such as gelatin, agar, albumin and cellulose later, demonstrated silica aerogels with exceptional mechanical properties. In the early 1940’s he has patented the process and commercialized inorganic silica aerogels and sold products for few decades under the trade name ‘Santocel’ (Pierre 2011). Nevertheless, the research and development of aerogel have faded into background for almost three decades because of complex multistage production process. In the year 1980, Hunt introduce the facile liquid CO2 assisted supercritical drying of silica gel where alcohol was substituted by gas, which revolutionalised the field of aerogels for various applications due to simple technique (Salimian et al. 2018). Researchers have demonstrated various practical applications for aerogels including thermal insulation, catalyst and water repellent using hydrophobicity. Aerogel possess unique physical and chemical properties such

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Fig. 3.2 General schematic representation towards preparation of synthetic (group A) and natural polymer (group B and C) based aerogels (Zhao et al. 2018a)

as high porosity, ultralow density and high surface area with exceptional mechanical and thermal stability. However, few disadvantages associated with silica aerogels such as increased density, decreased surface area and moderate mechanical strength are restraining the market growth (Pekala 1989). Alternatively, organic polymer-based aerogels were developed for wide range of application due to their chemical stability, flexibility and excellent mechanical strength. Unlike silica aerogel, polymer-based aerogels are environmental friendly and involves cost efficient manufacturing processes (Zhao et al. 2018a). Organic polymers can be broadly divided into non-biodegradable synthetic polymers and biodegradable natural polymers or biopolymers. These organic polymers are first transformed into gels/jellies by suitable crosslinking method later, removal of solvent system without collapsing three dimensional framework by supercritical drying generates aerogel (Fig. 3.2) (Kistler 1931; Zhao et al. 2018a). Generally, gels were prepared by mixing precursor and gel formation by sol–gel methods where, colloidal monomers crosslinks to form three dimensional macromolecules interconnected by strong chemical bonds. Then, aerogels were formed by separation of pore filling solvent without causing shrinkage in the volume of the gel structure. Due to capillary force generated in solid-gas-liquid interface, it is extremely difficult to separate liquid medium as the capillary pressure inversely proportional to the porous system in these three dimensional gel system without collapsing its structure (Zarzycki et al. 1982). Thus, supercritical drying was introduced by heating gel system above its critical temperature and pressure. To make the process feasible, in the earlier days, solvents were first replaced by another non-solvent system with reasonably lowercritical temperature followed by supercritical drying (Kistler 1931). For example, supercritical point of water is too high (374 °C, 22.1 MPa), thus water was first replaced with organic solvents such as ethanol (241 °C, 6.14 MPa) prior to supercritical drying. However, with resurgence development of facile protocol, researchers have widely used liquid CO2 (31 °C, 7.38 MPa) assisted super critical drying and further developed freeze drying methods (Fig. 3.3) (Takeshita et al. 2021). Since, supercritical drying is time consuming and requires large amount of solvents, freeze drying process were majorly followed for preparation of aerogels and established

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Fig. 3.3 Typical phase diagram of a solvent system and general schematic illustration of different routes of drying. (a) supercritical drying, (b) freeze drying, (c) vacuum drying and (d) oven drying (Salimian et al. 2018; Takeshita et al. 2021)

as greener process, more economical and nature friendly process. Freeze drying is a process where sublimation of frozen solid from the wet gel system which causes porous structure under low pressure (Path (b) in Fig. 3.3). However, due to formation of ice crystal during freezing, generally creates macropores structure and causes considerable amount of shrinkage compare to supercritical drying which leads to the lower in surface area and higher density (Zhao et al. 2018a; Nita et al. 2020). Recently, researchers have reported microwave drying to obtain aerogel with high porosity compare to freeze drying and also, faster technique with favorable results. In 1989, Pekala reported first ever organic aerogel by polycondensation of resorcinol with formaldehyde in slightly basicaqueous medium (Pekala 1989). These aerogels had lower thermal conductivity of 0.012 W/m/K and are most comprehensively studied organic aerogels. The aerogel derived from high temperature treatment of these organic aerogel resulted in multifunctional carbon aerogel. Later, the research community has witnessed massive growth in the organic polymer-based aerogel such as polyvinyl alcohol (PVA), polyurethane (PU), polyacrylonitrile (PAN), polyimide, polyethyleneimine, polyvinylidine difluoride (PVDF) etc. and biopolymers like cellulose, agarose, alginate, silk, chitosan, etc. were successfully employed for the preparation of aerogels (Mruthunjayappa et al. 2020; Lv et al. 2017; Zhao et al. 2018a, 2018b; Chaudhary et al. 2015; Tang et al. 2020; Zheng et al. 2014). Compare to silica aerogel, the organic polymer-based aerogel have low thermal conductivity and much stronger compressive modulus of 1–10 MPa nevertheless, possess low decomposition temperature of 95% rejection in a continuous flow setup (Zhang et al. 2013). The concept of hydrophobic/hydrophilic materials with highly porous structure facilitate robust separation of oil–water emulsion lead to the development of various aerogels system for water purification. PVDF is naturally hydrophobic in nature due to low surface energy thus, various research group has developed PVDF based aerogel system. Li et al. has reported GO/PVDF hybrid aerogel for oil–water purification and organic solvent adsorption (Li et al. 2014). Since, GO also exhibits hydrophobicity, the performance of PVDF aerogel was enhanced. Recently, polyimide based MXene incorporated hydrophobic aerogelwas developed for effective oil–water separation (Wang et al. 2019). The compression resistant hybrid aerogel exhibited excellent absorption upto 18–58 times of its own weight for various organic solvents. Recently, PPy and poly(N-isopropylacrylamide) combined melamine based aerogel exhibited excellent heavy oil adsorption irrespective of viscosity of solution (Wu et al. 2018). Further enhanced performance was observed under sunlight due to reduced viscosity caused by the photo thermal effect. Herein, synergistic combination of light-to-heat transfer property of PPy and thermoresponsive property of poly(N-isopropylacrylamide) enhances the absorption capacity of aerogel. Owing to the highly porosity and low density, PVA based GO hybrid aerogel was evaluated for the separation of oil-in-water emulsion (Liu et al. 2018). An asymmetric aerogel membrane was developed by hydrothermally crosslinking of PVA with GO which exhibited ultrafast permeation upto 135.5 × 103 L/m2/h/bar (LMH) with >99% rejection under gravity driven filtration setup. Similarly, organic solvent adsorption of PVA/boron nitride hybrid aerogel was also explored (Zhang et al. 2017). Other side, researchers have also developed synthetic polymer-based aerogel for dye separation. Han et al. reported GO/polyethylenimine based hybrid aerogel for dye adsorption (Sui et al. 2013). The porous GO/PEI aerogel exhibited maximum adsorption capacity of 800 mg/g for amaranth dye which is superior to the reported carbon aerogels attributed to high surface area and amine-rich graphene structure. In an extended study, GO/PEI has exhibited selective separation of anionic dyes attributed to extensive cationic surface chargeand the π-π interaction (Zhao et al. 2018b). Importantly, the surface charge can be tuned by varying the pH of the dispersion medium. Significantly, aerogel showed excellent performance for organic solvent recovery from the mixture of solvent. Chen et al. has developed poly(mphenylenediamine)/PVA/GO hybrid aerogel for purification of dye contaminated water and separation of heavy metal ion (Chen et al. 2019a). The hybrid aerogel showed effective adsorption capacity of 917 mg/g for Ag (I), and efficient separation

Pollutants separated

Graphene/PVDF

Poly(ethyleneimine)—GO sheets

Poly(ethyleneimine)—GO

PVA—CNT aerogel membrane

PAN—SiO2

PPy—poly(N-isopropylacrylamide) modified melamine

Poly(vinylidene fluoride-co-hexafluoropropylene) electrospun fiber

Poly(m-phenylenediamine)/PVA/GO

02

03

04

05

06

07

08

09

Cellulose from waste paper

Cellulose from wood pulp

10

11

800 mg/g for amaranth dye

Adsorption capacity of upto 3500% for organic solvents

Separation efficiency of >95%

Performance (Adsorption capacity/rejection)

Absorption of heavy oil with high viscosity ≈1.60 × 105 mPa s

>99% rejection with flux of 8,410 LMH

Wu et al. (2018)

Si et al. (2015)

>99% rejection with flux of 135,500 Liu et al. (2018) LMH

Zhao et al. (2018c)

Sui et al. (2013)

Li et al. (2014)

Zhang et al. (2013)

Referernces

Flow adsorption of nobel metal ion

Organic solvents from water mixture

Oil and organic solvents

Absorption of 59.3 g/g of pump oil

11–22 times absorption of organic solvents

917.4 mg/g for Ag(I)

Liao et al. (2016)

Jin et al. (2015)

Chen et al. (2019b)

Solar assisted water vapor generation Solar to vapor conversion efficiency Li et al. (2020b) from sea water of 86.5% with evaporation rate 10.9 kg/m2 /d

Solar assisted various kind of oil absorption

Water-in-oil emulsion

Oil–water emulsion

Cationic malachite green and anionic MO—331 mg/g and methyl orange dyes MB—249.6 mg/g at pH 10.5

Adsorption of acidic dyes

Oil–water separation and organic solvent recovery

Oil–water separation

Biopolymers and their composite based aerogels

Polyurethane

Synthetic polymers and their composite based aerogels

Polymer used

01

Sl. no.

Table 3.1 List of various polymers based aerogel membranes used for water purification and their performance

(continued)

3 Polymer Aerogels for Energy Storage and Water Purification Applications 41

PEI crosslinked CNF

CNF/PEI/CNF aerogel beads

Sisal leaves derived CNF/Cu

Titanate/CNF aerogel

Genipin crosslinked chitosan/agarose Oil–water purification

Chitosan/GO

Silane functionalised Graphene/chitosan

Magnetic chitosan/itaconic acid/Fe2 O3 aerogel

Fe/Al/Chitosan/Agarose

Agarose/Gelatin

13

14

15

16

17

18

19

20

21

22

Oil–water purification

Organic molecules, heavy metal ion and F

Oil–water separation

Oil–water separation

Dyes and heavy metal ion separation

Heavy metal ion adsorption

Oil separation from oil–water emulsion

Cu(II) ion adsorption

Dyes and heavy metal ion

Heavy metal ions

Cellulose from cotton

12

Pollutants separated

Polymer used

Sl. no.

Table 3.1 (continued)

Tang et al. (2019b)

Tian et al. (2018b)

Referernces

Mruthunjayappa et al. (2020)

Yin et al. (2020)

Hu et al. (2020)

Yu et al. (2017)

(continued)

>98% rejection with flux rate of 500 Chaudhary et al. (2014) LMH

Adsorption of 102.4 mg/g for As(VI) and 81.5 mg/g for fluoride

43.8 g/g absorption of organic solvents

18–45 g/g oil absorption

293 mg/g for Cr (VI) and 584.6 mg/g for methylene blue

>99% rejection with flux rate of 600 Chaudhary et al. (2015) LMH

2.46, 1.43, 2.51, 1.22, and Xiong et al. (2017) 1.98 mmol/gfor Pb (II), Sr (II), Cu (II), Ba (II), and Cd (II), respectively

164 g/g oil absorption and >97% oil Tang et al. (2020) rejection during filtration

Max. adsorption capacity of 163.4 mg/g

103.5 mg/g for Cu (II) and 265.9 mg/g for MO

48 mg/g for Pb (II); 43 mg/g for Cd (II); 10 mg/g for Cu (II); and 5.3 mg/g for Zn (II)

Performance (Adsorption capacity/rejection)

42 M. H. Mruthunjayappa et al.

Gelatin/TiO2 /PEI

Silk/Ag3 PO4 aerogel

Amyloid fibril aerogel

23

24

25

Organic contaminants

Solar assisted water evaporation

Dye and heavy metal ions

Pollutants separated

PVA-Cellulose

CNF-PEI

Nanocellulose—Nanochitin

Fluorinated polydopamine/chitosan/rGO

PANI-Cellulose

26

27

28

29

30

Dye contaminated wastewater

Oil–water separation

Dyes and heavy metal ions

Cu (II) ion adsorption

Oil, organic solvent and heavy metal ion absorbent/adsorbent

Natural polymer and Biopolymers hybrid based aerogels

Polymer used

Sl. no.

Table 3.1 (continued) Referernces

Maximum adsorption capacity of 600.7 and 1369.6 mg/g for Acid Red G and MB

21 times higher absorption of organic solvents

531 mg/g for MB; 217 mg/g for As(III)

Max. adsorption capacity of 485.4 mg/g

96 times oil absorption; Adsorption capacity of 157.5, 110.6, 151.3 and 114.3 mg/g for Hg (II), Pb (II), Cu (II), and Ag (I), respectively

69.6 54.2, and 50.6, mg/g for Ibuprofen, Bentazone, and Bisphenol A, respectively

Evaporation rate of 13.4 kg/m2 /h

Lyu et al. (2021)

Cao et al. (2017)

Zhang et al. (2019)

Mo et al. (2019)

Zheng et al. (2014)

Peydayesh et al. (2020)

Xue et al. (2019)

61.2 mg/g for Cu(II), then Jiang et al. (2019) 64.3 mg/g, 85.2 mg/g, 86.6 mg/g for CV, MO and CR dyes

Performance (Adsorption capacity/rejection)

3 Polymer Aerogels for Energy Storage and Water Purification Applications 43

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of methyl orange and Congo red dyes from water under continuous flow method. In sum, synthetic polymer-based aerogels possess high mechanical strength, high porous structure and chemical stability however, their applications are limited due to non-biodegradability. The discard of an exhausted synthetic aerogel has always been main concern due to potential environmental pollution. 2.

Natural or biopolymer-based aerogels

Natural or biopolymers are derived from living organism. Polysaccharides and proteins are the most fundamental units of living organism and are key elements to construct sustainable biomaterials for various applications. Polysaccharides are well known for their capability to self-assemble into definite physical forms. There are numerous review articles on design and development of biopolymer-based functional materials for various applications (Zhao et al. 2018a; Takeshita et al. 2021). Interestingly, biopolymers are naturally enriched with hydroxyl, amino and sulfonate functionalities with high surface charge makes them promising candidates for water purification. Among various biopolymers, cellulose, chitosan, alginate and agarose are most widely explored aerogel due to their hydrophilicity, abundance, low cost and biocompatibility and their respective chemical structure are provided in Fig. 3.7. The biopolymer-based aerogel can be synthesized in two path ways: (i) through colloidal formation by aggregation of molecular precursor obtained by disintegrated biological feedstock ex. chitosan, agarose, alginate and (ii) through assembling of nano-sized particle based precursor for ex. silk nanofibres, amyloid fibres and cellulose nanofibres etc. (Zhao et al. 2018a). However, the physical and chemical property of aerogel system is depending on the nature of precursors. Firstly, gels were prepared by varying parameters like pH, temperature or by crosslinking with suitable cross linkers followed by supercritical/freeze drying yields aerogels (Zhang et al. 2019). Cellulose is the most abundant, renewable, biodegradable hydrophobic polymer which is extensively utilized to prepare aerogels (Tang et al. 2019b). From past

Fig. 3.7 Chemical structure of some majorly explored biopolymers (Dehghani et al. 2018)

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decade various porous cellulose based aerogel derived from various precursors such as waste paper, cotton, wood pulp were developed for adsorption of dyes and heavy metal ions and purification of oil–water emulsion (Table 3.1). The hydrophobic modification of cellulose aerogel by silane functionalization resulted in excellent organic solvent adsorption (Jin et al. 2015) whereas, acrylic acid and PEI crosslinked aerogel exhibited considerable heavy metal ion adsorption (Tang et al. 2019b; Tian et al. 2018a). Interestingly, (3-glycidyloxypropyl) trimethoxysilane (GPTMS) grafted PEI crosslinked CNF yielded mechanically robust, shape recoverable aerogel with excellent adsorption capacity of 163 mg/g for Cu(II) ions (Tang et al. 2020). Further, in order increase adsorption capacity of cellulose aerogel, researchers have functionalised with the metal nanocomposites such as molecular organic frameworks (MOF), titanate, MnO2 . Cu2 O, Cu etc. and also with GO (Zhu et al. 2016a). Ultrahigh loading of various MOFs over CNF aerogel was demonstrated by Zhu and coauthors (Zhu et al. 2016b). The obtained aerogels show promising adsorption of heavy metal ions attributed to high surface area of MOF. Surprisingly, titanate functionalised CNF aerogel showed remarkable adsorption for heavy metal ions such as Pb (II), Sr (II), Cu (II), Ba (II), and Cd (II). In another study, Cu functionalised Sisal leaves derived cellulose aerogel quickly separated surfactant stabilized trichloromethane and water emulsion with >97% efficiency under gravity driven filtration (Li et al. 2019). Whereas, GO functionalised CNF aerogel exhibits 80–197 times its weightabsorption of oils attributed to super hydrophobicity (Mi et al. 2018). Thus, functionalization of cellulose aerogel is a promising technique to obtain superior performance for water purification. Chitosan is the second largely abundant biopolymer and are widely investigated as efficient material for water purification attributed to enriched hydroxyl and amine functionality and low-cost (Chaudhary et al. 2015). Recently, chitosan based aerogels started seeking huge attention due to hydrophilic nature and possess remarkable mechanical property. The chitosan is water insoluble, however protonated form of chitosan is soluble in acidic medium which is challenging in case of cellulose (Takeshita et al. 2021). In 2015, our group has reported highly crosslinked chitosan/agarose based aerogel membrane for oil–water separation (Chaudhary et al. 2015). Chitosan and agarose precursor were first dissolved in water and crosslinked using genipin to form hydrogel. The obtained hydrogel was freeze dried to get biodegradable aerogel with macro porosity. The obtained aerogel successfully separate water from oil–water emulsion with >99% efficiency with the flux rate of 900 LMH. The advanced crossflow demonstration of oil–water separation showed its potential in real wastewater treatment. Recently, we have also demonstrated iron and aluminium functionalized chitosan based aerogel for dye, pharmaceutical waste, heavy metal ion and fluoride separation from aqueous medium (Fig. 3.8) (Mruthunjayappa et al. 2020). Importantly, we have demonstrated the application of aerogel membrane for arsenic and fluoride contaminated real groundwater purification for drinking water. The 1 m2 of aerogel membrane can purify 4734 L of fluoride contaminated groundwater. Overall, aerogel membrane was demonstrated for universal water purification with ultrafast permeability attributed to hydrophilicity and unidirectional macro channels. Further, Yu et al. reported GO/chitosan aerogel for separation of

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Fig. 3.8 Schematic representation of Fe-Al functionalised chitosan based aerogel preparation and its application in gravity driven filtration (Mruthunjayappa et al. 2020)

organic dyes and heavy metal ions (Yu et al. 2017). The hybrid aerogel exhibit maximum adsorption capacity upto 293 mg/g for Cr (VI) and 584.6 mg/g for methylene blue dye. The aerogels were recycled upto 6 times. Whereas, chitin/GO hybrid aerogel exhibit comparatively lower adsorption efficiency of 165 mg/g for an organic dye (González et al. 2015). Thus, chitosan deliver superior performance compare to chitin. Other than, cellulose and chitosan various other biopolymers based aerogels such as agarose, gelatin, silk, amyloid fibrils etc. were explored for water purification. In 2014, our group has demonstrated genipin crosslinked agarose/galantine biobased aerogel for oil–water separation (Chaudhary et al. 2014). The aerogel with hydrophilic channel exhibited high water permeance rate of 500 LMH, with separation efficiency of >98% rejection for oil–water emulsion. Other side, recently, silk and amyloid based aerogels emerging as a promising materials for effective water purification. Silver phosphate functionalised silk nanofibril based unidirectional aerogel was demonstrated for solar assisted water purification (Xue et al. 2019). The aerogel exhibit water disinfection property due to antimicrobial nature of silver phosphate and further, the Ag2 PO4 was transformed into Ag2 S using anion exchange. The Ag2 S nanowires provides excellent photo thermal effect which enhance the solar driven water evaporation. Further, novel amyloids fibrils based aerogel was evaluated for the separation of dyes, organic solvent and emerging organic pollutants such as pharmaceutical drugs and pesticides from aqueous medium (Peydayesh et al. 2020). The amyloid aerogel showed remarkable efficiency in adsorption of crystal violet dye, absorption of n-hexane,further, Bisphenol A,Bentazoneand a pharmaceutical drug Ibuprofen from aqueous medium.

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Hybrid aerogels

Since, synthetic polymer exhibits high mechanical strength and thermally stable rather, non-biodegradable and possess limited functionalities. Other side, biodegradable biopolymers are comparably possess poor mechanical strength and thermal stability however, enriched with surface functionalities. Thus, optimistic combination of synthetic and biopolymer-based hybrid aerogel can be a potential materials for water purification. An optimised hybrid aerogel can possess high mechanical strength, thermal and chemical stability, rich surface functionality with porous structure (Liu et al. 2017). So, towards this, various researchers have designed and synthesized various hybrid aerogel by combining PVA, PANI, PEI and other synthetic polymer with chitin/chitosan and cellulose. Interestingly, silane treated PVA-cellulose hybrid aerogel exhibited superior adsorption efficiency for heavy metal ion (Zheng et al. 2014). As expected, PVA-CNF hybrid aerogel exhibited high mechanical strength than petroleum based polymer foam and makes it a potential candidate for industry wastewater treatment (Liu et al. 2017). Surprisingly, PANICNF hybrid aerogel exhibited excellent adsorption capacity of Maximum adsorption capacity of 600.7 and 1369.6 mg/g for Acid Red G and MB dyes, respectively (Lyu et al. 2021). The enhanced adsorption capacity is due to the synergistic combination of positively charged nitrogen from the PANI and acidic groups of cellulose fibrils. The superior performance suggest the potential application of hybrid aerogel in organic wastewater treatment.

3.5 Challenges and Future Scope Despite, recent boom in the research activity, very few polymer-based aerogels have yet made the transition to industrial production. Biopolymers with unique properties have attracted large scientific attention, but the uncontrolled contraction of the aerogel remains a challenge (Nita et al. 2020). To overcome this, researchers have prepared hybrid aerogels by the addition of synthetic polymers such as linear PVA chains to form a strong architecture for the gel structure. Another great challenge is the preparation of aerogel with controlled pore structure, and incorporation of multiscale techniques for aerogel modelling (Zhao et al. 2018a). It is challenging to tune atomistic structure and have sufficiently large system sizes and simulation times to model realistic material properties. On the other side, biopolymer-based aerogels are susceptible for organic and biofouling due to high surface functionality. This largely affects their application for real-time wastewater treatment. However, one can design antifouling aerogel system by tuning the physical and chemical properties by functionalization of polymers, introduction of anti-fouling agents and enabling self-cleaning ability.

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3.6 Concluding Remarks In summary, aerogels and more specifically polymer-based aerogels are diverse class of materials with superior mechanical strength, high porosity, high specific sur-face area and functionalities. High performance aerogel with remarkable physical and chemical property can be prepared by choosing suitable polymer for various applications. Importantly, polymer-based aerogels are promising candidate compare to silica aerogel and carbonaceous aerogels due to easy preparation, low temperature operation, less time consuming and ecofriendly. However, compare synthetic polymers based aerogel, bio-based aerogels were extensively studied for water purification and energy storage application. Although biopolymers are abundant, degradable and low-cost but, pilot scale preparation and commercialization of bio-based aerogels are still challenging due to limited mechanical strength, and facile drying process. This can be addressed by preparing synthetic polymer and biopolymer hybrid aerogel with suitable combination. Overall, the polymer-based aerogel are potential high performance materials for real time application in energy storage devices and water purification application in near future. Acknowledgements SKN thank DST-Technology Mission Project (DST/TMD/HFC/2K18/ 124G) Government of India for financial support. S.K.N. also thanks DST-NANOMISSION PROJECT (SR/NM/NT-1073/2016), Department of Science and Technology, Government of India and Talent Attraction Programme funded by the Community of Madrid Spain (2017-T1/AMB5610) for financial support.

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Chapter 4

Polymer Nanocomposites and Metal Halide Perovskites for Luminescent Solar Concentrator Applications—Host Materials Perspective G. Sahaya Dennish Babu and B. S. Madhukar Abstract One of the greatest persuasive classes of photonic devices depending on Stokes shift engineered emitters is the luminescent solar concentrators (LSCs). It has been recently proposed as an effective complement to conventional photovoltaic modules for the understanding of building-integrated photovoltaic (BIPV) devices. Luminescent solar concentrators (LSCs) are capable to proficiently gather solar energy through large-area photovoltaic windows, where fluorophores are precisely entrenched. Amongst various types of fluorophores, all-inorganic perovskite nanocrystals (NCs) are considered as an emerging class of absorbers/emitters in LSCs. This is due to their size, composition, dimensionality, tunable optical properties and high photoluminescence quantum yield (PLQY). However, due to the large overlap between absorption and emission domains, it is still challenging to fabricate high-efficiency LSCs. In this chapter, a new kind of material (metal halide perovskite NC) used to fabricate semi-transparent and large-area LSCs will be discussed in detail. Also this chapter will provide information about the potential of doped perovskite NCs for LSCs, as well as for other photonic technologies, that rely on low-attenuation, and long-range optical wave guiding. Keywords Host luminescent materials · Metal halide perovskites fluorophores · PLQY · Absorption and emission spectra

G. S. D. Babu (B) Department of Physics, Chettinad College of Engineering and Technology, Gandhigramam 639 114, Tamil Nadu, India B. S. Madhukar (B) Department of Chemistry, Sri Jayachamarajendra College of Engineering JSS Science and Technology University, Mysuru 570 006, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_4

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4.1 Introduction Luminescent solar concentrators (LSCs) are called as a new class of solar energy harvesting devices, which operate slightly different from photovoltaic solar cells (Batchelder et al. 1979). LSCs absorb sun light and re-emit them over a narrow band at shorter wavelengths. The first person to construct a solar collecting device was Lerner, who used a solution of laser dye between two glass sheets. Later on Weber and Lambe discussed two possible paths toward construction of a practically efficient collector of planar geometry: neodynium-doped glass, and organic dyes from dye lasers (Hermann 1982; Levitt and Weber 1977). Levitt and Weber constructed devices consisting of Owens-Illinois ED2 neodynium- doped laser glass and Rhodamine-6G doped poly- methylmethacrylate (PMMA). Then Swartz et al. described a device consisting of two laser dyes (Rhodamine-rG and Coumarin) dissolved in PMMA (a mixed dye system) (Levitt and Weber 1977; Zhou et al. 2016). Rapp and Boling were the first to report on a luminescent collector consisting of a thin luminescent film deposited on an undoped substrate, which could be used in broad range of luminescent collectors (Zhou et al. 2016; Bernardoni et al. 2021). LSC research and development is currently being conducted in at least nine different laboratories in the United States, and in laboratories in Germany, France, Switzerland, Israel and Japan. To be sure, the probable rewards are great. Luminescent solar concentrators are a major stride to crafting a bearable and renewable network of photovoltaic power plants implanted in glass-walled parts of urban structures. This could subsidise to cumulative the use of solar energy deprived of superfluous meddling with the landscape. The development of Building Integrated Photovoltaics (BIPV) has the potential to revolutionize urban architecture by making solar PV a structural element within the building envelope and thus transforming the outer shell into an energy production plant (Bernardoni et al. 2021; Jin et al. 2016; Navarro-Pardo et al. 2017; Selopal et al. 2019). BIPV as a rapidly developing sector has demonstrated a variety of different approaches and solutions, which mainly depend on crystalline silicon and thin film organic PV technology. LSCs offer several advantages over conventional PV technology: • LSCs greatly reduce the amount of required PV material due to the concentration of light at the edges. • LSCs can be made fully transparent and colourless by controlling the absorption and emission spectra of the luminescent material. • LSCs can collect both direct and diffuse irradiance, thereby eliminating the need for expensive solar tracking equipment. • The narrow-band width emission of the luminescent material can be matched with the bandgap of the attached solar cells, which significantly increases their energy conversion efficiency. LSC still hindered in significant market potential application due to limited photo stability. Also, LSC having other light loss processes such as non-radiative photon relaxation, reabsorption losses (Selopal et al. 2019; Tong et al. 2018), and restricted

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trapping efficiencies for glass. Among these factors, the most crucial is the reabsorption loss that occurs due to the larger overlap between the absorption and emission spectra of fluorophores (Debije and Verbunt 2012). Strong reabsorption restricts the mean path length of trapped photons and drives losses through non-radiative decay and out coupling. The reabsorption losses are mostly associated with the first generation LSCs employing commercial laser dyes such as coumarins, rhodamines, and perylenes (Jin et al. 2016; Navarro-Pardo et al. 2017; Selopal et al. 2019; Selopal et al. 2019; Tong et al. 2018; Mazzaro and Vomiero 2018; Zhou et al. 2018). Besides re-absorption, such dyes also display the concentration quenching effect. That is the formation of non-emissive aggregates at higher concentrations. Reduced concentrations of these dyes can be utilized to mitigate these issues but at the cost of decreased light absorption. Second generation LSCs are based on inorganic phosphors and semiconducting quantum dots (QDs) (Verbunt et al. 2009). In these cases, reabsorption loss can be reduced by controlling size and composition of phosphors and QDs. However, they normally exhibit decreased photoluminescence quantum yields (PLQY) compared to first-generation fluorophores, thus the overall performance of LSC is suppressed. So far, the most common host material used for LSC is poly(methyl methacrylate) (PMMA) (Navarro-Pardo et al. 2017; Debije and Verbunt 2012; Zhou et al. 2018). This is because of PMMA’s very good material properties, which include excellent transparency to visible and NIR photons; a suitable refractive index of ~1.5, and the high solubility of organic fluorescent dyes in this host. PMMA also exhibits relatively poor mechanical resistance, which results in brittle samples. Luminescent solar concentrators (LSCs) are the most promising technology for semi-transparent, electrodeless PV glazing systems. This can be assimilated ‘invisibly’ into the built environment deprived of disadvantageous effects to the building. Infrared radiation is not focused on the solar cells with this type of concentrator, and the LSC is more efficient at collecting diffuse sun-light than conventional flat-plate panels (Verbunt et al. 2009). The highest conversion efficiency achieved so far for a large-area LSC (40 cm × 40 cm × 0.3 cm) was 4.0%. This LSC contains a two-stack system of a shorter wavelength emitting plate coupled to gallium arsenide (GaAs) solar cells and a longer wavelength emitting plate coupled to silicon (Si) solar cells. Multi-layered mixed-dye thin-film LSCs of smaller dimensions (14 cm × 14 cm × 0.3 cm) achieved 3.2% using Si solar cells and 4.5% using GaAs devices (Coropceanu and Bawendi 2014; Delgado-Sanchez 2019). It was estimated that the maximum achievable conversion efficiency of LSCs that collected sunlight in the range 300– 900 nm was 8–12% (Delgado-Sanchez 2019). These limits were not reached due to problems that will be outlined in the following section. In recent years, there has been a renewed interest in LSCs due to the availability of new luminescent materials, such as semiconductor quantum dots (QDs), rare earth (RE) materials, and semiconducting polymers. Second, materials such as photonic layers and liquid crystals have also been utilized to reduce losses within the devices. Developments in ray-trace and thermodynamic modelling software have also encouraged further research.

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4.2 Architecture and Working Mechanism of LSC In general, LSCs offer a unique opportunity to utilize solar energy devices in cities through their architectural integration. Also, LSCs are having some functional limitations of opaque and electrode-based semi- transparent PV modules which hinder their public utilization (Zhou et al. 2016; Selopal et al. 2019; Mazzaro and Vomiero 2018). LSC consists of a transparent plate with a high refractive index, doped with centers as shown in Fig. 4.1. When the incident light on the surface of LSC is absorbed by the luminescent centers and isotropically reemitted over all the angles with a fraction of light (75% for PMMA). It is internally reflected within the plate and guided towards the edges. A small photovoltaic (PV) cells can be placed to convert the concentrated light into electricity. Diffuse reflecting paints can be placed on the non used edges in order to improve light collection and geometrical gain which is defined as the fraction between surface and edge areas of LSC. Since the collection of light is enhanced by total internal reflection, diffused sunlight has a higher probability of being collected and concentrated on PV cell. As a consequence, LSCs do not require light tracking systems, which represent an important and expensive component of conventional concentrating systems (Verbunt et al. 2009; Delgado-Sanchez 2019; Haines et al. 2012; Giebink et al. 2011). Thin film LSC devices consist of a 0.15–1 mm thick layer of luminescent material deposited in a thicker transparent substrate (≈30 mm), ideally of the same refractive index. Heavily doped luminescent species can be doped in a transparent thin film and placed on a highly transparent substrate having the same refractive index for optical matching. This configuration offers the possibility of reducing reabsorption effects by confining all the absorption and fluorescence to the thin film, while trapping and reflection events occur primarily in the clear matrix. TLSCs have several other

Fig. 4.1 The operation principle of luminescent solar concentrator (LSC)

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advantages, as they allow the stacking of the plates containing different types of luminescent species to utilize full solar spectrum (Giebink et al. 2011; Mateen et al. 2019; Krumer et al. 2017; Meinardi et al. 2017a; MacQueen et al. 2016). In addition, they reduce the fabrication cost as thin doped material is sufficient for allowing for more flexible employments of thin films with appropriate optical properties on any host substrate.

4.3 Luminescent Host Materials Used in LSC Luminescent materials are the prime one which is important for the performance of LSCs. These luminescent materials are working with the principle of photoluminescence. Luminescent materials captivate light and then re-emit this light with a different wavelength (MacQueen et al. 2016). Typically, some energy is lost in the process and the emitted photon has a longer wavelength (i.e., lower energy) than the adsorbed photon. For the design of a transparent and colourless LSC with maximum energy output, the luminescent material should fulfill several requirements. Ideally, the luminescent material needs to have: • A broad absorption band, allowing maximum solar energy conversion while avoiding a colored tint; • High absorption efficiency; • A large Stokes shift, eliminating self-absorption losses caused by an overlap between the emission and absorption spectra; • A high quantum yield, defined as the ratio of the number of photons emitted to the number of photons absorbed by the luminescent center; • Emission at wavelength below the bandgap energy of the PV cell (e.g., 700 nm); • High photo stability to ensure long-term operation. Over the last few decades, various types of luminescent materials have been explored and optimized with respect to their performance in LSCs (Delgado-Sanchez 2019; Mateen et al. 2019; El-Bashir et al. 2013). They can be divided into three categories: organic dyes, quantum dots and rare-earth elements. 1.

Organic Dyes

Organic dyes are organic molecules that absorb light due to their specific planar molecular structure. From the earliest stages of LSC research in the 1970s, organic dyes have been studied due to their high quantum yield, high absorption efficiency and miscibility with organic matrices (Hermann 1982; Delgado-Sanchez 2019; Krumer et al. 2017). In fact, the quantum yield of some contemporary organic dyes has even been shown to reach up to unity. The disadvantages of organic dyes include their small Stokes shifts, narrow absorption spectra and their low photo stability. The small Stokes shift of organic dyes causes considerable self-absorption losses, thereby

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limiting their performance in large-area LSCs. Moreover, organic dyes are prone to photo-degradation, which reduces their performance over time (Taleb 2002). The important characteristics of organic dyes are that they: • Can provide extremely high luminescence quantum efficiency (LQE) (near unity), • Available in a wide range of colours and, • New molecular species are now available with better re-absorption properties that may also provide the necessary UV stability. 2.

Quantum dots

Quantum dots (QDs) are nanocrystals typically made from semiconducting materials. Because their size is in the order of the deBroglie wavelength of the electron, electrons are confined in the semiconductor in a similar way to orbital electrons in atoms. Due to their crystalline structure, QDs are more stable than organic dyes (Mansour et al. 2002; Ying et al. 2019; Gong et al. 2018). In general, the optical properties such as optical band gap of the quantum dot material can be engineered by changing their composition and as well as their size. By combining materials with different band gaps in so called core–shell structures, QDs can be designed to have a larger Stokes shift than organic dyes. However, large-scale QD-based LSCs often suffer from selfabsorption losses due to the low quantum yield of QDs, which is typically, is in the order of 0.1–0.6 (Haines et al. 2012; MacQueen et al. 2016). The low quantum yield results in the fact that every time an emitted photon is absorbed by another QD, there is a significant chance, that no photon is re-emitted. Another disadvantage is that QDs absorb more light in the lower end of the spectrum, thereby typically leading to LSCs with a reddish tint. Moreover, there has been increased concern about the toxicity of some QDs, which has limited their application on a large scale. Still, at the time of writing, a QD-based LSC holds the record optical efficiency of 8.1% for a 10 cm2 device, which translates into an electrical power conversion efficiency of 2.2% (Krumer et al. 2017) QDs have following advantages over dyes: • Their absorption spectra are far broader, extending into the UV, • Their absorption properties may be tuned simply by the choice of nanocrystals size, and • They are inherently more stable than organic dyes. • The red-shift between absorption and luminescence is quantitatively related to the spread of QD sizes, which may be determined during the growth process, providing an additional strategy for minimising losses due to re-absorption. 3.

Rare-earth elements

Rare earth (RE) metals are a group of chemical elements that show characteristic luminescence depending on the filling of their 4f sub-orbital. In contrast to what their name suggests most of them are relatively abundant on Earth (Mansour et al. 2002; Ying et al. 2019). The luminescence of RE ions is caused by the excitation and relaxation of their orbital electrons by means of absorbing and emitting photons.

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RE-doped materials such as phosphors typically have high photo stability which is suitable for LSC applications (Gong et al. 2018). It can be tuned to have a large Stokes shift and broad absorption band. RE ions are found either as a complex surrounded by organic ligands or doped into inorganic host matrices, which play an active role in the luminescence process by enabling energy transfer to the RE ions (Bergren et al. 2018; Zhao et al. 2016; Anand et al. 2020). By controlling the valency of the RE ion and the composition of the host material, RE-doped materials can be designed to have a broad absorption band and an arrow emission peak. Common host materials include oxides, borates, phosphates, nitrides, oxynitrides, silicates, sulfides, selenides and halides. 4.

Al2 O3 Nanoparticles

Alumina (Al2 O3 ) nanoparticles are used in industry as a filler to enhance the toughness, fire resistance, antifriction properties and insulating properties. They are commercially available in the form of a powder or a colloid. The refractive index of Al2 O3 is significantly higher than that of common polymers, leading to increased scattering and higher interparticle attraction. The density of surface hydroxyl sites is relatively high, which increases the amount of anchor points for the stabilizer, but also the chance of agglomeration due to interparticle hydrogen bonding (Zhou et al. 2016; Tong et al. 2018; Zhou et al. 2018). Interestingly, Zhou et al. increased the emission intensity of YAG:Ce phosphor powder by coating it with Al2 O3 using atomic layer deposition (ALD) in a fluidized bed reactor. Al2 O3 nanoparticles will be used as a starting point, because they are relatively cheap and the mechanism of stabilization is similar to luminescent nanoparticles with hydroxylated particles. 5.

Amphiphilic copolymers

Chemical stabilization methods will be avoided due to their chemical specificity and potential perturbation of electronic states summarized, amphiphilic copolymers have proven to be effective stabilizers for a wide range of nanoparticles and polymer matrices. Amphiphilic polymer co-networks (APCNs) are nanostructured materials that consist of two covalently cross-linked polymers, one hydrophilic and the other hydrophobic, with nanoscale-separated domains. They are known to have healthy mechanical properties that can be tailored by tuning the polymer composition and chemical functionality (Ying et al. 2019; Gong et al. 2018; Bergren et al. 2018; Zhao et al. 2016). The selection of suitable amphiphilic copolymers for the experiments is unfortunately limited by their commercial availability. Although statistical copolymers, which are preferred over block copolymers for nanoparticle stabilization are typically easier to synthesize, it turns out that they are very hard to come by. Instead, the commercially available block copolymer PE-b-PEG with varying molecular weight and composition was selected for LSC applications (Anand et al. 2020). 6.

PE-b-PEG

Polyethylene-block-polyethylene glycol (PE-b-PEG) is an amphiphilic di-block copolymer of ethylene and ethyleneoxide, which is used in industry as emulsifier,

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lubricant, mold release agent and thickening agent. The EO units act as non ionic anchor groups, forming hydrogen bonds with hydroxylated nanoparticles surfaces (Slooff et al. 2007; Debije et al. 2008) In order to study the influence of the molecular weight and the composition of the stabilizer on the dispersion stability, different types of PE b PEG will be used. Depending on the composition, PE-b-PEG is soluble in polar as well as non-polar solvents such as toluene. Unfortunately, the crystalline nature of the PE-b-PEG copolymers turned out to them unsuitable for the fabrication of transparent nanocomposites. 7.

Matrix polymers

Apart from compatibility with the amphiphilic copolymer, the polymer matrix has to fulfill the requirements (Debije et al. 2009). A comparison of various common polymers with respect to these requirements is given in the following table. As the wave guiding substrate material is not yet known, the thermal expansion and refractive index are left out of the selection for now. In fact, they are quite similar for most organic polymers are CYTOP—Cyclized Transparent Optical Polymer, COC— Cyclic olefin copolymer, PMMA—Poly (methyl methacrylate), PET—polyethylene terephthalate, PETG—Polyethylene terephthalate glycol, PC—polycarbonate, PS— Polystyrene, PVC—Polyvinyl chloride, PP—polypropylene, LDPE—low density polyethylene, HDPE-high density polyethylene. More polymers have been considered than shown in Table 4.1 but have been omitted for various reasons that rendered them impractical (e.g., biodegradability and commercial availability). Concluding from the comparative table, CYTOP, cyclic olefin copolymer (COC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET) and glycol-modified polyethylene terephthalate (PETG) appear to be the most suitable polymers. Several notes should be added to this outcome. First, the extremely high transparency of CYTOP might outweigh the disadvantage of its fairly high oxygen transmission rate, which can be compensated for by adding an extra barrier layer (Wilson et al. 2010; Rowan et al. 2008; Rau et al. 2005; Gallagher et al. 2004). Secondly, PET in its natural state is an opaque semi-crystalline polymer. Transparent PET can only be obtained by rapidly cooling the molten polymer below its glass transition temperature or alternatively by stretch blow moulding, which is used for the production of PET bottles. Moreover, PET is very difficult to dissolve in common solvents. PETG is produced by replacing glycol with a bigger building block that inhibits crystallization, resulting in a transparent amorphous material that is also more easily dissolved. In the end, the decisive factor for the selection of a polymer matrix is compatibility with the selected stabilizer, yielding COC as the best option for PE-b-PEG. 8.

COC Polymers

COC are a group of polymers synthesized by copolymerization of ethylene and cyclic monomers such as norbornene, which is a combination known under the brand name TOPAS. COC is used for the production of optical components due to its excellent optical properties. It is soluble in common non-polar solvents such as toluene, allowing preparation of thin films by spin-coating. As a result of the polyethylene

7.4

1.34

Refractive index

OTR

LTEC (K-1 )

RTI (°c)

921

108

Haze (%)

0.4

–

Transmittance (%)

WVTR (g-mm)

95

Crystalline/amorphous

(cm3 -mil)

CYTOP

Amor

Polymers

1.53

6

0.3

100

130

0.4

91

Amor

COC

1.49

5

3.6

12

70

1.0

93

Amor

PMMA

1.57

6

1.2

13

80

0.6

90

Amor

PET

Table 4.1 Common polymers and their properties as luminescent film PETG

1.57

8

1.2

25

63

0.3

91

Amor

PC

1.58

7

74.0

300

100

1.0

89

Amor

PS

1.59

6

79.0

300

75

1.0

90

Amor

PVC

1.53

5

3.0

11

50

3.0

85

Amor

PP

1.49

6

0.3

240

100

11.0

90

Semi

LDPE

1.53

10

1.0

500

80

1.3

80

Semi

HDPE

1.53

6

0.3

185

100

6.0

80

Semi

4 Polymer Nanocomposites and Metal Halide Perovskites for Luminescent … 61

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G. S. D. Babu and B. S. Madhukar

chains in its molecular structure, COC forms homogeneous polymer blends with polyethylene (Richards and McIntosh 2007; Chatten et al. 2003). Therefore, it is expected that the PE-b-PEG stabilizer is to some extent compatible with a COC matrix, depending on its molecular weight and composition. The experiments that have been conductedwith COC are described. Ou and Hsu prepared COC/fumed silica nanocomposites containing 1–15 wt.% SiO2 nanoparticles by solution blending using tetrahydrofuran (THF) solvent. They found that the SiO2 particles could be dispersed in the COC matrix without large agglomerates, showing a transmittance of higher than 85% for a SiO2 content upto 10 wt.%. Dorigato et al. studied the effect of the particle dimensions on the thermal, mechanical and optical properties of 2 wt.% filled COC/fumed silica nanocomposites prepared by melt mixing. The authors showed that the nanocomposites containing the smallest primary particle size (7.8 nm) provided the highest transmittance (Shukla et al. 2017). However, the transmittance of these nanocomposites was still drastically lower, at around 50% of pure COC. Rou et al. succeeded in preparing transparent nanocomposites with a transmittance of upto 82% with the silica content of 3 wt.%. The difference might be attributed to pre-drying of the particles, as well as to different mixing equipment and allied parameters. 9.

CYTOP

If amphiphilic copolymers with fluorophilic functional groups could have been acquired during the project, the plan was to extend the scope of the research to fluoropolymers. These polymers would especially be suitable for the near-infrared emitting Ba3 (PO4 )2 :Mn5+ nanoparticles. This is because C-F bond vibrations are excited at wavelengths, further in the infrared than C-H bonds, rendering fluoropolymers very efficient waveguides for near-infrared light. Dispersing nanoparticles in a perfluoropolymer requires a stabilizer with fluorophilic functional groups (Verbunt et al. 2009; Zhao et al. 2016; Rowan et al. 2008). Unfortunately, fluorinated amphiphilic copolymers are very specific. Due to the substitution of carbon-hydrogen with higher energy carbon–fluorine bonds, fluoropolymers have some unique properties. They typically have high chemical, thermal and degradation stability, as well as a low refractive index, surface tension and dielectric constant. The term fluoropolymer is used for partially fluorinated polymers, whereas perfluoropolymers do not have any carbon-hydrogen bonds in their molecular structure. CYTOP is the brand name of an amorphous perfluoropolymer made by cyclopolymerization of perfluoro-3butenyl-vinyl ether (PBVE) (Debije et al. 2009; Rowan et al. 2008). Due to its amorphous structure, CYTOP exhibits exceptional transparency and good solubility in specific fluorinated solvents. Stelzig et al. synthesized in-situ functionalized silver and copper nanoparticles using laser ablation in tetrahydrofuran (THF) with statistical amphiphilic terpolymers bearing fluorinated side chains. The stabilized particles could be successfully redispersed into different THF-soluble fluoropolymers without forming agglomerates.

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4.4 Hybrid Perovskites Recently, halide perovskite nanocrystals (NCs) are considered as a promising solution processed emitters for low-cost optoelectronics and photonic devices (Ananthakumar and Babu 2018). The general crystal structure of perovskite is ABX3 . Organic materials such as methyl ammonium (CH3 NH3 ), formamidinium organic cations and metal ions such as Cesium (Cs), Rubidium (Rb) also can be used in A site (VanOrman and Nienhaus 2021; Cao et al. 2021; Mirershadi and Sattari 2021) Genrally, lead (Pb) is used in the place of B site. Due to the toxicity of Pb, tin (Sn), Germanium (Ge) is also suggested to be nominal candidate for the B Site. X-site must be a halide atom such as Chlorine (Cl), Bromine (Br) and Iodine (I). The crystal structure of perovskite system is given in the Fig. 4.2. These novel metal halide perovskite nanomaterials have recently emerged as potential candidates in a variety of optoelectronic and photonic technologies, including photovoltaic cells, photodetectors to light-emitting diodes, and lasers (Cao et al. 2021; Mirershadi and Sattari 2021; Nikolaidou et al. 2016; Li et al. 2017; Meinardi et al. 2017a, b, c; Sharma et al. 2017; Tan et al. 2017). It is important to mention here that these perovskite nanomaterials are kind of similar to traditional semiconductor nanocrystals. Especially, the optical properties of the nanocrystals can be tuneable through control of the particle size, shape and composition of the materials. These features are enabling these materials to exhibit narrow emission spectra which cover the whole visible spectrum. Metal-halide hybrid perovskite nanomaterials are widely used in the field of photovoltaic research for the past eleven years. It is due to their burgeoning improvement in power conversion efficiency (PCE) as compare than traditional second generation thin film solar cells (Mirershadi and Sattari 2021; Nikolaidou et al. 2016; Li et al. 2017; Meinardi et al. 2017a). The highest reported PCE currently stands at 24.1% compared to 22.9% for thin film chalcogenide solar cells and 26.7% for Si crystalline solar cells. Unfortunately, the device stability is the major concern of these perovskite systems which blocks the commercial implementation of solar photovoltaic systems. However, perovskite systems have better optical characteristics in juxtaposition with high carrier mobility. Hence, perovskites are considered as highly suitable for incorporation in LSCs as Fig. 4.2 Crystal structure of ABX3 perovskite system. Reproduced with permission from Ref. Adjokatse et al. (2017). Copyright 2017, Elsevier Ltd.

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well as traditional solar cells (Meinardi et al. 2017d; Sharma et al. 2017; Tan et al 2017; Zhao et al. 2017; Bergren et al. 2018). Not only efficiency blocks the practical implementation of LSCs, their scalability is the major problem. This scalability happens mainly arises from ‘self-absorption’ (SA) losses. In most of the nano host materials, the spectral overlap of the absorption and emission bands results in the emitted light being re-absorbed by the material, and barring 100% quantum yield (QY) (Meinardi et al. 2017a, b; Liu et al. 2018). It is identified that there are two opportunities are available to reducing SA. One is band gap engineering which helps to induce a large spectral separation between absorption and emission bands, which is normally called as Stokes shift. The other one is influencing the materials with higher QY. There has been some success with designing quantum dots with almost no SA losses, and although they have allowed the formation of relatively large LSCs, they have not necessarily translated to high efficiency devices. Stokes shift engineering of nanomaterials has boosted the LSC field to enable the understanding of efficient large-area devices. Various classes of semiconductor materials are used for this shift engineering such as II–VI or V–VI NCs, NCs doped with metal impurities or of ternary I–III–VI composition and Silicon (Si) nanomaterials (Nikolaidou et al. 2016; Li et al. 2017; Meinardi et al. 2017a, b; Bergren et al. 2018; Liu et al. 2018). Compare than the other traditional semiconductor nanomaterials, perovskite nanosystems has a feature of very small Stokes shift between their absorption and emission spectra. It will result in LSC in the part of strong reabsorption losses for propagation distances into few centimetre levels. An ideal emitter should contains and display high solar absorption, high photoluminescence quantum yield (PLQY), high stability, and low reabsorption. On the other hand, there are no ideal emitters are available which meets all the above requirements for LSCs (Gong et al. 2018). Therefore, still many ways are open up for the real life and practical implementation of nanomaterials or quantum dots based LSC devices. It will also include that the limited PLQY of the quantum dots which are embedded in the polymer matrix. There are three types of fluorophores have been exploited and tested so far in the LSC field, as emitting centers: (i) traditional fluorescent organic dyes; (ii) quantum dots (QDs) and (iii) lanthanide complex systems. However, organic dyes and quantum dots, nearby high fluorescence quantum yield (FQY), also it has high tunable and wide absorption range (Nikolaidou et al. 2016; Meinardi et al. 2017a). Nevertheless, photobleaching and overlapping amongst absorption and emission bands of organic dyes and quantum dots is a great predicament. Possessing high refractive index, broad absorption spectrum, and superior quantum yields, hybrid perovskite thin films are theoretically identified as ideal candidates for LSCs (Liu et al. 2018; Shu et al. 2018; Erwin et al. 2005; Liu et al. 2021). In practice, however, the possibility of high selfabsorption in a continuous film, coupled with the inherent instability of perovskite materials, have hindered their use in this circumstance.

4 Polymer Nanocomposites and Metal Halide Perovskites for Luminescent …

1.

65

Metal halide perovskites for LSC

Liu et al., fabricated a LSC with a stable zero-dimensional perovskite Cs4 PbBr6 nanocrystals material which was used as embedding phosphor in it. They have acknowledged that it will provide an extremely large Stokes shift up to 1.28 eV (Liu et al. 2021). They have found that the ensuing LSC featured both an edge coupling efficiency of 81% and power conversion efficiency (PCE) of 1.1%. To check its integration ability to electric devices, four pieces of LSC were tandemly stacked with two commercial silicon panels, whereby the output power was charged on a motor-driven fan. Such compact device was able to drive the fan through a xenon lamp radiation despite of its relatively low PCE (0.2%). To evaluate the performance of an individual LSC slide, Liu et al., have designed a test bed as shown in Fig. 4.3a. From the figure, it is shown that a standard crystallinesilicon (c-Si) solar panel was masked by black tape to form a coupling outlet for LSC edge (Liu et al. 2021). To recycle the transmitted light, they have used a blank A4 paper as a reflector. The reflector could basically improve the output power of LSC by a 92% augmentation. Under such a configuration, the solar panel power was recorded with and without LSC coupling (Fig. 4.3b), respectively. In this work, a glass slide of 5 × 5 × 0.4

Fig. 4.3 Performance characterization of an individual LSC. a Schematic of the test bed, where a black tape was used to block any scattered light from entrance into silicon panel. b The J-V curves of the c-Si solar cell with (red) and without (black) coupling to the edge of LSC. The efficiency of standard c-Si solar cell is 15.2%. c Output-power test of four sides of LSC with illuminated area of 4 × 5 cm2 , showing an essentially identical power gain. Inset is the photograph of LSC under a squire-shaped solar-simulator illumination. The output power plot against distance d and illuminated areas e Inset schematic shows how the distance and area was defined by placing a mask. f Power-output stability test under continuous irradiation of 405 nm laser (44 mW) for 1 h. Inset schematic shows the test bed. Reproduced with permission from Ref. Liu et al. (2021). Copyright 2021, Elsevier Ltd.

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Fig. 4.4 Performance characterization of LSC prototype device. a Schematic of LSC prototype device consisting two silicon panels and four pieces of LSCs. b The I-V curve and P–V curve of devices with varied LSC slides, including 1 (black), 2 (blue), 3 (green), and 4 (red) pieces. c The output power increases with the number of LSC slides. d The open voltage and short current were plotted against absorbed power from a xenon lamp, respectively. e The output power and power conversion efficiency of the device were plotted against varied input power. f The photograph of LSC device coupled with a motor fan. Reproduced with permission from Ref. Liu et al. (2021). Copyright 2021, Elsevier Ltd.

cm3 was used as the substrate. With an ILSC /ISC value of 3.3%, the optical conversion efficiency of an individual LSC was calculated to be 1.1%. This efficiency was extraordinary when related with 1.4% that attained from a classy LSC of several quantum wells. They have also designed a LSC prototype device with a sandwiched structure as shown in Fig. 4.4a. It includes a two silicon panels and four LSC slides in between. They have used a xenon lamp was used to generate a straight beam with a squared cross-section of 4 × 4 cm2 . They have found that when the number of LSC slides increased from 1 to 4 pieces, the output current is parallely increased from 12.5 to 22.0 mA. The maximum output power increased from 17 to 32 mW (Fig. 4.4c). The device output was characterized beside absorbed power as shown in Fig. 4.4d. It is important to mention here that the current increased almost linearly to power absorbed while the voltage remains identical at 2 V, which was similar to LSC-number dependence (Adjokatse et al. 2017; Guria et al. 2017; He et al. 2018; Zhang et al. 2017; Wei et al. 2019). This work paves the integration ability of LSC to real device and it was demonstrated in a compact box, which composing of both tandem LSCs and solar panels.

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Fig. 4.5 a and b Schematic diagrams of the LSC devices based on organometal halide perovskite. c I-V curves of the planer LSCs made of CH3 NH3 PbBr3 perovskite with (A) 2 wt.%, (B) 1.77 wt.%, (C) 1.55 wt.%, (D) 1.33 wt.% and (E) 1.11 wt.% in PVA solution. Inset: I-V curves of the solar cell with 0 wt.% hybrid. Reproduced with permission from Ref. Mirershadi and Sattari (2021). Copyright 2015, Elsevier Ltd.

2.

Methylammonium lead halide perovskites for LSC

S. Mirershadi et al., have prepared luminescent solar concentrators by widely dispersing Methylammonium Lead Halide Perovskites (CH3 NH3 PbX3 , X = Cl, Br and I), micro-particles in a Polyvinyl Alcohol (PVA) waveguide (Mirershadi and Sattari 2021; Bergren et al. 2018; He et al. 2018). Planar luminescent sheet on top of PV cells and bulk form of traditional LSC configuration with silicon PV cell attached at the edge. Schematic diagram of devices are shown in Fig. 4.5a, b. In this work, they have investigated perovskite particles as the active medium in planar and bulk form of LSCs. The variation of optical properties and LSC device performance, with different halogen sources in the perovskite based LSC precursors were investigated by spectroscopic and photovoltaic measurements. They have found that these superior performances of LSC are attributed to the high quantum yield of the halide perovskites. The obtained results show that to find a suitable condition for effective LSC, it is necessary to investigate the appropriate halogen atom in the synthesized perovskite, as well as the concentration of halide perovskite in LSC (Mirershadi and Sattari 2021). It is clear from this research work that, CH3 NH3 PbX3 perovskites are more resilient to lightening. The important thing, the stability of perovskites doped PVA layer is quite remarkable and it is also the most stable one (Ma et al. 2019; Papakonstantinou et al. 2021). It is noteworthy to mention here that due to its prominent optical properties (photo-stability and high luminescence), organometal halide perovskites are currently introduced as the material of choice for the emitting centers in LSC devices. Table 4.2 provides the list of various perovskites used for LSC fabrication and their output results. These results were encouraged a lot to implementation of perovskite thin films in LSCs.

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Table 4.2 Performance of LSCs based on various types of perovskites Perovskites

Stokes shift (meV)

λ range (nm)

QY (%)

Area (cm2 )

Ƞ opt (%)

References

CH3 NH3 PbX3 thin film

60

300–760

80

1.5 × 1.5

29

43

CsPb(Brx I1−x )3 QDs

25

300–650

60

1.5 × 9 2

60

Cs4 PbBr6 NCs

1500

300–500

58

10 × 10 2.4

62

Mn2+ :CsPb(Brx I1−x )3 QDs

1000

300–400

20

20 × 0.5

0.5

61

Yb3+ :CsPb(Brx I1−x )3 QDs

1850

300–400

118

5×5

3.7

63

HA2 MAn−1 Pbn X3n+1 NPLs

275

300–500

80

10 × 10 26

64

4.5 Concluding Remarks In this chapter, we have reviewed the fundamentals of luminescent solar concentrators and types of polymeric materials and metal halide perovskites to fabricate high efficiency and large-area LSC. The outstanding optical properties of perovskite are strappingly depending on their size, shape and composition of it. If we optimize the perovskite structure to obtain the suitable emitters for the beneficiation of LSCs, it will be a remarkable achievement in the respective research field. Among various types of perovskites, doped quantum dots offer a great opportunity to synthesize high quality perovskites with both high quantum yield and large Stokes shift, indicating the doped perovskites may be great candidates, as emitters for high efficiency LSCs. In order to get high PCE from LSC, there are still some issues needed to be solved: (1) no report is available for producing doped perovskites with wide absorption; (2) the lead toxicity is the drawback of usage of these perovskite materials for potential commercialization, there is need of lot of research in this aspect; (3) the long-term stability of the perovskites is not good compared to other reported semiconductor nanocrystals high-quality emitters due to its very sensitive to the moisture and UV light; (4) experimental fabrication of high optical efficient to prepare a large area (~1 m2 ), high performance LSCs is yet to be come in research and development sectors. Acknowledgements The authors are grateful to the management of Chettinad College of Engineering and Technology, Karur for constant support and encouragement.

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Jin L, AlOtaibi B, Benetti D, Li S, Zhao H, Mi Z, Rosei F (2016) Near-infrared colloidal quantum dots for efficient and durable photoelectrochemical solar-driven hydrogen production. Adv Sci 3(3):1500345 Krumer Z, van Sark WG, Schropp RE, de Mello Donegá C (2017) Compensation of self-absorption losses in luminescent solar concentrators by increasing luminophore concentration. Sol Energy Mater Sol Cells 167:133–139 Levitt JA, Weber WH (1977) Materials for luminescent greenhouse solar collectors. Appl Opt 16(10):2684–2689 Li Y, Miao P, Zhou W, Gong X, Zhao X (2017) N-doped carbon-dots for luminescent solar concentrators. J Mater Chem A 5(40):21452–21459 Liu G, Zhao H, Diao F, Ling Z, Wang Y (2018) Stable tandem luminescent solar concentrators based on CdSe/CdS quantum dots and carbon dots. J Mater Chem C 6(37):10059–10066 Liu Y, Li N, Sun R, Zheng W, Liu T, Li H, Zhang Y (2021) Stable metal-halide perovskites for luminescent solar concentrators of real-device integration. Nano Energy, 85:105960 Ma W, Li W, Liu R, Cao M, Zhao X, Gong X (2019) Carbon dots and AIE molecules for highly efficient tandem luminescent solar concentrators. Chem Commun 55(52):7486–7489 MacQueen RW, Tayebjee MJ, Webb JE, Falber A, Thordarson P, Schmidt TW (2016) Limitations and design considerations for donor–acceptor systems in luminescent solar concentrators: the effect of coupling-induced red-edge absorption. J Optics 18(6):064010 Mansour AF, El-Shaarawy MG, El-Bashir SM, El-Mansy MK, Hammam M (2002) Optical study of perylene dye doped poly (methyl methacrylate) as fluorescent solar collector. Polym Int 51(5):393–397 Mateen F, Oh H, Kang J, Lee SY, Hong SK (2019) Improvement in the performance of luminescent solar concentrator using array of cylindrical optical fibers. Renew Energy 138:691–696 Mazzaro R, Vomiero A (2018) The renaissance of luminescent solar concentrators: the role of inorganic nanomaterials. Adv Energy Mater 8(33):1801903 Meinardi F, Akkerman QA, Bruni F, Park S, Mauri M, Dang Z, Brovelli S (2017a) Doped halide perovskite nanocrystals for reabsorption-free luminescent solar concentrators. ACS Energy Lett 2(10):2368–2377 Meinardi F, Bruni F, Brovelli S (2017). Luminescent solar concentrators for building-integrated photovoltaics. Nat Rev Mater 2(12):1–9 Meinardi F, Bruni F, Brovelli S (2017c) Luminescent solar concentrators for building-integrated photovoltaics. Nat Rev Mater 2(12):1–9 Meinardi F, Ehrenberg S, Dhamo L, Carulli F, Mauri M, Bruni F, Brovelli S (2017d) Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots. Nat Photonics 11(3):177–185 Mirershadi S, Sattari F (2021) Effect of organic cation composition and halogen atom type on 2Dlayered organic–inorganic hybrids for luminescent solar concentrator. J Mater Sci Mater Electron 32(10):12939–12950 Navarro-Pardo F, Zhao H, Wang ZM, Rosei F (2017) Structure/property relations in “giant” semiconductor nanocrystals: opportunities in photonics and electronics. Acc Chem Res 51(3):609–618 Nikolaidou K, Sarang S, Hoffman C, Mendewala B, Ishihara H, Lu JQ, Ghosh S (2016) Hybrid perovskite thin films as highly efficient luminescent solar concentrators. Adv Opt Mat 4(12):2126– 2132 Papakonstantinou I, Portnoi M, Debije MG (2021) The hidden potential of luminescent solar concentrators. Adv Energy Mater 11(3):2002883 Rau U, Einsele F, Glaeser GC (2005) Efficiency limits of photovoltaic fluorescent collectors. Appl Phys Lett 87(17):171101 Richards BS, McIntosh KR (2007) Overcoming the poor short wavelength spectral response of CdS/CdTe photovoltaic modules via luminescence down-shifting: ray-tracing simulations. Prog Photovolt Res Appl 15(1):27–34 Rowan BC, Wilson LR, Richards BS (2008) Advanced material concepts for luminescent solar concentrators. IEEE J Sel Top Quantum Electron 14(5):1312–1322

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Selopal GS, Chahine R, Mohammadnezhad M, Navarro-Pardo F, Benetti D, Zhao H, Rosei F (2019) Highly efficient and stable spray assisted nanostructured Cu2 S/Carbon paper counter electrode for quantum dots sensitized solar cells. J Power Sour 436:226849 Sharma M, Gungor K, Yeltik A, Olutas M, Guzelturk B, Kelestemur Y, Demir HV (2017) Near-unity emitting copper-doped colloidal semiconductor quantum wells for luminescent solar concentrators. Adv Mater 29(30):1700821 Shu J, Zhang X, Wang P, Chen R, Zhang H, Li D, Xu J (2018) Monte-Carlo simulations of optical efficiency in luminescent solar concentrators based on all-inorganic perovskite quantum dots. Phys B Condensed Matter 548:53–57 Shukla AK, Sudhakar K, Baredar P (2017) Recent advancement in BIPV product technologies: a review. Energy and Buildings 140:188–195 Slooff LH, Kinderman R, Burgers AR, Bakker NJ, Van Roosmalen JAM, Büchtemann A, Schleusener M (2007) Efficiency enhancement of solar cells by application of a polymer coating containing a luminescent dye Taleb AM (2002) Self absorption treatment for the luminescent solar concentrators. Renew Energy 26(1):137–142 Tan L, Zhou Y, Ren F, Benetti D, Yang F, Zhao H, Ma D (2017) Ultrasmall PbS quantum dots: a facile and greener synthetic route and their high performance in luminescent solar concentrators. J Mater Chem A 5(21):10250–10260 Tong X, Kong XT, Zhou Y, Navarro-Pardo F, Selopal GS, Sun S, Rosei F (2018) Near-infrared, heavy metal-free colloidal “Giant” core/shell quantum dots. Adv Energy Mater 8(2):1701432 VanOrman ZA, Nienhaus L (2021) Recent advancements in halide perovskite nanomaterials and their optoelectronic applications. InfoMat Verbunt PP, Kaiser A, Hermans K, Bastiaansen CW, Broer DJ, Debije MG (2009) Controlling light emission in luminescent solar concentrators through use of dye molecules aligned in a planar manner by liquid crystals. Adv Func Mater 19(17):2714–2719 Wei M, de Arquer FPG, Walters G, Yang Z, Quan LN, Kim Y, Sargent EH (2019) Ultrafast narrowband exciton routing within layered perovskite nanoplatelets enables low-loss luminescent solar concentrators. Nat Energy 4(3):197–205 Wilson LR, Rowan BC, Robertson N, Moudam O, Jones AC, Richards BS (2010) Characterization and reduction of reabsorption losses in luminescent solar concentrators. Appl Opt 49(9):1651– 1661 Ying SP, Chen BM, Tseng WL (2019) Thin-film luminescent solar concentrators using inorganic phosphors. IEEE Trans Electron Devices 66(5):2290–2294 Zhang Y, Saidaminov MI, Dursun I, Yang H, Murali B, Alarousu E, Mohammed OF (2017) Zerodimensional Cs4PbBr6 perovskite nanocrystals. J Phys Chem Lett 8(5):961–965 Zhao H, Benetti D, Jin L, Zhou Y, Rosei F, Vomiero A (2016) Absorption enhancement in “Giant” core/alloyed-shell quantum dots for luminescent solar concentrator. Small 12(38):5354–5365 Zhao H, Zhou Y, Benetti D, Ma D, Rosei F (2017) Perovskite quantum dots integrated in large-area luminescent solar concentrators. Nano Energy 37:214–223 Zhou Y, Benetti D, Fan Z, Zhao H, Ma D, Govorov AO, Rosei F (2016) Near infrared, highly efficient luminescent solar concentrators. Adv Energy Mater 6(11):1501913 Zhou Y, Zhao H, Ma D, Rosei F (2018) Harnessing the properties of colloidal quantum dots in luminescent solar concentrators. Chem Soc Rev 47(15):5866–5890

Part III

Environment Related Applications of Polymer-Based Advanced Functional Materials

Chapter 5

Polymeric Membranes and Hybrid Techniques for Water Purification Applications Haradhan Kolya , Vijay K. Singh , and Chun-Won Kang

Abstract Sustainable supply of water and energy has always been essential for socio-economic development. Flocculation, adsorption, and membrane filtration are among the most cost-effective techniques for water purification. However, in today’s world, hybrid technology has emerged as a potential alternative for membrane filtration water purification. Further, the hybrid system is more energy-efficient and takes up less space than membrane filtration alone, including double-pass Reverse Osmosis. The reuse of wastewater for the production of drinkable water has indeed been made possible due to rapid developments in membrane filtration technology. The potential applications of membrane technologies and their existing position in the realm of water and energy sustainability are discussed in this chapter. Further, the rapidly progressing hybrid membrane filtering technologies, as well as future research prospects are also discussed in this chapter. Keywords Waste water purification · Membrane filtration · Hybrid methods

5.1 Introduction The water–population–energy nexus is becoming a worldwide concern because of several factors. In general, the percentage of useable water is very low (2.5%) in comparison with ocean water (97.5%) (Le and Nunes 2016; Gebreeyessus 2019). On the other hand, the global population, urbanization, and industrialization, all have increased at a faster rate in the last 3 decades (Gebreeyessus 2019). So, the H. Kolya (B) · C.-W. Kang (B) Department of Housing Environmental Design and Research Institute of Human Ecology, College of Human Ecology, Jeonbuk National University, Jeonju, Jeonbuk 54896, Republic of Korea e-mail: [email protected] C.-W. Kang e-mail: [email protected] V. K. Singh Department of Physics, Indian Institute of Technology Jodhpur, Jodhpur 342037, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_5

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need for freshwater increases day by day. Besides, the rapid development of industrialization has led to the contamination of fresh and marine water. Hence, effective water purification techniques have become extremely relevant, and robust materials are in great demand (Zhang et al. 2021).Conventional separation technologies, such as centrifugation (Gong et al. 2021), flocculation (Kolya and Tripathy 2014; Kolya et al. 2017; Patra et al. 2020), absorption (Kolya and Tripathy 2015; Sasmal et al. 2017), gravity settling (Shabani et al. 2021) etc. have limitations, such as high energy consumption, low efficiency, sludge production, and requiring the use of functional materials (Zhang et al. 2021). Going forward, separation of materials in various structures such as sponges, membranes, films, and pellets have been produced using a variety of approaches for application in a variety of disciplines, including water purification (Qayum et al. 2019). Wherein, membrane separation has attracted a lot of interest, because of its excellent separation performance, low energy consumption, simplicity, and ability to function continuously (Zhang et al. 2021). However, fouling is one of the major drawbacks, since it causes permeate flux to decrease, and hence membrane performance gets deteriorated. However, it may be avoided by creating efficient hybrid techniques and performing membrane pretreatment (Camilleri-Rumbau et al. 2021). Therefore, the prime objective of this chapter is to explore the advancement of membrane filtration and its performance enhancement using hybrid techniques for water and energy sustainability.

5.2 Membrane Filtration The membrane is usually used for microfiltration, nanofiltration and ultrafiltration techniques (Zularisam et al. 2006). The pore size of the membrane is the main difference between microfiltration, nanofiltration, and ultrafiltration. Microfiltration, ultrafiltration, and reverse osmosis are used to remove the macroparticles, microparticles, and macromolecules of inorganic particles, organic colloids, and dissolved natural matters (Shannon et al. 2009; Buruga et al. 2018). The intermediate membrane process between ultrafiltration and reverse osmosis is nanofiltration. The general membrane pore size is in the range of 0.1–10 µm for microfiltration, 0.002–0.1 µm for ultrafiltration and 0.2–2 nm for nanofiltration. Microfiltration and ultrafiltration membranes can be made from both ceramic and polymer materials. Among these, ceramic materials provide much chemical stability and mechanical strength, are easy to clean, and have long and reliable durability (Hofs et al. 2011). However, because of its brittleness, it is expensive and difficult to manufacture on a large scale. On the other hand, polymeric membranes have majorly occupied the market for a long time. Almost all the membranes for water purification are manufactured from polymeric materials (such as cellulose acetate, polyethylene, polytetrafluorethylene, polypropylene, polyvinylidene fluoride, polyether sulfone, polyacrylonitrile, polyfone, or other polymers) owing to their low cost, good mechanical strength, and operational flexibility. Membrane bioreactor technology has recently been used in industries for

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wastewater treatment (Daigger et al. 2005; Yang et al. 2006). Fouling is the cause of microbe-generated extracellular polymeric substances, polysaccharides, and natural matter (Carroll et al. 2002; Bassyouni et al. 2019). Fouling of polymer membranes depends on the floor morphology and membrane chemistry. Mostly polymers with porosity, precise chemical and mechanical steadiness, and high hydrophobicity are used for the development of membrane sheets. The natural foulants are adsorbed on the floor of membranes because of their lyophilic character. Graft copolymerization of hydrophilic monomers has an important role in minimizing adsorption foulants on the membrane floor. However, it additionally reduces inherent permeability by partially blocking off the surface pores (Ulbricht and Belfort 1996). Nowadays, graft copolymers containing hydrophobic and hydrophilic chains are used to fabricate membranes via in situ polymerization (Hester and Mayes 2002; Deratani et al. 2007). Graft copolymers are used to manufacture nanodomains or nanopores that are exceedingly permeable to water (Ulbricht 2006; Lu et al. 2007) and are very useful for ultrafiltration and microfiltration (Akthakul et al. 2004). Ultrafiltration membranes were reported for the removal of reactive blue 21 (RB21) and direct yellow 19 (DY19) from water (Karimi et al. 2019). The composite membrane was synthesized by zeolitic imidazolate framework-8 (ZIF-8) and polyvinylidene fluoride (PVDF). The modified membrane can reject coloured molecules with a high percentage (~98.32%) of RB21 and DY19 (~89.65%), because of the inter-ionic repulsion between the anionic dye molecules and negatively charged membrane (Karimi et al. 2019). The modified poly (ether sulfone = PES) with poly (methacrylic acid) antifouling membrane was reported for the microfiltration of Cu (II) ions with a broad range of pH (2–12) (Han et al. 2014). Similarly, the composite membrane of PES and poly (acrylonitrile-co-acrylic acid) was used to purify macromolecules of PEG-1000 and PG-10000 at a pH of 2.3 and 11.3, respectively. The results showed a good rejection rate at pH ~11.3 because a larger surface charge appeared in the alkaline condition (Qian et al. 2009). Poly (ethylene imine) grafted with PVDF and PVDF/polyacrylic acid (PAA) composite membranes were used for oil/water separation with high separation efficiency and superior antifouling properties for acidic pH (Zhu et al. 2015; Dutta and De 2017a). Poly (urethane) [PU] membranes can be used to remove Cr (VI) ions using keratin biofiber protein (Saucedo-Rivalcoba et al. 2011). At alkaline and acidic conditions, the percentage of rejection increased and decreased, respectively, perhaps because of the effect of the isoelectric point of keratin protein and morphological changes that occurred in the presence of acidic or alkaline conditions, as shown in Fig. 5.1 (Saucedo-Rivalcoba et al. 2011). The SEM micrographs (Fig. 5.1) reflect the compatibility to form hybrid membranes between polyurethane and protein bonds. These micrographs also indicate that the grafted keratin or biofiber in the solution plays a significant role in the structural configuration of the membrane. It is clear that biofiber application, in acid or alkaline solutions, affects the surface morphology and cell size (Saucedo-Rivalcoba et al. 2011). In addition, a PVA/silica nanofiber membrane modified with thiol was reported to be a better Cu (II) ion adsorbent than the PVA nanofiber membrane. The removal of toxic metal ions occurred via an electrostatic or chelation mechanism, as shown in

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Fig. 5.1 SEM micrographs of polyurethane–keratin membranes: a keratin salt, b dialyzed keratin, c alkaline biofiber solution, and d acid biofiber solution (Saucedo-Rivalcoba et al. 2011). Copyright 2010; reproduced with permission from Springer Science Business Media B.V.

Fig. 5.2. Similarly, PVA/poly (ethyleneimine) membranes were used for the rejection of Cu (II), Cd (II), Pb (II), and Hg (II) metal ions from wastewater (Bessbousse et al. 2012; Dutta and De 2017b). It has been found that the rejection rate is higher for Hg (II) ions and lower for Cu (II) ions. The better hydrolysable metal ions get adsorbed more by the membrane, which exhibited selectivity in the order of Hg (II) > Cu (II) > Pb (II) > Cd (II) for a mixed metal-ion solution (Bessbousse et al. 2012). Further, it has also been reported that the membrane prepared by PVA and poly (vinylimidazole) exhibited much higher rejection ratio of ~99.4% of Hg (II) at pH 2.5 (Bessbousse et al. 2010). Poly (ether imide)-based membrane is another prospect for removing toxic metal ions from water. Herein, poly (ether imide) acted as a metal-chelating ligand. The membrane composed of N-phthaloyl chitosan and poly (ether imide) was used for the removal of Pb (II), Cu (II), Ni (II), Cd (II), and Zn (II) from water. A reasonable rejection performance (~98%) was achieved in the order of Cr (III) > Zn (II) > Cd (II) > Pb (II) (Kanagaraj et al. 2015). PEI membrane increased the ultrafiltration of Cu (II) ions from water effluents as reported by Camarillo et al. (Camarillo et al. 2012). The ultrafiltration system consists of a thermostat bath, a feed gear pump, a flow meter, a tubular Micro Carbosep 20 UF module with axial outlets with an M2 Rhodia-Orelis ceramic membrane, and a feed-flow controller. Effective rejection of Cu (II) ions from effluents and regeneration of polymers could make this process cost-effective and ecofriendly (Camarillo et al. 2012). Recently, a new biomimetic

5 Polymeric Membranes and Hybrid Techniques … Fig. 5.2 The Cu (II) ion-adsorption mechanism on PVA/SiO2 composite nanofibers membrane (Wu et al. 2010). Copyright 2010; reproduced with permission from Elsevier, Ltd.

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Desor ption

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Diffusion

HS Cu 2+

coated PVDF ultra-filtration membrane with excellent wettability and fouling resistance has been reported. The membrane exhibited excellent performance (~99.5%) for oil/water separation. The biomimetic synergistic coating approach improved the membrane filtration via elegant surface manipulation towards a water-energy nexus (Yang et al. 2019). The biomimetic coating mechanism is shown in Fig. 5.3. Also, mussel-inspired chemistry in membrane science and technology has drawn widespread interest. Due to the rapid growth of this field over the past few years, major progress has been witnessed in both mussel-inspired chemistry and membrane surface engineering based on mussel-inspired coatings (Zhang et al. 2017b; Yang et al. 2018; Wu et al. 2020). PVDF modified catechol containing a PEG membrane improved the rejection of BSA separation due to the presence of hydrophilic catechol groups on the membrane surface. It exhibited a high flux-recovery ratio of ~ 93.8% and BSA rejection rate of ~ 93.8% (Sun et al. 2019). Recently, Himstedt et al. (2019) reported a magnetically responsive nanofiltration membrane manufactured by grafting polyhydroxyethylmethacrylate using the ATRP method (Himstedt et al. 2019). It was used to treat water produced by coal-bed methane in the presence of an external magnetic field. Calcium chloride (500 ppm) and magnesium sulphate (2000 ppm) solutions were used to study the filtration activity of synthesized membranes and the effect of the magnetic field. The rejection rate of CaCl2 and MgSO4 was higher in the presence of the magnetic field (Himstedt et al. 2019), perhaps because the permeability of the membrane surface and the antifouling properties increase in the presence of the magnetic field, which effectively increased the rejection rate of salt separation. A simplified schematic

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Fig. 5.3 Details of mussel/tunicate bio-adhesion-inspired coating using polyphenol tannic acid and cysteamine on the hydrophobic polymeric micro/ultra-filtration (MF/UF) membrane surface in alkaline aqueous buffer (Tris–HCl, pH = 8.5) for both oil-in-water emulsion and simulated protein-containing wastewater (Yang et al. 2019). Copyright 2019; reproduced with permission from Elsevier B.V.

representation for increasing the anti-fouling performance of a magnetically responsive nanofiltration membrane is shown in Fig. 5.4 (Himstedt et al. 2019). An Ar/O2 plasma-treated multi-walled carbon nanotubes (MWCNTs) membrane can be used for the removal of zinc from industrial effluents (Ali et al. 2019). These results showed that the super-adsorption properties or rejection of Zinc from a synthetic solution was 100% and from wastewater was 80%. The high adsorption performance of modified MWCNTs membrane results from the chemisorption between the Zn (II) ions and oxygen-containing functional groups of MWCNTs (Ali et al. 2019). A probable mechanism of adsorption of Zn (II) ions on the surface of membranes is depicted in Fig. 5.5. The regeneration at acidic pH and absorptivity of zinc has been reported as reversible, which increases the recyclability and reduces the cost. It could be a viable method for full-scale wastewater purification (Ali et al. 2019). The Graphene Oxide (GO)/PAM composite membrane showed the best comprehensive separation because of the presence of proper interlayer spacing of the composite, as shown in Fig. 5.6. The GO/PAM membranes provided prospective advantages in the design of molecular separation and water purification (Cheng et al. 2019). Currently, polymeric membrane-based disinfection of water has attracted immense attention because of its distinctive properties and wide applications. A clear idea of the antibacterial mechanism, biocompatibility, benefits, threats, and prospects of these membranes have been discussed by Mukherjee et al. (Mukherjee and De 2018). It has recently been reported that reduced graphene oxide (rGO) based nanofibrous membrane exhibited robust oil–water separation efficiency (99.19%) and flux (2040.04 L m−2 h−1 ) at the same time (Zhang et al. 2021).

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Fig. 5.4 A simplified schematic representation for increasing the anti-fouling performance of a magnetically responsive nanofiltration membrane (Himstedt et al. 2019). Copyright 2018; reproduced with permission from Elsevier B.V.

Zn2+ Functional CNT

Zn2+ Adsorption

Zn2+ Water Other metal ions

Fig. 5.5 A probable mechanism for adsorption of Zn (II) ions on the surface of membranes (Ali et al. 2019). Copyright 2018; reproduced with permission from Elsevier B.V.

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Fig. 5.6 Surface and cross-sectional SEM images of the (a, d) GO, (b, e) rGO, and (c, f) GO/PAM membranes; cross-sectional images of the g GO, h rGO, and i GO/PAM membranes (Cheng et al. 2019). Copyright 2018; reproduced with permission from the Springer Science Business Media, LLC, part of Springer Nature

5.3 Reverse Osmosis Reverse osmosis (RO) is the most essential desalination technique, and its application is growing fast across the world. In RO, an applied pressure is necessary to counter osmotic pressure. RO can remove a wide range of dissolved and suspended chemicals, as well as biological species (mostly bacteria) from water, and is useful in both manufacturing processes and drinkable water production. A semipermeable membrane possesses microscopic pores that reject pollutants but allow water molecules to pass through. Water becomes increasingly concentrated as it passed through the membrane via osmosis, to achieve equilibrium on both sides. In RO, water is pressured to move across the membrane from high concentration contaminates to low concentration contaminates, as shown in Fig. 5.7. Filtration in RO normally consists of four stages: a sediment filter, a pre-carbon block, a reverse osmosis membrane, and a post-carbon filter. Therefore, polymeric membranes have dominated the RO desalination market. The efficiency of RO membranes has been optimized by the use of poly-condensation catalysts and additives in membrane formation reactions. Besides, nanotechnology advancements in membrane materials research also provide an appealing alternative to polymeric materials. Membrane efficiency has also been enhanced by improving the functionality (selectivity and

5 Polymeric Membranes and Hybrid Techniques … Fig. 5.7 Schematic presentation of osmosis and reverse osmosis

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Less concentration

More concentration

Salt molecule

Semi permeable membrane More concentration

Fresh water

Semi permeable membrane

permeability) and applicability (durability, chemical, and mechanical). Additionally, the cost of RO membranes per unit volume of water has decreased by more than 10 times since 1978 due to the improved mechanical, biological, and chemical strength, as well as higher permeability of the membrane. Consequently, energy consumption has decreased from 12 kWh m−3 in the 1970s to less than 0.97kWh m−3 in 2021(Asif and Zhang 2021).In detail, the combined efforts of minimizing fouling and concentration polarization, as well as maximizing permeate flow and energy recovery, can reduce energy consumption. According to this concept, three layers of a polyester membrane (thickness 120–150 µm) have been marketed as the most effective in the RO membrane. Besides, spiral wound polyamide membranes are used in the manufacturing of RO/nanofiltration (NF) membranes (Lee et al. 2011; Warsinger et al. 2018).The RO/NF has a high rejection rate for dye molecules, but consumes a lot of energy and has serious membrane fouling issues (Tan et al. 2017).

5.4 Forward Osmosis The osmotic-driven forward osmosis (FO) process has recently gained the huge interest of academia and industry (Chung et al. 2012). FO is a spontaneous process that generates water permeation across the semipermeable membrane based on the osmotic pressure difference between the feed and draw solutions. FO also has the

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advantages of high solute rejections, high water recovery rate, low membrane fouling, and low energy consumption, making it a viable wastewater treatment technique (Zhang et al. 2017a; Ding et al. 2020). However, there is no guarantee that the membrane will recover its original efficiency. Potential integrated hybrid approaches can be used to improve the efficiency of the FO system (Suwaileh et al. 2020). The FO-extraction hybrid method has a substantially lower cost than the single extraction process (Ding et al. 2020). The excellent FO membranes should have (1) high salinity retention and high-water flux, (2) low concentration polarization, and (3) durability to a wide range of pH, as well as long-term mechanical and performance stability. The FO membrane for generating osmotic power in the pressure retarded osmosis (PRO) mode have also been established (Achilli et al. 2009).One may follow these papers for further details (Chung et al. 2012; Warsinger et al. 2018; Ding et al. 2020). The summary of the above discussion is presented in Table 5.1.

5.5 Hybrid Techniques Hybrid techniques are a promising research topic for wastewater purification (Hai et al. 2007). Polymer-based composite hybrid membranes are always preferred as hybrid adsorbents for water purification (Dong et al. 2009). It was found that the combined treatment of chemical and physical processes increased the percentage of pollutants removed from wastewater. Bu et al. reported that a mixture of coagulation and adsorption increased the elimination of organic pollutants and decreased the fouling of ultra-filtration membranes (Bu et al. 2019). The hybrid process is also used in photocatalytic membrane reactors (PMR) for water filtration (Lim et al. 2011). Vigneswaran et al. described the flocculation-adsorption membrane filtration for wastewater purification (Vigneswaran et al. 2004). It has been reported that the pretreated water obtained by flocculation and adsorption improved the antifouling of membranes and their filtration performance. PAC (poly aluminium chloride), activated carbon, and an NTR7410 membrane was used as flocculant, adsorbent, and ultrafiltration membrane, respectively. The membrane could remove the TOC by ~43.6% from wastewater. In contrast, the percentage of removal is ~69.3% while using pretreated wastewater by flocculation. Furthermore, ultrafiltration reached ~91% of TOC removal using pretreated wastewater by flocculation-adsorption. Similarly, a coagulation-adsorption-ultrafiltration (C-A-U) hybrid technique was used to treat domestic wastewater. C-A could remove ~86% of chemical oxygen demand (COD); turbidity removing was 18 NTU to 3.5 NTU at a pH of 5.5. However, the COD and turbidity removal become ~82.7% and 18 NTU to 0.5 NTU by a C-AU hybrid technique (Abdessemed et al. 2000). A pilot-scale wastewater treatment plant (Staoueli in Algeria) used a C-A-U hybrid technique for water purification. The turbidity of the suspended particles and COD value were 90 NTU and 165 mg O2 /l, respectively (Abdessemed and Nezzal 2003). Further, the COD and turbidity decreased to 23 mg O2 /l and 12 NTU after treatment with FeCl3 solution at pH 5.5. The value of COD and turbidity significantly decreased to 7 mg O2 /l and 0 NTU

Only PVDF

Modified PES membrane with Poly Cu (II) (methyl methacrylate-co-acrylic acid)/ poly (methyl methylacrylate-co-4vinyl pyridine) composites

PES/poly (acrylonitrile-co-acrylic acid) composites

Poly (ethylene imine) grafted PVDF/ PVDF-g-PAA composite

PVDF/ PVDF-g-PAA composite

PVDF

Modified poly (urethane) / keratin biofiber protein

PVA/SiO2 composites

PVA/PEI composites

2

3

4

5

6

7

8

9

10

Cu (II) Cd (II) Pb (II) Hg (II)

Cu (II)

Cr (VI)

Oil–water emulsion

Oil–water emulsion

Oil–water emulsion

PEG-1 K PEG-10 K

RB21 DY19

RB21 DY19

Zeolitic imidazolate framework-8 (ZIF-8) and PVDF

1

Pollutants

Membrane

Sl. no

Table 5.1 Recent reports of water purification using membrane filtration

49.9 41.8 75.2 85.9

93.1

38.0 11.0

96.3 96.9

99.4 99.8

99.96 99.97

49.5 68.5

53.1 to 97.7

82.25 65.45

98.32 89.65

Optimum rejection (%)

–

–

0.7

0.1

0.1

0.1

0.12

– –

2.0

2.0

Pressure (bar)

5 5 5 2.5

5–6

>8 to 90.0

99.5

99.4

Optimum rejection (%)

0.1

10.0

10.0

–

–

1.4

–

3.0

0.9

3.0

Pressure (bar)

5.2

6.0

–

–

7.0

7.9

–

11

7.4

2.5

pH

Tong et al. (2021)

Peydayesh et al. (2020)

Al-Gamal et al. (2021)

Cheng et al. (2019)

Ali et al. (2019)

Himstedt et al. (2019)

Sun et al. (2019)

Shao et al. (2013)

Yang et al. (2019)

Bessbousse et al. (2010)

References

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Stirrer Wastewater

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Flocculation --------- ------------------------------------------------- ---------

Valve

Polymer flocculants

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Fig. 5.8 Schematic representation of the hybrid technique adopted for wastewater purification

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MicroNano

Polymer membrane & RO Regeneration

when the effluent was treated with a hybrid method like C-A-U (Abdessemed and Nezzal 2003). The secondary effluent of Staoueli (Algeria) was also purified by a C-A-U method. This technique could reduce the COD and turbidity value from 46 to 12 mg O2 /l and 16 NTU to 3 NTU, respectively (Abdessemed and Nezzal 2005). Recently, the applicability of a hybrid membrane method in water treatment has been reviewed (Ang et al. 2015). The combination of coagulation/flocculation, adsorption, and nano-filtration suggest a great ability to eliminate contaminants from water. This hybrid technique could be considered for industrial effluent treatment and reuse of water. A schematic of the hybrid technique is presented in Fig. 5.8.

5.6 Concluding Remarks In summary, the advancement of membrane filtering techniques in wastewater treatment has been discussed in detail. Membrane filtering using RO and FO has also been explained in detail for energy-saving approaches. According to a detailed literature survey, the development of hybrid processes that combine other processes (flocculation, adsorptions, etc.) with membrane technologies is becoming increasingly important in the field of water treatment. There are still some challenges and scopes, which need to be addressed for sustainable water and energy supply. 1. 2. 3. 4.

Improving hollow fiber membrane technology. Improving hybrid technology with membrane filtration/RO. Membrane resistance for cleaning and antibacterial treatments can be improved. Pretreatment methods that are less expensive and have a lower environmental effect can be developed.

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Polymer membrane technology, which is improving multilayer membrane/membrane modification, will be useful in achieving these developments in potable reuse of water. Acknowledgements Professor Kang thankful to the Basic Science Research Program through the National Research Foundation (NRF) of Korea funded by the Ministry of Education (NRF2019R1I1A3A02059471) and was supported under the framework of an international cooperation program managed by the NRF of Korea (NRF-2020K2A9A2A08000181).

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Yang H-C, Waldman RZ, Wu M-B et al (2018) Dopamine: just the right medicine for membranes. Adv Funct Mater 28:1705327 Yang W, Cicek N, Ilg J (2006) State-of-the-art of membrane bioreactors: worldwide research and commercial applications in North America. J Memb Sci 270:201–211 Yang X, Yan L, Ma J, et al (2019) Bioadhesion-inspired surface engineering constructing robust, hydrophilic membranes for highly-efficient wastewater remediation. J Memb Sci 591:117353 Zhang M, Cui J, Lu T et al (2021) Robust, functionalized reduced graphene-based nanofibrous membrane for contaminated water purification. Chem Eng J 404:126347 Zhang M, She Q, Yan X, Tang CY (2017a) Effect of reverse solute diffusion on scaling in forward osmosis: a new control strategy by tailoring draw solution chemistry. Desalination 401:230–237 Zhang X, Huang Q, Deng F et al (2017b) Mussel-inspired fabrication of functional materials and their environmental applications: progress and prospects. Appl Mater Today 7:222–238 Zhu Y, Xie W, Li J et al (2015) pH-Induced non-fouling membrane for effective separation of oil-in-water emulsion. J Memb Sci 477:131–138 Zularisam AW, Ismail AF, Salim R (2006) Behaviours of natural organic matter in membrane filtration for surface water treatment—a review. Desalination 194:211–231

Chapter 6

Environmentally Significant Cellulose Fiber Reinforced Polymer Matrix Composites Yucheng Peng, Sanat Chandra Maiti, and Rajendra Kumar Bordia

Abstract Natural cellulose fibers have attracted significant interest for manufacturing advanced polymer composites due to their environmental friendliness (renewability and biodegradability), easy availability, high stiffness and strength, easy processability, and modifiable surfaces. Many applications have been developed and more are being explored for cellulose fiber reinforced polymer composites. In different regions in the world the focus is on developing and usingdifferent cellulose based polymer composites for a variety of applications. For examples, In North America, wood based cellulose fibers have been extensively researched for manufacturing polymer composites in applications in the construction sector, such as outdoor decking and siding. In Europe, these composites are being investigated for fuel efficient and recyclable automotive components. In India and South America jute and sugar cane fiber reinforced polymers are being investigated for structural applications in housing. In this chapter, the physical, mechanical, and chemical properties of cellulose fibers of different origins will be presented. The processes used to manufacture cellulose fiber reinforced thermoplastic composites will then be introduced followed by the performance of these composites. A major challenge in using natural fibers as reinforcement for polymers is the poor adhesion between the fibers and the matrices. As a result, surface modification of the fibers is an active area of research and development and is comprehensively covered in this Chapter. Another area of active investigation is the use of nano-fibers as reinforcements. The status and challenges in this area are also summarized. Keywords Cellulose · Thermoplastic · Composites · Mechanical properties · Surface modification Y. Peng (B) School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Drive, Auburn, AL 36849, USA e-mail: [email protected] S. C. Maiti · R. K. Bordia Department of Materials Science and Engineering, Clemson University, 161 Sirrine Hall, Clemson, SC 29634, USA © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_6

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6.1 Introduction The growing awareness of environmental issues and resource scarcity drives the increasing interest in using renewable and bio-based materials in a wide variety of applications in many industrial sectors, including building construction, automotive, and packaging (Dufresne 2008; Fang et al. 2020; Gardner et al. 2015; Immonen et al. 2020; Väisänen et al. 2016). Furthermore, the desire to achieve carbon neutrality globally set forth the industry to seek new materials and products derived from renewable and bio-basedresources (Akampumuza et al. 2017; Luz et al. 2010; Zuo et al. 2012). Cellulose is the most abundant renewable natural resource available on earth and it can be extracted from different plants and wood species in a fiber form with a range of sizes from millimeters, micrometers, to nanometers (Célino et al. 2014; Dufresne and Belgacem 2013; Hubbe and Grigsby 2020; Kalia et al. 2011). Different sizes of cellulose fibers have been commercially prepared and used in polymer composite manufacturing for many applications (Hubbe and Grigsby 2020). One of the major driving forces for using cellulose fibers is related to their renewability and biodegradability. Additional factors include low cost and easy availability around the world. In the early 1900s, renewable materials, mostly cellulose based, processed by the textile industry, nearly dominated all the resources used for the production of commodities and many technical products. Cellulose fiber reinforced phenol- or melamine–formaldehyde composites were manufactured as early as 1908 in large quantities to produce sheets, tubes and pipes (Bledzki and Gassan 1999).Over the past several decades, there has been a significant increase in product research and development using cellulosic fibers as reinforcing elements in polymeric matrices (Bledzki and Gassan 1999; Eichhorn et al. 2001). In most cases, cellulosic fibers in micrometer sizes were used and commercial products have been developed for different applications. In North America, cellulose fibers, mainly wood fibers, reinforced polymer composites have been extensively researched and developed for applications in the construction sector, such as outdoor decking and siding (Dufresne 2008; Gardner et al. 2015). In Europe, cellulose fiber composites are being investigated for fuel efficient and recyclable automotive components (Akampumuza et al. 2017; Bledzki and Gassan 1999). In India and South America, jute and sugar cane fiber reinforced polymers are being investigated for structural applications in housing (Bledzki and Gassan 1999; Dufresne 2008; Winfield 1979). Recently, the intensive research activities in nanocellulose has provided an opportunity for the research community to shift its focus to the development of nanocellulose based polymer composites (Dufresne and Belgacem 2013; Gardner et al. 2015; Peng et al. 2012, 2015, 2016b). Cellulose fibers have been used as reinforcements in different polymer systems, including hydrosoluble polymers, thermosetting and thermoplastics (Ansari et al. 2015; Oksman Niska and Sain 2008; Peng et al. 2015, 2016b; Rojo et al. 2014). The most common cellulose fiber polymer composites are currently manufactured by mixing wood fibers with thermoplastics and used as a structural component in demanding outdoor environments. In this chapter, we focus on the system of cellulose

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fiber reinforced thermoplastic composites. In this system, composites are generated through an engineering process by combining and mixing two or more non-miscible components, i.e., the matrix as the continuous phase and the filler/reinforcement as the dispersed phase, cellulosic fibers in this specific case, in such a way to achieve unique properties that would not be achievable from the individual constituents. Different ratios of the two phases, matrix and reinforcement, can be adjusted to achieve optimized performance for each specific composite system. Simultaneously, different functional additives, for example, processing aids, ultraviolet (UV) absorbers, and biocides can be added to the composite system during manufacturing to extend the composite service life and enhance resistance to different environmental conditions (Oksman Niska and Sain 2008). For the composite system using cellulosic fibers, a huge composite design potential exists due to the availability of a wide variety of matrices and cellulose fibers. In addition, cellulose fibers can be easily sourced locally from agricultural and forest by-products. This also prompts the development of local economy with the utilization of the agricultural and forest industry waste and residues which has become an enormous pool of untapped biomass resources and caused economic and environmental burdens on the local communities (Väisänen et al. 2016).The other main benefits of using these renewable cellulosic resources are associated with their low price, low density, high availability, high specific mechanical properties, and modifiable surface chemistry as compared with conventional reinforcements, such as calcium carbonate, talc, glass fibers and carbon fibers (Kalia et al. 2011; Oksman Niska and Sain 2008).

6.2 Cellulose Fibers Only a few of the many different cellulosic fibers in the world have been researched by the community for applications in reinforcing thermoplastic composites and we will cover the most widely studied cellulose fibers among them in this chapter. Although cellulose fibers from different origins can be obtained, including plants, animal or minerals the focus of this Chapter is on fibers from plants since they are the most abundant and most widely used. Among the many cellulosic fibers from plants, wood, cotton, flax, jute, hemp, sisal, ramie, abaca, pineapple leaf, coir, oil palm, bagasse, rick husk, and kenaf fibers have been extensively investigated and used in composites manufacturing (Célino et al. 2014; Faruk et al. 2012b). These cellulosic fibers can be categorized into fibers generated from primary and secondary plants. Primary plants are those grown for the purpose of production of fibers, such as cotton, jute, hemp, kenaf, and sisal, while secondary plants are those in which the fibers are produced as a by-product, for example, pineapple, oil palm and coir (Faruk et al. 2012b). Based on different fiber types and the locations the fiber is extracted, the renewable cellulosic materials can be divided into six different groups: bastor stem fibers (jute, flax, hemp, kenaf and ramie), leaf fibers (abaca, sisal and pineapple), seed fibers (coir, cotton and kapok), reed fibers (bamboo and sugar cane), straw fibers (wheat, corn,

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Fig. 6.1 Molecular structure of the repeating unit of cellulose (Park et al. 2010)

and rice), and wood fibers (Dufresne 2008; Faruk et al. 2014). Each group of the cellulose fibers has been investigated with respect to their chemical compositions, structures, and physical and mechanical properties. These characteristics are critical and highly control the performance of the composites. Most relevant characteristics of cellulose fibers are summarized below. 1.

Fiber Chemistry

The natural polymer, cellulose, is the essential and major constituent of all plantbased cellulose fibers. Cellulose is a linear syndiotatic homopolymer consisting of D-anhydroglucopyranose units (AGUs) which are linked together by β-(1 → 4)glycosidic bonds (Fig. 6.1) (Klemm et al. 1998; Park et al. 2010). Each of the AGUs possesses three hydroxyl groups at C-2, C-3, and C-6 positions, capable of undergoing the typical reactions known for primary and secondary alcohols. Generally, cellulose isolated from native sources is always polydisperse. It consists of a mixture of macromolecules with widely differing chain lengths. But the molecular size of cellulose is generally represented by its average degree of polymerization (DP). In nature, the linear cellulose chains have a DP of approximately 10,000 glucopyranose units in wood cellulose and 15,000 in native cotton cellulose (Sjostrom 1981). The cellulose chains in plant fibers aggregate to highly ordered structural entities, which are referred to as microfibrils. The tendency to form this supramolecular structure is the result of the chemical constitution and spatial conformation of cellulose polymer molecules. Microfibrils in the woody plant are nanoscale fibers with an average cross-sectional dimension of about 10 nm × 3.5 nm. They consist of crystalline and amorphous domains with cellulose polymer chains parallel to the microfibril axis (Gardner et al. 2008). A number of models have been proposed for the structural alignment of the crystalline and amorphous domains in microfibril. Based on the different description of amorphous phase (less ordered regions) of microfibrils, three basic structure models were proposed (Chakraborty et al. 2006; Fengel and Wegener 1998): (1) (2) (3)

Longitudinally arranged molecules change from one ordered region to the subsequent one, the transition areas being less ordered regions; The fibrillar units are individual cords consisting of longitudinally arranged molecules and sequences of ordered and disordered regions; and The ordered regions are packages of chains folded in a longitudinal direction, the areas containing the turns between adjacent chain packages being the less ordered regions.

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An extended network of hydrogen bonds consisting of inter-and intra-molecular bonds between the hydroxyl groups in AGUs is responsible for the aggregation of cellulose polymer chains to form the crystalline and amorphous regions in microfibrils. In the crystalline region of native cellulose, the existence of intramolecular hydrogen bonds was found between O-3-H and O-5 (the oxygen atom attached to carbon #5 of the same AGU), and between O-2-H and O-6 and the intermolecular hydrogen bonds are formed by linking O-6-H with O-3 of another cellulose chain (O-3 ) (Klemm et al. 1998). Under this situation, all the cellulose chains lie parallel, hydrogen-bonded edge to edge to form a sheet and the sheets are then stacked on top of one another along the microfibril with a stagger. At the same time, hydrophobic bonding has been suggested to link the cellulose sheets because with the polar hydroxyl groups ranged along the edges of each ribbon-like chain, its upper and lower faces are relatively nonpolar (Jarvis 2003). In addition, weak hydrogen bonds formed between C–H from one cellulose sheet and O from the next have also been proposed to hold sheets of cellulose chains together in a stack (Nishiyama et al. 2002, 2003). Besides the native cellulose, several other crystal morphologies are observed and these are generally referred to as cellulose II, IIII , IIIII , IVI , IVII . Much research has been done on the structure and morphology of these forms of cellulose (Brown 1982; Marchessault and Sundararajan 1983; O’Sullivan 1997; Sjostrom 1981; Sugiyama et al. 1991; Walton and Blackwell 1973; Wolfrom 1967). The primary difference between these morphologies is slight differences with respect to hydrogen bonding patterns. The hydrogen bond system of cellulose II appears to be more complicated than that of native cellulose and results in a higher intermolecular crosslinking density. One intramolecular hydrogen bond at O-3···H-5 -O and two interchain hydrogen bonds at O-6-H···O-2 and O-6-H·O-3 were reported in cellulose II, which is similar to native cellulose. In addition, an extra hydrogen bond was also added in cellulose II over native cellulose, in the form of an inter-sheet interaction between O-2-H and O-2 (Ishikawa et al. 1997; KroonBatenburg and Kroon 1997; Okano and Sarko 1980). Cellulose IIII has intramolecular hydrogen bonds between O-3-H···O-5 and 2-O···H-6 -O and intermolecular associations between 3-O···H-6 -O as in native cellulose. For polymorphs IVI and IVII , in addition to the usual two intramolecular hydrogen bonds present in most of the other crystalline celluloses, there seem to be intermolecular bonds of O-6·H-2 -O (Kennedy 1987; O’Sullivan 1997). Cellulose occurs in almost pure form in cotton fiber while it is coming led with lignin and hemicellulose in other plant fibers (Kalia et al. 2011). Hemicellulose comprises a group of polysaccharides with several different sugar units, exhibiting much lower degrees of polymerization than cellulose with a considerable degree of chain branching (Bledzki and Gassan 1999). Different plant fibers have different constituents of hemicellulose (Nevell and Zeronian 1985). Lignins are three-dimensional hydrocarbon polymers with complex aliphatic and aromatic constituents. The main functional/building blocks of lignins are often referred to as phenylpropane units with different linear side chains attached to the phenyl rings. The detailed structure of lignin is still under investigation and some structures have

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been proposed (Heitner et al. 2016). In addition to the three major constituents cellulose, hemicellulose, and lignin, plant fibers include a small amount of pectin, wax, inorganics, and others. Depending on the plant species, growth climatic conditions, age, and fiber extraction process, the chemical compositions vary among different cellulose fibers. In Table 6.1, the mean values of the three major constituents in representative plant based fibers are presented in weight percentage (wt.%) (Faruk et al. 2012b; Rowell 2012). 2.

Fiber structure

Cellulose fibers can be extracted as partial, individual or bundles of thick-walled plant cells. These cells are non-living and elongated in shape with the long axis aligned with plant height direction (FPL 2010). Depending on the plants, the cell size can be in micrometers to millimeters (Dufresne 2008; Dufresne and Belgacem 2013; Faruk et al. 2012b). Two main domains exist in most plant cells: the cell wall and the lumen. The lumen is an elongated empty space enclosed by cell walls and is critically responsible for water or nutrient conduction for living trees and plants. The cell wall is the major supporting structure for plants and is highly organized. A typical wood cell wall structure is shown in Fig. 6.2 (FPL 2010). Three layers are included in the cell wall structure: the middle lamella (ML), the primary wall (P), and the secondary wall (S1, S2, and S3) (Fig. 6.2). In each layer, the cell wall Table 6.1 The mean weight percent of the primary constituents of common plant based fibers (Faruk et al. 2012b; Rowell 2012)

Fiber

Cellulose (wt.%)

Hemicellulose (wt.%)

Lignin (wt.%)

Bagasse Bamboo

55.2

16.8

25.3

26–43

30

21–31

Flax

71

18.6–20.6

2.2

Kenaf

70

19

3

Jute

61–71

14.20

12–13

Hemp

68

15

10

Ramie

68.6–76.2

13–16

0.6–0.7

Abaca

56–63

20–25

7–9

Sisal

65

12

9.9

Coir

32–43

0.15–0.25

40–45

Oil Palm

65

–

29

Pineapple

81

–

12.7

Curaua

73.6

9.9

7.5

Wheat straw

38–45

15–31

12–20

Rice husk

35–45

19–25

20

Rice straw

41–57

33

8–19

Softwood

40–45

7–14

26–34

Hardwood

38–49

19–26

23–30

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Fig. 6.2 Schematic of the wood cell wall (FPL 2010)

has the three main chemical components: cellulose, hemicellulose, and lignin. The weight percentage of each component in each layer varies. Cellulose is present as microfibrils embedded in the matrix of lignin in all layers with different alignments to the cell axis in each layer. The branched hemicellulose is thought to function as a compatibilizer helping to bridge cellulose and lignin (FPL 2010; Rowell 2012). The middle lamella layer is the outer most shell of the plant cell and facilitates the bonding among individual cells to form a solid structure of the plant. The primary wall is closely adhered to the middle lamella and cellulose microfibrils are randomly distributed inside it. The secondary cell wall is the thickest part accounting for around 90% among the three layers, and its primary function is to provide structural support for the plants (Célino et al. 2014; FPL 2010). It can be distinguished to be composed of three layers as S1, S2, and S3, based on the alignment of cellulose microfibrils with the long axis of the cell which is also called microfibril angle. The microfibril angle of the S2 layer (5°–30°) is much smaller than those in layers of S1 (50°–70°) and S3 (>70°). Simultaneously, the S2 layer which represents around 70–80% of the secondary cell wall is the thickest layer and mainly determines the properties of the cell wall. This layer also determines the properties of the extracted cellulose fiber properties at a macroscopic level. The microfibril angle of the S2 layer has a strong correlation with cellulose fiber mechanical properties. However, the exact relationship is not fully understood. The aggregation of individual plant cells bonded by the middle lamella layer forms cellulose fibers. Depending on the fiber separation technologies, cellulose based fibers in different size scales can be generated, ranging from micrometers of an individual cell or cell bundles to nanometers of microfibrils. The fiber quality obtained after the fiber separation depends on the chemical composition and morphology of the fiber. Separation of cellulose fiber from original plants can proceed in different routes. Single individual plant cell fibers can be generated from woody plants during the conventional pulping process by dissolving lignin using a thermal treatment method and various chemicals. Wood fibers mostly used in reinforcing thermoplastics are generally composed of cell bundles obtained from the mechanical milling process. A scanning electron microscope image of wood fibers is shown in Fig. 6.3, in which wood fibers in bundles of wood cells can be identified (Oksman Niska and Sain 2008). With the recent development of nanotechnology, cellulose fibers in nanometer size can be commercially obtained. Two major categories of nanoscale cellulose fibers are available: nanofibrillated cellulose (NFC) and cellulose

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Fig. 6.3 Scanning electron micrograph of pine wood fiber (Oksman Niska and Sain 2008)

nanocrystal (CNC) (Peng et al. 2012). NFC is produced by processing dilute slurries of pulp fibers or microcrystalline cellulose through grinding or high-pressure homogenizing action while the production of CNC involves the digestion of amorphous cellulosic domains by acid hydrolysis process. After manufacturing, an aqueous suspension with evenly dispersed cellulose fibers in nano-scale can be obtained. The strong hydrogen bonds between water and cellulose fibers enable the system to remain thermally or kinetically stable over a broad range of water content. The transmission electron microscopy (TEM) micrographs of NFC and CNC are shown in Fig. 6.4. However, these nanometer cellulose fibers can only exist in suspension format and drying them leads to formation of agglomerates which are much larger in size. As a result, the advantages of nano-scale reinforcemtns are lost (Peng et al. 2012). Many research groups have been searching for suitable methods to dry NFC and CNC without agglomeration (Nemoto et al. 2015; Peng et al. 2012; Sinquefield et al. 2020; Voronova et al. 2012). 3.

Physical and Mechanical Properties

Cellulose fibers demonstrate a wide variety of physical and mechanical properties depending on the fiber origin, chemical composition, growth history, moisture

Fig. 6.4 Transmission electron microscopy micrographs of negatively stained NFC (a) and CNC (b) (Peng et al. 2012)

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content, fiber manufacturing process, internal fiber structure, microfibrillar angle, cell dimensions and defects, which vary between different parts of a plant, as well as between different plants (Dufresne 2008; Dufresne and Belgacem 2013; Faruk et al. 2012b). As one of the main chemical components in fiber, cellulose is a stiffer component compared with lignin and hemicellulose and higher cellulose content fiber leads to better mechanical properties. The microfibrillar angle has also a major influence on the mechanical properties of the cellulose fibers. Fibers with a smaller microfibrillar angle have higher mechanical properties along fiber axis. The physical and mechanical properties of some cellulose fibers from different plants are shown in Table 6.2 (Célino et al. 2014; Dufresne 2008; Faruk et al. 2012b). Glass and carbon fibers are added in the table for comparison. A wide property distribution can be seen for cellulose fibers from the Table 6.2. Differences in fiber structure and defects due to the environmental conditions during growth may drive the broad range of mechanical behaviors of cellulose fibers (Dufresne 2008). For fibers extracted from different plants, significant differences are also observed for mechanical properties, including Young’s modulus, tensile strength, and elongation at break. Different mechanical properties measurement methods may play a role for the data reported here. As can be seen, cellulosic fibers with a broad range of properties are available. As expected the modulus and strength are lower than those of glass and carbon fibers but the elongation to break, for most cellulosic fibers, is higher, and the density lower than glass and carbon fibers. The other critical factors contributing to the wide property distribution of the cellulose fibers include the fiber dimensions and separation process. The mechanical properties of cellulose fiber with a bundle structure are significantly lower than that of the individual fiber cell due to the porous structure formed with cell lumen and Table 6.2 Physical and mechanical properties of different cellulose fibers (Célino et al. 2014; Dufresne 2008; Faruk et al. 2012b) Fiber

Density (g/cm3 )

Young’s modulus (GPa)

Tensile strength (MPa)

Elongation at break (%)

Flax

1.54

2.75–85

345–2000

1–4

Ramie

1.5–1.56

27–128

400–1000

1.2–3.8

Hemp

1.47

17–70

368–800

1.6

Jute

1.44

10–30

393–773

1.5–1.8

Sisal

1.45–1.5

9–22

350–700

2–7

Coconut

1.15

4–6

131–175

15–40

Cotton

1.5–1.6

5.5–12.6

287–597

7–8

Nettle

1.51

24.5–87

560–1600

2.1–2.5

Kenaf

1.2

14–53

240–930

1.6

Bamboo

0.6–1.1

11–17

140–230

–

E-glass

2.5

70

2000–2500

2.5

Carbon

1.4

230–240

4000

1.4–1.8

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the weak adhesion between different cells in the middle lamella layer. Therefore, the potential of using cellulose fibers in reinforcing polymer is not fully exploited under the circumstance of using bundle fibers instead of the individual fibers. In reality, most of the applications use fiber bundles rather than individual fibers (Oksman Niska and Sain 2008). For cellulose fibers from wood, the mechanical properties of the fibers increase as the fiber size decreases. The Young’s modulus of bulk wood was reported at about 10 GPa (Bledzki and Gassan 1999; Vincent and Currey 1980). The small size cellulose fibers separated from wood through pulping processes can reach moduli up to 40 GPa (Vincent and Currey 1980). Further subdivision of cellulose pulp fibers by hydrolysis followed by mechanical disintegration into nanofibrils increases the elastic modulus to 70 GPa (Vincent and Currey 1980) or 145 GPa (Beecher 2007).When cellulose fibers are refined to the elementary building blocks in the form of NFC and CNC, the mechanical properties mainly depend on the inter- and intramolecular hydrogen bonds. The intramolecular hydrogen bonds are responsible for the considerable stiffness of the cellulose chain and stabilize the spatial conformation of crystalline cellulose. The intermolecular hydrogen bonds are the predominant factor responsible for interchain cohesion. This interchain cohesion is favored by the high spatial regularity of the hydrogen-bond forming sites and by the involvement of all three hydroxyl groups in the hydrogen-bond network (KroonBatenburg and Kroon 1997). The Young’s modulus of the crystalline domain has been measured by applying uniaxial tensile load along the fiber axis and monitoring the lattice deformation along the chain axis using X-ray diffraction. The obtained values of Young’s moduli are in the range of 115–140 GPa (Ishikawa et al. 1997; Matsuo et al. 1990; Nishino et al. 1995; Sakurada et al. 1962). All the results were obtained based on the assumption that the stress on each crystallite is in general considered to be identical to the stress applied to the macroscopic sample. The theoretical evaluation of the elastic moduli of crystalline cellulose in native form has also been conducted and the results showed that the Young’s modulus along the chain axis is about 160 GPa (Tashiro and Kobayashi 1991). A direct measurement of the Young’s modulus was conducted in two directions of a cellulose fiber. In the direction perpendicular to the chain axis the Young’s modulus was calculated as 14.8 ± 0.8 GPa while in the chain axis direction it was reported as 220 ± 50 GPa (Diddens et al. 2008). Due to the extraordinary properties of nano-scale cellulose fibers, there is a huge potential to develop advanced polymer composites using nano-scale cellulose fibers. 4.

Limitations of Cellulosic Fibers as Reinforcements for Polymers

The limitations of using cellulose fibers in thermoplastic polymer composites mainly involve the discontinuous and highly variable nature, anisotropic properties, hydrophilic nature of fibers, dimensional instability, and low thermal resistance. When cellulose fibers are embedded in thermoplastic, one of the major concerns is associated with poor adhesion between fibers and matrix (Bledzki and Gassan 1999; Célino et al. 2014; Dufresne 2008; Dufresne and Belgacem 2013). In composites, the thermoplastic is a continuous phase and functions as a binder for cellulose fibers, transferring external stress applied to composite to the stronger cellulose fibers. The

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poor adhesion between cellulose fibers and matrix would jeopardize the reinforcing effect of the fibers and the desired composites properties will not be achieved. Many factors affect the adhesion between cellulose fibers and thermoplastic matrix. The hydrophilic nature of cellulose fibers, due to many hydroxyl groups on each cellulose chain, is a major cause of poor adhesion between fibers and matrix. Several surface modification strategies have been developed to increase the compatibility between cellulose fiber and matrix and the detail is summarized in Sect. 6.5 of this chapter. In addition to the low compatibility between cellulose fiber and matrix, water absorption of cellulose fibers during the service life of composites generates wollen fibers, resulting in differential deformations between fibers and matrix. These leads to internal stress, especially at the fiber and matrix interface. The moisture absorption and desorption cycles of cellulose fibers leading to cycles of fiber swelling and shrinkage can lead to void formation and degradation of composite properties and their durability. Another concern of using cellulose fibers to reinforce thermoplastic is related to the variability of their properties depending on fiber origin, separation process, physical property, and geographical difference. As shown in Sect. 2.3, these factors influence the properties of the fibers and hence the composites. Therefore, the use of different cellulose fibers increases the complexities of composite design, manufacturing, and characterization. Fibers extracted from different parts of the same plant also showed different mechanical properties (Charlet et al. 2007). The low thermal resistance of cellulose fibers poses another challenge to develop thermoplastic polymer composite. In general, thermoplastic composites are commonly processed by melt compounding, extrusion, and injection molding. When cellulose fibers are included in the system, the processing temperature of composites is restricted at about 200 °C because cellulose based materials start to degrade near 230 °C. Even for pure cellulose, the most thermally stable constituent in the cellulose fibers, the glass transition temperature is in the range of 200–230 °C, and the thermal decomposition starts at about 260 °C (Gardner et al. 2008; Goring 1963).

6.3 Polymer Matrices and Additives Many thermoplastics have been used as matrices to manufacture fiber reinforced polymer composites. When using conventional reinforcements, such as glass fiber, carbon fiber, talc, many polymers, including high performance thermoplastics, can be used. However, due to the low thermal resistance of cellulose fibers, thermoplastics with processing temperature lower than the thermal degradation temperature of cellulose fibers are required. As a result, the most common commercial thermoplastics as matrices with cellulose fibers are polyethylene (PE) (Li and Wolcott 2004; Santi et al. 2009), polypropylene (PP) (Ferreira et al. 2021; Wang et al. 2020, 2021), poly (vinyl chloride) (PVC) (Hoang et al. 2018; Nadali and Naghdi 2020), and polystyrene (PS) (Adeniyi et al. 2021; Ling et al. 2020; Tawfik et al. 2020). At the research stage, cellulose fibers reinforced engineering thermoplastics, such

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as nylon and polyethylene terephthalate (PET), have also been studied (Chen and Gardner 2008; Peng et al. 2016b; Rahman et al. 2013). In addition, renewable and bio-based polymer matrices play an active role in the research community for the development of cellulose fiber reinforced thermoplastic composites. The studied bio-based polymer matrices include thermoplastic starch (Cobut et al. 2014; Yin et al. 2020), poly (lactic acid) (PLA) (Behalek et al. 2020; Rasheed et al. 2021; Zhang et al. 2021), polycaprolactone (PCL) (Aguiar and Marques 2016, 2018), polybutylene succinate (PBS) (Mochane et al. 2021), and polyhyroxy alkanoates (PHAs) (Bhardwaj et al. 2014). The development of cellulose fiber reinforced bio-based polymer composites helps to reduce our dependency on petroleum products. In addition, the entire composite is biodegradable, eliminating the environmental pressure posed by plastic pollution. There are some limitations when bio-based polymer matrices are used. In most cases, the properties of the bio-based polymers are inferior to petroleum-based polymers. The composite manufacturing process is also designed for petroleum-based polymers and needs to be adapted for processing bio-based polymers. Knowledge accumulation for processing bio-based polymers takes time. The current high cost of the bio-based polymer and a limited shelf life of the composites are also concerns for the industry to adapt this category of material. A wide variety of additives are used in the composite formulation for manufacturing cellulose fiber reinforced thermoplastic composites. The most common additives include lubricants, coupling agents, stabilizers, biocides, density reduction additives, and flame retardants. The choice of additives depends on the final applications of the composites (Oksman Niska and Sain 2008). As an example composite formulation, with important additives, based on cellulose fiber and PE matrix system is shown in Table 6.3 (Oksman Niska and Sain 2008). Lubricant is a chemical used to change the flow of composite during a thermal compounding process and different names have been used interchangeably, such as process aid, anti-stick, slip agent (Adhikary et al. 2011; Dai et al. 2019; Harper and Wolcott 2004; Manka 2002; Oksman Niska and Sain 2008). Determined by the functionalities of lubricant, internal and external lubricant can be categorized. External lubricant is not compatible with composite melt and migrates to the composite melt surface during processing, helping to release the composite from metal dies. Internal lubricant is compatible with the composite melt, facilitating the improvement in processing and output by lowering the composite melt viscosity. The importance of lubricant can be shown in Fig. 6.5f or extruded wood fiber based polymer composite (Oksman Niska and Sain 2008). Melt fracture can be observed in a high throughput extrusion process if no lubricant is included in the formulation. Coupling agent is used in a composite manufacturing process to increase the bonding strength between polymer matrix and cellulose fibers (Ling et al. 2020; Liu et al. 2019; Poletto 2020; Ranjbarha et al. 2021). It also belongs to one of the strategies used to modify cellulose fiber surface and will be covered in detail in the Sect. 6.5 of this chapter. Stabilizers included in the composite formulation are to minimize the quality degradation of composite from the beginning of composite manufacturing to end of its service life. The two most common stabilizers are antioxidants and

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Table 6.3 Composite formulation of cellulose fibers reinforced PE (Oksman Niska and Sain 2008) Function

Material

Loading level (wt.%)

Matrix

PE

Balance such that total % adds up to 100%

Reinforcement

Cellulose fiber

30–60

Coupling agent

Maleated polyolefin

2–5

Lubricant(s)

Stearates/esters/other

3–8

Antioxidants

Phenolics/phosphites

0–1

Acid scavengers

Stearates/hydrotalcites

0–1

UV protection

Benzophenones/benzotriazoles

0–1

Mineral filler

Talc

0–10

Biocide

Zinc borate

0–2

Density reduction

Microspheres/chemical or physical blowing agent

0–5

UV protection

Pigments

As required

Flame retardants

Various

As required

Fig. 6.5 Extruded wood fiber reinforced thermoplastic composites with and without lubricant (Oksman Niska and Sain 2008)

UV stabilizers. Antioxidants are mainly designed to prevent and minimize thermal degradation of polymer matrix during the thermal processing. Traditional antioxidant chemistries are phenolics, phosphates, and thioesters (Ab Ghani and Ahmad 2011; Oksman Niska and Sain 2008). The antioxidants, simultaneously, could also slow down the degradation of composite at the end of life of the composite (Peng et al. 2014). UV stabilizers are mainly used in composite formulation for outdoor applications. UV radiation can initiate photochemical degradation of polymer long chains and generate radicals. UV stabilizers can function in three different ways to control the degradation. UV blocker can block the UV penetration, protecting the main body of the composite; UV absorber competitively absorb UV lights, diminishing the UV radiation that interacts with the composite; and radical scavenger, trapping radicals generated by UV radiation before they can harm the matrix. Due to the inclusion of cellulose fibers, outdoor applications of the reinforced thermoplastic composites have a risk of biological degradation. The chemical components of the fibers provide a good source of food for a variety of biological organisms including fungi and bacteria. The required conditions for the biological degradation

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include suitable temperature and moisture content. Cellulose fibers are hygroscopic, easily absorbing moisture from atmosphere. As a general rule, fungal decay starts at around 20% moisture content (Naghipour 1996). This condition can be achieved for wood fibers for the outdoor applications under long-term service or marine exposures, providing the necessary conditions for biological attack. In this case, antimicrobial additives are required for products designed for long-term service. An inorganic biocide, for example, zinc borate, is used at a loading level of 8 wt.%) due to the extraction of the excess noncellulosic compound, which reduced the strength of hemp fiber. According to different studies, different

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Table 6.5 Surface modification by silane group and its impact Fiber-matrix composites

Treatment conditions

Key results after surface modification

References

Cellulose-PVC

Surface treatment is carried out in a solvent-free system by spraying and mechanical mixing by 0.1% silane

Treated cellulose fibers form chemical bond with PVC Improves the tensile strength of the composites significantly

Matuana et al. (1998)

Pineapple fiber-PE

Dried fibers are mixed with silane (4 wt.%) and heated under reflux for 2h

Composites are more George et al. (1996) mechanically and thermally stable than the untreated fiber

Banana fiber-polyester Fibers are treated with Silane modification alkali before silanization has improved the for better results storage modulus of the composite

Pothan and Thomas (2003)

Cellulose fiber-PVS and PS composites

Silane solution is sprayed Significant increases Beshay and Hoa over dried fiber and kept in the tensile strength (1990) for several hours at 60 °C of the composites

Wood fiber-PE

Fibers are pretreated with alkali solution (2 wt.%) and then treated with silane (0.01 wt.%)

Improve the tensile strength of the composite

Henequen fibers-HDPE

Alkali treatment followed by silane treatment for better interlocking with matrix

Fiber-matrix Valadez-Gonzalez adhesion is enhanced et al. (1999) by silane treatment

Pineapple fiber-polyester

The fibers are treated 0.3% solution of silane

Significant (40%) increase in tensile strength of the composites 7% increase in flexural strength

Pickering et al. (2003)

Devi et al. (1997)

fibers require different concentrations and times of exposure with NaOH solution to get improved results (Asumani et al. 2012; Bachtiar et al. 2008; Gomes et al. 2007). For example, the tensile strength of the coir fiber-reinforced PBS/PE composites decreased with alkali treatment (5% NaOH solution) for more than 72 h soaking time of the fibers (Moon et al. 2011; Prasad et al. 1983). Acetylation reaction. Acetylation, also known as esterification, is another kind of chemical process for modifying natural fibers. The process involves the reaction of acetyl groups (CH3 CO–) with the hydrophilic hydroxyl (–OH) groups which are found in natural fibers and takes out the existing moisture. Therefore, the fibers are more dimensionally stable since they are less hydrophilic after the reaction (Sreekala

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(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(l)

Fig. 6.7 SEM images of natural fibers with various surface treatments: a Jute without treatment; b Jute alkaline treatment; c Jute mixed alkaline and silane treatment; d Ramie without treatment; e Ramie alkaline treatment; f Ramie mixed alkaline and silane treatment; g Sisal without treatment; h Sisal alkaline treatment; i Sisal mixed alkaline and silane treatment; j Curauá without treatment; k Curauá alkaline treatment; and l Curauá mixed alkaline and silanetreatment (de Araujo Alves Lima et al. 2020)

et al. 2000). The treatment also provides rough surfaces with less void content that allow better mechanical interlocking with the matrix (Beecher 2007; Tserki et al. 2005). Fibers are first soaked in acetic acid and then treated with acetic anhydride between 1 and 3 h at a higher temperature. The general form of acetylation reaction with and without catalyst are shown in Fig. 6.9 (Mwaikambo and Ansell 1999). Rowell et al. (2004) found that treatment with acetic anhydride improved the water resistance of different natural fibers by removing hemicellulose and lignin

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Fig. 6.8 Tensile strength of single fibers as a function of surface treatment (de Araujo Alves Lima et al. 2020)

Fig. 6.9 Schematic for acetylation reaction (Mwaikambo and Ansell 1999)

constituents from the treated fiber. Also, the thermal properties of the flax fiber is enhanced after the treatment of acetylation (Bledzki et al. 2008). Table 6.6 summarizes the effect of surface modification involving acetylation reaction and key improvements of the properties of the composites. Peroxide treatment. The interaction between hydrophobic matrix and hydrophilic cellulose can be improved by different peroxide treatments. Out of various peroxides, benzoyl peroxide (Kaushik et al. 2012), alkaline peroxide (Peng et al. 2016a), hydrogen peroxide (Razak et al. 2014), and dicumyl peroxide (Razak et al. 2014) are very common for surface modification. Peroxides tend to decompose easily and form

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Table 6.6 Surface modification by acetylation group and its impact Fiber-matrix composites

Treatment conditions

Key results after surface References modification

Flax fiber-PP

Acetylation of flax fiber is carried out by acetic anhydride and small amount catalyst perchloric acid (60%) at 60 °C for 1–3 h

Reduced moisture absorption 18% degree of acetylation shows highest tensile and flexural strength (25% improvement) as compared to untreated fibers

Bledzki et al. (2008)

Biofiber/glass-Polyester resin

Alkali treatment followed Reduced moisture by acetylation containing absorption H2 SO4 for 5 min Better fiber-matrix bonding and improved flexural strength

Mishra et al. (2003)

Sisal fiber-PS

Alkali treatment (18%) followed by acetylation in presence of H2 SO4 catalyst

Better mechanical Nair et al. interlocking by (2001) introducing rough surface and voids Thermal stability of the composite is enhanced than untreated fibers Improved storage modulus

free radicals, which react with the hydroxyl group of the fiber and with the matrix. As a result, good fiber matrix adhesion along the interface occurs. Moreover, the treatment reduces the moisture absorption capacity and enhances thermal stability (Beecher 2007). The reaction scheme for cellulose fibers and PE matrix composite in the presence of peroxide is given below (Joseph et al. 1996; Paul et al. 1997): R O−O R → 2R O ◦

(6.2)

R O ◦ + P E−H → R O H + P E

(6.3)

R O ◦ + Cellulose−H → R O H + Cellulose◦

(6.4)

P E + Cellulose◦ → P E−Cellulose

(6.5)

The fibers are coated with a certain percentage of peroxide (depends on the type of peroxide) in acetone medium for 30 min after alkali pre-treatment (Beecher 2007; Paul et al. 1997; Sreekala et al. 2002). The alkali pre-treatment removes the unwanted impurities, lignin, and hemicellulose (Ahmad et al. 2019). Table 6.7 summarizes the

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Table 6.7 Surface modification by peroxide group and its impact Fiber-matrix composites

Treatment conditions

Key results after surface modification

References

Sisal fiber-PE

Alkali treated fibers are soaked with a 6% solution of dicumyl peroxide (DCP) in acetone for 30 min

Improved composite tensile strength Hydrophilicity of the fiber decreased

Joseph et al. (1996)

Pineapple fiber-PE

Benzoyl peroxide (1 wt.%) and DCP (0.5 wt.%) is added in the melted PE and then mixed with fibers

Composites are more George et al. (1996) mechanically and thermally stable than the untreated fiber

effect of surface modification involving peroxide treatment and key improvement of the fiber-matrix composites. Maleated coupling agent. Maleic and Succinic anhydride grafting provide efficient way to enhance the fiber-matrix interface (John and Anandjiwala 2008; Mohanty et al. 2001; Singha et al. 2009). Plastics manufacturers use this technique to improve adhesion at the interface between two immiscible substances (Pradipta et al. 2017).The same technique has been used to enhance the interaction between fiber-matrix interfaces (Amor et al. 2014; González-López et al. 2018).Unlike other chemical methods, maleic anhydride is used to modify the fiber surface and modify the polymer matrix for better interfacial bonding (Gassan and Bledzki 1997; Joseph et al. 2003; Van den Oever and Peijs 1998). Anhydride groups have a high reactivity that can attach chemically to hydroxyl groups in cellulose fibers, improving the interaction between the matrix and fibers (Hong et al. 2008). The schematic of the reaction is shown in Fig. 6.10. It is reported that the efficiency of maleic type functionality is better than succinic treatment towards the improvement of fiber-matrix interaction Reddy et al. (2013). Table 6.8 summarizes the effect of surface modification involving maleated coupling treatment and key improvement of the fiber-matrix composites. The maleic acid anhydride copolymerized with propylene is referred to as MAA-PP. Acrylation treatment and acrylonitrile grafting. Acrylic acid (CH2 =CHCOOH) is also used to enhance interfacial bonding between the natural fiber and polymer matrix. The carboxylic group from coupling agents form ester linkages with the cellulose hydroxyl groups. Therefore, fibers with hydrophilic hydroxyl groups are reduced from the structure and are more resistant to moisture (Kabir et al. 2012). For this technique, alkali-treated fibers are immersed in acrylic acid for 1 h at high temperatures, washed in an aqueous alcohol solution, and oven-dried (Beecher 2007). The reactions between fiber-OH groups and acrylic acid are given in Eq. (6.6). Fiber − OH + C2 H3 COOH → Fiber − OOC2 H3 + H2 O

(6.6)

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Fig. 6.10 The reaction of cellulose fibers with hot MAA-PP copolymers (Bledzki et al. 1996) Table 6.8 Surface modification by maleated coupling group and its impact Fiber-matrix composites

Treatment conditions

Key results after surface modification

References

Jute fibers-PP

Maleic anhydride grafted PP as a coupling agent for the surface modification of jute fibers

Nearly 72.3% increase in flexural strength Significant decrease in the water absorption capacity

Mohanty et al. (2004)

Banana, hemp, sisal fiber–novolac resin

Fibers are treated with 2% maleic anhydride in xylene at 65 °C for 18 h

Reduced water absorption and steam absorption Young’s modulus, hardness, and impact strength increased after treatment

Mishra et al. (2000)

Flax-PP

Maleic acid anhydride propylene is used and compared with pure propylene

Flax-propylene interfacial strength increases by thirty percent for the MAA-PP treatment

Van de Velde and Kiekens (2001)

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Li et al. (2004) reported higher tensile strength properties for acrylic acidtreated flax fiber HDPE composites. The treatment also reduces the water absorption capacity. Similarly, acetonitrile (CH2=CH–CN) is also used to modify the natural fibers. The reaction is shown in Eq. (6.7). Free radicals are generated from acetonitrile to react with cellulose molecules by dehydrogenation and oxidation. Once the free radical sites have been activated, they interact with the matrix monomer and enhances the interlocking efficiency at the interface (Kabir et al. 2012; Kalia et al. 2009). The acetonitrile treatment of sisal fiber reduces the water absorption efficiency up to 25%. It also enhances the composite material’s tensile strength and modulus properties (Beecher 2007). Table 6.9 summarizes the effect of surface modification involving acrylation treatment and acrylonitrile grafting treatment and key improvement of the fiber-matrix composites. Fiber − OH + C2 H3 COOH → Fiber − OOC2 H3 + H2 O

(6.7)

Isocynate treatment. Finally, isocyanate has been used as an effective coupling agent in composites with fiber reinforcements (Joseph et al. 1996; Paul et al. 1997; Sreekala et al. 2000). The hydroxyl groups of cellulose and lignin in fibers react readily with the functional group −N = C = O in isocyanate (Frederick and Norman 2004) (Eq. 6.8). R−N = C = O + HO−Fiber → R−NH − CO−Fiber

(6.8)

where R could be any alkyl or aryl groups. Maldas et al. reported that isocyanatetreated composites have better mechanical properties than silane-treated composites (Maldas et al. 1989). Table 6.9 Surface modification by acrylation treatment and acrylonitrile coupling group and their impact Fiber-matrix composites

Treatment conditions

Key results after surface References modification

Flax fibers-LLDPE

Flax fibers are Higher tensile strength immersed in NaOH is observed for treated solution and then fiber composite soaked in acrylic acid solution and kept 50 °C for 1 h

Abdelmouleh et al. (2004)

Sisal fiber-polyester amide

Graft copolymerization Significant of acrylonitrile on to improvement of tensile 5% NaOH treated and flexural strength fibers are carried out using [Cu+2 –IO4 ] as initiator at 40 °C

Mishra et al. (2002)

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6.5 Mechanical Performance of Cellulose Fiber Reinforced Thermoplastic For polymers, one of the primary reasons for adding reinforcements, to create composites, is to improve the modulus and strength of the polymers. As a result, this section describes the mechanical performance of cellulose fiber reinforced thermoplastic composites. Surface modification of cellulose fibers play a critical role in the characteristics of the composite mechanical properties. 1.

Tensile Properties

Young’s modulus and ultimate tensile strength are the two main properties measured during the tensile test. For untreated fibers, in general, tensile strength decreases with higher fiber content. The weak interfacial area between the fiber and matrix increases with increasing fiber load. Therefore, the tensile strength decreases (Haque et al. 2010a; Karim et al. 2013; Rahman et al. 2008). The interaction between fiber and matrix is different for different fibers and can be improved by surface modifications (Sect. 6.5). For example, banana fiber-reinforced composites exhibited the highest tensile strength, while palm composites showed the lowest tensile strength (Salit et al. 2015). Surface modifications by physical method (like plasma, irradiation, corona and steam explosion) in general improve the roughness of the fiber and increase the wettability and, consequently strength of the composite. Various researchers reported that chemical treatments (like silane, alkali, acetylation, anhydride grafting, and peroxide treatment) are more beneficial than physical treatments regarding increasing the tensile strength of composites (Faruk et al. 2014). The chemical modification of fiber surfaces involves the reaction of different functional groups with the hydroxyl groups, which reduces the hydrophilicity of the fiber surface and improves the compatibility of fiber-matrix interface. Matuana et al. (1998) showed that cellulose fibers with silane treatment significantly enhance the tensile strength of cellulose-PVC composite. Devi et al. (1997) reported around 40% increase in tensile strength after silane treatment for pineapple fiber-polyester composite. Chemical modification by alkali removes lignin, wax, and other impurities, exposes shorter fiber length crystallites and increases the roughness. Therefore, the strength of the composite is improved (Adeniyi et al. 2019; Beckermann and Pickering 2008; Mwaikambo and Ansell 2006). Within the elastic deformation range of both cellulose fiber and polymer matrix, the modulus of the composite can be calculated using the rule of mixture (Bledzki and Gassan 1999; Dufresne 2008). For composites with the same volume fraction of cellulose fiber, the higher the modulus of the cellulose fiber, the higher the modulus of the composite. The Young’s modulus of composite also increases with increasing fiber content (Haque et al. 2010a, b; Karim et al. 2013; Rahman et al. 2008). Surface modification by physical and chemical methods (Mishra et al. 2000; Nair et al. 2001; Pothan and Thomas 2003) also significantly enhances the Young’s modulus of the composite (Rahman et al. 2014; Zaman et al. 2009).

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Flexural Properties

In many applications, the structure is used in flexure (bending). In general, flexural strength and flexural modulus increase with increasing fiber loading. Natural fibers have a high modulus, which means greater stress is required to achieve the same deformation in polymer composites. Increased fiber–matrix adhesion provides increased stress transfer between them (Haque et al. 2010a, b; Karim et al. 2013; Rahman et al. 2008). Surface modification by physical and chemical method creates roughness as well as form chemical bonds between fiber and matrix interface (Devi et al. 1997; Mishra et al. 2003). Therefore, the flexural property is significantly improved (Li et al. 2007; Tserki et al. 2005). Bledzki et al. have demonstrated a 25% increase in the flexural strength of sisal fiber—polystyrene composite by acytalation treatment (Bledzki et al. 2008). 3.

Impact Strength

In engineering, impact strength is measured by how well a material resists fracture or the energy needed to cause a crack to propagate. The impact strength of natural fiber-reinforced polymer composites increases with fiber addition. The properties of fiber, polymer and fiber-matrix interfacial bonding are primarily responsible for impact strength. Fiber agglomeration is increased with high fiber content, resulting in areas of stress concentration. These regions require less energy to propagate cracks. Therefore, proper surface modification of the fibers, which improves the dispersion in the polymer matrix, is required to increase the impact strength. In addition, it also helps to strengthen the bond between fiber and matrix. Surface modification by chemical method significantly reduces the fibers’ hydrophilicity (Joseph et al. 1996). Consequently, fiber fragmentation and disaggregation rate increase and improve the polymer matrix dispersion (Ali et al. 2018; Joseph et al. 1996). Fiber pullout is another cause of impact failure of composites. As the fibers content increases, it takes more force to pull the fibers out. As a result, the impact strength of composite material is enhanced (Haque et al. 2010a, b; Karim et al. 2013; Rahman et al. 2008). 4.

Hardness

The hardness of natural fiber polymer composites generally increases with increased fiber loading. In composites loaded with fiber, hardness is increased due to the increase in stiffness (Haque et al. 2010a, b; Karim et al. 2013; Rahman et al. 2008; Salit et al. 2015).

6.6 Concluding Remarks Cellulose fiber reinforced thermoplastic composite contributes to enhancing the sustainable development of our society in regards of the demand of high performance and high value-added products from bio-based resources. Cellulose fibers can

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be generated from a variety of agricultural and forestry industrial sectors, including residues and wastes. The traditional cellulose fiber reinforced thermoplastic composites continue to mature for various applications including in construction, automotive, and consumer goods and they will find more and more application in the near future, especially with the increasing pressure on sustainability requirement from the society and the legislative organization. This will be especially true with the development of natural fiber reinforced bio-polymer matrix composites. This will lead to fully degradable composites. The goal of developing cellulose fiber reinforced thermoplastic composites is to produce composites possessing high-quality performance, serviceability, durability, and reliability. The incompatibility between cellulose fibers and thermoplastics determines the critical properties of the composites and will remain the key concern in terms of overall composite performance. The chemistry, structure, physical and mechanical properties of cellulose fibers from different origins has been introduced in this chapter. Different types of surface modification for cellulose fibers and composite manufacturing processes have also been summarized in detail. The effect of cellulose fiber surface modification on mechanical behavior of the composites is presented as well. This area will remain an important avenue for research and development. Further comprehensive research is required to overcome the limitations of using cellulose fibers in reinforcing thermoplastics such as moisture absorption, low impact strength, and reduced long-term durability for outdoor applications at different environments. The large variety of cellulose fibers from different origins also pose challenges for manufacturing the composites. Systematic models need to be established to predict the composite behaviors under different service environmental conditions. The low thermal resistance of cellulose fibers limits the flexibility of the melt compounding process in a commercial scale. The throughput of the extrusion process is also restricted due to the thermal stability of cellulose fibers. Significant research is required in developing innovative melt compounding procedures to lower the overall cost of producing cellulose fiber reinforced thermoplastic composites. Finally, the recent explosive growth in research and development on nanoscale cellulose fiber formulation without agglomeration during manufacturing provides further opportunities for developing composite materials with substantial improvement in properties. Acknowledgements YP acknowledges the support for this work by the USDA National Institute of Food and Agriculture, McIntire Stennis project ALAZ00079 and by the Alabama Agricultural Experiment Station. SCM and RKB acknowledge partial support for this work from the US National Science Foundation EPSCoR Program under NSF Award # OIA-1655740. However, opinions, findings and conclusions or recommendations expressed in this chapter are those of the author(s) and do not necessarily reflect those of the US National Science Foundation.

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Chapter 7

Factors Limiting the Application Window of Acoustically Important Natural Fiber Based Polymer Reinforcements and Their Related Control Strategies K. M. Rakesh, Srinidhi Ramachandracharya, and K. S. Nithin Abstract A single natural fiber is a three-dimensional biopolymer and a composite in itself. It consists of cellulose, hemicellulose, and lignin. And these natural fibers are explored for various applications, which include in construction as alternate building materials, in hospitals, offices, and classrooms as acoustical materials, in the automobile industry and home appliances as noise control materials, and so forth. Nevertheless, the widespread commercial applicability of such natural fibers and their composites are often limited, owing to their higher moisture absorption, lesser fire retardancy, and higher microbial growth. This chapter presents a comprehensive view of factors that check the widespread applications of biopolymers rich natural fibers and their allied control strategies.

7.1 Introduction Lately, natural fibers and their composites are being explored extensively towards numerous commercial applications. A few such applications are in the field of construction as alternate building materials, in hospitals, offices, and classrooms as acoustical materials, in the automobile industry and home appliances as noise control materials, and so forth. An increase in the utilization of these natural materials is due to the ever-escalating awareness and concern among researchers and the general public for the need for environmentally friendly green materials and products (Arenas and Asdrubali 2019; Rakesh et al. 2020). Also, such materials offer lower costs, better availability, and renewability. Besides, with its higher recyclability and low carbon emission during fabrication and burning (Pickering et al. 2016; Putra et al. 2018). K. M. Rakesh (B) · S. Ramachandracharya Department of Mechanical Engineering, JSS Science and Technology University Mysuru, Mysore, India K. S. Nithin Department of Chemistry, The National Institute of Engineering Mysuru, Mysore, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_7

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7.2 Natural Fiber Natural fibers are classified mainly into three types, which include plant fibers, animal fibers, and mineral fibers, as depicted in Fig. 7.1. Further, different types of biopolymer-based natural materials, and in various forms (fibers, felts, mats, panels, boards, composites, and so forth) are explored continuously for different commercial applications beginning with building materials to acoustics, ballistic to automobile, and many more. A.

Chemical Composition of Natural Fibers

Natural fibers primarily consist of cellulose, hemicellulose, pectin, lignin, ash, and moisture. Table 7.1. is the representative percentage chemical composition of some plant-based natural fibers, such as straw fiber (rice), cane fiber (bamboo), grass fiber (esparto), wood fiber (coniferous), leaf fiber (sisal), bast fiber (jute), and fruit fiber (coir) in descending order. B.

Effect of Chemical Composition on Physical and Mechanical Properties of Natural Fibers

The chemical composition of natural fiber has a crucial role in deciding their suitability towards noise control applications. The Natural material used for noise control

Fig. 7.1 Classification of natural fibers (Rowell 2008; Saxena et al 2011; Akil et al 2011; Mohanty 2002)

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Table 7.1 Representative chemical composition of some plant-based natural fibers. (Rowell 2008; Jin and Chen 2007; Mwaikambo and Ansell 2006; Bledzki et al. 1996) Fiber

Cellulose

Hemicellulose Lignin

Rice straw

30.3–38.2 19.8–31.6

7.2–12.8 NA

7.8–15.6 4.2–9.8

Jin and Chen (2007)

Bamboo

34.5

26

NA

NA

Mwaikambo and Ansell (2006)

Esparto

Rowell (2008)

20.5

Pectin Ash

NA

Moisture References

33–38

NA

17–19

NA

6–8

NA

Coniferous 40–45

NA

26–34

NA

25% add-on 2. Contains large amount of CO2 3. Less durable finish on treated material 4. Protein based fire retardants are prone to toxic microbes 5. Currently available in lab scale only

Disadvantages

1. To impart adequate flame retardancy > 450 gpl to be used 2. Adversly affects physical and chemical properties of the material

1. Eco friendly—obtained from waste plant and animal 1. Easily available in market source 2. They contain nitrogen, phosphorous sulphuretc, helps to catalos dehydration of treated cellulosic material. As a result, there in increase in LOI (limiting oxygen index) and enhanced char formation

Advantages

DNA extracted from Herring sperm & testis

Silanosol Nanoclay

Hydrophobin

1. Treatment deposition is not uniform 2. Treatment is not durable for washing or rubbing

1. Lower Add-on % 2. Higher surface area—as they are in nano scale

Carbon nanotubes (CNTs)

Pomegranate rind extract (PRE)

PROBAN (tetrakishysroxymethylphosphonium chloride)

Whey Protein

Nano titanium dioxide (TiO2)

Banana pseudo stem sap (BPS)

Pyrovatex (n-methylol dimethyl phospho-propionamide)

Casein

Nano-based fire retardant

Spinach Juice

Commercial fire retardants Protein based

Plant based

Natural fire retardant

Table 7.4 Various fire retardant materials, their advantages and disadvantages (Mohsin and Malik 2018 and Basak et al. 2018)

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Table 7.5 Micro-Organism Growth Preventive Materials (Banks et al. 2014 and Maia and Moore 2011) Plant- based natural agents

Waste Plant Extract Synthetic Compounds

Metal & Metal Oxide Nanomaterials

Clove Oil

Coconut Shell Extract

Quaternary ammonium compounds

Boron

Cardamom

Pomegranate rind extract

Chlorine—based triclosan

Silver

Tulsi stem

Cationic Polyhexamethylonebiguanide (PHMB)

Gold

Curry leaves

Urea

Titanium Oxide (TiO2)

Neem

Diammonium Phosphate (DAP)

Zinc oxide (ZnO)

Aloe vera

Copper oxide (CuO2)

2005). Biocides such as triclosan, polyhexamethylenebiguanide (PHMB), quaternary ammonium compounds, and silver are currently used as the active agents in anti-microbial commercial textiles as reported by Gao et al. (2008). Nevertheless, to improve the bactericidal functionality of natural fibers, Flaczyk and Walentowska (2008) proposed to apply the ammonium-based ionic liquid with nitrate anion during the finishing process. Also, quaternary ammonium salts are non-toxic for homeothermic organisms besides well known for their high anti-microbial activity (Jacobs 1916), along with ionic liquids are a new group of quaternary ammonium salts discovered (Seddon 1997). Table 7.5 summaries and lists different types of microbial growth prevention materials.

7.6 Concluding Remarks The practical applicability of natural fibers and their composites get restricted by a number of its inherent Physico-chemical properties. Of these, the three major limiting factors, which include higher moisture absorption, lesser fire retardancy, and higher microbial growth. This chapter discusses these three factors in detail with their correlations. With an increase in moisture absorption, there is a reduction in the flammability and mechanical properties of the fibers. Also, the higher moisture content in natural fiber creates a conducive environment for microbial growth. Hence moisture absorptions of natural fibers are to be reduced. One such method is by use of chemical treatment. Once fibers are made more resistant to moisture, then their fire retardancy might be an issue to consider. As these fibers become rough and dried due to chemical treatment they are easily prone to fire. Thus, this issue may be addressed, with the addition of such fire retardant materials to natural fibers, which doesn’t increase moisture absorption and encourages microbial growth. In a sense, the fire retardant material to be used must also possess anti-microbial and moisture resistant

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properties. In this way, such anti-microbial agents are to be selected which exhibit good fire retardancy and moisture resistance besides inhibiting microbial growth. Thus, while choosing a chemical treatment or a fire retardant or anti-microbial agent care must be taken that they are better inhibitors of fire, microbial growth, and moisture absorption. Identifying such chemical treatment, fire retardant material, and an anti-microbial agent is a challenging task, need of the hour.

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Chapter 8

Advanced Functional Polymer-Based Porous Composites for CO2 Capture Ravi Vaghasia, Bharti Saini, and Anirban Dey

Abstract Due to the uncontrolled release of greenhouse gases into the atmosphere through anthropogenic activities, the planet’s temperature and natural ecosystem are being adversely affected globally. Fossil-fueled power plants and transportation are the major sources for the release of CO2 into the atmosphere. Carbon capture and sequestration (CCS) is one of the promising alternatives for CO2 mitigation. To capture this CO2 , highly selective and high storage capacity adsorbent material is required. Also, the adsorbent should be chemically stable, highly porous, large surface area, minimal energy input, easy to regenerate and low cost. Aminebased technology has long been used for CO2 mitigation but this process is very much energy intensive. Physical sorbents with high CO2 selectivity are available in powder form and cannot be used for real-world applications. There is a need to transform it in some particulate form or one can form a porous framework and that can be easily done using polymers and polymers are known to be mechanically, thermally and chemically very stable. Also, polymers due to the presence of abundant functionalizable sites can be functionalized to make the polymer surface rich in CO2 -philic moieties. So, this chapter is focused to highlight various functionalized organic porous polymers and their CO2 uptake capacity, CO2 /N2 selectivity, regenerability and also challenges and potential of this kind of materials in gas separation is finally discussed. Keywords Carbon dioxide capture · Functionalized porous polymer · Gas separation · Adsorption · Selectivity

R. Vaghasia · B. Saini (B) · A. Dey Department of Chemical Engineering, School of Technology, PanditDeendayal Energy University, Gandhinagar, Gujarat 382007, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_8

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Nomenclature List of Symbols BET BHMAA BHMI BisADA CCS CNTs DAC DBN Di Dj FFV GHG GO GPU MBB MOFs OPDA PBO PBI PBZ PEO Pi PI POF POPs Si Sj SNWs TFN Tg TR αij

Brunauer-Emmett-Teller Bis(o-hydroxyl) maleamic acid Bis(o-hydroxyl)-maleimides Bisphenol A type dianhydride Carbon capture and sequestration Carbon nano tubes Direct air capture 1,5-Diazabicyclo [4.3.0]-non-5-ene Diffusion coefficient of gas CO2 Diffusion coefficient of another gas (N2 , H2 or CH4 ) Fractional free volume Greenhouse gas Graphene oxide Gas Permeation Unit Molecular building blocks Metal organic frameworks 4,4 -oxydiphthalic anhydride Polybenzoxazole Polybenzimidazole Polybenzothiazole Poly (ethylene oxide) Permeability of species i Polyimides Porous organic framework Porous organic polymers Solubility coefficient of gas component CO2 Solubility coefficient of another gas (N2 , H2 or CH4 ) Schiff base networks Thin film nanocomposite Glass transition temperation Thermally rearranged Ideal selectivity of species i over j

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8.1 Introduction Combustion and nonfuel applications of carbon fuels account for about 83% of greenhouse gas (GHG) emissions. Rising fossil fuel usage and related combustion product emissions have led to major environmental consequences like global warming and climate change. Thus, the scientific community has focused its efforts on restricting the emission of carbon dioxide into the environment which is the primary source accounting for GHG emissions (Karanikolos 2020; Kontos et al. 2014; Seul-yi and Park 2014; Mittal et al. 2015; Darunte et al. 2016; Iqbal et al. 2017; Bae and Snurr 2020; Mathai et al. 2020). Such impact could be mitigated by using high-efficiency collecting and storing strategies or by adopting better environmentally friendly (green) sources of energy. CO2 is extensively present in the air is continually rising quantities that presently surpass the 409 ppm (2019) mark among the primary combustion flue gas elements, especially CO2 , SO2 , N2 O, N2 and unburnt fuel (Luo and Zhong 2011; Olivares-Marin and Maroto-Valor 2012; Dillon et al. 2015; Mittal et al. 2015; Mathai et al. 2020). Industrial chemical processes, oil and gas refineries, along with naturally occurring volcanic eruptions, have also indeed lead to the increase in CO2 levels (Shen et al. 2017). Carbon capture and sequestration (CCS) seems to be the most promising methods for reducing CO2 build-up in the atmosphere and its harmful consequences, and they frequently provide a good balance of cost and performance (Dzubak et al. 2012; Man et al. 2008; Mikkelsen et al. 2010; Mathai et al. 2020). One of the principal applications for the capture of CO2 is mainly to be a larger point of sources available. Fossil fuel based powerplants, fuel process plants, industrial power plants, production of steel, iron materials, cement and some chemicals etc. are some major point sources of CO2 .Capturing CO2 directly from smallscale sources like transportation/mobile sources, commercial sectors and residential building sectors, might be expensive, more complex and difficult when compared to other large kinds of sources. It is very challenging to capture CO2 from the ambient air of the atmosphere as the concentration of CO2 is likely to be more than 100 ppm, and in flue gas, it is about 380 ppm. The most cost saving and effective method to capture CO2 from the air with the help of increasing rate of biomass growth (Kim et al. 2017). In general, three types of basic systems are used to capture CO2 from fossil fuels plants and/or biomass plants are post-combustion carbon capture, pre-combustion carbon capture and oxy-fuel combustion. Among which post-combustion capture is by far the most frequently used CO2 capture technique, owing to its adaptability as well as the ease with which it can be adapted to pre-existing fossil-based power plants. Capturing CO2 from the surrounding atmosphere, also known as direct air capture (DAC), is a new technique that can accomplish point source capture by capturing CO2 from both isolated and dispersed locations and canalso handle residual emissions. DAC does have capability to improve or reduce atmospheric CO2 levels in a myriad of contexts. DAC includes compensating the emissions by mobile sources, being suitable for remote storage facilities, reclaiming leaked CO2 and assisting in the

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revelation of negative levels of emission (Kim et al. 2017; Shi et al. 2019; Wijesiri et al. 2019). A lot of work has been done showing that CO2 may be captured successfully using absorption, membrane separation, cryogenic distillation methods and adsorption (Favvas et al. 2019; Iqbal et al. 2016; Labropoulos et al. 2015; Perdikaki et al. 2015; Rao and Rubin 2006; Sakpal et al. 2012; Tzialla et al. 2013; Zainab et al. 2017). The application of CO2 capture by aqueous amine scrubbing in industrial operations such as syngas refinement, H2 S elimination, and a variety of other process schemes has made it a widely acknowledged technique. However, due to the high heat of sorption associated with CO2 , the high heat capacity of water, as well as the related necessity of high regeneration temperatures, the desorption and regeneration of collected CO2 using these liquid amine processes is an energy expensive operation. This huge increase in regeneration energy contributes to a major operational cost to the CO2 capture system, as well as a major carbon impact. Furthermore, in such traditional aqueous amine approaches, disadvantages like equipment corrosion, restricted capability for raising amine content, high diffusion limiting process and amine leaks in the surrounding are common. Because of amine leakage, photooxidation of amines as in presence of ambient oxidants, and indeed the subsequent production of compounds including nitramines, amides and nitrosamines the environmental effect of CO2 separation schemes based on amines seems critical. Such chemicals can have a negative impact on one’s health as well as represent a threat to the environment. Nitrosamine, for example, is hazardous at extremely small doses and has the potential to induce cancer, mutagenicity, and reproductive consequences (Karl et al. 2011; Nielsen et al. 2012). To address the aforementioned problems, extensive efforts have been made to create innovative solvents and solvent combinations with lesser volatility, greater thermal stability, limited corrosive properties, low degradation rates, and cheaper regenerative costs. An adsorption is a desirable option because it uses little energy for regeneration, has a high capture capacity and selectivity, is easy to operate, is cost effective, and causes a minimal effect on the environment (Choi et al. 2009; Sayari et al. 2011; Samanta et al. 2012; Xian et al. 2015; Nigar 2016; Pan et al. 2016; Mathai et al. 2020). Once CO2 gets into touch with a solid sorbent, either by weak physical contacts or strong chemical bonds, surface-dominated adsorption occurs. The physisorption or physical adsorption is primarily caused by electrostatic or van der Waals forces. While chemisorption or chemical adsorption is mostly caused by chemical bonding (Eames and Kale 1998; Yang 1997; Alessandro et al. 2010; Bhown and Freeman 2020; Mathai et al. 2020). This collected CO2 can subsequently be dissociated in the regeneration stage and used for subsurface sequestration, fuel and chemical conversion, enhanced oil recovery and other applications (Man et al. 2008; Meth et al. 2012; Zhang et al. 2016). Adsorbents’ unsatisfactory performance in terms of adsorption capacity and selectivity under lower partial pressure circumstances has been one of the disadvantages (Mittal et al. 2015). This is exacerbated in the presence of water since water can inhabit active sites or jeopardize the stability of adsorbent materials (Chaffee and Verpoort 2007). Adsorbent functionalization has garnered a lot of interest as a way to solve these problems (Didas et al. 2015; Drage et al. 2008; Mathai

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et al. 2020; Zhang et al. 2016). The inclusion of numerous amine-containing basic moieties into porous solid adsorbents, for instance, has been reported to significantly improve the CO2 capture capacity via chemical means, resulting in the formation of carbamates and bicarbonates when CO2 interacts with the amine in anhydrous and hydrous conditions, respectively (Xian et al. 2015; Darunte et al. 2016; Shen et al. 2017). There are four techniques that can help reduce CO2 emissions from the vast number of power plants necessary to satisfy the rising demand. The first step is to cut down on carbon emissions. The second goal is to make power generation cycles more efficient. The third step is to research and develop novel power generation processes including oxy-combustion and chemical looping. The fourth goal is to create innovative and cost-effective capture systems that can be scaled up to meet the needs of the non-power and power sectors.

8.2 Thermo-Kinetic Aspects of CO2 Adsorption The thermodynamic and kinetic concepts of CO2 adsorption are essential for understanding the thermodynamic and kinetic components of CO2 adsorption. 1.

Thermodynamic principles

In contrast to high-pressure CO2 adsorption on porous materials, which is driven by adsorbate-adsorbent interactions, low-pressure CO2 adsorption is dictated by adsorbate-adsorbent interactions as well as significant CO2 chemical affinity (Millward and Yaghi 2005; Zhao et al. 2015). The BET (Brunauer–Emmett–Teller) method, which uses apparent free adsorption enthalpy with specific surface area among essential parameters, successfully explains gas adsorption on porous surfaces for the very first time (Emmett 1936). This enthalpy of adsorption is directly proportional to polarizability/polarity of the adsorbate gas as well as the adsorbent material when addressing the adsorbate-adsorbent van der Waals interactions and disregarding particular chemical bonding. Unless an adsorbent material possesses high polarizability, which makes van der Waals interactions less exclusionary but also has strong selectivity above other adsorbent materials regulated mostly by the difference in polarity of adsorbents, it’ll be a possible choice for all adsorbate molecules. CO2 has a little greater polarizability (26.3 × 10–25 cm2 ) than N2 (17.6 × 10–25 cm2 ), and its quadrupole moment (13.4 × 10–40 C m2 ) is slightly larger than N2 (4.7 × 10–40 C m2 ), although this contributes significantly to just the interactions at typical surfaces. These basics are always worth knowing, even if they seem ubiquitous (Alessandro et al. 2010). The second part, in addition to adsorbate-adsorbent polarisation interactions, is the morphological triggering of the pore size of the adsorbent. Because the BET model only considers smooth straight surface, whereas adsorbate molecules are adsorbed and fits into the pores. This results in a larger bonding interface and significant polarisation interactions between adsorbate and adsorbent. Aside from that, there’s

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the molecular sieve influence, which states that perhaps a pore should be large enough to accommodate the adsorbent molecules, otherwise the inner surface will be difficult to reach. It’ll be covered in more detail in the section on kinetic principles. Because CO2 does have a significantly different kinetic diameter than other gas molecules, this same mechanism of molecular sieving obviously assists in the efficient separation of CO2 /O2 , CO2 /CH4 , CO2 /H2 , and CO2 /N2 . The pore size and kinetic diameter discrepancy seems to be a possible source to attain exceptional selectivity during gas separation, and so it is recognized for hydrate ion adsorption into the carbon pores mostly in the vicinity of an electrical charge, which is referred to as ion sieving (Arruda et al. 2013; Noked et al. 2009). When it comes to CO2 capture, pore size engineering is commonly used (Wang et al. 2012; Arruda et al. 2013; Oschatz et al. 2015). In comparison with super-micropores (0.7–2 nm) or mesopores (40 nm), ultramicropores (0.5–0.7 nm) having large surface area and substantially high pore volume must be available for high CO2 adsorption capability. Furthermore, it should be also noted thattheadsorption ability o4f several trace gases, particularly H2 O and O2 , rises at small pore sizes. Because of its low working load during dynamic processes, theoverall enthalpy of adsorption in van der Waals systems is generally very low and due to that CO2 capture saturation occurs at room temperature and between 0.1– 0.2 bar CO2 partial pressure. A difference of adsorption uptake between adsorption and regeneration settings is much more important than uptake at lower temperatures or higher pressures as in the case of the continuous cyclic process. In other terms, CO2 adsorption isotherms with a convex curve are preferable. When a cyclic process is driven with temperature fluctuation rather, a high apparent sorption enthalpy is advantageous once again. Typical entropy work for raising up gas at 400 ppm to the bulk density porous material is about (19.5 kJ/mol). This the least energy dissipation as well as the minimal heat of adsorption to run the system in a continuous cycle, irrespective of heat management optimization. The loss of energy, obviously, will add a significant cost to the CO2 capture equipment. One such comparable factor applies to a thermodynamic limit, where selectivity of 1500 equates to an 18 kJ/mol disparity in the enthalpies of adsorption of two sorbents. For facilitating Rubisco-like binding, for instance, if 30 kJ/mol is required for binding O2 then CO2 would bind at 48 kJ/mol. As a result, several surfaces functionalizing techniques were developed in order to induce particular adsorbate-adsorbent interactions in order to improve CO2 selectivity (Hao et al. 2010; Kim et al. 2017; To et al. 2016; Vaidhyanathan et al. 2014; Yunfeng Zhao et al. 2012). For selective CO2 collection, such tests in thermodynamic constraints are required. 2.

Kinetic principles

Aside from pore diameter engineering and morphological concepts for creating particular interactions amongst CO2 molecules and adsorbent pores, size exclusion, also called molecular sieving, is another method to obtain CO2 separation selectively. A pore diameter higher than the CO2 kinetic diameter (3.30) and lesser than that of the competitive components such as N2 (3.64) or O2 (3.45) might potentially be used to selectively separate CO2 from other GHGs. Actual molecular sieving of CO2 has yet to be achieved, or, to put it in another way, many of the sorbents used for CO2

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capture do have a BET surface area of more than 1000 m2 /g so far. In such circumstances, the less selective mechanism, which is invariably van der Waals adsorption, will take precedence (Li et al. 2013). The key obstacle in molecular sieving would be the kinetic diameters of adsorbate molecules whose magnitude is very close to each other. Also, researchers won’t rule out the possibility of finding viable zeolites and MOFs with consistent pore size inside the pertinent range of sizes and fierce adsorbent-adsorbate bindings, and hence enticing molecular traps for CO2 capture. Nevertheless, the existence of moisture is a great disadvantage of zeolites and MOFs since water does have a smaller kinetic diameter (2.65 Å) than CO2 (3.3 Å), and therefore the competitive affinity for CO2 adsorption would rise simultaneously with the affinity of water. Another important element to highlight in the view of adsorption kinetics/pore diffusion is the rate of adsorption. For example, it is well noted how zeolites’ pores create an issue while catalytic operations and gas separation. In most cases, extra pores for transport are being added to try to solve the problem (Christensen et al. 2008). Conversely, the increment in thesurface area caused due to inclusion of these extra transport holes could reduce selectivity at the very same time. As a result, the size and volume of extra transport holes required to completely use the whole volume of pores for successfully collecting CO2 in an acceptable period remain a mystery. The features and circumstances of an adsorption process (such as temperature, contact time with the adsorbent and other gas components, CO2 pressure and other gas components) might prescribe the solution to the above issue from a technical standpoint.

8.3 Gas Transport in Polymeric Membranes Membrane-based separation depends upon the capacity of the membrane material to regulate the penetration of various species. A penetrant dissolve inside membrane first, then diffuses along chemical potential gradient and finally desorbs to the downstream side, all propelled by the partial pressure gradient. The solution-diffusion mechanism of transport is a well-accepted theory for gas permeation, where segregation is accomplished by a variation in the quantity of penetrant that dissolves in the polymer and the rate at which the penetrant diffuses through the polymer. CO2 can react reversibly with a Brønsted base, such as KOH, or a Lewis base, such as amine, due to its peculiar structure. Such bidirectional processes were used as a reactive diffusion route for CO2 penetration through the membrane. As a result, a facilitated transport membrane is generally defined as a thin polymer phase having abundant reactive sites. These two gas transport processes are covered in this part as a basic knowledge of the large polymeric membrane materials in the literature given the distinct physical and chemical characteristics. 1.

Solution-diffusion transport mechanism

The lighter gas molecules dissolve in the compact polymer phase initially, then diffuse through the membrane, and finally dissociate in the low pressure downstream

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in the absence of reactive moieties. The permeability coefficient (Pi ), which is the product of thesolubility coefficient (Si ) and the diffusion coefficient (Di ), is the kinetic component of the process (Wijmans 1995). Pi = Si × Di The Barrer is the most widely used unit for Pi, with 1 Barrerequaling 1 × 10–10 cm3 (STP) · cm · cm−2 · s−1 · cmHg−1 . Permeance, which reflects the flow of permeate per unit of permeation driving force, is a more readily quantifiable characteristic of the membrane. Permeance is classically measured in Gas Permeation Units (GPU) (1 GPU = 1 × 10–6 cm3 (STP) · cm−2 · s−1 · cmHg−1 ). As a result, the permeability of a non-porous and homogeneous membrane may be determined by dividing the permeance by the thickness of the membrane. Because mentioning an effective membrane thickness is problematic as in many asymmetric or thin-film composite membranes, due to which the permeability is rarely specified. In other terms, permeance is a practical measure of a membrane’s separation performance in a particular configuration, whereas permeability is an inherent feature of a membrane material (selective layer). The ideal selectivity αij , the ratio of two gas permeabilities, defines the membrane’s separation capabilities. It may also be written as a solubility selectivity (Si /Sj ) and a diffusivity selectivity (Di /Dj ) using Eq. (1). αi j =

Si Di × . Sj Dj

As a result, the variation in solubility and/or diffusivity can be used to accomplish separation. Light gases’ solubility in the polymer is primarily influenced by their condensability and affinity for membrane materials. With rising critical temperature, penetrant condensability rises. The gas molecule diffusion in a polymer is caused by the polymer’s free volume properties. The random mobility of the chain segments and the chain-to-chain spacing enables molecules to diffuse through tiny kinetic diameters (Robeson 2008). By the decreasing kinetic diameter and rising free volume the penetrant diffusivity increases in common polymers. CO2 has a higher solubility than the other gases due to its higher critical temperature. Because of its greater critical temperature, the solubility of CO2 is greater than the other gases. As a result, the solubility selectivity favours CO2 . CO2 ’s kinetic diameter is lower than that of N2 and CH4 , leading to better diffusivity selectivity. Usually, CO2 /N2 and CO2 /CH4 separation membranes have a CO2 -selective characteristic as a result of these two variables. However, in the case of CO2 /H2 , the diffusivity selectivity favours H2 , which is a much smaller molecule. As a result, the polymer design determines the ultimate CO2 /H2 selectivity. CO2 -selective membrane uses CO2 -philic moieties for improving solubility selectivity, whereas H2 -selective membranes, such as PBI-based (PBI— polybenzimidazole) membranes, use glassy polymers having size-sieving capacity. Thermally rearranged (TR) polymers, (PEO)-based polymers (PEO—Poly(ethylene oxide)), polymers of intrinsic micro porosity (PIM), iptycene-containing polymers

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and fluoropolymers are five types of polymers having the potential of selective CO2 separation based on the solution-diffusion process (Dong et al. 2013). 2.

Facilitated transport mechanism

The reversible interaction between thepenetrant and reactive carriers can improve mass transfer in assisted transport membranes (Goddard and Schultz 1974). The penetrant dissolves in the polymer matrix upstream, where it interacts with a carrier to form a reaction product, analogous to a solution-diffusion transport process. This product formed travels down a concentration gradient if it has sufficient mobility. Also, at downstream, the penetrant’s low partial pressure promotes the reaction product’s reverse reaction, releasing the penetrant and regenerating the carrier. The rate of permeation of the reactive penetrant is substantially increased when Fickian diffusion is added on top of it. Penetrants thatare inert to the carrier, on the contrary, are mainly excluded owing to the unavailability of a reactive diffusion route. CO2 is generally preferred to be selectively separated in CO2 separation procedures due to its acidic character, which allows it to react quickly with basic carriers (Taylor et al. 2011). Despite the fact that a variety of inorganic and organic bases are being utilized as CO2 carriers, much success has been gained by utilizing the rich amine-CO2 chemistry. As a result, the processes of CO2 and amine reactions are simply explored in this section. The significant electrons deficit of the carbon linked to both the strongly electronegative oxygens gives CO2 its reactivity. The amine serves as a nucleophile, or Lewis base, in the primary and secondary amines having a lone pair of electrons on the nitrogen atom, attacking the electrophilic carbonyl group of CO2 to produce a zwitterion. The other amine immediately deprotonates the zwitterion, forming a more stable carbamate ion, resulting in 2 mol of amine from 1 mol of CO2 . Water could hydrate the carbamate molecule at a lower pH level, thereby releasing bicarbonate and a free amine (Denkwart 1978). Because of the carbamate’s stable structure, the hydration process takes a long time. A tertiary amine, which is not like primary and secondary amines, can only function as a Brønsted base, neutralising the carbonic acid produced by CO2 in the presence of moisture. In this reaction, 1 mol of amine is consumed for 1 mol of CO2 . Due to the slower production of carbonic acid, the overall reaction is slow (Kortunov et al. 2015). The movement of CO2 vs other inert light gases via a facilitated amine-containing transport membrane is depicted in Fig. 8.1 (Yanan Zhao and Ho 2012). The amino groups are linked to the polymeric matrix in this scenario, and the CO2 units leap between them (Yanan Zhao and Ho 2012). In nature, this hopping process is guided by the chemical potential gradient originating through carbamate ion concentration gradient (Cussleret al. 1989). Through a dense polymer matrix, the solution-diffusion process governs the movement of non-reactive gases. As a result, a high selectivity between CO2 and gas (N2 , H2 , or CH4 ) may be attained.

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Fig. 8.1 Gas transport through an amine-containing facilitated transport membrane. (Yanan Zhao and Ho 2012)

8.4 Liquid Polymers Disposable and ecologically acceptable substitutes to current carbon capture solvents are being found in liquid polymers like polyethylene glycol and polyethyleneimine (containing 1,2-ethanediamine and aziridine) (Taylor et al. 2011). Polyethylene glycol is a polymer of ethylene glycol that may be produced from sugars or modified E. coli. It is a by-product of the petrochemicals industry (Monazam et al. 2013). It is a solvent having low melting point that lowers the aqueous solutions polarity, allowing greater variety of reactions. At ambient temperature, branched polyethyleneimines are liquids, but they are insoluble in cold water and organic solvents such as acetone and ethyl ether. Polyethylene glycol is commonly combined with and mixed with other materials to create composites and blends with strong CO2 collection capabilities. Because of the plasticization action of polymers, CO2 solubility into polyethylene glycols enhances as pressure rises (Wiesmet et al. 2000). This is integrated with an original membrane made with acrylonitrile–butadiene– styrene and polyethylene glycols, higher absorption capacity was observed with larger molecular weight polyethylene glycols, the optimum performance was found

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with polyethylene glycol-20000 having 10% wt composition, having high permeability and selectivity (Ghanbari 2010). Polyethylene glycols being combined with Pebax and multi-walled carbon nanotubes for creating membranes having excellent single-gas CO2 permeability. Thanks to the use of higher molecular weight polyethylene glycols having compositions between 0 to 40% by weight (Wang et al. 2014). Polyethylene glycol diacrylate has shown to have good selectivity upon CO2 absorption and therefore is utilised in air purification (Rochelle 2009). It could be utilised as an alternate membrane material in gas separation once treated with aminosilane (Cong and Yu 2010). Polyethyleneimine is commonly utilised for the development of adsorbent materials in different forms for collecting CO2 from industrial emissions. In a 15% CO2 and N2 combination, polyethyleneimine is loaded on mesoporous carbons having high pore volume, owing to optimum composition of 65 wt% polyethylenimine-600, that showed CO2 loading of 4.82 mmol CO2 /g of adsorbent (Jitong Wang et al. 2013). Polyethyleneimine had also been grafted and fixed on a fluid bed, with mesoporous silica functioning as a support. The absorption capabilities ranged from 86 to 122 mg of CO2 /g of adsorbent (Monazam et al. 2018). The combination of nano fibrillated cellulose and polyethyleneimines resulted in a foam-like structure with exceptionally large porosity and surface area. At an optimal polyethyleneimine dosage of 44 wt%, good stability, and at mid-time of just 10.6 min, CO2 sorption capacity was 2.22 mmol/g (Sehaqui et al. 2015). For nano adsorbents built of polyethyleneimines and SiO2 , branched polyethyleneimines are found more efficient for CO2 capture than linear polyethyleneimines, having greatest uptake capacity for branched polyethyleneimine/800-silica, that contained 202 mg of CO2 /mg of adsorbent (Li et al. 2014). Polyethyleneimines when coupled to natural clays (like montmorillonite and kaolinite) for producing sorbents with sorption capacity of 112 mg/g at a 50 wt% polyethyleneimine loading upon the montmorillonite support, may be increased to 142 by adding water (Wang et al. 2014). The adsorbent was made from polyethylene glycol-200, polyethylene glycol-1000, and polyethyleneimine, using SBA-15 as the support. By addition of polyethylene glycol-200 the thermodynamic efficiency was increased by 60%, as long as access to the openings and active sites was not hampered (Sakwa-novak et al. 2015). Because of its CO2 -capture capabilities and dispersing capacity, it has also been utilised to stabilise tetraethylenepentamine which is supported on silica (Tanthana and Chuang 2010). Resins exhibiting highly selective CO2 adsorption abilities are often made from polyethylene glycols and polyethyleneimines. Mesoporous HP20 resins were impregnated using polyethyleneimines, which resulted in a sharp rise in CO2 uptake, and the equilibrium is achieved within only 6 min at 75 °C. Out of a 400 ppm CO2 composition, CO2 sorption was found to be 99.3 mg/g, only with optimum dose of polyethyleneimine of 50 wt% (Chen et al. 2013). Amino acid-imprinted polymers were proved promising to absorb CO2 out of a gaseous mixture with great selectivity (Chaterjee and Krupadam 2018). Mostly in presence of DBN, the CO2 absorption performance of polyethylene glycol-based liquids having various molecular weights (200, 400, and 600) was tested at 25 °C. The absorption capacity of 0.5 g of DBN incorporated to 5 g of polyethylene glycol-based liquid is been observed to be considerably higher compared to the same liquid without DBN, first-order rate expression

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was followed during the complete absorption process, with the increasing molecular weight the absorption capacity also increased. Under similar experimental circumstances, DBN being employed to evaluate the CO2 absorption of polyethyleneiminebased solvents, using polyethyleneimine having molecular weight-800 exhibited a considerably greater capacity compared to polyethyleneimine having 25,000 molecular weight. This is because the number of electron-rich centres (amino groups) present on the surface is significantly larger. If comparing polyethylene glycols, DBN has less effect on polyethylenimines (Pandey et al. 2019). Polyethylene glycols also when mixed to room-temperature ionic liquids to develop solvents had extremely high solubilities, similar to best-performing ionic liquids (Bara et al. 2007) (Table 8.1).

8.5 Polymers of Intrinsic Microporosity Budd and McKeown were the first to synthesize polymers of intrinsic microporosity (PIMs) with polycondensation reaction amongst tetrahydroxy-monomers containing spiro- or contorted centres and tetrafluoro-monomers. Chains of PIMs differs from ordinary polymers in two ways: it lacks large-scale conformational change and it has a twisted shape. The earlier one is triggered by the PIMs backbone’s stiffness, though the other one is induced by the polymer backbone’s stochastic twisting. As a consequence of the increased porosity of PIMs-based membranes, gases might diffuse quicker. PIMs’ total selectivity is indeed improved by the existence of selective ultra-micropores linked by large pores. Due to its good permeability and selectivity, PIMs are regarded as potential membrane material for the separation of CO2 (Budd et al. 2004; Swaidan et al. 2015; Liu et al. 2016). PIM would be readily converted to a membrane because it is solution-processable. PIM might be utilised as the only constituent in a freestanding membrane or mixed with some other polymers or inorganic compounds. The other option would be to utilise PIMs as the selective layer in a thin film nanocomposite (TFN), where the selective layer could be made up of PIM or a nanocomposite. Due to the high FFV (Fractional free volume), PIMs have rather high gas permeability as a pristine membrane than other polymers. The extent of FFV, on the other hand, is dependent on preparation and treatment used during membrane manufacturing (Bhavsar et al. 2018; Budd et al. 2008; Jue et al. 2015; Zeng et al. 2018). Since the solvent is removed completely while casting a membrane and the FFV is increased, PIMs treated using alcohols generally exhibit greater gas permeability to untreated PIMs. PIMs-based membranes’ CO2 separation performance may therefore be enhanced in a variety of pathways. PIMs have nitrile groups on their backbones, which could be functionalized further using amine, thioamide, beta-cyclodextrin, and tetrazole to increase their affinity for CO2 .Since the functional groups occupy the pores, functionalized PIMs exhibit decreased CO2 permeability, despite being more selective. Another potential approach is crosslinking. UV (Ultraviolet) light irradiation, heat treatment, or chemical substances such as pyrene might all be used to cross-link the molecules.

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Table 8.1 Application of liquid polymers in CO2 capture Chemical constituents of liquid polymer

CO2 loading capacity

Remarks

References

Propylene carbonate (PC) + poly (propylene glycol) monobutyl ether system

XCO2 = 0.2900 at a mole fraction of 0.2501 of PC in the solvent, 298.15 Kand 1256.5 kPa

At higher pressures, Li et al. CO2 absorption is (2020) more when PC was added in lower amount Absorption of CO2 seen to increasewith pressure

CTF-Nx (CTF—Covalent triazine-based frameworks)

CTF-N4 —3.4 mmol/g CTF-N6 —5 mmol/g at 273 k and 1 bar

When compared to Liao et al. CTF-N6 , CTF-N4 (2020) had the greatest CO2 uptake But CTF prepared at high temperature (600 °C) showed high CO2 uptake (5.0 mmol g−1 at 273 K/1 bar)

CTF-Ox

CTF-O4 —3.1 mmol/g When compared to CTF-O6 —4.5 mmol/g at CTF-O6 , CTF-O4 273 k and 1 bar had the greatest CO2 uptake

Liao et al. (2020)

CTF-Sx

CTF-S4 —2.6 mmol/g When compared to CTF-S6 —4.0 mmol/g at CTF-S6 , CTF-S4 273 k and 1 bar had the greatest CO2 uptake when compared withCTF-N4 and CTF-O4 , CTF-S4 possessed the lowest Qst value (27 kJ mol–1 )

Liao et al. (2020)

Cellulose acetate butyrate

CO2 /N2 selectivity was 3.14

The membrane Ng et al. selectively removed (2020) higher CO2 over N2

Hybrid choline-2-pyrrolidine-carboxylic acid/polyethylene glycol/water absorbents

0.0292 g CO2 / g solvent at 50 °C

CO2 uptake remained unchanged after 5 cycles of regeneration When the weight fraction of water was increased to 50% from 20% the CO2 uptake was found higher

Chen et al. (2020)

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Fig. 8.2 SEM images of a defect-free PIM-1 hollow fiber membrane a cross section, b asymmetric substructure, c internal boundary, and d skin layer spun with a 17.5 wt% THF in 1-butanol sheath layer. (Source Jue et al. 2017)

The FFV of cross-linked PIMs membranes is generally decreased, resulting in gas permeability reduction. Moreover, that increases the diffusive-selectivity of PIM, leading to improved H2 /CO2 , CO2 /CH4 , and CO2 /N2 selectivity. PIMs featuring increased CO2 solubility may be developed, leading to better CO2 /N2 selectivity for mixed gas separation by preventing N2 penetration (Mason et al. 2011; Robertson 2011; Li et al. 2012; Li et al. 2012; Mcdonald et al. 2015; Liu et al. 2017; Satilmis et al. 2018). Jueet al. recently synthesized PIM-1 hollow fibre membrane by phase inversion method. The membrane exhibited the permeance of 360 GPU and 22.4 CO2 /CH4 selectivity. The SEM images of PIM-1 is shown in Fig. 8.2 (Jue et al. 2017).

8.6 Thermally Rearranged Polymers Polybenzoxazole (PBO), polybenzothiazole (PBZ) and polybenzimidazole (PBI) are aromatic polymers containing heterocyclic rings that have a stiff chain structure and high gas separation capability yet is difficult to dissolve in ordinary solvents. As a result, a thermal route for synthesizing the insoluble aromatic polymer out of a soluble polyimide precursor has been presented (Park et al. 2007). Because the precursor polymers being soluble in the common solvents, they may be readily

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converted into membranes by using traditional solution casting approach, then heated to produce aromatic polymeric membranes. A TR polymer membrane is the ultimate membrane. TR (Thermally rearranged) polymeric membranes is normally prepared in three steps: (i) soluble precursor polymer synthesis that usually comprises an imidization process, (ii) membrane preparation from polymer precursor, and (iii) membrane’s thermal rearrangement. The resulting TR polymer membrane’s desired properties include FFV, microcavity size, and distribution that might be controlled by engineering the structure of the polymer, selecting the synthesis process, and selecting the heating diagnostic protocols. By changing the monomer structures, various polymer frameworks may be achieved. Chain stiffness as well as the existence of bulkier bridge and/or pendant groups is the two key factors (Moo 2016). High chain strength monomers might reduce chain relaxation following the heat treatment, leading to higher FFV as well as gas permeability. By disrupting the packing density of polymer chains, the existence of bulky bridges and dangling groups in polymer chains could then increase the free volume elements. As a result, TR polymer membranes made of non-bulky, adaptable polymer chains like 4,4 oxydiphthalic anhydride (OPDA) exhibit the least CO2 permeability and selectivity when compared to TR polymers made of bulky, stiff structures. TR polymer membranes are often prepared in three stages, as seen in Fig. 8.3:

Fig. 8.3 Synthetic route and chemical structures of precursor bis(o-hydroxyl)-Maleimides (BHMIs) and Thermally rearranged bismaleimides (TR-BMIs) for the fabrication of membrane. (Source Do et al. 2016)

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first step is the preparation of a soluble precursor polymer, this usually involves an imidization process. Then in the next step membrane construction from the polymer precursor. Later Thermal rearrangement of membrane is done in the final step. The resulting TR polymer membrane’s desired properties include FFV, microcavity size, and distribution, which may be controlled by creating the polymer structure, selecting the synthesis process, and selecting the heat treatment protocols. Thermal, chemical, ester-acid and azeotropicimidization techniques could all be used to make precursor polymers. Varying imidization techniques yield various precursor polymer structures, which affect FFVs (Han et al. 2010). Due to low polymer chain mobility, the thermal imidization technique favours the production of FFV throughout imidization, leading to increased gas permeability when converted into a membrane. TR-PBO made with chemically-imidized precursors (cTR-PBO) had the maximum CO2 permeability, trailed by TR-PBO synthesized using thermallyimidized precursors (aTR-PBO).The latter, on the other hand, exhibited the best selectivity for CO2 /N2 and CO2 /CH4 (Han et al. 2010; Kim et al. 2013). PIM-PIs (intrinsically microporous polyimides) were also employed as precursor polymers (Li et al. 2013; Shamsipur et al. 2014; Type and Nasser 2017). To enhance microporosity, the approach integrates PIMs with TR polymer structure. The resultant membranes (PIM-TR-PBO or spiroTR-PBO) beat the PIM precursor and many other TR-PBO membranes in terms of CO2 permeability. The precursor membranes were typically heated at around 300 and 450 °C in a high-purity argon environment for thermal rearrangement. The polymer structure is converted during such an operation, and microcavities being produced, which is governed by the process parameters. Lower temperatures and limited duration rearrangement generally produce low degree TR polymer, but elevated temperatures creation might end in precursor breakdown and brittle membrane. Heat treatment under ideal circumstances results in high conversion to form TR polymer, increasing FFV and surface area (Kim et al. 2012; Li et al. 2013; Shamsipur et al. 2014; Liu et al. 2016; Alghunaimi et al. 2017). The FFV of the resultant TR polymer membranes is typically between 0.19 and 0.35 (Han et al. 2010, 2012; Hoon et al. 2010; Li et al. 2013), which would be analogous to high-free-volume glassy polymers like PTMSP (0.29) (Freeman and Hill 1999), Teflon AF1600 (0.31), and Teflon AF2400 (0.33) (Tiwari et al. 2015). In addition, the FFV in TR polymer membranes were 3D linked microcavities which are counterparts for micropores in some adsorbents, which includes carbon molecular sieves. It might then aid in improving the gas permeability of the membrane. Both chemical structure (chain rigidity) and glass transition temperature (Tg ) of such precursor polymer must be taken into account when choosing the optimum thermal treatment methods as it impacts the temperature for thermal conversion. For example, employing a bisphenol A type dianhydride (BisADA) in polymer fabrication reduced the precursor Tg , thereby lowering the temperature of imide-to-benzoxazole conversion by around 100 °C (Guo et al. 2013). For manufacturing purposes and mechanical characteristics of the resultant membrane, a lower heat treatment temperature is also desired. Thermal rearrangement, like previously indicated, could have a detrimental influence on the TR mechanical characteristics as

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this membrane might become brittle (Liu et al. 2015). Non-TR-able diamines (Bryjak et al. 2015; Ye et al. 2019), thermally labile units (Chua et al. 2013), and spirobisindane, can be included in TR polymeric membrane to remedy this issue. It may be due to the existence of a flexible ether group present in the non-TR-able unit (Bryjak et al. 2015; Li et al. 2013).Additionally, forming a reduced GO (Graphene Oxide) scaffold within TR polymer to build composite membranes could give mechanical robustness and exceptional CO2 permeance (Serhan et al. 2019). Due to its high FFV, TR polymeric membranes might potentially experience physical aging. Following 150 days of operation, the CO2 permeability decreased by up to 50%, accompanied by an increase in CO2 /CH4 selectivity from 27 to 35, relative to a pristine TR membrane. To overcome this problem, an in-situ restoration method utilising methanol and the addition of oxidised CNTs (Carbon Nano Tubes) to the precursor solution had been suggested (Brunetti et al. 2016). Operating parameters including pressure, temperature, and feed composition have an impact on the separation performance of TR polymeric membranes. Because the pressure was raised in upstream, the CO2 permeability decreased, but the permeabilities of less condensable gases were practically unaffected (Smith et al. 2015; Swaidan et al. 2013). Due to this, selectivity dropped as well. The preferential competitive sorption of CO2 over CH4 , the selectivity of TR polymeric membranes enhanced after mixed-gas CO2 /CH4 was employed (Smith et al. 2015), and further increased with higher pressure due to greater sorption of CO2 over CH4 . In addition, TR polymeric membranes are resistant to CO2 -induced plasticization. Unlike unconverted PI, which began to plasticize at 20 bar, TR polymers only experienced minor plasticization and can even withstand pressures up to 50 bar (AlQahtani and Mezghani 2018). They also were resistant to SO2 and H2 S plasticization, and that is relevant in real-world situations where sulphur-based gases are present. Unfortunately, due to competing adsorption, they appear to be unable to survive the presence of moisture. To overcome this problem, hydrophobic crosslinked TR polymer membranes have been suggested (Cersosimo et al. 2015; Lee et al. 2017; Scholes et al. 2017). Using a TR polymeric membrane to separate CO2 at an elevated temperature improved CO2 permeability, although to a lesser amount than the other gases (O2 and N2 ), leading to reduced selectivity (Cersosimo et al. 2015). This is due to the decreased solubility, which makes CO2 transport more difficult. CO2 permeability was considerably lower than H2 in gas mixtures with H2 , resulting in greater H2 /CO2 selectivity. As a result, the TR polymeric membrane has the potential to be used in CO2 extraction prior to combustion.

8.7 Porous Organic Polymers (POPs) The application of porous materials to adsorb CO2 by physisorption is a cost-effective method for lowering CO2 levels. The formation of weak bonds is required to adsorb CO2 onto porous adsorbents that require far less energy than using liquid amines, wherein CO2 is chemically bound with amines. At lower pressure, porous adsorbents

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must have excellent adsorption efficiency and selectivity for CO2 (Li and Wang 2013; Liebl and Senker 2013; Wilmer et al. 2012). The creation of porous materials for technologies that employ clean energy sources, like natural gas adsorbents and H2 storage, is very critical. POPs are chemically and physically very stable, allowing them to be utilised in extreme environments like higher temperatures, moisture, pressure and acidity. Heterogeneous catalysis, molecular separation, pollutant adsorption and gas capture and storage are all possible applications (Mckeown et al. 2006; Zhang et al. 2009; Wang et al. 2012). Furthermore, POPs are being developed to incorporate different functions specific molecular building blocks (MBBs) or monomeric units, as its pore diameters enable for selective CO2 collection over other gases in flue gas (75% N2 ) or natural gas (95% CH4 ) [103, 104]. Several microporous organic polymers (MOPs) exhibit higher stabilities, larger surface area, and narrow pore size distribution (Liu and Zhang 1833; Co et al. 2007; Côté 2007; Zwaneveld 2008; Hunt et al. 2008; Yuan et al. 2010; Konstas et al. 2012; Liu et al. 2013). Covalent organic frameworks, crosslinked polymers, polymers with inherent micro porosity and hyper crosslinked polymers are the four most frequent kinds of MOPs. MOPs have been the most promising materials for gas collection, although there is still room for development (Liu et al. 2013). POPs are being created using a variety of synthetic methods. Imine creation, Sonogashira–Hagihara cross-coupling, boronic acid condensation, cobalt-catalysed acetylene trimerization and nitrile trimerization are the most prevalent. In the case of POPs, which have a high adsorption ability at low pressure due to pore filling, the micropore structure is far more important than surface area. MOFs (Metal organic frameworks), on the other hand, have large polar pore surfaces and effectively absorb CO2 however, its chemical instability makes them impractical for use in critical applications. Gas capture and storage, heterogeneous catalysis, organic vapour capture and selective adsorption are all possible applications for POPs with persistent micro porosity (Furukawa and Yaghi 2009; Jin et al. 2011a; Rabbani et al. 2011; Ding et al. 2012; Yan and Han 2012; Chen et al. 2014; Wang 2014). Pores in porous organic frameworks (POFs) could be regulated throughout the synthesis process for applications such as gas storage and separation, sensors, heterogeneous catalysis and electricity. POFs are made by combining commercial monomers with strong Lewis acids as catalysts. For high-performance porous polymer networks, Schiff base networks (SNWs) with large surface areas are being created. POP heteroatoms play a very critical role in the preferential adsorption of CO2 over other gases including N2 and CH4 . MOPs with heterocycles and sulfonate-grafted porous polymer networks have been utilised to selectively adsorb CO2 at low pressure (Xiang and Cao 2000; Han et al. 2009; Schwab et al. 2009; Mckeown and Budd 2010; Jin et al. 2011b; Feng et al. 2012; Li et al. 2012; Luo et al. 2012; Zhang and Riduan 2012). Under Sonogashira–Hagihara conditions, POP (Fig. 8.4a) was effectively synthesised by cross-coupling 4,6-dibromopyrimidine, 3,5-dibromophenol, 3,5dibromopyridine, and 1,3,5-triethynylbenzene in dimethylformamide and triethylamine for 30 h at 80 °C. The chemical functionality of POPs is reported to have a substantial impact on the heat of adsorption for the adsorption of CO2 . The heat of adsorption (23.8–53.8 kJ mol−1 ) of POPs with electron-donating Lewis base sites

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c) Azo-linked porous organic polymer

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b) Azo-linked porous organic polymer

d) Azo-linked porous organic polymer

e) Iron containing porous organic polymer Fig. 8.4 Structures of different porous organic polymers employed for CO2 capture

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was observed to be greater (Li et al. 2017). Azo-linked POPs had shown large surface areas (BET surface area = 862–1235 m2 g−1 ), excellent chemical and physical stabilities, and adequate gas storage capabilities at increased pressure. At 273 K and 1 bar, CO2 absorption was strong (up to 5.37 mmol g−1 ). Azo-linked POPs (Fig. 8.4b–d) had high heats of adsorption for CO2 (28–30 kJ mol−1 ), CH4 (18–21 kJ mol−1 ), and H2 (7.5–8 kJ mol−1 ) at low pressure. The storing capacity of CO2 (304 g L−1 at 298 K and 40 bar), H2 (24 g L−1 at 77 K and 70 bar), and CH4 (67 g L−1 at 298 K and 70 bar) for the polymer illustrated in Fig. 8.2b were all high at high pressure (Arab et al. 2014). The iron-based POPs (Fig. 8.4e) showed the surface area around 715– 1050 m2 g−1 with 14.8% CO2 loading capacity at room temperature and atmospheric pressure (Alkordi et al. 2015).

8.8 Concluding Remarks Material selection is crucial for this application of CO2 capture, irrespective of the sort of microporous materials used. They need to be tough and able to resist extreme working conditions. Materials compliance is particularly crucial in the case of composite membranes in order to get membranes that operate well. A composite of tough microporous materials may then become a viable option. This may be accomplished, for example, by employing microporous polymers as the continuous phase to achieve a higher permeability membrane that is additionally loaded with MOF or POF to improve molecular sieving capabilities. Interestingly, inorganic–organic frameworks seem promising for H2 /CO2 separation, while microporous polymers are satisfactory for CO2 /CH4 and CO2 /N2 separation. This might be caused since the pore size in inorganic–organic hybrid frameworks is easier to be tuned than in microporous polymers resulting in enhanced molecular sieving. Therefore, apart from further pore fine-tuning, enhancement in the preferential adsorption should be further optimized to improve gas separation with similar sizes such as encountered in CO2 /N2 and CO2 /CH4 separation. Tuning the interchain stiffness and gap, on the other hand, might be significant variables in improving the molecular sieving properties of microporous polymers. Finally, there are certain critical issues about operating conditions that should be considered. One of the key challenges, specifically for polymer membranes, is CO2 -induced plasticization. TR polymeric membranes with high levels of TR conversion are resistant to CO2 -induced plasticization, even when exposed to SO2 and H2 S. Meanwhile, this might still be a big problem for a PIM-based membrane, as integrating intrachain stiffness into the structure doesn’t really appear to increase resistance substantially. Because CO2 feed streams often contain additional pollutants including water vapour, NOx , and SOx , research under this context is required, as a mixed-gas study by itself does not appear to be enough. This is particularly crucial in order to determine if the membrane structure has been permanently damaged as a result of exposure to this hostile environment. Meanwhile, one of the key challenges for long-term operation is physical aging. This is especially essential for a thin membrane, which ages more

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quickly than a larger one. If all these factors can be reconciled, Membrane technology based on microporous materials has the great potential to replace traditional technology, resulting in more efficient CO2 capture processes.

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Chapter 9

Functional Polymer Materials for Environmental Monitoring and Safety Applications Sreeramareddygari Muralikrishna, Sureshkumar Kempahanumakkagari, Ramakrishnappa Thippeswamy, and Werasak Surareungchai Abstract This chapter enumerates polymer functionalized nanostructured materials for the sensing of environmentally toxic substances such as heavy metal ions, pesticides and other phenolic compounds along with food safety applications. Among the variety of functional polymer composites, conducting polymers, molecularly imprinted polymers (MIPs), and biopolymer composites are found to be promising materials in a variety of environmental monitoring sensors and food safety applications. The various polymers were used to functionalize with metal nanoparticles, metal oxide nanoparticles, deoxyribonucleic acid (DNA), quantum dots (QDs), graphene oxide (GO), reduced graphene oxide (rGO), and carbon nanotubes (CNTs). The resulting materials were used as electrode modifiers/electrocatalysts and nanozymes for electrochemical or optical sensing systems. The optical properties include naked eye colour change, absorption and emission of the composites. These materials are also used to fabricate materials for safety applications like monitoring the quality of food during package and transport.

S. Muralikrishna · W. Surareungchai Pilot Plant Development and Training Institute, King Mongkut’s University of Technology Thonburi, Bangkhuntien-chaitalay Road, Thakam, Bangkok 10150, Thailand S. Kempahanumakkagari (B) · R. Thippeswamy (B) Department of Chemistry, BMS Institute of Technology and Management, Doddaballapura main road, Avalahalli, Yelahanka, Bengaluru, Karnataka 560064, India e-mail: [email protected] R. Thippeswamy e-mail: [email protected] W. Surareungchai School of Bioresources and Technology, Nanoscience and Nanotechnology Graduate Programme, and Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkhuntien-chaitalay Road, Thakam, Bangkok 10150, Thailand © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_9

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9.1 Introduction Over the last two decades, the rate of deterioration in the quality of air, water, and soil all over the world due to environmental pollution has threatened the environmental protection agencies. This results in ecological imbalance, the introduction of toxic chemicals in the food chain, and global climate change. Besides this, environmental pollution is also responsible for causing diseases in humans that lead to increased costs for diagnosis and curing in health centers. The wide use of heavy metal ions (HMIs), pesticides, insecticides, phenolic compounds, hydrazine’s, plasticizers, antibiotics, and xenobiotics in industrial, agriculture and medical applications are the main cause for the increased environmental pollution. The Majority of these pollutants are structurally stable and low degradable. Therefore, these are considered as the emerging contaminants or contaminants of emerging concern (CECs). Many of these chemicals are found in household products, industrial chemicals, health care products, cosmetics, biocides, surfactants and plasticisers. In this regard, environmental protection agencies introduced several measures to protect the environment from the toxic substances; as such it will be a sustainable environment for the future generations. The primary task in pollution combating is monitoring the concentration levels of the pollutants in the environmental matrix. However, monitoring the toxic analytes from the environmental matrix (water and soil) is quite challenging due to their wide variety of chemicals in the trace quantities and their different physical and chemical properties. Therefore, environmental analysts are looking for highly sensitive, selective and non-precious metal based analytical tools for the detection of these contaminants. Various nano structured materials including metal nanoparticles, metal oxides, metal chalcogenides, metal organic frameworks and polymers/polymer functionalized materials are widely used for the detection of these pollutants using cost effective electrochemical and optical methods. Among these materials, polymer functionalized materials are most promising candidates to fabricate the sensors. Polymer (conducting polymers, molecularly imprinted polymers (MIPs) and biopolymers) functionalized nanostructured materials including carbon materials, metal oxides, metal nanoparticles and hydrogel composites are attracted to the researchers, and triggered for the development and investigation of necessary functionalities in the new generation sensor systems(Deng et al. 2019; Ho et al. 2005; Jenkins et al. 2001; Mahmoudpour et al. 2020; Xue et al. 2020). This is because of their large scale productions, easy process abilities and inexpensive fabrication process, high stability, flexibility, good adsorption and bridging properties as well as embedding abilities with other materials. Furthermore, the polymer materials can be tuned to perform specific function and interaction to induce selectivity, wettability, quick response and better transduction properties. Another reason for exponential growth in the use of polymers composites in sensor fabrication is due to their simple production protocols like blending and other methods in order to load functionalities during polymer composites fabrication. The advanced technologies to produce composites like three-dimensional (3D) printing, stereo lithography and prototyping extensively utilizes the functional polymer composites in

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producing advanced smart devices for diverse applications. The sensing approaches developed using the polymer composites are mainly electrochemical and optical methods (Khadem et al. 2016; Parnsubsakul et al. 2018). The composites of nanostructured materials with conducting polymers, biopolymers, MIPs, and electroactive polymers are widely used to develop electrochemical sensors for the detection of various environmental contaminants (Hemin Wang and Yuan 2019). In the electrochemical sensing platforms, polymer substrates act as transducers while the functionalized component (carbon material/metal nanoparticles/metal oxides) acts as functional units/reorganization units (Hemin Wang and Yuan 2019). In case of carbon polymer composites, the carbon substrate enhances the conductivity of the composites, which results in increasing the sensitivity (Hemin Wang and Yuan 2019). In the conducting polymers composites, polymeric units help in the higher electron transfer rates due to its high electrical conductivities and where the functional materials like reduced graphene oxide (rGO), provides large surface area along with higher electron transfer rates. Another interesting class of polymer composites used in electrochemical sensing are molecularly imprinted polymer composites (MIPCs) (Mahmoudpour et al. 2020).These are found to be highly specific to particular analyte due to its specific binding functional units present in their 3D networks of the MIPs. Furthermore, the MIPs are conjugated with carbon substrates [carbon nanotubes (CNTs), graphene oxide (GO), rGO and carbon quantum dots (QDs)] and nanomaterials as signal enhancers (Mahmoudpour et al. 2020). The electro active polymers, are also in the race as electrochemical sensing materials, provide more active sites, good stability and strong adherence to the electrode surface, the necessary factors in electrochemical monitoring applications. The environmentally sustainable polymer materials alternative to synthetic materials discussed above were biopolymers (Parnsubsakul et al. 2018). These are found to be non-toxic, biodegradable and can be used as matrix/layered material or functional units for the fabrication of electrochemical sensors (Parnsubsakul et al. 2018). The polymer composites were also used for the development of optical sensors based on absorbance and emission spectra (Wei et al. 2020; Xue et al. 2020). The polymer composites such as, MIPs composites, deoxyribonucleic acid (DNA) conjugated polymer composites, conductive polymer composites, biopolymer composites and polymer stabilized metal nanoparticles were used to develop optical sensors (Deng et al. 2019; Ho et al. 2005; Wei et al. 2020; Xue et al. 2020). The general principle involved in optical sensing is based on the fluorescence resonance energy transfer or charge transfer energy between analyte and sensing substrate (Wei et al. 2020). The sensing mechanism in other polymer substrates will be conformational change fluorescence intensity; and analyte induced catalytic oxidation of substrate in the presence of polymer composite (Ho et al. 2005). In the colorimetric method, functional polymers or polymer stabilized nanoparticles are used as artificial enzymes (also referred as nanozymes) for the catalytic effect to enhance/decrease the chromogenic substrates colour (Deng et al. 2019). Along with sensing applications, functionalized polymer composites were used in developing safety applications like food packing materials (Makvandi et al. 2021). The food packing materials made up of polymer nanocomposites were found to

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exhibit better antimicrobial, mechanical and barrier properties (protection from Ultraviolet (UV),O2 and other gases) than the reported pristine polymeric materials (Makvandi et al. 2021). This chapter enumerates the design, synthesis of various polymer composites used as electrocatalysts/electrode modifiers for electrochemical monitoring of environmentally toxic analytes and safety materials (food package materials) and also for the development of optical sensors. The different strategies reported for synthesis of polymer nanocomposite, development, optimization and fabrication of electrochemical and optical sensors and its sensing mechanisms were also discussed. Similarly, the synthetic and fabrication strategies of food package materials, their efficiency, stability, and barrier property studies were briefly discussed.

9.2 Synthetic Strategies of Functionalized Polymer Composites The different polymer composites reported for environmental monitoring and safety applications includes functionalized conducting polymer composites, functionalized MIPCs, functionalized electroactive polymers and functionalized biopolymer composites.

9.2.1 Functionalized Conducting Polymer Composites The conducting polymers composites including polyaniline (PANI), polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and polyethyleneimine (PEI) based carbon composites, DNA hybrids and metal nanoparticle/metaloxides composites were used for the development of electrochemical/optical sensors. The PPy or PANI composites reported for electrochemical sensing of heavy metal ions are PPy-rGO, hydrogels of GO and PANI, PANI-alanine-rGO and glycine-rGO-PANI composites (Akhtar et al. 2020; Hanif et al. 2019). Initially, GO was synthesized by Hummers method and used in insitu polymerization of aniline in the presence of ammonium persulfate, followed by gelation at elevated temperature. In case of PPy or amino acid functionalized rGO-PANI composites, initially GO was reduced to rGO by heating in the presence of reducing agents (NaBH4 or with ammonia and hydrazine). Later, composite of PPy-rGO or rGO and amino acid was obtained through in-situ oxidative polymerization reaction to obtain the final PPy-rGO or amino acid functionalized rGO-PANI composites by using either ammonium peroxysulfate/ammonium peroxydisulfate as an oxidising agent (Akhtar et al. 2020; Hanif et al. 2019). The PEI-Ag clusters reported for oxidoreductase mimic colorimetric monitoring of Cr6+ ions were synthesized in one pot method (Xue et al. 2020). Initially, PEI was mixed in

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Scheme 9.1 The steps involved in the synthesis of SNS-NH2 monomer. Reproduced from ref. (Yildiz et al. 2008), with permission from [Elsevier], Copyright

distilled water by sonication, followed by addition of HEPES buffer, AgNO3 solution and formaldehyde for reducing purpose was added in required quantities to obtain the final product (Xue et al. 2020). The acetyl cholinesterase (AchE) covalently functionalized with poly(4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1yl)benzenamine)(poly(SNS-NH2 ))-multi-walled cabon nanotubes (MWCNTs) was reported for amperometric determination of organophophoruous pesticide (Kesik et al. 2014). The 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine (SNS-NH2 ) was synthesized as given in Scheme 9.1 (Yildiz et al. 2008). The graphite electrode was deposited MWCNTs and electrochemically oxidised to induce COOH groups yield MWCNTs-COOH. Then SNS-NH2 monomer was electropolymerized onto MWCNTs-COOH. The obtained poly (SNS-NH2 ) functionalized graphiteMWCNTs-COOH was used for covalently appending AchE through amide bond between NH2 of poly (SNS-NH2 ) and COOH of MWCNTs through the help of 1ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC/NHS) coupling agents (Kesik et al. 2014).

9.2.2 Functionalized Molecularly Imprinted Polymer Nanoparticle Composites MIPs have been extensively used in electrochemical and optical sensing substrates because of their selectivity, chemical/mechanical stability, inexpensiveness, and

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ease of preparation. MIP technique involves preassembly of template molecule and functional monomers followed by copolymerization in the presence of cross linker (Rebelo et al. 2021). Then, removal of template molecules from the matrix leaves the active/reorganization sites complementary to template molecule with respect to shape, size, and functional sites. The selectivity and sensitivity of MIPs will be correlated to number of active sites imprinted on polymer matrix. Furthermore, the active sites on polymer sites can be increased through increasing the imprinting polymer thickness (Rebelo et al. 2021). However, increase in thickness of polymer matrix leads to slow diffusion of template molecule to active sites and hindering the contact between the transducer and matrix. In order to increase the sensitivity, and response times of MIP systems, the surface area can be increased by associating the imprinted polymer matrix with nanostructures (Rebelo et al. 2021). The electrochemical sensor platforms were reported for monitoring various toxic substances like pesticides, insecticides, and herbicides using MIPs nanocomposites as electrode modifiers. The MIP nanocomposites used in electrochemical and optical sensors are metal oxide-MIPs composites, metal nanoparticle-MIP, single-walled or multi-walled carbon nanotubes (SWCNT/MWCNTs)-MIP composites, C3 N4 carbon nanotube-MIP composites, graphene QDs-MIP composites, GO/rGO-MIP composites and QDs-graphene@ionic liquid-MIPs (ILMIPs). The steps involved in MIPs assembly, signal enhancement by carbon nanoparticles during electrochemical sensing are as given in the Fig. 9.1 (Rebelo et al. 2021). These MIPs were prepared by bulk/mass polymerization, electropolymerization, and sol–gel methods. Among these, bulk polymerization is a popular approach because of its simple production process and also less production costs. In this method, functional monomer, template, cross linker and free radical initiator were cooked together resulting in a homogeneous polymer matrix, which was later crushed

Fig. 9.1 The steps involved in assembly of MIPs, signal enhancement by functional carbon material and mechanism involved in electrochemical sensing. Reproduced from ref. (Rebelo et al. 2021), with permission from [Elsevier], Copyright

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and grinded to fine powder. The five sequence of events were followed in bulk polymerization approach includes, (i) Pre-polymerization of functional monomer along with template molecule (ii) Addition of cross linker and initiator molecules (iii) Postpolymerization by heating the reaction mixture (iv) Removal of template molecule from the matrix and finally (v) Crushing and grinding the obtained polymer matrix into fine powder (Rebelo et al. 2021). Another three approaches for obtaining spherical MIPs are precipitation, suspension and emulsion polymerizations. All the three approaches were very similar to the bulk polymerization approach, however, post treatment process are not necessary in these approaches to make them advantageous. This is because the post-treatment processes in the bulk polymerization approach involves crushing and grinding, resulting in loss of several active centres in the polymer matrix (Rebelo et al. 2021). The precipitation polymerization approach involves precipitation of final insoluble polymer from the large volume of organic solvent. We can have control over the size of MIPs obtained through precipitation polymerization approaches, but the shape of MIPs will be irregular. The micro spherical and mono disperse MIPs can be obtained through suspension and emulsion polymerization approaches, but the final MIPs obtained may be impure (associated with traces of surfactants used during the polymerization process) and decrease their sensing properties. Another interesting approach to produce MIPs is the electrochemical polymerization (Rebelo et al. 2021). This approach is quite simple, quick and reproducible, which involves three steps namely (i) Interaction of functional polymer with template by dissolving it in a suitable solvent (ii) Electrochemical coating usually by cyclic voltametry (CV) technique followed by (iii) Removal of the template from the polymer matrix. In contrast to earlier approaches, the electrochemical polymerization approach is reproducible, because we can have control over the thickness and morphology of polymeric film. This can be obtained by controlling the cycling time during electropolymerization (Rebelo et al. 2021). In addition, the template can be easily removed because the polymeric film obtained in this approach is very thin and functional cavities are formed on the outer surface of this thin film. The greener approach to produce MIPs is sol–gel process, because this technique is usually performed in aqueous medium at ambient conditions. The sol–gel approach uses Si based materials and involves two steps, namely (i) Hydrolysis of silane monomers with acid/base catalyst followed by (ii) Condensation of silane monomers to form siloxane bonds. The final product obtained with this approach is a highly porous, 3D network with high thermal and mechanical stability. However, absence of a functional unit makes the MIPs obtained with this approach less selective, and increased response time due to slow diffusion of analytes during electrochemical and optical sensing studies (Rebelo et al. 2021). Many nanomaterials have been used for surface modification during the molecular imprinting process such as Fe3 O4 , SiO2 , and Au nanoparticles. Besides the higher surface area, the magnetic properties of Fe3 O4 nanoparticles helps in pre-concentration of analytes during electrochemical and optical sensing studies (Mahmoudpour et al. 2020). The SiO2 nanoparticles provide solid support and impart higher stability due to their mesoporous structure. Similarly, the Au nanoparticles provide a larger surface area along with higher electron transfer rates when used

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Fig. 9.2 Steps involved in the synthesis of QDs-G@ILMIPs through micro emulsion approach. Reproduced from ref. (Wei et al. 2020), with permission from [Elsevier], Copyright

as functional materials along with MIPs in electrochemical sensors. Furthermore, carbon functional nanomaterials like CNTs (SWCNTs and MWCNTs), GO, and rGO, have been included into imprinted shell layers to increase the electron transfer rates (Mahmoudpour et al. 2020). The presence of graphene with the MIPs helps in pre-concentration of aromatic analytes during electrochemical sensing because of π- π interactions between π electron cloud of analyte and graphene. The QDs are found to be highly photo stable with broad absorption spectrum, narrow emission bands and quantum size effects (Mahmoudpour et al. 2020). The combination of QDs with above mentioned properties along with MIPs enables to the development of alternate selective, and sensitive optical sensors for environmental contaminants. The synthesis steps involved in fabrication of heteroatom doped QDs functionalized grapheme @ ionic liquid sensitized MIPs via micro emulsion approach were as given in Fig. 9.2 (Wei et al. 2020).

9.2.3 Functionalized Biopolymer Composites The metal nanoparticle/metal oxide nanoparticle/MoSe2 functionalized biopolymers like chitosan and peptide were reported as colorimetric and electrochemical substrates. The zwitterionic peptide capped Au nanoparticle composite was reported for colorimetric sensing of Ni2+ ions (Parnsubsakul et al. 2018). The Au nanoparticles were synthesized by standard citrate method. Briefly, HAuCl4 solution was treated with trisodium citrate solution under hot conditions to yield red coloured citrate capped Au nanocolloids. Then Au nanoparticles were capped with the zwitterionic

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peptide by ligand exchange process (Parnsubsakul et al. 2018). Another MoS2 functionalized chitosan (CS) was reported for Hg2+ ions colorimetric determination. This non noble metal functionalized biopolymer composite was synthesized by green approach by grinding bulk MoSe2 along with CS in the presence of ionic liquid as dispersing agent (Huang et al. 2019). The Fe3 O4 nanoparticle functionalized CS–single stranded calf thymus DNA (ssCT-DNA) biocomposite modified indium tin oxide (ITO) electrode was reported for nucleic acid sensor (Kaushik et al. 2009). This biocomposite was fabricated in a step wise manner. Initially, Fe3 O4 nanoparticles were synthesized by co-precipitation method then mixed with CS and sonicated to obtain CS-Fe3 O4 composites. The surface charged Fe3 O4 particles bind with positively charged CS through hydrogen bonds and electrostatic interactions. Then, CS-Fe3 O4 composites were treated with ss-CT-DNA, to give CS-Fe3 O4 -ss-CT-DNA biocomposite. The ss-CT-DNA bind electrostatically with positively charged CS through negatively charged phosphate backbone. The CS-Fe3 O4 -ss-CT-DNA biocomposite was modified with ITO and used as a nucleic acid sensor. The ITO coated glass electrode modified biocomposite was illustrated in Fig. 9.3 (Kaushik et al. 2009). Another chitosan-Fe3 O4 nanoparticles composite modified fluorine doped tin oxide (FTO) aptasensor for electrochemical sensing of malathion was fabricated as illustrated in Fig. 9.4 (Prabhakar et al. 2016).

Fig. 9.3 The ITO coated glass electrode modified biocomposite. Reproduced from ref. (Ajeet et al. 2009), with permission from [Elsevier], Copyright

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Fig. 9.4 The steps involved in fabrication of aptasensor for electrochemical sensing of malathion. Reproduced from ref. (Prabhakar et al. 2016), with permission from [Elsevier], Copyright

9.3 Applications of Functionalized Polymer Composites 9.3.1 Environmental Monitoring Various polymer functionalized nanostructured materials have been proposed for the detection of environmental contaminants including heavy metal ions, pesticides and other small molecules such as dihydroxybenzene isomers, nitrophenols and aminophenols by electrochemical and optical sensors.

9.3.1.1

Heavy Metal Ions Detection

Heavy metal ions are one of the major contaminants in the environment due to the rapid industrialization and urbanization in the developing countries. The trace level accumulation of these ions in the biological process may cause serious health issues to the living system. Therefore, the rapid and selective detection of various metal ions at low concentration levels is necessary for environmental protection. Carbon based materials; nanostructured materials and polymer functionalized nanocomposites are widely reported for the electrochemical and optical sensing of heavy metal ions. Among them, polymer functionalized nanostructured materials show promising candidates for the detection of toxic heavy metal ions with high sensitivity, better selectivity and low detection concentration levels. This is due to the fact

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that the binding capabilities of ligands present in the polymers, enhanced electrical, optical and catalytic properties. Different types of polymers such as conducting polymers, biopolymers and cross linked polymers functionalized with nanostructured materials are utilised for the detection of heavy metal ions. Conducting polymers functionalized with carbon materials such as CNTs, GO, rGO/graphene (G), metal chalcogenides based materials are most widely used materials in the electrochemical detection. The oxygen functional groups present in the CNTs and GO/rGO utilised to functionalize with polymers either through covalent or non-covalent interactions. The enhanced electrical conductivity and number of metal ions binding sites in the polymer as well as carbon surface leads to the sensitive and selective detection of heavy metal ions. Among many functional composites, GO/rGO are the best materials to functionalized with polymers due to the large number of oxygen functional groups present on the carbon surface that interacts with the functional groups of monomers either through electrostatic/covalent/hydrophobic (ππ stacking)/hydrogen bonding. Several conducting polymer nanocomposites were reported for highly sensitive electrochemical detection of heavy metal ions. For example, polypyrrole/reduced graphene oxide (PPy-rGO) nanocomposite was used as an electrode material for the selective electrochemical detection of Hg2+ ions in the presence of other metal ions such as Zn2+ , Cd2+ , Pb2+ and Cu2+ (Zhao et al. 2012). The authors believed that the nitrogen’s present in pyrrole units selectively coordinate with the Hg2+ ions. Square wave anodic stripping voltammetric (SWASV) detection of Hg2+ ions using PPy-rGO nanocomposite modified glassy carbon electrode (GCE) showed a linear range up to 100 nM with a high sensitivity of 0.124 μA nM−1 and limit of detection (LOD) 15 nM. The high sensitivity of the developed sensor is attributed to the increased conductivity of nanocomposite and hence better electron transfer between the electrode and electrolyte interface (Zhao et al. 2012). Later, PEDTO-GO nanocomposite modified glassy carbon electrode (GCE) was used for differential pulse anodic stripping voltammetric (DPASV) detection of Hg2+ ions (Zuo et al. 2016). The developed method showed a linear concentration range from 10 nM to 3 μM with a LOD of 2.78 nM (Zuo et al. 2016). Further, Lcysteine-functionalized graphene oxide (sGO)- PPy nanocomposite grown on screenprinted carbon electrode (SPE) was utilized for the highly sensitive detection of Pb2+ ions(Seenivasan et al. 2015). DPASV detection of Pb2+ ions using sGO-PPy-SPE showed three linear rages ranging from 1.4 to 14 μM and a low detection concentration of 0.07 nM (Seenivasan et al. 2015). The obtained linear ranges and LOD are several times better compared to L-cysteine functionalized reduced graphene oxide modified GCE for DPASV detection of Pb2+ ions (linear range-s 0.4–1.2 μM and LOD-0.416 nM) and PPy–rGO/GCE electrodes (Muralikrishna et al. 2014; Zhao et al. 2012). The enhanced electroanalytical properties of sGO-PPy/SPE due to the increased binding capabilities of metals ions through the functional groups of cysteine, GO and PPy and enhanced electrical transfer rate (Seenivasan et al. 2015). In the other strategy, hydrogels of PANI and GO modified GCE (HPANI-GO/GCE) was reported for the square wave anodic stripping voltammetric (SWASV) detection of Pb2+ ions. In this sensor, Pb2+ ions are binding through the nitrogen and oxygen

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functional groups present in the conducting HPANI-GO nanocomposite (Muralikrishna et al. 2017a). The electrode showed a linear range between 0.2–250 and 250– 3500 nM with low detection concentration of 0.04 nM. The longer linear range and low detection concentration of Pb2+ ions are attributed to the high adsorption properties of hydrogels and enhanced electrical conductivity. The schematic representation of the electrochemical sensing mechanism is illustrated in Fig. 9.5 (Muralikrishna et al. 2017a). The same research group has developed the PPy-rGO hydrogel modified GCE (PPy-rGO/GCE) for SWASV detection of Pb2+ ions (Suvina et al. 2018). The developed platform showed a linear range from 0.5 to 450 nM with a LOD of 0.3 nM (Suvina et al. 2018). The reported hydrogel composites showed better electroanalytical properties for the detection of Pb2+ ions in terms of low LOD, longer linear ranges and high sensitivity compared to conventional conducting polymer and its composite electrodes such as PANI/GCE (linearity: 300–2000 nM and LOD: 20.7 nM) (Wang et al. 2011), graphene-polyaniline/SPE (linearity: 1–300 nM and LOD: 0.1 nM) (Ruecha et al. 2015) and graphene/polyaniline/polystyrene nanoporous fibers modified SPE (linearity: 10–500 nM and LOD: 3.3 nM). However, the later electrode reported also a simultaneous detection of Pb2+ , Cd2+ and Zn2+ ions (Promphet et al. 2015). The hydrogel composite electrodes can also tested for simultaneous detection of Hg2+ , Cu2+ , Pb2+ and Cd2+ ions. Furthermore, glycine functionalized-rGO-PANI composite modified GCE (g-rGO-PANI/GCE) for simultaneous detection Pb2+ and Cd2+ ions (Hanif et al. 2019) and alanine functionalized rGO-PANI composite modified GCE (a-rGO-PANI/GCE) for simultaneous detection of Cd2+ , Pb2+ and Cu2+ ions, respectively (Akhtar et al. 2020). Nitrogen and phosphorous doped carbon dots and biopolymer chitosan (N, PCDs-CS) composite was used as a signal molecule carrier and redox active thionine (THi) was used as a signalling probe for the aptamer based electrochemical sensing of Pb2+ ions (Xiao et al. 2018). In this sensor, thiol-modified single-stranded DNA

Fig. 9.5 Schematic representation of electrochemical sensing mechanism of Pb2+ ions using HPANI-GO/GCE. Reproduced from ref. (Muralikrishna et al. 2017), with permission from [Elsevier], Copyright

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(ssDNA) aptamer (APT) immobilized on gold electrode (GE) and 6-Mercapto-1hexanol (MCH) was used to block the nonspecific binding interactions. N, P-CDsCS and THi were adsorbed on APT-MCH-Au electrode through π-π stacking (Xiao et al. 2018). Differential pulse voltammetry (DPV) signal is high for this composite due to the electroactive THi. After introducing the Pb2+ ions, the ATP interacts with these ions and forms a more stable G-quadruplex structure. During this process, the adsorbed N, P-CDs-CS and THi released from the electrode surface and hence the DPV peak signal decreased. The decreased peak current is directly proportional to the concentration Pb2+ ions. The developed biosensor showed a linear range from 0.01 to 10 nM and detection limit as low as 3.8 pM (Xiao et al. 2018). Biopolymers such as peptides and chitosan functionalized nanoparticles and metal chalcogenides are utilized for the optical detection of heavy metal ions. For example, zwitterionic polypeptide conjugated gold nanoparticles (ZPP-AuNPs) are utilized for the selective colorimetric detection of Ni2+ ions (Parnsubsakul et al. 2018). The zwitterionic nature arises from the adjacent carboxylic acid and amine groups present in the peptides can able to sense the metal ions and maintain colloidal stability. Ni2+ ions present in Au-polypeptides can trigger the aggregation of AuNPs resulting in colour change from red to purple and used to detect visual as well as UV–Visible absorption spectroscopy (Parnsubsakul et al. 2018). The developed method can detect Ni2+ as low as 34 nM within 15 min. with a linear range from 60 to 160 nM (Parnsubsakul et al. 2018). Silver (Ag) metal and ITO coated by PPy and CS (Ag-ITO-MI-PPy-CS) was used as a probe for surface plasmon resonance (SPR) based fibre optic sensor for detection of heavy metal ions Cd2+ , Pb2+ and Hg2+ ions (Verma and Gupta 2015). PPy and CS acts as a good sorbent for the heavy metal ions. The sensor works on the wavelength interrogation technique and is capable of detecting heavy metal ions at trace levels (Verma and Gupta 2015). In the other strategy, polymer stabilized metal nanoparticles are used as artificial enzymes (also referred as nanozymes) for the detection of heavy metal ions. For example, chitosan-stabilized platinum nanoparticles (CS-PtNPs) for ultrasensitive colorimetric detection of silver (Ag+ ) ions through inhibiting oxidase activity of CS-PtNPs. 3,3’,5,5’-Tetramethylbenzidine (TMB) was used as a substrate (Deng et al. 2019). In the absence of Ag+ ions, CS-PtNPs catalyses the oxidation of TMB (colourless) by utilising dissolved oxygen to produce oxidised TMB (blue colour). However, the addition of Ag+ ions inhibits the oxidation of TMB and hence decreases the formation of blue colour. The decreased oxidase-like activity is possibly due to the interaction between Ag+ ion and Pt2+ on the surface of CS-PtNPs, which can weaken the affinity for the TMB substrate and inactivate the oxidase properties of CSPtNPs. The linear range obtained for this method is 5–1000 nM with a low detection of 4 nM. The developed method is highly selective for Ag+ ions (Deng et al. 2019). In the other work, noble metal free CS functionalised MoSe2 nanocomposite (CSMoSe2 NC) was utilised as a duel [peroxidase (in the presence of H2 O2 and TMB) and oxidase (in the presence of dissolved oxygen and TMB)] nature of nanozyme for the highly sensitive and selective detection of Hg2+ ions. The sensing mechanism is based on enhancing the nanozyme activity of CS-MoSe2 by Hg2+ ions through the in situ reduction of CS captured Hg2+ ions. The developed method is able to detect

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Fig. 9.6 Schematic illustration for detection of Hg2+ ions using CS-MoSe2 nanozyme. Reproduced from ref. (Huang et al. 2019), with permission from [American Chemical Society], Copyright

as low as 3.5 nM by UV–Visible spectrophotometric method and 8.4 nM Hg2+ by portable smartphone method within 15 min with high specificity. The schematic representation for the sensing mechanism is illustrated in Fig. 9.6 (Huang et al. 2019). Furthermore, polyethylenimine-stabilized silver nanoclusters (PEI-AgNCs) are used as oxidoreductase mimic for the detection of Cr6+ ions (Xue et al. 2020). In the Absence of PEI-AgNCs, Cr6+ ions also react with TMB to produce oxidised TMB by reducing itself by Cr6+ to Cr3+ . However, the redox reaction kinetics is slow, which results in poor sensitivity for detection of Cr6+ ions. The presence of PEI-AgNCs significantly promotes the reaction kinetics due to the oxidoreductase properties. The reaction system does not affect the presence and absence of dissolved oxygen. The detection limit was 1.1 μM (Xue et al. 2020). Interesting naked eye colorimetric sensor for Cu2+ ions, based on polysulfone functionalized phenolphthalein hydrazide was reported (Sreeramareddygari et al. 2019). The authors pre-synthesized phenolphthalein hydrazide by condensation reaction between phenolphthalein and hydrazide. Then it was blended with polyrsulfone monomer to yield sheet. The sheet was later cut into small strips and used as solid naked eye sensor for Cu2+ ions in various environmental water samples. The strip when dipped in Cu2+ ions containing solutions induces the pink color to the solution. This was due to hydrolysis of phenolphthalein

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hydrazide to phenolphthalein by Cu2+ ions, followed by leaching of phenolphthalein into the solution (Sreeramareddygari et al. 2019). The fluorescence sensor for toxic heavy metal ions like Hg2+ and As3+ were reported based on the dansyl amine-nanobiopolymer composite and conducting polymer-carbon dot nanocomposite (Saikia and Karak 2018; Wang et al. 2012). The dansylamine-chitosan nanoparticle (DA-CS) was prepared by simple substitution reaction between amine groups of chitosan and chloride groups of dansyl chloride. The chitosan acts as platform for holding fluorescent molecule dansyl amine. Upon treating with Hg2+ ions, fluorescence of the DA-CS composite quenches quantitatively, due to froster resonance energy transfer (FRET) between Hg2+ ions and composite. The DA-CS fluorescence sensor has been used for Hg2+ ions monitoring in water samples (Wang et al. 2012). Similarly, As3+ ions quantitatively quench the fluorescence of PANI nanofibre carbon dot hybrids, and this nanocomposite has been used for monitoring As3+ ions in natural underground water samples (Saikia and Karak 2018).The polyethyleneimine stabilized Ag clusters (PEI-Ag clusters) was used for fluorescence monitoring of Cr6+ ions in real water samples (Zhang et al. 2016). The Cr6+ ion surrounds the PEI-Ag clusters through binding via oxygen of Cr6+ ions and nitrogen atoms of PEI. This result in electron transfer from PEI-Ag clusters to electron deficient Cr6+ ions. The electron transfer between the Cr6+ ions and PEI-Ag clusters results in fluorescence quenching of PEI-Ag (Zhang et al. 2016). The analytical parameters of functionalized polymer sensors for heavy metal ions monitoring were as given in Table 9.1.

9.3.1.2

Pesticides Detection

Over the past five decades, pesticides concentrations are continuously increasing in the environment due to their importance in agriculture production. They inhibit and prevent the growth of harmful animals, insects, weeds, invasive plants and fungi. The repeated applications result in the accumulation of soils and transported into an aquatic environment that leads to a toxic system for the living beings. Among the various available pesticides, insecticides, herbicides, and fungicides are the most used types (Rebelo et al. 2021). Electropolymerization method was adopted to fabricate MIPs and MIPs functionalized nanostructured material based electrodes for the detection of pesticides. For example, self-assembly followed by electropolymerization strategy was used to fabricate the molecularly imprinted (MI) polyaminothiophenol (PATP)-AuNPs modified GCE using chlorpyrifos (CPF) as template (Xie et al. 2010a). In this system, aminothiophenol (ATP) self-assembled on the AuNPs surface through the thiol group (Au–S linkage) and the free amine group interact with nitrogen/oxygen atoms present in the template CPF through hydrogen bonding. After the electropolymerization, the template was removed by washing three times with 0.5 M HCl. They examined bare GCE, AuNPs-GCE, non-imprinted PTAPAuNPs-GCE, imprinted MI-PTAP-AuNPs/GCE and imprinted PTAP-Au electrode for the detection CPF. Among them, imprinted MI-PTAP-AuNPs/GCE showed better electrocatalytic activity and low overpotential for the oxidation of CPF.

Analytical technique

Electrochemical (SWASV)

Electrochemical (DPASV)

Electrochemical (DPASV)

Electrochemical (SWASV)

Electrochemical (SWASV)

Electrochemical (SWASV)

Electrochemical (SWASV)

Electrochemical (SWASV)

DPV

Colorimetric

Colorimetric

Polymer composite

PPy-rGO/GCE

PEDOT-GO/GCE

sGO-PPy-SPE/SPE

HPANI-GO/GCE

PPy-rGO/GCE

G-PANI/SPE

g-rGO-PANI/GCE

a-rGO-PANI/GCE

ssDNA-Au and THi- N,P-CDs-CS

ZPP-AuNPs

CS-PtNPs

10–3000 1.4–14,000 0.2–3500 0.5 -450 1–300 1–300 1–300 0.1–1000 0.1–1000 0.08–100

Hg2+ Pb2+ Pb2+ Pb2+ Pb2+ Cd2+ Zn2+ Pb2+ Cd2+ Cu2+ 0.063

0.07

0.072

1.0

0.1

0.1

0.3

0.04

0.07

2.78

15

LOD (nM)

60–160 5–1000

Pb2+ Ni2+ Ag+

4

34

0.03 3.8 × 10–3

0.01–10

Cd2+

0.045

Up to 100

Hg2+

Pb2+

Linear range (nM)

Analyte

Tap and lake water

Urine, soil, sea, tap, and drinking water

Lake, river, tap and purified water

Tap water

Tap water

Human serum

Lake water

Spiked and industrial samples

Spiked and industrial samples

Tap water

–

Real samples

Table 9.1 The analytical parameters of functionalized polymer sensors for heavy metal ions monitoring

(continued)

Deng et al. (2019)

Parnsubsakul et al. (2018)

Xiao et al. (2018)

Akhtar et al. (2020)

Hanif et al. (2019)

Ruecha et al. (2015)

Suvina et al. (2018)

Muralikrishna et al. (2017a)

Seenivasan et al. (2015)

Zuo et al. (2016)

Zhao et al. (2012)

References

192 S. Muralikrishna et al.

Analytical technique

Colorimetric

Colorimetric

SPR Colorimetric Fluorescence Fluorescence Fluorescence

Polymer composite

CS- MoSe2 NC

PEI-AgNCs

Ag-ITO-MI-PPy-CS Phenolpthaleine-Polysulfone Dansylamine-Chitosan Polyaniline-carbon dots PEI-AgNCs

Table 9.1 (continued)

Hg2+ Cu2+ Hg2+ As3+ Cr6+

Pb2+

– 0–22 0.1–3

Cd2+ , 0.796 0.276 – 0.000001 0.04

0.440

0.256

1100

5–100 ×

Cr6+

103

3.5

25–2500

Hg2+

LOD (nM)

Linear range (nM)

Analyte

– Lake and tap waters – –

Tap and lake water

Spiked water and serum

Real samples

Verma and Gupta (2015), Sreeramareddygari et al. (2019), Xie et al. (2010b), Do et al. (2015), Zhang et al. (2016)

Xue et al. (2020)

Huang et al. (2019)

References

9 Functional Polymer Materials for Environmental Monitoring … 193

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S. Muralikrishna et al.

Cyclic voltammetry (CV) was used to detect CPF. The linear range obtained for imprinted MI-PTAP-AuNPs/GCE is 0.5–10 μM and the detection limit estimated 0.33 μM (Xie et al. 2010a). A similar MI-PATP-AuNPs membrane developed on the Au electrode (MI-PATP-AuNPs/AuE) was used for linear sweep voltammetric (LSV) detection of glyphosate. However, the electrical signal is generated based on the [Fe (CN)6 ]3−/4− redox probe (Do et al. 2015). Wu et al. (2014) used the extended protocol to fabricated 2-mercaptoethane sulfonic acid and ATP functionalized AuNPs-PATP-AuNPs-multi-walled carbon nanotubes (MWCNT)/GCE (MIfAuNPs-PATP-AuNPs-MWCNT) using methyl-parathion template (Do et al. 2015). The fabricated electrode detects methyl-parathion in the ppb level by linear stripping sweep voltammetry (LSSV). The improved conductivity by AuNPs decorated MWCNT results in the enhanced electroanalytical performance (Wu et al. 2014). Chemical method was used to synthesize the MIPs functionalized nanostructured materials for electrochemical detection of pesticides. For example, Sgobbi and Machado (2018) used a chemical method for the synthesis of acetylcholinesterase (AChE) mimic functional polymer for the detection of paraoxon-ethyl, fenitrothion and CPF. Polyhydroxyalkanoate (PHA) and poly(ethylene glycol) methyl ether (mPEG) were used to immobilise on the SPE (PHA-mPEG/SPE). PHA is a functionalized polyacrylamide which mimics the AChE enzyme and mPEG was used to prevent the leaching of PHA through the formation of polymer blend, which promoted the film stabilization on the SPE surface. The developed platforms detect paraoxon-ethyl, fenitrothion and CPF in the ppm level (Sgobbi and Machado 2018). Gálvez et al. developed a disposable screen printed electrode based on MIPs decorated Fe3 O4 magnetic nanoparticles (MNPs) for the electrochemical impedance spectroscopic detection of tributyltin. Schematic representation for the development of tributyltin sensor and TEM images of Fe3 O4 MNPs and MIP- Fe3 O4 MNPs are shown in Fig. 9.7 (Zamora-Gálvez et al. 2017). The developed sensor detects tributyltin as low as 5.37 pM with a linear range from 5 to 5 μM (Zamora-Gálvez et al. 2017). Zhang et al. (2013) synthesized microgel based MIPs using 2-methacrylic acid (MAA), chlorohemin, ethylene glycol dimethacrylate (EGDMA), azobisisobutyronitrile (AIBN) and 2,4-dichlorophenol (2,4-DCP). The synthesized MIP microgels (MIPmgels ) are immobilized on Nafion (Nf) and chitosan (CS) modified GCE (MIPmgels -Nf-CS/GCE) for DPV detection of 2,4-DCP. The electrochemical signal is based on the formation of a benzoquinone group in the presence of H2 O2 . The hemin group present in the MIP microcages catalyses the reaction between 2,4-DCP and H2 O2 to form chlorobenzoquinone. The developed sensor selectively detects 2,4-DCP in the linear range from 5–100 μM with a detection limit of 1.6 μM (Zhang et al. 2013). The use of carbon paste electrode (CPE) has several advantages such as easy surface modification, renewability and very low ohmic resistance (Rebelo et al. 2021). Khadem et al. (2016) developed a MIP based CPE for the electrochemical detection of diazinon. Methacrylic acid (MAA) as a monomer and ethylene glycol dimethacrylate as acrylamide used to fabricate the electrode. The developed method showed a good electroanalytical performance for the detection of hexazinone (linear range: 0.019– 0.11 nM, LOD: 2.6 pM) (Toro et al. 2015). Different monomers and templates were

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Fig. 9.7 a Schematic representation for the development of tributyltin sensor TEM images of b Fe3 O4 MNPs and c MIP-Fe3 O4 MNPs. Reproduced from ref. (Zamora-Gálvez et al. 2017), with permission from [Elsevier], Copyright

used to develop MIP-MWCNT-CPE for the detection of diuron, chloridazon, and dicloran in the ppb levels (Adel Ghorbani 2020; Khadem et al. 2016; Wong et al. 2015). Sol–gel technique was used to fabricate MIPs with Pt-UiO-66 metal organic frameworks for the detection of phosalone using SWV (Xu et al. 2020c). Electrochemiluminescent (ECL) combined with MIPs strategy can greatly enhance the selectivity and sensitivity of the analyte. Xu et al. (2020a) used Nafion-MIP CdSe quantum dots (QDs)/MWCNT modified GCE (Nf-MIP-QDsMWCNT/GCE) for the rapid detection of cyfluthrin (CYF) (Xu et al. 2020b). In this method sol–gel technique was used to develop MIP-QDs using 3-Aminopropyltriethoxysilane (APTES) as monomer and CYF as template. In this sensor, QDs act as luminophores to generate ECL in the presence of H2 O2 . MWCNT enhances the catalytic activity of H2 O2 decomposition and also improves the electrical conductivity (Xu et al. 2020b). Nafion facilitates the adhesion and ionic transport across the electrode. In the presence of CYF, the catalytic activity for the generation of ECL inhibited. Therefore, the decreased ECL intensity is directly proportional to the concentration of CYF. The LOD estimated for this sensor is 0.12 nM. Schematic illustration of fabrication of electrode and sensing mechanism is shown in Fig. 9.8 (Xu et al. 2020b). The polymer functionalized materials have been also utilized for the development of different types of optical sensors including colorimetric, fluorescence, chemiluminescence, surface plasmon resonance and surface enhanced Raman scattering (SERS) (Mahmoudpour et al. 2020). Among them, colorimetric, fluorescence and chemiluminescence are simple and cost effective methods. Therefore, we have discussed these three optical sensors based on MIPs functionalized materials in this section. For example, Ye et al. (2018) developed a simple turn-off colorimetric method for the

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Fig. 9.8 Schematic illustration for the fabrication of electrode and ECL sensing mechanism. Reproduced from ref. (Xu et al. 2020a), with permission from [MDPI], Copyright

detection of 3-Phenoxybenzaldehyde (3-PBD) as metabolite of pyrethroid pesticides using MIPs on silica nanoparticles through sol–gel method. Aminopropyltriethoxysilane (APTES), phenyltrimethoxysilane (PTES), tetraethyl orthosilicate (TEOS) and 3-PBD were used to imprint the polymers on silica nanoparticles. In this composite, 3-PBD interacted with polymer through hydrogen bonding and π- π stacking. Potassium permanganate (KMnO4 ) was used to oxidise 3-PBD to 3-phenoxybenzoic acid, which results in colour fading of KMnO4 . The detection of 3-PBD using MIP-silica nanoparticles is highly sensitive compared to the colour fading property of KMnO4 directly. The developed sensor showed a linear range from 0.1 to 1 nM with a detection limit of 0.052 nM (Ye et al. 2018). Similarly, Wei et al. (2020) developed a turn-off fluorescence method for the detection of λ-cyhalothrin based on ionic liquidsensitized molecularly imprinted polymers (MIPs) based on Mn and Cu co-doped ZnIn2 S4 quantum dots (QDs) functionalized graphene (QDs-G@ILMIPs). Mn and Cu doped QDs play a dual role in avoiding toxicity of the heavy metals and also enhance the fluorescence performance. This method showed a linear range from 1 to 350 nM/mL and detection limit 0.246 nM/mL. The enhanced sensitivity is due to the high specific surface area of graphene, which significantly enhances the number of binding sites to facilitate the electron transfer process (Wei et al. 2020). Xie et al. (2010b) used chemiluminescence (CL) method for highly sensitive online sensing of triazophos (TAP) in the presence of luminol/H2 O2 . MIPs were developed by using acrylamide as functional monomer, ethylene glycol dimethacrylat (EGDMA) as cross-linker, azobisisobutyronitrile (AIBN) as initiator and TAP as template. The selective adsorption of TAP with MIPs enhances the CL of luminol/ H2 O2 . The

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linear concentration range obtained for this sensor is 4.0 nM to 1.0 μM with a LOD of 2.5 nM (Xie et al. 2010c). Micro fluidic paper-based analytical device was also fabricated based on MIPs for turn-off CL detection of 2,4-dichlorophenoxyacetic acid (Wang et al. 2013) and turn-on detection of dichlorvos (Liu et al. 2015). The analytical parameters of functionalized polymer sensors for pesticides monitoring were as discussed in Table 9.2.

9.3.2 Safety Applications of Functionalized Polymers The widely used area of functionalized polymers in safety applications is food packing materials. The main aim of good food packing materials is to provide better barrier properties to UV rays, and toxic gasses, improved stability and antimicrobial properties. In order to attain all these properties, the polymer materials can be blended with diverse active agents like clays, metal nanoparticles, metal oxide nanoparticles and active carbon structures. The nanomaterials blended in polymer matrix to obtain better improved food packing properties are nanoclays, zeolites, Zn, Ag, ZnO, MgO Ag2 O, SiO2, TiO2 and CNT nanoparticles (Makvandi et al. 2021). The use of CNTs, Ag2 O and SiO2 are due to their antimicrobial properties. The polymers like polyamide, polypropeleyene and polylactic acid exhibited 200% water transmission rate when coupled with the CNTs. In addition to antimicrobial resistance, the SiO2 polymer composites improve the barrier as well as the mechanical properties when used as food packaging materials (Makvandi et al. 2021). The usually used clay materials in synthesing food packing functional polymers are montmorillonite and alumina silicate clays, while the polymer matrix used are polyamide, polyimide, polyesterence, polylactide and nylon (Makvandi et al. 2021). In order to attain better barrier properties with clay-polymer composites, homogeneous dispersion of clay particles with polymer matrix is very much necessary and this is possible when there are constructive interactions between the clay and polymer materials. This can be obtained by using polar solvents like alkyl-ammonium surfactants (Makvandi et al. 2021). The addition of polyester to clay-polymer composites enhances the exfoliation and intercalation of clay particles in the polymer matrix. The resulting clay-polymer composite exhibited up to 30% moisture permeability and 50% CO2 permeability(Pessan et al. 2017). Another organo clay polymer (polyethylene) composite shows moisture barrier properties which are interdependent on clay content (Makvandi et al. 2021). The polylactic acid-montmorillonite composites based packing materials increased the shelf life of meat products by reducing the oxidation of lipid content in packed meat products (Vilarinho et al. 2018). The liquid, solid, acidic and fat rich food packed with Ag and TiO2 -polyethylene blend materials exhibited microbial growth inhibition up to 10 days (Ajaal and Metak 2013). The proposed antibacterial mechanism of Ag nanoparticles includes attaching to cell surface, penetrating into the microbe cell, oxidation of lipopolysaccharides, damaging the DNA of microbes, and releasing the antimicrobial Ag+ ions which penetrates into the cell wall and forms pits (Makvandi et al. 2021).

Analytical technique

Electrochemical (CV)

Electrochemical (LSV)

Electrochemical (LSSV)

Electrochemical (DPV)

Electrochemical (CV)

Electrochemical (Amperometry)

Electrochemical (Amperometry)

Electrochemical (EIS)

Electrochemical (DPV)

Polymer composite

MI-PTAP-AuNPs/GCE

MI-PATP-AuNPs/Au

MI-fAuNPs-PATP-AuNPs-MWCNT

MI-PPy/AuE

MI-PP-NGS/AuE

AChE-MI-PPDPBMWCNT/GE

MI-PHA-mPEG/SPE

MIP- Fe3 O4 MNPs/SPE

MIPmgels -Nf-CS/GCE

4.90 × 10–3 360

5 × 10–3 – 0.1 and 0.1–12.5 1 × 103 –10 × 103

Chlor-fenvinphos

2,4-dichlorophenol

Tributyltin

Chlorpyrifos

Fenitrothion

Paraoxon-ethyl

5 × 103 –1 × 105

–5 ×

0.542 × 10–3

1 × 10–3 – 0.01 and 0.01–7

Parathion

5× 103

2.46 × 10–3

5 × 10–3 – 0.1 and 0.1–10

Paraoxon

10–3

38

3.8 × 102 –3.8 × 104

Methyl-parathion

1.6 × 103

5.37 × 10–3

803

610

1.6

30–4.7 × 103

Glyphosate

Sea and MilliQ water

Tap water

Water

River water

Tap water

Soil

2.1

49–4.7 × 102

Glyphosate

Glyphosate

Tap water

3.3 × 102 Tap water

5 × 102 –1 × 104

Real samples

LOD (nM)

Linear range (nM)

5.9 × 10–6 –5.9 –

Chlorpyrifos

Analyte

Table 9.2 The analytical parameters of functionalized polymer sensors for pesticides monitoring

(continued)

Zhang et al. (2013)

Zamora-Gálvez et al. (2017)

Sgobbi and Machado (2018)

Kesik et al. (2014)

Xue et al. (2014)

Zhang et al. (2017)

Wu et al. (2014)

Do et al. (2015)

Xie et al. (2010a)

References

198 S. Muralikrishna et al.

Analytical technique

Electrochemical (SWV)

Electrochemical (SWV)

Electrochemical (SWV)

Electrochemical (DPV)

Electrochemical (SWV)

Electrochemical (SWV)

Electrochemical (SWV)

Electrochemical (SWV)

ElectroChemilum inescent

Polymer composite

MIP-MWCNT-CPE

MIP-CPE

MIP-CPE

MIP-CPE

MIP-MWCNT-CPE

MIP-MWCNT-CPE

MIP-MWCNT-CPE

MIP-Pt-UiO(Zr)66

Nf-MIP-QDs-MWCNT/GCE

Table 9.2 (continued)

Cyfluthrin

Phosalone

Dicloran

Chloridazon

Diuron

Hexazinone

Parathion

Diazinon

Diazinon

Analyte

Tap, river and Alizadeh (2009) lake water River water

0.79

0.5 2.6 × 10–3 9 62

0.48 0.078 0.12

1.7–9.0 × 102 0.019–0.11 52–1.3 × 103 5.0 × 102 –4.0 × 105

1.0 × 103 − 1 0.50–2.0 × 104 0.46–2.3 × 102

Fish and Seawater

Lake water and soil

Tap and river water

Ground, surface, seawater and drinking water

River water

Well water

(continued)

Xu et al. (2020b)

Xu et al. (2020c)

Khadem et al. (2016)

Adel Ghorbani (2020)

Wong et al. (2015)

Toro et al. (2015)

Motaharian et al. (2016)

Khadem et al. (2017)

2.5–1.0 × 102 1.0 × 102 –2.0 × 103

Tap and river water

0.13

References

0.5–1.0 × 103

Real samples

LOD (nM)

Linear range (nM)

9 Functional Polymer Materials for Environmental Monitoring … 199

Analytical technique

Colorimetric (Turn-off)

Fluorescence (Turn-off)

Chemiluminescence

Polymer composite

MIPs-Silica NPs-KMnO4

QDs-G@ILMIP

MIPs

Table 9.2 (continued)

4–1000

1–350*

λ-cyhalothrin Triazophos

0.1–1

Linear range (nM)

3-Phenoxybenzaldehyde

Analyte

2.5

0.246*

0.052

LOD (nM)

Vegetable samples

Vegetable samples

Spiked samples

Real samples

Xie et al. (2010c)

Wei et al. (2020)

Ye et al. (2018)

References

200 S. Muralikrishna et al.

9 Functional Polymer Materials for Environmental Monitoring …

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9.4 Conclusions In conclusion, this chapter enumerates the different functionalized polymer composites reported for the monitoring of environmentally toxic substances like heavy metals, pesticides, insecticides, herbicides, and nitroaromatic compounds and packing materials for food. The synthetic strategies of functionalized polymer composites, fabrication procedures of electrochemical and optical sensors and mechanisms involved in sensing for environmental toxic substances were discussed. The type of polymer materials (conducting polymers, MIPs, biopolymer) and type of functional materials like metal nanoparticles (Au and Ag), metal oxide nanoparticles (Fe2 O3 , TiO2 and SiO2 ) carbon nanomaterials (GO, rGO, CNTs, and grapheme QDs) and their roles in polymer composites in enhancing the sensing properties were also discussed. The analytical features of the developed electrochemical/optical sensor materials were also discussed. Furthermore, the synthetic strategies and efficiency of these materials as food packing materials like antimicrobial and barrier properties were discussed.

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Chapter 10

Progress in Functionalized Polymeric Membranes for Application in Waste Water Treatment Prachi Nilesh Shah, Tanmay Sanghvi, Arya Shah, Bharti Saini, and Anirban Dey Abstract Water shortage, inadequate fresh water resources, increasing water demand and rise in water pollution would be the major threat to the human society, nature and our planet in near future. As a solution to this problem, membrane technology is extensively recognized as a means of generating different grades of water from surface water, bore well water, brackish water, seawater and waste water. In the present situation, polymers and their derivatives direct our fast-evolving daily needs and indicates enormous potential for the expansion of membrane technology, as polymers are the base materials for polymeric membranes fabrication. In coming future, functional polymers will play vital role and largely incorporated in different uses. Therefore, polymeric membranes with inherent advantages emerge as an extremely competitive candidates for recovery and reuse of water, due to high efficiency, ease of employment, low cost and little environmental impact. In waste water treatment or desalination application, the major problem in polymeric membrane technology is often the loss of membrane performance due to organic and bio-fouling. This problem can be overcome by integration of functional groups with the polymeric membranes. This chapter delivers a comprehensive review on the development of advanced functionalized polymeric membranes. Keywords Functionalized polymers · Membranes · Fouling · Ultrafiltration · Separation

10.1 Introduction In recent times, membranes are popular in industries and are used in various separation processes, which are process to achieve the separation of two or more chemical species from a solution containing distinct species. The separation operation is considered as one of the major and important unit operations in every chemical P. N. Shah · T. Sanghvi · A. Shah · B. Saini (B) · A. Dey Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, Gujarat 382421, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_10

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process industry (Purkait et al. 2018a). From the past several years, Membranes and membrane separation processes have achieved milestone by experiencing enormous growth starting from the laboratory level to the industrial scale with much technical impact. The membrane technology is popularly being used in various chemical industries, such as textile, food and beverages, chemical and petrochemical, metallurgy, automotive, paper and pulp, biotechnology, pharmaceutical, dairy (Purkait et al. 2018a). There are various treatments used for the purification of water, (1) physical processes, like sedimentation, filtration, distillation, evaporation, etc.; (2) biological processes, like active carbon, sand filters, biological filters, etc.; (3) chemical processes, like chlorination, flocculation, and the use of ultraviolet light (Popescu et al. 2017). The membrane separation process is better than other conventional separation technologies because it has the following advantages: (1) Continuous operation can be carried out for the separation process; (2) It is energy efficient process, as compared to other conventional treatments; (3) The operation is quite simple and requires low maintenance; (4) No use/addition of any chemical is done during the separation process and thus the feed and permeate constituents remains same and (5) The produced permeate have excellent quality such that it can be directly discharged into environment or any water body Purkait et al. (2018b). However, the membrane separation processes possess some major drawbacks, such as durability (lifespan) of membrane and low selectivity because of membrane fouling, but different approaches and ways are being explored to incorporate desired characteristics into membrane. In this chapter, the different method for the functionalization of polymeric membrane and the advancement that has been done in this field is presented in detail.

10.1.1 Membrane Classification The membrane can be classified mainly in two categories based on its phase (either solid or liquid), however further classification is shown in Fig. 10.1.

10.1.2 Membrane Fabrication Methods There are numerous techniques for membrane fabrication such as interfacial polymerization, track-etching, phase inversion, stretching, and electrospinning, etc. Among different membrane fabrication methods, a particular method is chosen depending upon various desired parameters of membrane and the type of the polymer chosen.

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Membrane

Solid Membrane

Isotropic membrane

Porous membrane

Non porous dense membrane

Liquid Membrane

Anisotropic membrane

Supported liquid membrane

Unsupported liquid membrane

Asymmetric membrane

Composite membrane

Electrically Charged membrane

Fig. 10.1 Membrane classification according to morphology (Purkait et al. 2018a)

10.1.2.1

Phase Inversion Method

Initially, the homogeneous polymer solution consisting of pore former is converted from liquid phase to solid-state in a controlled way. Phase inversion is widely used to make porous membrane (Purkait et al. 2018b). The choice of polymer and additives used in casting solution plays a crucial role, as it decides the membrane morphology during the phase inversion process (Popescu et al. 2017; Purkait et al. 2018b). Figure 10.2 defines the phase inversion method with the help of ternary phase diagram. In ternary phase diagram, the corners of triangles represent the three components such as solvent, polymer, and non-solvent which are there in the casting solution, though any point which lies in between the triangle represents all three components.

10.1.2.2

Interfacial Polymerization Method

This method is used to fabricate thin film composite Reverse Osmosis and Nano Filtration membranes. This technique is commonly used for commercial fabrication (Lalia et al. 2013a). The major advantage of Interfacial Polymerization technique is that it allows the researchers to experiment with optimization of the skin layer and the microporous substrate (support) layer (Lau et al. 2012; Petersen 1993). The composition and morphology of the barrier membrane layer mainly depends on different

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Fig. 10.2 Graphics of the Ternary phase diagram explaining membrane development via waterprecipitation (Saini et al. 2020)

factors that includes solvent type, concentration of monomers, post-treatment conditions and reaction time (Petersen 1993; Saini et al. 2019; Roh et al. 2006; Ghosh et al. 2008).

10.1.2.3

Electrospinning Method

This method is used to fabricate a porous membrane that is used in various applications such as filtration and desalination (Prince et al. 2012; Lalia et al. 2013b; Gopal et al. 2006). In electrospinning method, a high potential is applied between the grounded collector and the polymer solution droplet, and this disables the surface tension of the droplet, owing to high electrostatic potential. As a result of that a charged liquid jet is formed. There are several factors such as applied electric potential, environmental conditions, solution viscosity, and the flow rate of the solution that can be optimized to achieve precise morphology of the electro spun fibers (Bhardwaj and Kundu 2010).

10.1.2.4

Track-Etching Method

Track etching method is used to fabricate non-porous polymeric films. This method is carried out by irradiating and bombarding membrane surface with powerful heavy ions, which develops broken tracks across the polymeric membrane. This method is known for its accurate control of various parameters like pore size, pore size

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distribution, and pore density (Trinh 2017). The porosity of the membrane depends on the time of irradiation by heavy ions and the etching temperature, here irradiation time is an important factor to determine the pore size of the membrane. This method also ensures the less defected to no defected pores in final membrane (Fleisher et al. 1975). The pore size distribution is considered to be very precise and sharp in a membrane resulting from track etching technique (Martin et al. 2001).

10.1.2.5

Stretching Method

In this method, the polymer is forced out into thin film like sheet, followed by stretching by heating it above melting point to fabricate a microporous membrane. The crystalline portions of the membrane provide mechanical strength and the amorphous regions helps informing a porous structure and resulting product is highly crystalline in nature. This method is mainly carried out in two steps; that includes cold stretching and hot stretching. In cold stretching, the nucleation of micropores in the precursor film takes place (Sadeghi 2006; Zhu et al. 1996; Trommer and Morgenstern 2010).

10.2 Functionalization of Polymeric Membrane Functionalization of polymeric membrane is a novel approach to minimize unwanted interactions or to introduce another characteristic responsiveness for entirely different functionalities, thereby improving the performance of polymeric membranes. There are a number of polymeric substances that have very good chemical and physical properties, still they do not hold the desirable surface properties required for particular applications. Therefore, surface enhancement of polymeric membranes is considered important task in various industries using membrane technology. It provides unique way for independently improving and optimizing the surface characteristics such as hydrophilicity/hydrophobicity, anti-fouling, antistatic, biocompatibility, roughness, antibacterial properties, etc. In this chapter, the physical and chemical modification methods are been reviewed such as coating, self-assembly, surface graft polymerization, chemical treatment, and plasma treatment (Xu et al. 2009).

10.2.1 Physical Modification Methods 10.2.1.1

Coating

In coating, three mechanisms may be used for physical deposition of hydrophilic materials on membrane surface: (1) adsorption/adhesion–the additive layer is physically deposited on the polymer; where the binding strength can be enhanced by

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performing many interactions between the functional group in macromolecular layer and base polymer in the membrane; (2) interpenetration between the added functional material and the polymer in an interphase; (3) mechanical interpenetration of an added additive layer and the pore structure of the membrane. This method helps the membrane to convert from hydrophobic to hydrophilic and non- biocompatible to biocompatible. However, the major drawback of this is that the materials adsorbed on surface wash away easily, resulting in an unstable surface (Mackerle 2005; Dickson et al. 1998). Razmjou et al. (2011) fabricated PES membranes having thin mesoporous coatings of TiO2 nanoparticles via low temperature hydrothermal (LTH) approach, aided with two main techniques:(1) blending (Yu et al. 2009; Wu et al. 2008; Luo et al. 2006), and (2) depositing onto the surface (Lou et al. 2005; Mansourpanah et al. 2009; Rahimpour et al. 2008). In the blending method, it may be easily performed, but affects the distribution of nanoparticles and can also change the membrane morphology while immersion precipitation process. Also, it is difficult to achieve uniform distribution, in the absence of any surface treatment. On the other hand, the deposition technique has the limitation that it may lead to instability of the coating layer and non-uniform distribution of nanoparticles. There is also a third approach in which coating of titanium sol is followed by heat treatment to make a crystalline TiO2 film, which may produce more even distribution of TiO2 on the membrane surface. LTH techniques for creating nano-composite coatings have been recently developed, allowing for new techniques to modify hierarchical surface structure, surface chemistry and hydrophilicity of polymeric surfaces. TiO2 is crystallized by soaking the coating in hot water rather than annealing it at high temperatures. Many methods like thermal treatment, concentration, humidity, withdrawal speed and organic structure directing agents and additives can be performed to alter the topography and porosity of the surface (Kajihara et al. 1998; Kajihara and Yao 1998; Matsuda et al. 2000). Razmjou et al. (2011) used LTH method to create mesoporous TiO2 coatings on Ultra Filtration membranes. They coatedTiO2 nanoparticles onto the surface of polyethersulfone UF membranes, and the coating were stabilized by low temperature heat treatment procedure. They characterized the membrane with comprehensive techniques to study the properties of coating on the basis of photocatalytic activity, mechanical robustness, surface chemistry, and, chemical and microstructure. Even if the number of dip-coating times is increased, one cycle (single) of coating is insufficient to achieve hydrophilic surfaces for the dip coating parameters. Nevertheless, a substantial improvement in hydrophilicity can be seen by increasing the coating cycles instead of increasing the number of coating times. Some researchers termed superhydrophilicity as those surfaces that could reach contact angle (CA) of 5° or lower than that, within 5 s (Lam et al. 2009) or in 0. 5 s (Gan et al. 2007a). Mostly in literature, attaining zero CA with 5 s is used for superhydrophilicity. For commercial PES membranes coated for three cycles, zero CA were attained in roughly 12 s. Studying the effect of templating additive is also a necessary thing, as incorporating organic additives into the precursor solution in sol–gel technology is a method for carefully controlling the nanostructure architecture of inorganic films (Kajihara and Yao 1998; Matsuda et al. 2000; Lam et al. 2009; Gan et al. 2007a, b). The

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Pluronic F127 was dissolved in ethanol and mixed to the TiO2 solution before being dip-coated onto the membranes. The membrane containing F127 showed a greater initial CA than the membrane without F127. The CA of F127 coated membrane was improved by 10%, which indicated that some content of nanoparticles had been dislodged from the membrane. The membrane coated without F127 exhibits larger surface clusters, resulting in a higher surface roughness, according to SEM images. As a result, the coated membrane’s surface roughness has been sacrificed, in order to improve nanoparticle adhesion to the substrate. The surface hydrophilicity of the membrane could be improved further by more efficient removal of remaining F127 or the use of different types of templating agents. The hydrophilicity attained during 3 cycles of coating was found to be strong in nature. Two groups of membranes were coated additionally to see if this phenomenon was caused by TiO2 distribution or heat treatment. They coated membranes once, followed by three stages of heat treatment in the first set, and three times in the second set, with one stage of heat treatment at last. It is summarized that the TiO2 distribution during the three coating cycles is critical for achieving hydrophilicity. Another key contributing component in developing superhydrophilicity is an increase in roughness (Wenzel model). In fact, when the surface roughness increases from cycle 2–3, the wettability of the surface may be pushed to extremes. Razmjou et al. (2011) gave confirmation about the uniform coating layer on a membrane surface that had good stability and durability and is it less prone to fouling. Over multiple cycles of use, the coatings showed a maintained photocatalytic activity. After three cycles of coating, a long-term hydrophilicity was attained without continuous UV light irradiation. While the coating resulted considerable enhancement in fouling performance of coated membranes. While dip-coating was used to coat flat sheet membranes in this study, the approach can also be used to coat hollow fibers and other membrane topologies using alternate methods such as filtering, as demonstrated earlier for titania coating on PVDF membranes (Lim et al. 2010). With more surface functionalization, a robust hierarchically rough surface can be formed, allowing for the creation of both super hydrophilic and superhydrophobic microporous membranes. Yalcinkaya and Chaloupek (2015) fabricated PVA/TiO2 coated PSF membrane; the solution used for coating was generated by dissolving Polyvinyl alcohol (PVA) in distilled waterwithTiO2 followed by stirring for specific duration. Nikkola et al. (2014) fabricated thin-film-composite polyamide RO membrane modified by atomic layer deposition (ALD) technique using trimethylaluminium (AlMe3 ). Li et al. (2016) synthesized modified PVDF membrane using atomic layer deposition technique that has been reviewed briefly in this chapter. Atomic layer deposition technique helps in forming a hydrophilic layer on membrane surface and in holes of membrane as well by adsorption reaction between the membrane and precursor. This type of technique or technology could help us in achieving a very accurate control of deposition thickness of nanometric level accuracy by only controlling the number of deposition cycles. However, achieving improved separation performance and flux at low deposition cycle is of great importance. Li et al. (2016) used PVDF membranes in ALD modification as substrates, deionized water (H2 O) as oxygen precursor and Diethylzinc (DEZ) as zinc precursor for growth of ZnO. NO2 and diethyl zinc were

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utilized by them for the pretreatment of membrane. The pretreatment of membrane was done in an atomic layer deposition reactor. The DEZ and NO2 were alternatively sent into the ALD chamber so that adsorption type reactions take place within the membrane. ZnO was used to modify PVDF membranes, which were used with or without NO2 and DEZ pretreatment using different range of ALD cycles of 20, 50, 100, 150 and 200. It was observed that growth rate increased proportionally with increase in deposition cycles from 20 to 200 for the modified layer. Furthermore, the rate of growth of modified layer with hydrophilic nature on membranes with NO2 and DEZ pretreatment was larger as compared to the rate of development on membranes which were made without the pretreatment. After NO2 and Diethyl zinc pretreatment, the surface of membrane and its pores were covered by hydrophilic layer (Li et al. 2016). They observed that the mean pore size decreases for membranes with modified parameters including or not including NO2 /DEZ pretreatment as the number of deposition cycles increased, indicating that the membrane pore walls had a successful deposition of ZnO modified layer on it (Li et al. 2016). Further, they used FTIR to detect the formation of deposition of ZnO layer. The nature of functional groups that were formed on the surface of membrane after modification was reported to be hydrophilic in nature. The increase in hydrophilicity was reported by them with the increase in the number of ALD cycles. At same deposition cycles, the modified membranes with NO2 /DEZ pretreatment had more hydrophilic nature in comparison to non-pretreated modified membranes. In case of the pure water flux, it was observed that at ALD cycles from 20 to 200, the pure water flow of membranes with NO2 /DEZ pretreatment modification was substantially higher when compared to that of membranes that were modified directly. Which implied that the modified membranes had a very high level of wettability along with activation (Li et al. 2016). The amount of mass of BSA adsorbed on the surface of the membrane showed the fouling propensity of modified membranes. It was worth noting that, when the ALD cycles increased, the modified membranes had lesser amount of BSA adsorption. Furthermore, membranes with NO2 /DEZ pretreatment modification had resulted in decrease in BSA adsorption in comparison to the direct modified membranes, which were subjected with same ALD cycles (Li et al. 2016). At the same ALD cycles, ZnO pretreated modified membranes with NO2 /DEZ retained more BSA, than membranes that have been modified directly, resulting in decreased relative modified membranes flux with increase in number of ALD cycles (when BSA solution was filtered) (Li et al. 2016). The probability of chemical interactions among the precursors during the pretreatment of membrane with NO2 and DEZ was confirmed by these findings, and the layer with “ZnO-like” structure was most likely generated on the surface of membrane after activation. The reaction can be expected as: 2Zn(CH2 CH3 )2 + 14NO2 → 2ZnO + 8CO2 + 10H2 O + 7N2 The formation of functional groups containing oxygen on the surface of membrane was aided by several cycles of NO2 and DEZ pretreatment process, which enhanced the process of hydrophilic modification (Li et al. 2016). The modified membrane with pretreatment had a greater superior water flux and solute rejection than the

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simple modified membrane. ALD (atomic layer deposition) method for depositing materials of high-quality with great uniform nature, precise control of growth, and great conformal nature is scalable (Li et al. 2016).

10.2.2 Chemical Modification Methods 10.2.2.1

Self-assembly

Self-assembled monolayers (SAMs) and layer-by-layer (LBL) assembly are the techniques used for functionalization of membrane surface. The self-assembled monolayers can be achieved by an adsorption of an active anionic/ cationic compound on a solid surface (Ruckenstein and Li 2005; Ulman 1996). The molecular assemblies are formed in proper order because of a spontaneous formation of chemicals in form of layers at the interface. As the system tends to get stable. SAMs are known for its controlling behavior towards the functional group concentration, as surface properties are usually controlled by the outermost layer on a polymeric film. In 1991, Decher and co-researchers explored a similar method of an alternate adsorption of polycations and polyanions on film assembly (Decher, 1997; Lvov et al. 1993). Figure 10.3 shows schematic representation of self-assembly technique. During this process, the most crucial feature is to control the excessive adsorption of the polycation/poly anion assembly at all stage, which tends to recharge the outer most surface of film formation at every step. The molecular build-up is simple, and the method can be accepted and repeated to most of surface as far as charges are present on surface. This method possesses many advantages over other methods, for example, the adsorption of ions (chemicals) is totally spontaneous in nature and the surface functionality can be maintained without any stoichiometric control, the spontaneously fixed molecular layers show a greater mechanical and thermal stability. Fig. 10.3 Basic molecular picture of the first two adsorption

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Chemical Treatment

This method is used to improve surface of membrane by incorporating variety of functional groups onto the membrane surface. In this modification technique, the interfacial properties are changed while keeping the mechanical properties intact. This method can be done by various ways such as addition, hydrolysis, substitution, and oxidation. In oxidation, the dry or wet oxidation is usually involved and is known for its controlling behavior towards chemically modified reactions (Barton et al. 1997; Lu et al. 2005; Pradhan and Sandle 1999). The gaseous oxidation agents such as oxygen, carbon dioxide or ozone are generally used in case of dry oxidation method. Functional groups like hydroxyl and carboxyl groups which contain oxygen are supplied on to the membrane surface via corona discharge method. Wet oxidation method can be used to introduce oxygen containing functional groups. In this method, it demands the involvement of different chemicals such as sulfuric acid, phosphoric acid, nitric acid or blends with dichromate of potassium, permanganate, sodium hypochlorite, hydrogen peroxide, transition metal nitrates, etc. The reactions other than oxidation are also considered powerful tool for incorporating functional groups in the polymeric films (Xu et al. 2009).

10.2.2.3

Plasma Treatment

The fourth state of matter is called Plasma, and it is consisting of highly energetic and super excited particles. The occurrence of plasma-surface reaction is a result of high chemical potential of radicals. Therefore, surface enhancement using this method is considered to be an efficient and economical surface modification method for membranes (Chu et al. 2002; Denes and Manolache 2004; Förch et al. 2005; Kang et al. 2001). In plasma modification, the major benefit is that the bulk properties remain same while the biocompatibility and surface properties can be improved selectively. As depicted in Fig. 10.4, there are three different ways to put plasma treatment into practice and those includes plasma sputtering, implantation, and spraying. Plasma Sputtering–Plasma sputtering is an easy yet complex physical treatment process. It involves the triggering of inert gases to induce plasma and stimulate towards the membrane substrate. Due to collision of materials with surface atoms, the transformation of energy take place, and thus surface atoms gain sufficient energy to get away from the substrate to the vacuum chamber. The contamination on the surface will be flushed off because of the ample sputtering time, and thus plasma sputtering is also called as plasma cleaning. Plasma Implantation–The process ‘Implantation’ can incorporate chemicals onto the membrane surface without facing any thermodynamic restrictions. In this process, the electron from hydrogen atom is removed to form radicals, these polymer radicals then get bonded with the radicals that were generated by the plasma gas to form different types of functionalities on the polymer chain (Ramakrishna et al. 2011).

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Fig. 10.4 Schematic illustration of plasma treatment technique

By the formation of oxygen functionalities, the membrane surface which was earlier hydrophobic converts to hydrophilic, which improves many desirable properties such as bio-compatible, adhesion strength etc. Besides oxygen functionalities, chlorine functionalities are created using CHCl3 and CCl4 plasmas that can contribute to an increase in the hydrophilicity of the membrane (Chu et al. 2002). Plasma Spraying–In this method, the powders form of materials are sprayed into the plasma torch area at atmospheric condition. The melted powders are stimulated towards the membrane substrate at very high speed, and thus the plasma forms a coating with a lamellae structure due to high temperature and flux velocity.

10.2.2.4

Graft Polymerization

This technique involves binding of suitable functionalities onto membrane surface via covalent bonding (Bhattacharya and Misra 2004; Kato et al. 2003). In this technique, the membranes can be modified to obtain particular and novel characteristics using different grafting monomers, while keeping the sub layer properties intact. This method possesses one major advantage over the physical modification method i.e., the covalent bonding between additive and polymer chains are so strong that they don’t possess tendency to wear off from the surface and thus resulting membrane from this method is considered as more durable than others. As depicted in Fig. 10.5, this method can be categorized into two ways, i.e., ‘grafting-to’ and ‘grafting-from’ processes. First, ‘grafting to’ method here the polymer chain which carries the reactive groups that are at the side chains are attached by covalent bond onto the membrane surface. Whereas in the second method i.e., ‘grafting-from’, the active atoms and molecules that are present on the membrane

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Fig. 10.5 Schematic illustration of “grafting to” and “grafting from” technique (Zhao and Brittain 2000)

surfaces are utilized to initiate the polymerization of monomers from the surface towards the outside bulk phase by generating radicals. Various methods used for the generation of radicals can be categorized as photochemical, radiation, chemical, and plasma-induced. Grafting Initiated by Chemical–Chemical grafting can be initiated by means of generating radicals on the membrane surface and reacting with monomers or macromolecules. The type and species of the initiator determine the path of grafting process. In these two paths, initiators are used to produce active sites and transfer to the sub layer to react with the monomer and then to form grafted co-polymers. Grafting Initiated by Radiation Technique–On irradiating the membrane surface, there occurs a homolytic fission of polymer chains which generates free radicals on the surface for further grafting polymerization. There are two ways to classify radiation graftings: (1) pre-irradiation, and (2) mutual irradiation techniques. In ‘pre- irradiation technique’, the membrane surface is initially bombarded to generate radicals, so radical-possessing substrate along with monomer is grafted. In the second method ‘mutual irradiation technique’, membrane as well as monomer is irradiated together, which generates free radicals and subsequent graft polymerization. The advantage in pre-irradiation technique over mutual irradiation technique is that here radiation are not on monomers and only on membrane, hence it prevents homopolymer formation, which generally takes place in the process of mutual irradiation. But there is one disadvantage too, as irradiation is done directly on the membrane surface, it decreases the mechanical strength of membrane substrate. Factors affecting the outcomes of radiation grafting are membrane properties, duration of irradiation, reaction temperature, and concentration of monomer, the medium, etc. This technique has one major drawback, as the radiation is stimulated towards the outmost layer of the membrane, and as this radiation are of high-energy there are chances of changes in the chemical or physical properties of the substrate. Photochemical Grafting–When light falls on surface of membrane, the functional groups absorb the light and moves to the excited states, leading to generation of radicals and then begins the grafting process (Dyer 2006). The advantage of photochemical grafting is that it does not disturb the original properties of polymer as process is happening at the outermost surface of the membrane.

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The hydrophilic modification of the hydrophobic membrane is an appropriate solution to avoid fouling and diminishing of flux. There are many methods to functionalize polymeric membrane and one of the best ways to do it is by blending the additives with base polymer and solvent, since the fabrication and modification of the membrane could be achieved in sole step (Liu et al. 2011; Zhao et al. 2013) [58–59]. The main aim of grafting functional amphiphilic polymer groups on the membrane is to incorporate desired properties such as hydrophilicity, increased porosity, fouling resistance, durability, etc. After introducing the amphiphilic copolymer, the segregation of water loving part from the amphiphilic copolymer take place such that they remain actively intact on the membrane surface to be in a stable state. And the intricacy of the water repellent parts from amphiphilic copolymer with hydrophobic polymer chains can closely and tightly hold all the hydrophilic parts together within the membrane during the phase inversion process (Ma et al. 2016). To enhance the membrane’s hydrophilicity, reduce the fouling and improve the various performance parameter of membrane, the blending of modifiers and additives in the polymer matrix is viable approach in the field of membrane technology. There are mainly two types of modifiers blended into the polyethersulfone matrix and those can be categorized as mentioned here: (i) polymer and (ii) inorganic nanoparticles (NPs). The polymers includes polyvinylpyrrolidone, polyethylene glycol, chitosan, polyethylene oxide, polyamide, etc. Nanoparticles includes titanium, silver, aluminum, silica, iron, zirconium, magnesium-based NPs, etc. (Otitoju et al. 2018). Nguyen et al. prepared Polysulfone (PSF) with different amount of graphene oxide (GO) and TiO2 (Nguyen et al. 2019). Saini et al. (2020) fabricated the PVDF-g-PMEMA (poly 2N-morpholino ethylmethacrylate) amphiphilic copolymer using a technique called atom transfer radical polymerization (ATRP) shown in Fig. 10.6. Saini et al. (2020) observed that the variation in hydration capacity (HC) of the fabricated PVDF membranes with respect to the change in temperature and pH which is shown in Figs. 10.7 and 10.8, the conclusion can be made that the HC of the membranes show an increasing trend with increase in MEMA content in modified membrane at all temperature and pH conditions. P0 was a plane membrane and the membranes P1 and P2 were modified with 1 and 2% MEMA respectively. Modified PVDF membranes exhibited increased hydrophilicity compared to bare PVDF membrane and this is to be owed to MEMA chains grafted on amphiphilic

Fig. 10.6 Schematic illustration of the step wise process

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Fig. 10.7 Hydration capacity of membrane with respect to temperature (Saini et al. 2020)

Fig. 10.8 Hydration capacity of membrane with respect to pH (Saini et al. 2020)

copolymer. The bare PVDF membrane exhibited the higher water CA compared to modified membrane (Saini et al. 2020). The notable decrease in the quantity of the adsorbed BSA is observed in case of modified membrane, as compared to bare membrane. The reason being is the presence of polar groups of MEMA on the membrane surface. In case of modified membrane, the approximated porosity is higher because of the higher hydrophilic moiety of PMEMA (Saini et al. 2020). It was reported that the greater increase in pure water flux was seen in case of modified membrane as compared to plain membrane. The membranes that have higher affinity towards water (higher hydrophilicity) are less prone to fouling by hydrophobic impurities. The surfaces of modified membranes exhibit greater hydrophilicity compared to bare PVDF membrane. As

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Fig. 10.9 o/w emulsion flux and rejection (Saini et al. 2020).

shown in Fig. 10.9, the o/w emulsion rejection was found higher in case on modified membrane compared to bare membrane. The enhanced membrane exhibits phenomenal hydrophilicity because of the presence of additive, simultaneously showing an excellent antifouling property. The porosity has also increased in case of modified membrane compared to bare membrane. The stimuli responsive behavior of 2-Nmorpholino ethyl methacrylate was capable enough to control and change the hydration capacity of the PVDF-g-PMEMA membrane. A prominent and significant o/w emulsion rejection and JRR was shown by the modified membrane. These results point out that the enhancement of PVDF membrane in terms of hydrophilicity using PVDFg-PMEMA copolymer is a unique and novel approach to prepare a multi-purpose membrane. There are different methods available for functionalization of the membrane surface. Many researchers have conducted experiments on different base polymers and studied how the performance of membranes changes by using different techniques for functionalization and based on observations they have tried to optimize the surface properties. Table 10.1 summarizes the research done by different scientists on different base polymers such as PVDF, PES, PSEBMA, PSF, etc. and their improvement in performance in terms of hydrophilicity, porosity, flux, permeability, etc.

10.3 Conclusion Membrane separation is anticipated as a prominent alternative technology in the field of food and beverages, domestic and industrial water supply, biotechnology, metallurgy, pharmaceutical, etc. However, the long-term use of this technology on industrial scale is challenged by limitations that include fouling, durability, economic

0. 1%

PDMA-EMA + PEGMA + PMAA

PSF-g-POEM

PEG

PS-b-PAA

Acryla-mide

PMAAn-F127-PMAA

PSF

PES

TMA & BPPO

PES

PES

PES

1. 92

12. 5

– mg/cm3

3. 5–8. 7%

5%

15%

F127-b-PDMAEMA

PES

20%

PNIPA-Am

20%

Amino termin-ated PEG –

PDMA-EMA

PES

2. 36%

PSEBMA

AgNP

PVDF

Additive loading (wt%)/(mg/cm3 )

PES

Additive

Base polymer

Grafting

Grafting

–

Blending

Grafting

Selfassembly

Blending

Grafting

Grafting

Grafting

Blending

Technique

88. 6–89. 3

–

–

–

–

–

–

41. 42–78. 22

–

–

80. 5–85. 4

Change in porosity ε (%)

Table 10.1 Summary of functionalized polymer membranes and their properties

–

–

–

0–252

–

1547–1712

–

–

18. 76–110. 2

18. 76–126. 7

87. 5–261. 8

Change in flux

–

–

–

Water permeability (LMH/atm)

~56 to 39

~550 to 40

~70 to 50

–

85 to 52

91. 1 to 70

~72 to 53

–

~500 to 0

–

–

–

–

–

91. 76 to 71. 16 -

~84 to 71

~84 to 56

–

Hydrophilic change (CA°)

(continued)

Su et al. (2015)

Sawada et al. (2012)

Luo et al. (2014)

Tang et al. (2005)

Yi et al. (2010b)

Soltannia et al. (2020)

Yi et al. (2010a)

Tripathi et al. (2012)

Yi et al. (2012)

Yi et al. (2012)

Abdul-Majeed (2018)

References

220 P. N. Shah et al.

Additive

PSBMA

PSA-PVP

PVP-b-PMMA-b-PVP

p(CAA-co-TMA)

PES-g-PSBMA

Base polymer

PP

PES

PES

PA

PES

Table 10.1 (continued)

15%

1%

5%

Blending

Grafting

Blending

Blending

Grafting

0. 45 mg/cm3

1%

Technique

Additive loading (wt%)/(mg/cm3 )

–

–

–

77. 6–82. 9

–

Change in porosity ε (%)

–

–

–

12. 3–244. 2

1020–5230

Change in flux

90 to 60

~38 to 5

73 to 60

~76 to 68

~ 142 to 20

Hydrophilic change (CA°)

–

~6. 079 to 3. 647

~19–72

Water permeability (LMH/atm)

Zhao et al. (2016)

Yang et al. (2020)

Ran et al. (2011)

Jalali et al. (2016)

Yang et al. (2010)

References

10 Progress in Functionalized Polymeric Membranes for Application … 221

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viability and operational constraints. The recent advancement and research in material science and study of the nature of membrane surface has led to the rampant application of functionalized polymeric membrane in laboratory experiment as well as in industries. A wide range of surface modification processes via different methods have been tested and developed and successfully applied for the facile production of novel membranes with enhanced and modified intrinsic properties. Research over the past decade in this field showed benefits in exploiting the mechanical stability and chemical stability of these modified membrane, combined with their extra ordinary surface chemistry for the fabrication of high-performance novel membranes. Several studies have also reported cost-effectiveness, more durable membranes, and easy fabrication, thus, making functionalization robust way for membrane modifications and applications in many fields. In this chapter, the functionalization of polymer membrane has been discussed using two different methods one is physical modification method ‘coating’ by atomic layer deposition technique and another is ‘blending followed by grafting’ by atomic transfer radical polymerization technique. The common parameters and properties like hydrophilicity, separation, performance, fouling factor, morphology, surface roughness, pure water flux, protein adsorption of membrane was reported in case of plain, pretreated and modified membrane. Afterall it is worth noting that the goal of constructing modified layer with the help of coating method or changing membranes’ surface property and nature via blending, chemical treatment or self-assembly has become essential in order to achieve long-lasting performance to meet the requirements of real applications.

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Chapter 11

Fungal Chitin-Glucan: Renewable Nanofibrils for Water Treatment and Structural Materials Andreas Mautner

and Ernst Wintner

Abstract Materials on the nanoscale, for instance carbon nanotubes or polymer nanofibers, both well-known for high strength and modulus, have become focal points of research in material science. In the quest for sustainable materials exhibiting those characteristics, nano-sized materials based on renewable resources would be a major leap forward. Natural nanofibrils are thus an attractive development to combine advantages of the nanoscale with renewable raw materials. Specifically, nanocellulose has attracted great attention in this regard, in particular nanocellulose sheets, i.e. nanopapers, have shown huge potential both in composite and water treatment applications. This is based on nanoscale fibrils having high specific surface areas resulting in remarkable mechanical properties, together with the possibility to establish specific chemical and surface properties enabled by a plethora of functional groups attachable. Even though chitin was identified prior to cellulose as load-bearing component in natural structures, research into nanocellulose has already seen a significant rise over the course of the past two decades, whereas chitin nanofibrils have slightly lagged behind this trend. However, extraction of chitin nanofibrils from fungi has initiated a new direction of research. Fungal chitin nanofibrils are natively already present in nanoscale and thus can be isolated with very little energy demand and effort compared to nanocellulose. These nanofibrils can be directly employed in water treatment but nanopapers utilizable in structural applications are also facilitated. Furthermore, utilization of mycelium, that is the vegetative part of fungi, could allow for an even more sustainable approach to attain renewable nanofibrils, as there is no competition with an edible food product present. Keywords Fungi · Chitin · Chitosan · Glucan · Nanofibrils · Nanopaper · Mycelium A. Mautner (B) Institute of Materials Chemistry & Research, University of Vienna, Währinger Straße 42, 1090 Wien, Austria e-mail: [email protected] E. Wintner Photonics Institute, Vienna University of Technology, 1040 Wien, Austria e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_11

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11.1 Chitin Chitin was discovered by Henri Braconnot in the early 1800s and thus almost three decades before cellulose (Payen and Hebd 1838; Braconnot 1811; Children 1824), however, research into chitin and application development have always lagged behind those of cellulose. This was caused by the ubiquitous availability and easy harvest of cellulose (Nawawi et al. 2019). Yet, the developments and progress achieved for cellulose have eventually also been utilized for chitin. Analogous to cellulose in green plants, chitin’s primary biological function is constituting the structural scaffold providing support to the exoskeleton of insects and crustaceans or the fungal cell wall (Rinaudo 2007). In addition, chitin fibrils are present in mycelia, which are the “roots” of fungi constituting their vegetative part. In the various forms of life mentioned, the function of providing structural integrity is fulfilled differently on the base of their diverse physio-chemical properties. In chemical terms, chitin is (1 → 4)-linked N-acetyl-β-D-glucosamine naturally occurring in three different allomorphs (α, β, and γ) with α-chitin primarily being present in “hard” structures and considered the most abundant form and β- and γ-chitin prevalent in more flexible structures (Rinaudo 2007; Kaya et al. 2017; Blackwell 1969). Orthorhombic α-chitin, with two antiparallel molecules running per unit cell, is present for instance in fungi, crustaceans and arthropods, monoclinicβ-chitin is present in marine diatoms or the pen of squids, and γ-chitin, on which existence there is still controversy, appearing to just being a variation of α-chitin, can be found in the stomach of squids or cocoon fibers of beetles (Rinaudo et al. 2007; Blackwell 1969; Jang 2004; Seenuvasan 2020; Minke et al. 1978). As consequence of the crystalline formation, α-chitin exhibits a strong inter sheet and intra sheet hydrogen bond network, whereas β-chitin has weak intra sheet hydrogen bonds (Rudall and Kenchington 1973). The latter facilitates higher reactivity of β-chitin in modification reactions and higher solvent affinity compared to α-chitin (Jang 2004; Kurita et al. 1993, 1994). By acid treatment, both β- and γ-chitin can be converted irreversibly into α-chitin (Yui et al. 2007; Saito et al. 1997).

11.1.1 Chitosan Chitin is highly available, biodegradable, biocompatible, and non-toxic also exhibiting antimicrobial activity and low immunogenicity, however, its insolubility (apart from certain special solvents) and intractability, that are attractive properties in several applications, limit the broad utilization of chitin (Pillai et al. 2009). To circumvent this drawback, chitin’s deacetylated counterpart chitosan, which is an important chitin derivative, has found widespread use. By definition the differentiation between chitosan and chitin is based on their solubility in various media (Pillai et al. 2009). Chitin shows excellent solvent and acid/base stability; however, chitosan is soluble in acidic environment, enabling easier processing e.g. by solution-casting methods.

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These solubility differences are down to the chemical structure of both compounds thus limiting their applicability either for solvent-casting methods or film formation from aqueous dispersion, respectively. Whereas chitin has an N-acetylglucosamine backbone, chitosan’s monomer is glucosamine, which can be derived by deacetylation of N-acetylglucosamine. Moreover, due to its abundant free hydroxyl and amine groups (Ghaee et al. 2010), chitosan has remarkable metal ion sorption properties (Vold et al. 2003; Sarode et al. 2019) based on its ability to bind metal cations by chelation and anions through electrostatic interactions (Guibal 2004).This allows chitosan to be utilized as efficient adsorbent material (Bilal et al. 2013; Findon et al. 1993). 100% pure chitosan or chitin, respectively, are rare and usually the degree of deacetylation (DDA) or degree of acetylation (DA) are defined to specify the extent of (de)acetylation. The DA is the ratio of acetyl groups present divided by the number of saccharide monomer units; the DDA equals one minus DA. Often, albeit not 100% correct (see paragraph above), at a DA higher than 50% (DDA < 50%) materials are commonly referred to as chitin and at a DA smaller than 50% to chitosan. In Fig. 11.1 two examples of chitin having a DA of 75% and chitosan having a DA of 25%, respectively, are shown (Pillai et al. 2009).

Fig. 11.1 Chemical structures of chitin (top) and chitosan (bottom) with degrees of acetylation of 0.75 and 0.25, respectively (Pillai et al. 2009)

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11.1.2 Chitin Sources Similar to cellulose in plant matter in which cellulose fibers are associated with hemi-celluloses and lignin, chitin is accompanied with a variety of by-products in the various forms of life it is present. For instance in shellfish, chitin typically comes in association with sclerotized proteins and minerals (Nawawi et al. 2019), while in fungi chitin is combined with other polysaccharides such as glucan, chitosan, or mannan, depending on the species (Muzzarelli 2011). To date most studies about the use of chitin utilized animal sources for the extraction of chitin and films or (nano)papers prepared therefrom (Muzzarelli and Pariser 1978; Kataoka and Ando 1979; Yusof et al. 2004; Ifuku et al. 2011; Kadokawa et al. 2011; Fan et al. 2012; Mushi et al. 2014; Duan et al. 2013; Ifuku et al. 2014; Hassanzadeh et al. 2014; Mushi et al. 2014; Jin et al. 2016; Kaya et al. 2017; Casteleijn et al. 2018; Kaya et al. 2018; Kim et al. 2018). The reasons for this are the presence of further non-chitinous polysaccharides, diminishing the purity of chitin and requiring additional processes for the extraction of pure chitin, and the high water content of fungi. However, opposed to fungal chitin, for the isolation of chitin from crustaceans a harsh demineralization process is required that is not necessary for fungal chitin. Notwithstanding the prevailing preference for utilizing crustacean chitin, the potential of fungal chitin was recognized quite early on (Allan et al. 1978). Although chitin nanomaterials derived from animal sources have been proposed e.g. as a sustainable reinforcement in composite materials, uncertainty and inconsistency of the availability of crustaceans, which is subject to regional and seasonal supply fluctuations, intensifies the necessity to consider fungal chitin as a viable alternative to animal-derived chitin (Nawawi et al. 2019). In addition, in its native state fungal chitin is already present in the form of nanofibrils that can be isolated from fungal cells/biomass utilizing a mild alkaline extraction process followed by blending with low-energy input (Nawawi et al. 2019; Jones et al. 2020). The easy isolation and availability of sustainable nanofibrils renders fungal chitin-glucan (CG) not only a viable alternative to animal chitin (Fig. 11.2) but in particular to nanocellulose fibrils, which are commonly derived from plant materials utilizing high-energy defibrillation processes (Nawawi et al. 2019; Jones et al. 2019). Over the past two decades nanocellulose has attracted extensive interest (Klemm et al. 2011), with a broad collection of composites (Lee et al. 2014; Oksman et al. 2016), but also membrane materials (Mautner et al. 2014; Metreveli et al. 2014; Mautner et al. 2015) having been developed. In this regard utilizing nanocellulose, particularly in a 2D-macroscopic sheet, i.e. nanopaper, has been demonstrated to be of great potential (Mautner et al. 2017; Nakagaito et al. 2005; Nogi and Yano 2008; Ansari et al. 2014; Henriksson et al. 2011). This constitutes an approach also particularly attractive for chitin-glucan from fungi considering the native nanoscale dimensions of CG fibrils. Thus, chitin-glucan nanofibrils are a valuable source of new chitin-based materials, with utility in composites, packaging materials, for example mycelium composites (Jones et al. 2020), but also for water treatment processes (Janesch et al. 2020).

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Fig. 11.2 Chitin extraction process for crustacean- and fungi-derived chitin, comprising mechanical (crushing or blending) and chemical (demineralization, deproteination, and decolorization) treatments. Reprinted under CC BY 4.0 license from (Jones et al. 2020)

11.1.3 Fungal Chitin The reason why fungal based chitin was broadly neglected so far is based on the presence of glucan and other polysaccharides that are covalently bond to the chitin macromolecule backbone. However, what was often considered to be a drawback, for glucan was frequently removed to yield pure chitin, was eventually found being advantageous as it provides physico-chemical and surface properties different to those of crustacean chitin (Nawawi et al. 2019). It was demonstrated by several studies that in fungi covalent links exist between chitin and glucan or other polysaccharides such as mannoprotein or galactomannan, respectively. Opposed to animal-derived chitin, in which only residual fractions of proteins or other polysaccharides are present, fungal chitin fibrils comprise significant proportions of the polysaccharide glucan, which share is often even higher than the proportion of chitin itself (Nawawi et al. 2019; Janesch et al. 2020; Cabib and Arroyo 2013; Kollár et al. 1995; Kollár et al. 1997; Sietsma and Wessels 1979; Surarit et al. 1988; Hartland et al. 1994; Heux et al. 2000; Fontaine et al. 2000; Stalhberger et al. 2014). For instance in white button mushrooms, chitin is covalently bond to (1 → 3)/(1 → 6)-β-glucan (Fig. 11.3) at the chitin’s C3 atom, with approximately equal portions of chitin and glucan, respectively (Nawawi et al. 2019). These flexible glucan chains can be considered to constitute a flexible matrix, greatly improving film formation properties (Nawawi et al. 2019), in which the strong and stiff chitin fibrils are covalently attached and embedded thus shaping fungal chitin nanofibrils (FChNF). In such FChNF films or nanopapers, chitin is responsible for stiffness and strength while glucan increases both flexibility as well as toughness and governs surface properties of the films. Furthermore, the crustacean allergenic protein tropomyosin is not contained in fungal chitin (Lopata et al. 2010), by which the potential applicability is further extended. For example, a chitin-glucan

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Fig. 11.3 Structure of glucan commonly present in mushrooms: (1 → 3) / (1 → 6)-β-glucan (Nawawi et al. 2019)

complex isolated from the black mold Aspergillus Niger is already marketed as food supplement (Versali et al. 2009; EFSA 2010). Natively nano-sized FChNF are further set apart from nanocellulose and crustacean chitin by easy isolation processes that require much less energy as compared to energy-intensive grinding and chemical extraction procedures necessary for the extraction of crustacean-chitin nanofibrils or nanocellulose (Khor 2001). This opens up a multitude of potential applications not easily performed with pure chitin derived from non-fungal sources. Fungal chitin is present for instance in the fruiting bodies of mushrooms, that is stalk and cap. A well-known species serving as ideal model substrate for the extraction of fungal chitin-glucan and to study CG nanofibrils and products is white button mushroom (Agaricus Bisporus, AB) for its high availability in abundant amounts fabricated by large-scale cultivation, thus warranting reasonable stability in composition and properties, already established. AB is an edible mushroom that is not only nutritious but can also be utilized as functional food due to its free radical scavenging and antioxidant activity (Lin et al. 2017; Guan et al. 2013; Lindequist 2005). Essentially, AB comprises chitin, glucan, and proteins forming the fungal cell wall in addition to soluble proteins and non-structural polysaccharides (Hammond 1979). AB exhibits a characteristic odor, which is ascribed to flavor volatiles, e.g. 8-carbon atom compounds (Noble et al. 2009) for example 1-octen-3-ol (Dong et al. 2012). Moreover, human health is potentially promoted by some secondary compounds, with genoprotective, cytostatic, and anti-mutagenic activity reported, based on the presence of the enzyme tyrosinase and lectins (Yu et al. 1993; Shi et al. 2004; Lindequist 2005). Ethical issues regarding the use of food products as materials need, however, to be considered when utilizing the fruiting body of edible mushrooms. As

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alternative non-edible mushrooms, e.g. tree brackets, or mycelium, that is the vegetative part of fungi, could constitute raw materials for which these ethical concerns are much less pressing.

11.1.4 Mycelium Chitinous micro-fibers (hyphae), forming the vegetative growth of filamentous fungi are collectively known as mycelium (Jones et al. 2019). This form of chitinous material has attracted increasing academic and commercial interest over the past decade as a natural binder, e.g. for packaging, textile materials, construction applications, or acoustic and thermal insulation, by generating environmentally benign and economical materials via digesting and bonding organic biomass (Appels et al. 2019; Jones et al. 2017; López Nava et al. 2016; Camere and Karana 2018; Holt et al. 2012; Karana et al. 2018; Jones et al. 2018). For instance, several textile or shoe manufacturers have recently demonstrated products such as leather based on this type of material (Forbes-Magazine 2021; Jones et al. 2021). Mycelium constitute a continuous fibrous matrix phase (Pelletier et al. 2013; Thakur and Si˙ngha 2013) that binds and thus interfaces with the dispersed phase of organic matter that is partially digested, thus constituting mycelium composite materials (Fig. 11.4). This process increases the material volume, with the organic material acting as a filler through a network of hyphal microfilaments (Jones et al. 2017; Holt et al. 2012; Pelletier et al. 2013; Thakur and Si˙ngha 2013; Haneef et al. 2017; Islam et al. 2017). This natural biological growth empowers the production of environmentally friendly alternatives to synthetic planar materials such as polymer films and sheets facilitating a low energy demanding manufacturing process (Haneef et al. 2017). Also, larger low-density objects, for instance foams and light-weight polymer materials, can be targeted (López Nava et al. 2016; Camere and Karana

Fig. 11.4 Schematic of the manufacturing process of mycelium composites detailing the key stages, purpose and possible variations in the processes utilized during each stage. Reprinted under CC BY 4.0 license from (Jones et al. 2020)

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2018; Holt et al. 2012; Karana et al. 2018; Pelletier et al. 2013; Travaglini et al. 2013). Several key advantages have been identified for materials derived from mycelium over traditional synthetic materials. These include low environmental impact and carbon footprint, low cost and energy demand as well as biodegradability (Haneef et al. 2017; Arifin and Yusuf 2013). On the downside, due to very low density and thus a high fraction of pores, mycelium-derived materials, unfortunately, commonly exhibit mechanical properties only in the range of polymer foams. Typical mycelium composites comprise a combination of fungal mycelium together with undigested biomass, which are usually lignocellulosic fibers, having ultimate tensile strengths of up to 10 MPa but are regularly much weaker (Haneef et al. 2017; Appels et al. 2018). Mechanical strength is generally limited by the poor quality of the substrate that is employed in the production of mycelium composites. Those substrates are often low-strength agricultural waste-streams, side-streams, or by-products, which are merely weakly bond by the hyphal filament matrix (Appels et al. 2019). Moreover, the strength of the mycelium matrix itself is limited by the presence of non-structural elements, such as lipids, cytoplasm, and proteins (Kavanagh 2005). The reason for this has to be sought in the attitude that was underlying the initial approach of designing mycelium composites. This was originally based on the idea of upgrading biomass that otherwise was considered to be waste. Such waste or side-streams are commonly of rather poor integrity and strength thus limiting the final properties of the resulting composites (Jones et al. 2021). One strategy to improve the mechanical performance of mycelium-derived materials would be to eliminate these low-strength by-product or side-stream substrates as fillers, but instead utilizing them solely as nutrient source for fungal growth and extraction of the fungal structural components, i.e. chitin and other associated polysaccharides, by removing non-structural compounds from the isolated mycelium (Jones 2019). Applying such a process facilitates the conversion of industrial or agricultural side-stream biomass into natural polymers by the fungal growth. Natural polymers thus isolated are for instance the nitrogenous polysaccharide chitin that can be extracted from the cell walls of the hyphae within the mycelial biomass and in fungi is natively present in the shape of nanofibers (Rinaudo et al. 2007; Jones 2017). Chitin nanofibrils exhibit a very high tensile strength of ∼1.6–3.0 GPa (Bamba et al. 2017), which is caused by the hydrogen bond network along the macromolecule backbone responsible for rigidity and strength (Webster and Weber 2007). These chitinnanofibrils are furthermore associated to branched, flexible β-glucan or chitosan macromolecules, which results in a native nanocomposite architecture that is both strong and tough (Nawawi et al. 2019). Accordingly, in analogy to chitin derived from the fruiting bodies of fungi, mycelium-based chitin nanofibrils constitute a renewable, easily isolated, cheap, and abundant alternative to regionally and seasonally limited, potentially allergenic crustacean chitin (Di Mario et al. 2008; Hassainia et al. 2018; Ifuku et al. 2014). On top of these advantages, mycelium-derived chitin is even more sustainable compared to mushroom (fruiting body) derived fungal chitin, which not just takes longer to grow fruiting bodies than mycelium, but, in case edible mushrooms are utilized, also directly competes with food supply.

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11.2 Water Treatment Worldwide, access to clean potable water is becoming more and more a struggle. Still, particularly in Central or Western Europe, clean water is often considered commonplace; however, also in regions so far almost unaffected, the climate crisis and hence shifted periods of rain caused on one hand severe droughts but on the other hand more catastrophic storms and inundations, thus taking the situation to the edge of change (European Environment Agency 2016). The water crisis is rated the number one global societal risk by the World Economic Forum; this is signified by about 800,000 people dying each year caused by consuming polluted drinking water, the lack of appropriate sanitation services, which are not available to 4.2 billion people, or inadequate hand-washing facilities (UNESCO 2020; UN 2017). The latter is explicitly crucial in fighting potentially lethal viral infections such as influenza or corona viruses (Teslya et al. 2020; Kampf et al. 2020). Globally, it is projected that toward the end of the twenty-first century clean water will have become one of the most precious commodities on earth. Already now access to unpolluted drinking water is not safeguarded for 2.2 billion people (UNESCO 2020), albeit access to clean potable water is one of the most important human rights (UN General Assembly 2010). One estimation proposes that 50% of the population of the world will live in water-stressed areas by 2025 (WHO 2021). Scarcity of potable and clean water can be assigned to a number of factors, e.g. over-population, urbanization, globalization, the climate crisis, dietary change, and biofuel demand (UNESCO 2020; Chartress ansd Varma 2010). Furthermore, unequal distribution of clean water is contributing to the problem. For instance, in the USA or Europe per capita consumption of drinking water is larger than 500 L/day and about 300 L/day, respectively, while in some regions of the Earth, mostly in developing countries, it is less than 30 L/day (Chartress ansd Varma 2010). Another important factor is lack of appropriate waste water treatment before polluted water is released into the environment. One estimation proposes that more than 80% worldwide, and up to 95% in some developing countries, of waste water is not treated at all before it enters the environment (UN 2017). This problem is fortified by numerous emerging pollutants, i.e. substances for which no regulations are currently in place, such as nanoparticles or drugs, threatening the safety of drinking water supply, are constantly being identified (Liu et al. 2019; Adhikari et al. 2019). Regulatory bodies such as the European Commission or the World Health Organization have addressed this by revising regulations, e.g. the Drinking Water Directive, to safeguard water resources (European Commission 2021). In order to meet these and forthcoming regulations, devices and materials tackling such pollutants need to be established, which in turn requires research and development of novel materials and treatment processes.

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11.2.1 State of the Art Treatment of both waste and drinking water can be categorized into various processes and depends on the type of pollution, source, and application of the water to be remediated spanning physical, chemical, and biological treatment techniques, or often a combination of those (Speight 2020), for example combining filters/membranes and adsorbent materials to generate adsorbent filters. State of the art remediation of water by adsorption and filtration approaches, for instance membranes or filters, are currently mostly based on synthetic materials, frequently polymer filters and membranes or synthetic ion-exchange resins (Paul and Jons 2016; Mohammad et al. 2015; Yang et al. 2019; Eyley and Thielemans 2014). Filters are devices rejecting matter, i.e. solid particles, bigger than micrometers and operating in a pore flow regime, i.e. pollutants and contaminants are rejected based on their size. Membranes with pore sizes > 1.5 nm similarly operate based on this size-exclusion mechanism, whereas for particles < 1 nm the rejection mechanism of membranes is typically based on the solution-diffusion model (Wijmans and Baker 1995). The latter is, however, only of minor relevance in the field of nanopapers and sustainable nanofibril architectures, such as devices based on chitin nanofibrils, but important for synthetic membranes including e.g. regenerated cellulose (Sato and Kim 1984; Romero et al. 2013; Chitpong and Husson 2017). Two properties are commonly used in order to quantify the efficiency of water treatment membranes and filters: pure water permeance (L m−2 h−1 MPa−1 ), providing information about the amount of water that can be cleared, i.e. water flux (volume of liquid passing through unit membrane area in unit time, L m−2 h−1 ) corrected for the applied driving pressure (MPa), and the pore size, i.e. the size of particles or compounds that are rejected by a filtration device (Mautner 2020). Filtration processes and accordingly membranes being used in those processes are categorized by the size of the particles they are tackling and able to reject: microfiltration (MF, 100 nm–10 μm), ultrafiltration (UF, 2–100 nm), nanofiltration (NF, 1–2 nm), and reverse osmosis (RO, 0.1–1 nm). The filtration regime applicable is directly linked to the pore size which in turn is dependent on characteristic dimensions of the membrane or filtration material. For instance, in random networks of nanofibrils (i.e. nanopapers) the pore size mirrors the diameter of the fibrils (Sharma et al. 2020; Ma et al. 2011; Zhang 2006). This has also direct practical relevance as there is a direct correlation between pore size and water flux and accordingly the driving pressure required. Small pore sizes are generally associated with larger driving pressure required to force the water through the membrane (Yang et al. 2019). For size-exclusion filtration, the fundamental concept is that the pore size of such membranes is smaller than the size of the materials and compounds to be rejected. Size-exclusion filtration can be applied from particulate filtration with particles rejected having dimensions in the millimeter-range down to ultra- and nanofiltration rejecting matter with dimensions in the nanometer-scale (Mautner 2020). Direct determination of the pore size in the latter regimes at the nanometer scale is often complicated and hence pore size analysis implemented indirectly. This is based on the

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hypothesis that a distinct pore size is correlated to the rejection of particulate matter or macromolecules of defined size. Accordingly, appropriate materials or compounds for pore-size determination are either nanoparticles with defined and at best homodisperse dimensions, usually the diameter of spherical particles, for instance gold nanoparticles (Marchetti et al. 2014; Vandezande et al. 2008), or macromolecules of definite and homo-disperse length, for water filtration typically polyethylene glycol (PEG) or polyethylene oxide (PEO) standards dissolved in water (Pearce 2007). For the latter, the so-called molecular weight cut-off (MWCO) (Pearce 2007), which is the molecular weight (M w ) of molecules of which 90% are rejected, is defined. It is determined by measuring the reduction of the concentration (= retention) of solutes after having passed a membrane. Analysis of the concentration of dissolved macromolecules is commonly performed by gel permeation chromatography (GPC) or high-performance liquid chromatography (HPLC), respectively. The selection of the method depends on the pore size and accordingly the M w range of the polymers required. In the case of utilizing nanoparticles for pore size determination, the intensity of the typical distinct color of their dispersion, e.g. red at a wavelength of about 515–520 nm for gold nanoparticle dispersions, is analyzed by UV–Vis spectroscopy before and after filtration. The reduction of the intensity is then correlated to the rejection of the nanoparticles during filtration by applying calibration curves (Janesch et al. 2020). In the filtration regimes of interest for chitin filters and membranes, i.e. in NF and UF, currently mostly polymer thin-film-composite membranes are applied. These structures are typically based for example on polyamides, poly(ether)sulfones, polysiloxanes, polyacrylonitrile, or fluoro polymers, e.g. polyvinylidene fluoride (Mohammad et al. 2015; Galanakis et al. 2016; Oatley-Radcliffe et al. 2017; Shi et al. 2014). These polymer membranes are developed to a high level and devices based on these structures are commonly highly efficient in terms of water volumes cleared and rejection of matter or adsorption/ion-exchange capacities for certain pollutants. Unfortunately, these materials often contribute to environmental issues themselves as they add to environmental pollution when disposed of after being used or by regeneration processes requiring chemicals and energy. An alternative option to synthetic polymer membranes are ceramic membranes which facilitate a broad range of applications tackling various separation/remediation problems, and constitute highly efficient devices with regards to rejection of pollutants. On the other hand, they are typically linked to energy-intensive, high-temperature fabrication processes (Li 2007). Thus, there are a lot of materials and membrane structures available that have been shown to facilitate filtration processes. However, if those processes could be based upon more sustainable, renewable, or even degradable materials this would constitute a giant leap forward. Preferably, such sustainable water treatment approaches and devices should be available at low costs, too. All these requirements are in principle very well met by natural polymer fibers such as cellulose or chitin. Conventional micro-sized cellulose or chitin-based compounds, for instance natural fibers or crustacean extracts, have already found a vast diversity of possible applications in water treatment as these biomacromolecules are available at low cost, potentially even

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from waste biomass or agricultural/industrial waste and side-streams. Yet, the efficiency of those renewable materials in terms of rejection/adsorption of pollutants and/or the amount of water that can be cleared in reasonable times are frequently only moderate (Wan Ngah and Hanafiah 2008; Connell et al. 2008; Samoila et al. 2019; Anastopoulos et al. 2017). Consequently, more efficient materials derived from sustainable, renewable resources would be desired to be applicable in water treatment. Based on its properties by constituting a native nanofibrillar material with an abundance of functional groups present on the surface of the fibrils, this could be fungal chitin fibrils.

11.2.2 Chitin in Water Treatment Chitin is already utilized in the treatment of water mostly in the form of batch-wise applied particulate adsorbents but also fabricated into films and membranes (Samoila et al. 2019). The utility of chitin for this application is based on the surface properties of chitin fibrils, where an abundance of free hydroxy and acetamide groups provides high affinity toward metal ions, making these renewable sorbents effective for water treatment (Sarode et al. 2019; Shaheen et al. 2013; Hubert Ribeiro and dos Santos 2019). Chitin membranes have, so far, been mostly based on animal-derived chitin processed by regeneration or casting methods. For instance, UF membranes were prepared by regeneration of chitin solutions in dimethylformamide, dimethylacetamide, or N-methyl-2-pyrrolidone, optionally with pore forming agents such as lithium chloride (Samoila et al. 2019; Uragami et al. 1981; Aiba et al. 1985). Opposed to those chemically demanding processes, utilizing nano-sized fibrils in a porous network capable of rejecting nanoparticles by generating size-exclusion and/or adsorptive filters and membranes directly by a papermaking process from aqueous dispersion would be a sustainable alternative. Whereas chitin is definitely of use in water treatment application, chitosan is even more frequently used for its high attraction toward positively charged pollutants compared to chitin carrying N-acetamide groups (Muzzarelli and Pariser 1978; Allan et al. 1978; Rostamian et al. 2019; Paulino and Santos 2008; Zhang et al. 2016). Chitosan is an important chitin derivative that exhibits free amine groups, readily available from chitin by deacetylation of the N-acetylglucosamine backbone utilizing cleavage of the N-acetyl groups under alkaline conditions, e.g. in a concentrated solution of NaOH at elevated temperatures. Furthermore, due to its inherently higher solubility compared to chitin, processing of chitosan and formation of films, e.g. by solution-casting methods, is easier performed and thus more often utilized. Overall, chitosan constitutes a more efficient renewable sorbent material compared to chitin, e.g. for heavy metal ion removal from aqueous solutions and thus both fresh and waste water (Bilal et al. 2013; Findon et al. 1993). This is based on excellent metal ion sorption properties (Findon et al. 1993; Sarode et al. 2019) facilitated by its abundant free hydroxy and, even more importantly, amine groups (Ghaee et al. 2010; Vold et al. 2003; Rostamian et al. 2019; Khalil et al. 2020; Dragan and Dinu

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2020; Preethi et al. 2017). At and around neutral pH as well as in acidic environment, chitosan is capable of binding cations by means of metal chelation and anions through electrostatic interactions, respectively (Guibal 2004). The mechanism of this chelation process, i.e. how chitosan interacts with metal cations, is still controversially discussed, with two suggested models, the hanging-drop and the bridge model, having been proposed (Modrzejewska 2013). Apart from high attraction to metal cations, chitosan exhibits a flexible structure (Roberts 1992) that assists the sorption of ions, irrespective of size or physical shape of chitosan materials (e.g., powder, hydrogel, film, or in solution), which permits for competitive adsorption capacities when compared to traditional synthetic adsorbent materials. Furthermore, biodegradability, low costs of raw materials, film, or in solution and easy manufacturing processes are parameters in favor of chitosan (Shaheen et al. 2013). Similar to chitin, chitosan membranes are commonly processed by dissolution/regeneration techniques, which can be done easier in case of chitosan due to its higher solubility. Frequently, preparation processes for chitosan utilize chemically modified chitosan, e.g. obtained by the reaction with succinic anhydride (Samoila et al. 2019; Kumar et al. 2013). By utilization of fungal chitin nanofibrils as precursor for chitosan fibrils, papermaking processes would be enabled for chitosan as well, due to the anticipated presence of glucans, which are covalently bond to the chitin/chitosan macromolecular backbone (Nawawi et al. 2019; Sietsma and Wessels 1979; Surarit et al. 1988). By this, easy water-based membrane and filter preparation would be facilitated and fungal-based chitin/chitosan-glucan nanopapers could be prepared for use in size-exclusion filtration and dynamic adsorption processes. This would also include the benefit of reduced ecological footprint compared to traditional membrane manufacturing processes (Mautner et al. 2015; Honda et al. 2002).

11.3 Fungal Chitin Nanopapers Nanopapers, random networks of flexible nanofibrils, i.e. papers fabricated from nano-sized fibrils rather than from fibers with diameters on the microscale, have originally been developed for nanofibrillated cellulose (Lee et al. 2012). Such nanopapers were demonstrated to be versatile structures for the use in composite materials (Lee et al. 2014; Benítez and Walther 2017) and water treatment applications (Mautner 2020). Excellent mechanical properties and membrane separation efficiencies were reported, which are based on the nanoscale dimensions of nanocellulose providing large specific surface area and an abundance of functional hydroxy groups. These developments also benefitted the use of a different kind of biomacromolecule nanofibril: fungal chitin-glucan. Even more so, due to the native nanoscale dimensions of fungal CG, the energy demand for the fabrication of nanofibrils and subsequently nanopapers is lower compared to cellulose and furthermore, additional functionality is present in the form of N-acetyl groups at the C2-position of the

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polysaccharide backbone, whereby fungal chitin was proposed to be beneficial over nanocellulose (Nawawi et al. 2019; Nawawi et al. 2020a).

11.3.1 Chitin-Glucan Nanopapers from Mushroom Commonly, due to its limited solubility, fabrication of films from chitin is an affair of limited attractiveness, and more often chitosan is applied based on its higher solubility (Janesch et al. 2020). However, the presence of glucan, covalently bond to the macromolecular chitin backbone is proposed to expedite film formation properties thus supporting generation of a tough and strong nanopaper network structure (Nawawi et al. 2019; Nawawi et al. 2020a). Moreover, fungal chitin-glucan fibrils are natively generated in the nanoscale and hence extraction of renewable nanofibrils is possible without the requirement for energy-intense nanofibrillation procedures. It was demonstrated for nanocellulose that the pore size of a nanopaper size-exclusion membrane is controlled by the fibril diameter (Mautner et al. 2014). This correlation was also proposed for chitin-glucan nanofibrils. Hence, pore sizes of CG nano papers were expected to be in the low nm range. Additionally, chitin possesses an N-acetamide functional group attached at the C2 position of its polysaccharide backbone. This polar group exercises attraction toward positively charged moieties, for instance metal cations, thus facilitating adsorption of certain classes of pollutants. This would allow for the preparation of membranes exerting separation function in both size-exclusion and adsorption regime. Deacetylation of these N-acetyl groups yielding glucosamine moities would permit for even stronger interaction with positively charged ions. Starting point for the studies on fungi to be used as raw material for nanopaper fabrication was the extraction and characterization of fungal chitin nanofibrils. Nanopapers were subsequently prepared from FChNF and surface properties investigated. FChNF were extracted from white button mushroom A. bisporus used as model system, which was selected because of its high availability and continuity of the composition for a natural material, as it is already manufactured in large-scale industrialized agriculture. Various parts of the fungi, i.e. stalk, cap, or whole fruiting body, were utilized to isolate FChNF from AB. To successfully extract FChNF it is key to develop a mild procedure avoiding cleavage of glucan. Commonly, for the extraction of chitin from crustaceans, harsh processes are performed utilizing strong alkaline and acidic media as well as high temperature. Such conditions would also result in the hydrolysis of covalent bonds through which glucan is bond to the chitin backbone. Eventually, optimal conditions for extraction of CG included a hot-water treatment to separate water soluble ingredients, such as some types of proteins or low molecular weight sugars, and a mild alkaline treatment (1 M NaOH) necessary for the complete removal of proteins and other by-compounds (Nawawi et al. 2019; Nawawi et al. 2020a). The chemical composition of FChNF was analyzed by means of elemental analysis and polysaccharide analysis (HPLC), which revealed that approximately 50 wt.-%

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of the extract was chitin and the other part was glucan. From electron microscopy the diameter of FChNF was determined to be about 15 nm, which was smaller than chitin fibrils from crustaceans but also common unmodified nanocellulose, for instance derived from wood pulp. Importantly, the presence of glucan benefitted and ultimately facilitated film formation (Fig. 11.5 top), thus circumventing a drawback of pure chitin derived from animal sources which yield nanopapers exhibiting poor properties. Furthermore, glucan also induced surface hydrophobicity of FChNF nanopapers, which was indicated by higher water contact angle values (θ = 65° for FChNF compared to θ = 24° for crustacean chitin from Cancer pagurus, Fig. 11.5 bottom). Investigating the influence of varying the grammage and thus thickness of FChNF nanopapers revealed a decisive impact in particular on the mechanical properties. An optimal grammage for nanopapers of 80 g per square meter, similar to ordinary printing paper, was established. FChNF nanopapers had a tensile strength of up to more than 200 MPa, which is a multiple of office paper and a value on par

Fig. 11.5 Top: Dried chitin-glucan (left) and crustacean chitin (right) suspensions on a copper grid demonstrating film formation due to the presence or absence, respectively, of glucan. Bottom: a water contact angle θ of water droplets after 1 min resting on nanopapers from (left to right) C.pagurus as well as stalk and cap of AB and whole AB; pictures of water drops after 1 h on b stalk and C.pagurus, c AB coated blotting paper, and d AB coated filter paper. Reprinted from (Nawawi et al. 2020a), Copyright (2020), with permission from Elsevier

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with nanopapers fabricated entirely from chemically unmodified cellulose nanofibrils, that were extracted by energy-intensive defibrillation (Nawawi et al. 2020a; Nawawi et al. 2019). White button mushroom FChNF nanopapers were shown to have mechanical and surface properties profoundly varying to those of crustacean derived chitin, which is caused by the presence of glucan that makes up about 50% of FChNF. The amount of glucan present does, however, significantly vary for different fungi species. For example, FChNF isolated from tree bracket fungi (Daedaleopsis confragosa) exhibit by far higher glucan contents compared to those of white button mushrooms with glucan contents reaching up to 99% (Nawawi et al. 2020b). This high glucan content facilitates tremendously high flexibility of tree bracket-derived FChNF nanopapers. Moreover, blending of CG extracted from various fungi species thus allows for tailoring the mechanical properties of nanopapers by formulating FChNF mixtures from different fungi species, e.g. white button mushroom and tree bracket fungi, from highly rigid to highly flexible, i.e. from plastic to elastic (Fig. 11.6). Yet, the surface hydrophobicity/hydrophilicity was at large the same for FChNF nanopapers prepared from white button mushrooms or tree brackets, respectively. Thus, it is possible to design mechanical properties as required but without altering surface properties in the course (Nawawi et al. 2020b). Very high mechanical strength and stiffness were demonstrated for FChNF nanopapers, with additionally having the opportunity to tailor mechanical properties, which is based on the native nanoscale dimensions of FChNF. These nanoscale dimensions should also facilitate preparation of random network structures formed by these fibrils in a nanopaper similar to nanocellulose papers (Mautner et al. 2014, 2015), that are proposed to exhibit pore sizes in the nm range as well. Such network structures of FChNF nanopapers derived from A. bisporus could be utilized for ultrafiltration processes in the size exclusion regime coupled with additional interaction of the N-acetyl group in chitin that facilitates adsorption of (heavy metal) ions from Fig. 11.6 Mechanical properties as shown by stress–strain curves for chitin-glucan nanopapers obtained from A. bisporus, D. confragosa and blends thereof compared to chitin papers from C. pagurus. Reprinted under CC BY 4.0 license from (Nawawi et al. 2020b)

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Fig. 11.7 Molecular weight cut-off (MWCO) of FChNF nanopapers for a PEG in aqueous solution and b polystyrene (PS) in tetrahydrofuran (THF). MWCO relates to the molecular weight of a solute which is 90% retained by a membrane. Reprinted from (Yousefi et al. 2021), Copyright (2019), with permission from Elsevier

aqueous solution (Yousefi et al. 2021). For FChNF nanopapers from AB an inverted logarithmic correlation between permeance and nanopaper thickness and grammage was reported, similar to nanocellulose papers. The pore size of such nanopapers, as expressed by the molecular weight cut-off for PEG (17 kDa), was about 10 nm (Fig. 11.7), similar to the diameter of the FChNF (15 nm). Thus, FChNF nanopapers facilitate filtration of nanoparticles in tight UF range. Furthermore, in addition to rejection of nanoparticles, metal ions could be adsorbed with an adsorption capacity, analyzed for copper as model heavy metal compound, of more than 40 mg g−1 . This was thus slightly lower compared to adsorption capacities of crustacean chitin and could be explained by the presence of glucan, which inherently reduces the fraction of chitin present per unit mass and accordingly N-acetyl amino groups, which are primarily responsible for adsorption. In an attempt to increase the efficiency of FChNF nanopapers in terms of primarily permeance but also adsorption capacity, cellulose microfibers were blended into the formulation used to manufacture papers. This yielded highly porous composite filters that were capable of adsorbing metal cations while permeated. The adsorption of copper ions was 805 mg m−2 membrane area, which relates to an adsorption capacity of 81 mg g−1 . The higher adsorption capacity was explained by better availability of chitinous functional groups within such porous networks compared to dense nanopapers consisting solely of nanofibrous CG (Yousefi et al. 2021).

11.3.2 Chitosan-Glucan Prepared by Deacetylation of Fungal Chitin When chitin is deacetylated, i.e. acetyl groups are cleaved, chitosan is obtained. This chitin derivative exhibits primary amine groups instead of N-acetyl groups, whereby due to the lone pair at N and less steric hindrance, chitosan is more prone to adsorption of ions compared to chitin. The deacetylation reaction of chitin is

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usually completed by hydrolysis in alkaline media, for instance in NaOH solution. For crustacean chitin as substrate this process can be performed under pretty harsh conditions, i.e. concentrated alkaline solution at high temperatures, which also helps to remove certain by-products that are present in the hard structure of the exoskeleton of crustaceans. Furthermore, in crustacean chitin fibers there is no glucan present that also undergoes hydrolysis during treatment with concentrated alkaline media. Thus, for fungal chitin as substrate, deacetylation needs to be performed carefully as glucan, responsible for good film formation properties, can easily be cleaved under similar conditions as required for deacetylation and can actually be removed as a whole (Nawawi et al. 2019). As model system for the deacetylation of fungal chitin, white button mushroom was selected. Initially CG was extracted from the fruiting body of AB and deacetylation of FChNF derived from AB executed with NaOH of different concentrations (20, 40, and 60%) yielding chitosan-glucan (CSG) (Janesch et al. 2020). The chemical composition of the various grades of CSG was analyzed with a set of different analytical techniques (elemental analysis, carbohydrate analysis, nuclear magnetic resonance (NMR) and Fourier-Transform infrared (FT-IR) spectroscopy) that were combined for the determination of the fractions of all the three components present: chitin, chitosan, and glucan. By increasing NaOH concentration and treatment time, the chitosan content increased up to 39% which corresponds, when corrected for the glucan content present as determined by carbohydrate analysis, to a degree of deacetylation (DDA) of 58%. Furthermore, it was reported that already at an NaOH concentration of 20% a certain fraction of glucan (amounting to approximately 30% of glucan originally present) was cleaved but the majority of glucan was still present (Janesch et al. 2020). The influence of reduced glucan content was indicated by reduced mechanical properties of the nanopapers as determined by tensile tests. Furthermore, the impact of alkaline concentration utilized for the deacetylation reaction was revealed: for moderate NaOH concentration (20%) the strain to failure remained at more than 5% but significant yielding at about 100 MPa approximately halved the ultimate tensile strength compared to chitin-glucan nanopapers. For higher concentrations (40% NaOH) both strain and strength were lowered and yielding commenced already at lower stresses. This alteration of mechanical properties was explained by hydrolysis/chain cleavage in alkaline medium at elevated temperature but in particular removal of glucan. The goal of deacetylation was, however, primarily to impact the surface properties by altering the functional groups present on the surface of FChNF and also the filtration performance. Indeed, cleavage of acetyl groups showed the desired, significant effect on the surface properties of CSG nanopapers. The surface charge, as expressed by the zeta (ζ)-potential plateau, became more negative and the iso-electric point, i.e. the pH at which no net charge is present, increased. Both those effects indicated the presence of a higher proportion of amine groups, as opposed to N-acetyl amino groups, present on the surface of FChNF and thus on the surface of the nanopapers (Fig. 11.8). In terms of membrane properties, nanopapers from the various grades of CSG had permeances slightly lower compared to chitin-glucan nanopapers. This was explained by enhanced interaction of more hydrophilic amine groups with water,

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Fig. 11.8 ζ-potential as a function of pH for CG nanopapers and chitosan-glucan nanopapers partially deacetylated. CSG20-1: 20% NaOH for 1 h, orange open squares; CSG40-1: 40% NaOH for 1 h, blue full squares; CSG40-2: 40% NaOH for 2 h, green open triangles. Reprinted from (Janesch et al. 2020), Copyright (2019), with permission from Elsevier

yielding a chromatography effect. More importantly all grades of nanopapers had pore sizes of about 10 nm as demonstrated by their capability of completely rejecting 10 nm gold nanoparticles, thus similar to CG nanopapers and in accordance with the hypothesis, considering that the diameters of CSG were at large the same as for CG. Composite filters with cellulose microfibrils were designed in order to improve filtration properties, in particular the permeance, which was achieved. Remarkable adsorption capacities of 162 mg g−1 were realized. These results (Janesch et al. 2020) confirmed that papers fabricated from fungal chitin derived chitosan could be obtained by a simple water-based papermaking process, without the necessity to dissolve chitosan first and manufacture films by casting processes. Those papers exhibited excellent size-exclusion properties but also adsorptive filters with high adsorption capacities could be shaped.

11.3.3 Chitin-Glucan from Mycelium Fruiting bodies of mushrooms have been demonstrated to be a particularly suitable source for the extraction of chitin(-glucan) and subsequently chitosan(-glucan) nanofibrils, facilitating the preparation of nanopapers with appropriate properties for filtration and structural applications. The reason for using white button mushrooms as raw material for FChNF extraction was down to its large-scale cultivation and thus reproducibility of properties. This makes it an ideal model system, but still one needs to be aware of the implications present when utilizing edible biomass in material applications. On the downside of using an edible mushroom is of course competition with food supply which constitutes an ethical issue. Thus in order to improve sustainability, avoiding the use of (edible) mushroom fruiting bodies, the culture and use of the vegetative part of mushrooms, i.e. mycelium, rather than the fruiting body, as source for chitin and chitosan would be an intriguing approach, circumventing

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competition with food (Jones 2017, 2021, 2020). Similar to the fruiting body of mushrooms, mycelia majorly consist of chitin fibrils covalently bond to glucan or other polysaccharides. Also, in mycelium chitin fibrils are natively present in the form of nanofibrils (Jones et al. 2020). Typically, mycelium materials are used as-prepared, which means the combination of substrate and in-grown mycelium. This commonly resulted in low mechanical properties caused by the substrate’s low mechanical integrity. This triggered the idea to not just grow mycelium on cheap, abundant, and biocompatible agricultural side or waste-streams but to isolate chitin(-glucan) nanofibrils from the composite generated and utilize these FChNF for the fabrication of nanopapers. The first step in this endeavor was to identify suitable culture substrates that are derived from agricultural side-streams, e.g. sugarcane bagasse, wheat straw, rice hulls, or blackstrap molasses (Jones et al. 2019). Blackstrap molasses was found to be a particularly excellent choice for growing mycelium. This substrate actually outperforms highquality growth media such as malt extract, which is frequently used as nutrient in laboratory experiments. The second step after a suitable culture medium was identified was to screen various fungal species for their efficacy in the production of chitin nanofibrils (Jones et al. 2019). Different species yielded different types of combinations of chitin with other polysaccharides, e.g. chitin-glucan or chitin-chitosan. These structural polymer fibrils were isolated from fungal mycelium biomass grown on blackstrap molasses. Isolation of FChNF from mycelium comprised a hot-water and an alkaline treatment, subsequently followed by vacuum filtration and hot-pressing to fabricate homogeneous nanopapers (Fig. 11.9). Dry content yields of mycelium chitin-compounds based on Allomyces arbuscular, Mucor genevensis, and Trametes versicolor were on par with yields reported for A. bisporus fruiting body and similar to yields obtained for extracting chitin from crustacean sources (Nawawi et al. 2019; Jones et al. 2019; Nawawi et al. 2020a). Analysis of the chemical composition by elemental and carbohydrate analysis showed that the glucan-fraction in mycelium extracts was significantly higher compared to those

Fig. 11.9 Nanopaper production process from mycelium cultures. A molasses medium is initially inoculated with the species of interest which grows to form a thick hyphal network. The biomass can then be treated using NaOH, the residue collected, vacuum-filtered and hot-pressed to produce the final nanopaper. Reprinted with permission from (Jones et al. 2019). Copyright (2019) American Chemical Society

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Fig. 11.10 Advancing contact angle (θA , blue full squares (H2 O) and open circles (CH2 I2 )), surface tension (mJ m−2 ), and specific surface area (SBET , hollow red triangles, m2 g−1 ) for A. arbuscula and M. genevensis NaOH treated mycelium-derived nanopapers. A. bisporus fruiting body-derived nanopapers and A. arbuscula NaOH and H2 O2 or HCl treated nanopapers are also displayed, with the transition between hydrophobic and hydrophilic properties following HCl or H2 O2 treatment marked by red dashed boxes. Reprinted with permission from (Jones et al. 2019). Copyright (2019) American Chemical Society

obtained from A. bisporus fruiting bodies. This was indicated by lower nitrogen and glucosamine contents. Consequently, lower mechanical strength and stiffness of resulting nanopapers had to be accepted compared to the excellent values of chitin-glucan obtained from the fruiting body of white button mushrooms. This was caused by the presence of high glucan contents and other carbohydrate (predominantly galactose but also arabinose or maltose) fractions inherently resulting in lower chitin contents. Moreover, impurities, for instance caused by biomineralization of calcium, were present (Jones et al. 2019). Yet, mycelium nanopapers were close to the mechanical properties of nanopapers prepared from animal chitin (Nawawi et al. 2019). Accordingly, extended extraction and purification processes need to be researched and developed in order to improve the mechanical performance. Above all, the growth of mycelium on suitable agricultural residues and extraction of chitinnanofibrils from the culture allowed the surface properties of according nanopapers to be controlled from hydrophilic to hydrophobic (Fig. 11.10). This demonstrated the feasibility of a sustainable raw material (fungal mycelium) for the fabrication of renewable nanopapers exhibiting controllable properties (Jones et al. 2019).

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11.4 Concluding Remarks Nano-sized polymer fibers are an important class of materials, facilitating high mechanical properties for instance in composite materials. Addressing environmental issues, preparing such nanofibers from materials derived from sustainable and renewable resources would contribute to ecologically benign solutions. Currently, sustainable nanofibers are prepared from cellulose or animal-derived chitin by defibrillation of microfibers, e.g. wood pulp, necessitating high energy input and/or harsh chemical treatment. The native nanoscale dimensions of chitin fibers extracted from fungi could reduce the energy input required and furthermore provide additional surface functionality. The presence of glucan in fungal chitin fibers moreover facilitates the preparation of nanopapers by a scalable water-based papermaking process. Such nanopaper networks exhibit controllable mechanical properties depending on the species used for the extraction of nanofibrils. Surface properties more hydrophobic than for films or papers from crustacean chitin also allow for such filtration processes or structural applications for which highly hydrophilic chitin nanopapers would not be an appropriate choice. Deacetylation of fungal CG yields chitosan-glucan that exhibits enhanced attraction toward (heavy metal) ions and thus more efficient application in adsorption membrane processes. Slightly decreased mechanical strength has to be accepted due to the co-hydrolysis of glucan during the deacetylation reaction reducing the flexibility. Even more sustainable a raw material for the extraction of chitin-glucan nanofibrils is mycelium, the vegetative part of fungi. Competition with food supply by using fruiting bodies of mushrooms triggers ethical issues that can be minimized by utilization of mycelium. Currently, mycelium materials are mostly composite materials in which a, frequently agricultural residue, substrate is bond by growing mycelium through the porous network of the substrate. Due to the intended upgrade of waste materials, mechanical properties of such composite structures are commonly moderate at best, as the substrate itself is usually of low mechanical integrity. However, utilizing the substrate solely as nutrient for growing mycelium and subsequently extracting chitin-glucan from the cultures would circumvent this drawback. CG thus extracted can be fabricated into nanopapers similar to CG derived from the fruiting body of mushrooms. Still, lower mechanical properties have currently to be accepted compared to mushroom fruiting body derived nanopapers for higher amounts of by-products are present. This could in future research be mitigated by developing improved extraction and purification processes.

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Chapter 12

Advanced Functional Materials for the Detection of Perfluorinated Compounds in Water Satya Ranjan Jena, Sudesh Yadav, Anchal Yadav, M. B. Bhavya, Ali Altaee, Manav Saxena, and Akshaya K. Samal Abstract Per- and polyfluoroalkyl substances (PFAS) are toxic and anthropogenic fluoro organic compounds found in the natural environment and living organisms, including humans. Numerous treatment methods have been investigated for these hazardous compounds, including physical, biological, and chemical processes. According to current trends, destructive treatment processes that result in the degradation and mineralisation of PFAS are the most desired by researchers and policymakers. Recently, nanomaterials have demonstrated their utility in a variety of applications, including energy, sensors, and separation technologies. However, their ability to degrade PFAS is still in its early stages. Thus, this chapter aims to provide valuable insights into various nanomaterials used for degradation of PFAS. Lastly, future research directions are suggested for a sustainable environment. Keywords Pre- and polyfluoroalkyl substances (PFAS) · Fluoro organic compounds · Toxic · Degradation · Nanomaterials

Jena and Yadav: These authors contributed equally. S. R. Jena · M. B. Bhavya · M. Saxena · A. K. Samal (B) Centre for Nano and Material Sciences, Jain University, Ramanagara, Bangalore, Karnataka 562 112, India e-mail: [email protected] S. Yadav · A. Altaee (B) Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, Ultimo, NSW 2007, Australia e-mail: [email protected] A. Yadav School of Chemistry, Monash University, Clayton VIC-3800, Australia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 N. K. Subramani et al. (eds.), Polymer-Based Advanced Functional Materials for Energy and Environmental Applications, Energy, Environment, and Sustainability, https://doi.org/10.1007/978-981-16-8755-6_12

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12.1 Introduction Globally, rapid urbanisation and increased industrialisation exacerbate a variety of environmental problems, including soil and water pollution (Bhol et al. 2021; Yadav 2020). Emerging pollutants resulting from pesticides, industrial waste, flame retardants, detergents, and other organic compounds generated by humans pose a serious threat to future generations (Tang et al. 2019). PFAS are examples of emerging contaminants that are extremely persistent in the human body and environment over an extended period due to their unique physicochemical properties such as hydrolysis process, photolysis, and microbial degradation methods (Hogue 2019). PFAS is a generic term used to describe very stable artificial perfluorinated chemicals (PFCs) that include perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), GenX, fluorotelomer alcohols (FTOHs), and over 4,000 other human-made chemicals. Originated in the United States in the 1940s, PFAs have been commercialized in the 1950s and used in various household and commercial products around the globe (Nakayama 2019; Buck et al. 2011). The chemical structure of PFOA and PFOS is shown in Fig. 12.1. The PFAS are generally made up of aliphatic compounds containing saturated C-F bonds with different carbon chain lengths and include varying amounts of oxygen and hydrogen. The C-F bond is highly stable and is resistant to chemical, physical, and biological degradation (Smart 1994). PFAs are also known as “forever chemicals” because once released into the environment, they do not break down and are absorbed in the human body, which accumulates in the human body with time. As compared to polyfluoroalkyl compounds (carbon chain with the presence of C-H bonds among C-F bonds), perfluoroalkyl compounds (fully fluorinated carbon chain) tend to be more persistent and toxic in the environment (Buck et al. 2011; Kah et al. 2020). Exposure to PFAs in water is primarily through ingestion, while the other household water usage is not significant. The contamination could occur from the release of PFAs to the industrial facility, where PFAs are used for manufacturing the goods, oil refineries, where PFAs are used in firefighting equipments, discharge from PFAs contaminated sewage treatment plants (Hogue 2019; Ross et al. 2018; Dean et al. 2020). Fig. 12.1 Chemical structure of a PFOA and b PFOS

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As a result, the European Commission has included PFOS to its list of critical elements, with an Environmental Quality Standards (EQS) of 0.65 ng/L for freshwater and 9.1 ng/L for biota (Directive 2013/39/EC) (Valsecchi et al. 2017). The Stockholm Convention’s catalogue of emerging determined biological pollutants was supplemented in 2009 (Wang et al. 2009), and the US Environmental Protection Agency (EPA) included PFOS as incipient pollutants of alarm (Post et al. 2012). Because of their extended accumulation periods in the human body, both PFOS and PFOA, which were introduced before the 12th century, have been linked to obesity, cancer, hormone disruption, and high-fat levels (Betts 2007; Jian et al. 2017). Evidence that significant sources of PFAS exist in Northern Italy, with significant impacts on surface and groundwaters, prompted the Italian government to form an employed assembly on EQS for PFAS compounds, to include some of them in the catalogue of international precise organic pollutants for superficial water observing and determining their presence (Castiglioni et al. 2015; Valsecchi et al. 2015). EQS can protect freshwater bodies and marine habitats against the short- and long-term effects of organic contaminants, as well as human health when drinking water or many food items derived from aquatics. However, at present India lacks a regulatory mechanism or framework governing the use or detection of PFAS. To begin, the Bureau of Indian Standards (BIS) announced on 28 September 2020, that it would adopt International Standards Organization (ISO), ISO 3696:1987; ISO 5667–1 and ISO 8466–1:1990 benchmarks for PFOA and PFOS as Indian Standards (IS). PFOS and PFOA are considered the most stable and do not degrade naturally in the environment. According to the studies on the fate and behavior of these contaminants in wastewater treatment plants, biological treatment would be ineffective in their removal (Yu et al. 2009). The addition of the adsorption process (Hansen et al. 2010), sonochemical method (Moriwaki et al. 2005), weakening with a zero-valent ion in less censorious and contaminated water (Hori et al. 2006), and membrane filtration process (Tang et al. 2006) are all well-known methods for removing perfluoroalkyl acids from drinking water processing. However, for PFAS degradation, UV-activated photoreduction (Sun et al. 2017), UV-photo decomposition (Jin et al. 2014), and the laccasemediator reaction (Luo et al. 2018) are among the efficient methods available at present. Recently, numerous nanomaterials are used for PFAS degradation from water. For instance, Wang et al. synthesized ferric-mediated ions that were used to photocatalyze the degradation of PFOA using UV light with a wavelength of 254 nm (Wang et al. 2008). They propose that PFOA forms a complex with the low-state ferric ion and that excitation with UV light at 254 nm causes PFOA to decompose in a stepwise fashion (Wang et al. 2008). The current chapter began with a brief description of the occurrence of PFAS. The following section discusses the physical and chemical properties of PFAS, followed by a discussion of recent developments in the degradation of existing and emerging PFAS in water. Finally, future research directions and a summary of PFAS degradation technologies for a clean and sustainable environment are discussed.

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12.2 Physical and Chemical Properties of PFAS 12.2.1 Physical Properties (a)

Physical state

The PFAS are generally solids, waxy solids, crystalline, or either used in powder form at room temperature (25 °C) and one atmospheric pressure. However, the shorter chained compounds and, in particular, acid forms of perfluoroalkyl carboxylates and perfluroralkane sulfonates are liquids at room temperature. Like most organic compounds, the melting point of PFAS increases with the increase in the fluorinated chain length. For example, perfluorobutanoic acid (PFBA) has a melting point of 17.5 °C, while perfluorododecanoic acid has 108–110 °C (Rahman et al. 2014). (b)

Density

Density plays a vital role in determining the behavior of the PFAS in the environment. If the density of the liquid PFAS is greater than that of water, it can migrate downward through the water column in groundwater or surface water as a dense non-aqueous phase liquid (Rahman et al. 2014). (c)

Solubility

Perfluoroalkyl compounds have a non-polar hydrophobic carbon chain as a fully saturated tail with fluorine atoms attached to a hydrophilic polar (nonfluorinated) functional group as the head. Due to this difference in the head and the tail, the PFAS aggregates into micelles, hemimicelles, or mixed micelles (Ross et al. 2018). The PFAS form films at the air–water interface, with the hydrophobic carbon–fluorine tail oriented outwards and head dissolved in water. This enhances aerosol-based transportation and deposition while accumulation of PFAS at water surfaces. The micro dispersions of micelles are accounted while determining the solubility of PFAS. The values for solubility of different PFAS (usually measured in milligrams per litres (mg/L) or moles per litres (mol/L)) may vary depending upon various factors such as the acid or salt used to determine the solubility, molecular weight, pH and salinity. For example, while PFOA and PFOS are highly soluble, the solubility of PFOA and PFOS tends to decrease with molecular weight, which is due to the concomitant increase in the length of the perfluorinated alkyl chains, which are hydrophobic (Nguyen et al. 2020). (d)

Vapor Pressures (Vp )

Vapor pressure doesn’t play a significant role in assessing the mobility and transportation of PFAS in the environment due to the very low vapour pressure of the PFAS. Compounds with higher vapor pressure are highly volatile and in the gaseous phase, converted to water vapors in the atmosphere and serve as transport media for long-range transport via air. For example, FTOH has varying vapor pressures,

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but compared with other PFAS, the vapor pressure of FTOHs is higher, making it a volatile compound. FTOH can be transformed to PFOA resulting in contamination of surface water and groundwater through precipitation. On the other hand, compounds with lower vapor pressures are less volatile and more likely to remain in solid or liquid form and can be transported via soil or surface/groundwater (Berger et al. 2011). (e)

Henry’s Law Constant (Kh )

The Henry’s law constant (Kh ), indicates the relative concentrations of a compound between an aqueous solution and gas phase at equilibrium (air–water distribution ratio). It is also useful in indicating the propensity of a chemical to remain dissolved in water as compared to volatilizing into the gas phase. PFAS with higher Henry’s law constant will have lower solubility and higher volatility and can volatilize from water into the air and be distributed over a large area (Johansson et al. 2017). For most organic compounds of moderate to low solubility, Kh can be approximated evaluated using Eq. 12.1:   Kh = Vp (M)/S

(12.1)

where Kh is denoted as Henry’s law constant, Vp is the vapor pressure, M is the molecular weight, and S is the solubility. PFAS dissociate into anions and cations, and Henry’s law constant is pH-dependent. Since, Henry’s coefficients for the most PFAS are not known, the reported constants may not be applicable depending on the pH conditions within the solution.

12.2.2 Chemical Properties (a)

Carbon–Fluorine (C-F) Bonds

Due to the high electronegativity (3.98) of fluorine and the presence of strong covalent C-F bonds, PFAs have shown very high chemical and thermal stabilities. They are resistant to degradation by oxidative and reductive processes involving the gain and loss of electrons. Furthermore, the low polarizability of fluorine gives the PFAs “amphiphilic” characteristics associating with both water and oils (Sznajder-Katarzy´nska et al. 2019). (b)

Functional Group

The functional groups of PFAS dictate the properties and behaviour of PFAS. The functional group in PFAS comprises carboxylates, sulfonates, sulfates, phosphates, amines, and others (Yadav 2020). The available experimental data and calculated pKa values indicate that both PFOA and PFOS are strong acids and are present as water-soluble anionic (deprotonated and negatively charged) forms environmentally relevant pH values. However, some PFAs are acids and may be present as

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cationic (protonated and positively charged) or a mixture of both called zwitterionic, depending on the pH of the environmental matrix and the compound’s acid dissociation constant (pKa) (Sznajder-Katarzy´nska et al. 2019). Not just the C-F bond, the stability of PFAS is also determined by the specific functional group that is attached to the fluoroalkyl tail. PFOA and PFOS are the most stable fluorinated surfactants. PFAS decomposes at temperatures greater than 400 °C, but complete mineralization occurs at temperatures greater than 1000 °C (Lassen et al. 1475).

12.3 Degradation of PFAS Since PFAS degradation produces additional toxic and harmful byproducts, integrated techniques using absorption by functionalized nanomaterials (such as powdered activated carbon, carbon nanotubes, functionalized polymers, and resins) is widely investigated (Lin et al. 2012; Xiao et al. 2017). While the literature supports using high-performance absorbents for long-chain PFAS, it remains devoid of integration with real-time degradation methods (Zhang et al. 2019). Niu and colleagues, synthesised sonicated graphene quantum dots (GQDs) for the decomposition of PFOS compounds. Also, the authors synthesised SiC/GQDs due to their superior and excellent activity compared to bare GQDs. Figure 12.2 a illustrates the highly uniform surface topology of SiC/GQDs in the presence of homogeneous GQDs with a size range of 1.8–3.6 nm embedded in SiC nanoparticles. Figure 12.2 a illustrates the mechanism of PFOS degradation via directional electron transfer using SiC/GQDs. The decomposition experiment was conducted using a nanocomposite containing 0.019 mmol/L PFOS and 40 mg SiC/GQDs. When the photochemical electrons are directly attached to the PFOS molecule, delocalization of the electron pair attached to the sulphur atom occurs due to the lone pair attached to the sulphur atom. Following that, the SO2 radical accepts the H+ ion to eliminate OH— ions. Then, through the addition of HF and hydrolysis, it is converted to the carboxylic (COOH) compound carbon-fluoride (Cn F2n-1 ) (Huang et al. 2017). Finally, the Cn F2n-1 -COOH dissociated completely to form Cn F2n-1 and CO2 (Fig. 12.3). UV radiation triggers the dissociation of carbon fluoride bonds (Huang et al. 2017). The UV–Visible spectrum analysis of the GQDs nanocomposite is shown in Fig. 12.2b. UV–Visible spectral analysis reveals peaks at 310 and 340 nm. The 340 nm absorption peak corresponds to the nonbonding and π*orbitals (n-π*), while the 310 nm absorption peak corresponds to π-π* orbital. These corresponding absorbance peaks appear on the same fluorescence emission-excitation map as the PL excitation. In PLE spectral analysis, two prominent electronic transitions at 260 nm (4.77 eV, Peak A) and 310 nm (4.00 eV, Peak B) were detected (Fig. 12.2c). To determine the crystallographic structure of nanomaterials, XPS spectrum analysis was used, and C1s exhibits peaks at 282.8, 284.8, 286.0, and 288.8 eV corresponding to Si–C, C = C, C–O, and C = O bonds, respectively. Numerous factors contribute to the stability of the GQDs molecules on the surface of the SiC molecule. Between those variables, the surface oxygen-containing functional layer plays a critical role. SiC/GQDs are completely

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Fig. 12.2 a SEM morphology and reaction mechanism (Directional electron transfer) of SiC/GQDs reaction with PFOS and its substituents, b UV–Visible spectral analysis of SiC/GQDs nanocomposite, and c PL spectra of SiC/GQDs nanocomposite analysis on fluorescence emission-excitation map (Huang et al. 2017)

Fig. 12.3 Proposed decomposition mechanism for PFOS using SiC/graphene (Huang et al. 2017)

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stabilised in the presence of that surface oxygen. The PFOA and its substitutes, such as C3 F7 COO— (PFBA), C4 F9 COO— (PFPeA), C5 F11 COO— (PFHxA), and C6 F13 COO— (PFHpA), are photochemically degraded using a stabilised SiC/GQDs nanocomposite. These results were obtained at room temperature (25 °C) using triplestage quadrupole mass spectrometry (TQ-MS/MS). Accordingly, the detection times for the PFOS substituents are 1.99, 2.36, 2.95, 3.76, and 4.64 min, respectively. The PFOS and its substituents are detected and decomposed in time variations using zero-dimensional and semiconductor SiC/GQDs (Huang et al. 2017). Later, Huang and co-researchers also demonstrated that PFOS degradation could be achieved through the reactive electrochemical membrane (REM) using a responsive porous Magneli phase titanium suboxide ceramic membrane nanomaterial (Shi et al. 2019). By employing REM, it was possible to obtain complete removal of PFOS, 98.30%, which was achieved using an anodic potential of 3.15 V vs a standard hydrogen electrode (SHE). The crystallographic structure of the magneli phase titanium suboxide ceramic membrane is shown in Fig. 12.4a. The characteristic peaksof Ti9 O17 , Ti6 O11 , and TiO2 indicate that the primary component of this titanium suboxide mixture is Ti9 O17 . Figure 12.4b illustrates the surface topology of a titanium suboxide ceramic membrane, which reveals an extensive pore network

Fig. 12.4 a XRD pattern of Ebonex anode material (Magneli phase titanium suboxide ceramic membrane nanomaterial), b SEM morphology of anode material, c L-PFOS concentration profiles in group EO system at unalike current density (0.5–4.0 mA cm−2 ), and d reaction mechanism of PFOS degradation using REM membrane (Shi et al. 2019)

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on the anode surfaces; additionally, the calculated pore size is close to 0.5–3 μm. Purposive experiments in conjunction with density functional theory (DFT) computations were used to investigate the reaction’s performance, routes, and mechanisms. The concentration of linear PFOS (L-PFOS) vs applied current densities in the presence of a reactive electrochemical membrane is depicted in Fig. 12.4c. According to multiple reaction monitoring, the ratio of L-PFOS to branched PFOS (B-PFOS) is 16.5. Once an electric current is applied to the system, it increases the current density while simultaneously decreasing the PFOS concentration. By 120 min, a significant amount of PFOS concentration was removed, 98.30% at 4 mAcm−2 . The author conducts a comparison experiment with varying current densities in the presence of a solution of 2 μM PFOS in 100 mM of Na2 SO4 . The reaction mechanism is shown in Fig. 12.4d. When the current density is increased simultaneously, the PFOS concentration decreases, mimicking REM conditions. The linear scan voltammetry of a 100 mM of Na2 SO4 solution with varying concentrations of PFOS. At a scan rate of 20 mV/s, no increase in peak in electric current was observed upon PFOS addition, even though the applied current decreased with increasing concertation of the PFOS amount. Using DFT to calculate the electrode potential, the energy profile values of 2.96 and 3.24 versus SHE are obtained experimentally. This may indicate that the contribution of ·OHdis to PFOS degradation on the Ebonex anode during EO is limited compared to the surface-bound ·OHads (Shi et al. 2019). In another study, Li and coworkers used the solvothermal process to synthesise In2 O3 nanostructures with a variety of shapes. They have synthesised various structures such as microspheres, nanocubes, and nanoplates using different reducing agents and temperatures (Li et al. 2013). The atomic structure of PFOA plays a significant role in the catalytic degradation process (Zhang et al. 2007), particularly in the case of increased activity. Additionally, the varying sizes and shapes of In2 O3 play a significant role in the PFOA degradation process (Li et al. 2013). When it comes to degradation activity, In2 O3 microspheres outperform nanocubes and nanoplates. Figure 12.5a illustrates how the surface topology of In2 O3 microspheres with a diameter of approximately 180 nm results in the formation of small nanoparticles of 15–20 nm diameter. Since calcination is a homogeneous process, the smaller particles aggregate to form the larger particle. The surface morphology of In2 O3 nanocubes and nanoplates are depicted in Fig. 12.5b and c, respectively. In Fig. 12.5b, the In2 O3 nanocubes are shown in their natural state, but their structure is not perfectly cube-like, whereas, in Fig. 12.5c, they show a uniform nanoplates-like structure. Figure 12.5d shows UV–Visible spectral analysis of In2 O3 nanostructures of various shapes. The band gaps of In2 O3 microspheres, nanocubes, and nanoplates corresponding to 2.68, 2.76, and 2.72 eV, respectively. XPS spectral analysis reveals that different nanostructures exhibit the same binding energy peaks. The current peaks at 444.2 and 451.7 eV correspond to the 3d5/2 and 3d3/2 levels of In. Overall, due to the high concentration of surface oxygen in In2 O3 nanomaterials, they exhibit a greater range of photocatalytic activity than TiO2 and P25 TiO2 . The UV results demonstrate that PFOA decomposition occurs at a wavelength of 254 nm or greater (Fig. 12.5d).

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Fig. 12.5 SEM morphology different shapes of In2 O3 nanostructures, a In2 O3 microspheres, b In2 O3 nanocubes, and c In2 O3 nanoplates. d UV–Visible spectral analysis of In2 O3 nanostructures (Li et al. 2013)

In this experiment, In2 O3 microspheres outperformed nanoplates, nanocubes, and TiO2 in terms of photocatalytic activity. However, in the case of TiO2 , only 28.5% decomposition occurs in three hours. Contrary, microspheres take 20 min to decompose, nanoplates and nanocubes take 40 and 120 min, respectively, to decompose the PFOA mixture. The decomposition of PFOA was the pseudo-first-order reaction. As with PFOA, the In2 O3 microspheres exhibit superior photocatalytic activity compared to the In2 O3 nanoplates and nanocubes. Further, the standardisation and time dependence study of the photocatalytic decomposition of perfluoro carboxylic acids (PFCA), including perfluoro heptanoic acid (PFHpA), perfluoro hexanoic acid (PFHpA), perfluorononanoic acid (PFPeA), perfluoro butanoic acid (PFBA), and trifluoroacetic acid (TFA) in the presence of noble In2 O3 microspheres (Li et al. 2013). Results showed that In2 O3 microspheres have a high potential for real-time degradation processes. However, the process optimization is still at an early stage.

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12.4 Future Research Directions and Summary While several technologies have been investigated for the degradation of PFASs in the environment and, more specifically, wastewater. This review has concentrated on treatment methods that utilize nanomaterials in the degradation process. AOPs based on photolysis and photocatalysis are still being developed for the degradation of PFAS. Photolysis is a low-energy process (99.2 KWh/m3 ) with a moderate removal efficiency of 82%. In comparison, the photocatalysis process achieves 89% removal efficiency, but consumes a lot of energy (2106 KWh/m3 ). In comparison to previously reported AOPs, the advanced reduction process (ARPs) is still in the research stage and achieves a removal efficiency of 91.4% with relatively low energy consumption (166.1 KWh/m3 ) (Olatunde et al. 2020). However, the low yield and lack of efficient methods for generating eaq − in ARPs continue to be a challenge. Among semiconductor-based nanomaterials such as TiO2 and various shapes of In2 O3 , In2 O3 microspheres demonstrated the highest degradation activity and can be further investigated in future studies. Additionally, several advanced oxidation processes have been demonstrated to be effective at degrading PFOS and PFOA, including direct photolysis, photochemical oxidation, photocatalytic oxidation, activated persulfate oxidation, sonochemical decomposition, subcritical water, and electrochemical oxidation, with removal efficiencies ranging from 60 to 100%.To conclude, PFAS degradation pathways are highly dependent on their head groups. Fluoroalkyl chain lengths may also affect the reductive degradation patterns of specific PFAS types. The degradation and defluorination efficiencies of PFAS are strongly influenced by solution chemistry parameters and operating factors such as pH, the dose of chemical solute (i.e., sulphite or iodide) used for dissolved oxygen, humic acid, nitrate, and temperature. In general, future research should focus on developing energy-efficient and economically viable methods for completely degrading PFAS without producing secondary waste. Hybrid methods are still in their infancy, and a thorough techno-economic analysis is required to develop sustainable technology.

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