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Nanostructured Polymer Membranes
Scrivener Publishing100 Cummings Center, Suite 541J
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Publishers at ScrivenerMartin Scrivener ([email protected])
Phillip Carmical ([email protected])
Nanostructured Polymer Membranes
Edited byVisakh P.M. and Olga Nazarenko
Volume 1: Processing and Characterization
Copyright © 2017 by Scrivener Publishing LLC. All rights reserved.
Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Beverly, Massachusetts.Published simultaneously in Canada.
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Library of Congr ess Cataloging-in-Publication Data:
ISBN 978-1-118-83173-1
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
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Contents
Preface xv
1 Processing and Characterizations: State-of-the-Art and New Challenges 1Visakh. P. M. 1.1 Membrane: Technology and Chemistry 1 1.2 Characterization of Membranes 3 1.3 Ceramic and Inorganic Polymer Membranes:
Preparation, Characterization and Applications 4 1.4 Supramolecular Membranes: Synthesis
and Characterizations 5 1.5 Organic Membranes and Polymers to Remove Pollutants 7 1.6 Membranes for CO2 Separation 8 1.7 Polymer Nanomembranes 9 1.8 Liquid Membranes 11 1.9 Recent Progress in Separation Technology Based on
Ionic Liquid Membranes 121.10 Membrane Distillation 131.11 Alginate-based Films and Membranes: Preparation,
Characterization and Applications 14References 15
2 Membrane Technology and Chemistry 27Manuel Palencia, Alexander Córdoba and Myleidi Vera2.1 Introduction 272.2 Membrane Technology: Fundamental Concepts 28
2.2.1 Basic Parameters 312.3 Separation Mechanisms 33
2.3.1 Pressure-driven Membrane Methods 342.3.2 Liquid Membranes 402.3.3 Other Methods 41
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2.4 Chemical Nature of Membrane 412.5 Surface Treatment of Membranes 42
2.5.1 Chemical Methods for Membrane Modification 422.5.1.1 Chemical Treatment 422.5.1.2 Grafting 432.5.1.3 Chemical Initiation Technique 442.5.1.4 Photochemical and Radiation Initiation
Techniques 442.5.1.5 Plasma Initiation Technique 452.5.1.6 Enzymatic Initiation Technique 45
2.5.2 Physical Methods for Membrane Modification 462.5.2.1 Coating 462.5.2.2 Blending 462.5.2.3 Composite 462.5.2.4 Combined Methods 47
2.5.3 Current Research about Membrane Modification 472.6 Conclusions 48References 48
3 Characterization of Membranes 55Derya Y. Koseoglu-Imer, Ismail Koyuncu, Reyhan Sengur-Tasdemir, Serkan Guclu, Recep Kaya, Mehmet Emin Pasaoglu and Turker Turken3.1 Introduction 563.2 Physical Methods for Characterizing Pore Size
of Membrane 563.2.1 Microscopy 573.2.2 Bubble Pressure and Gas Transport 593.2.3 Porosimetry 613.2.4 Liquid-vapor Equilibrium 633.2.5 Liquid-solid Equilibrium (Thermoporometry) 643.2.6 Gas-liquid Equilibrium (Permporometry) 65
3.2.6.1 Capillary Condensation 653.3 Membrane Chemical Structure 67
3.3.1 Fourier Transform Infrared Spectroscopy (FTIR) 673.3.2 Raman Spectroscopy 683.3.3 Energy-dispersive X-ray Spectroscopy (EDS) 70
3.3.3.1 Basics of EDS 703.3.3.2 Applications of EDS in Membrane
Characterization 703.3.4 X-ray Photoelectron Spectroscopy (XPS) 71
Contents vii
3.3.5 Electron Spectroscopy 733.3.5.1 Auger Electron Spectroscopy (AES) 733.3.5.2 Electron Energy Loss
Spectroscopy (EELS) 743.3.6 Atomic Force Microscopy (AFM) 74
3.3.6.1 Basics of AFM 743.3.6.2 Applications of AFM in Membrane
Characterization 763.3.7 Secondary Ion Mass Spectrometry (SIMS) 783.3.8 Surface Hydrophilicity and Surface Energy 79
3.3.8.1 Determination of Hydropilic/ Hydrophobic Nature of Membranes 79
3.3.8.2 Contact Angle Measurement by Drop Profile Analysis 80
3.3.8.3 Surface Energy 833.4 Conclusions 85References 85
4 Ceramic and Inorganic Polymer Membranes: Preparation, Characterization and Applications 89Chiam-Wen Liew and S. Ramesh4.1 Introduction 90
4.1.1 Overview of Polymer Electrolytes 904.1.2 Methods to Enhance Ionic Conductivity of
Polymer Electrolytes 904.1.3 Ionic Liquids 91
4.1.3.1 Advantages of Ionic Liquids 914.1.3.2 Applications of Ionic Liquids 92
4.1.4 Fillers 924.1.4.1 Types of Fillers 934.1.4.2 Advantages of Addition of Fillers 94
4.1.5 Applications of Nanocomposite Polymer Electrolytes (NCPEs) 95
4.2 Recent Developments in Filler-doped Polymer Electrolytes 954.2.1 Al2O3 954.2.2 TiO2 984.2.3 ZrO2 994.2.4 SiO2 1014.2.5 Supercapacitors 103
4.2.5.1 Types of Supercapacitors 103
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4.2.5.2 Advantages of Supercapacitors 1044.2.5.3 Applications of Supercapacitors 104
4.3 Methodology 1054.3.1 Materials 1054.3.2 Sample Preparation 1054.3.3 Sample Characterization 106
4.3.3.1 Ambient Temperature-ionic Conductivity and Temperature- dependent Ionic Conductivity Studies 106
4.3.3.2 Differential Scanning Calorimetry (DSC) 106
4.3.3.3 Linear Sweep Voltammetry (LSV) 1074.3.4 Electrode Preparation 1074.3.5 Electrical Double-layer Capacitors
(EDLCs) Fabrication 1084.3.6 Electrical Double-layer Capacitors (EDLCs)
Characterization 1084.3.6.1 Cyclic Voltammetry (CV) 1084.3.6.2 Galvanostatic Charge-discharge
Analysis (GCD) 1084.4 Results and Discussion 109
4.4.1 Ambient Temperature-ionic Conductivity Studies 109
4.4.2 Temperature-dependent–ionic Conductivity Studies 112
4.4.3 Differential Scanning Calorimetry (DSC) 1144.4.4 Linear Sweep Voltammetry (LSV) 1174.4.5 Cyclic Voltammetry (CV) 1194.4.6 Galvanostatic Charge-discharge Analysis (GCD) 124
4.5 Conclusions 127Acknowledgment 128References 128
5 Supramolecular Membranes: Synthesis and Characterizations 137Cher Hon Lau, Matthew Hill and Kristina Konstas5.1 Overview 1385.2 Supramolecular Materials 138
5.2.1 Porous Materials 1395.2.1.1 Metal-organic Frameworks 1405.2.1.2 Zeolitic Imidazole Frameworks (ZIFs) 146
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5.2.2 Porous Organic Materials (POMs) 1485.2.2.1 Covalent Organic Frameworks (COFs) 149
5.2.3 Cages 1535.2.4 PAFs 154
5.3 Supramolecular Membranes 1575.3.1 Concepts of Supramolecular Chemistry in
Polymeric Membranes 1575.3.1.1 Poly(dialkylacetylenes) 1585.3.1.2 Polymers with Intrinsic
Microporosity (PIMs) 1635.3.2 Supramolecular Concepts in Nanocomposite
Membranes 1655.3.2.1 Metal Organic Frameworks (MOFs)
in Polymer Membranes 1665.3.2.2 Porous Aromatic Frameworks (PAFs)
in Super-Glassy Polymers 1685.4 Membrane Fabrication Using Supramolecular Chemistry 170
5.4.1 Molecular Recognition – CO2 Affinity 1725.4.2 Host-guest Chemistry 1755.4.3 Self-assembled Membranes 1785.4.4 Self-assembled Polymers as Membranes 1795.4.5 Self-assembled Molecules and Nanoparticles
as Membranes 1815.5 Conclusions 184References 186
6 Organic Membranes and Polymers for the Removal of Pollutants 203Bernabé L. Rivas, Julio Sánchez and Manuel Palencia6.1 Membranes: Fundamental Aspects 204
6.1.1 Membrane Transport Theory 2056.1.2 Pressure-driven Membrane Methods 2086.1.3 Hybrid Methods Applied for Removal
of Pollutants 2096.1.3.1 Membrane Bioreactor (MBR) 2096.1.3.2 Electro-ultrafiltration 2106.1.3.3 Ultrafiltration Coupled to Ultrasound 2106.1.3.4 Flotation Coupled with Microfiltration 2106.1.3.5 Liquid-phase Polymer-based
Retention (LPR) 211
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6.1.3.6 Surfactant Liquid Membrane Coupled with Liquid-phase Polymer-based Retention 211
6.1.4 Fouling 2116.2 Liquid-phase Polymer-based Retention (LPR) 212
6.2.1 Theory and Fundamental Aspects 2136.3 Applications for Removal of Specific Pollutants 216
6.3.1 Removal of Inorganic Species by LPR 2176.3.1.1 Heavy Metals 2186.3.1.2 Inorganic Anions 222
6.4 Future Perspectives 2286.5 Conclusions 228Acknowledgments 228References 228
7 Membranes for CO2 Separation 237Abedalkhader Alkhouzaam, Majeda Khraisheh, Mert Atilhan, Shaheen A. Al-Muhtaseb and Syed Javaid Zaidi7.1 Introduction 2387.2 Fundamentals of Membrane Gas Separation 239
7.2.1 Membrane Gas Permeation Mechanisms 2407.2.2 Robeson’s Upper Bound 242
7.3 Polymeric Membranes for CO2 Separation 2457.3.1 Polyimides 2467.3.2 Polysulfones 2517.3.3 Polymer Blends 253
7.4 Mixed Matrix Membranes 2587.5 Supported Ionic Liquid Membranes (SILMs) for CO2
Separation 2637.5.1 SILM Permeation Properties for CO2/N2
and CO2/CH4 Separation 2687.5.2 SILMs Stability in Gas Separation 276
7.6 Conclusion 2787.7 Overall Comparison and Future Outlook 279Abbreviations 282References 285
Contents xi
8 Polymer Nanomembranes 293Giuseppe Firpo and Ugo Valbusa8.1 Introduction 2938.2 Materials 294
8.2.1 Rubber Polymers 2948.2.2 Glassy Polymers 2958.2.3 Mixed Matrix and Nanocomposite 297
8.3 Nanomembrane Fabrication 2988.3.1 Spin Coating 2988.3.2 Layer-by-Layer Assembly 3008.3.3 Chemical Vapor Deposition 3018.3.4 Other Techniques 3028.3.5 Surface Treatments 303
8.4 Characterization 3048.4.1 Gas Permeability and Selectivity 3048.4.2 Mechanical Properties 3078.4.3 Long-term Stability 309
8.5 Applications 3108.5.1 Gas Purification 3108.5.2 Water Desalination 3128.5.3 Biomedical Devices 3138.5.4 Sensors 315
References 316
9 Liquid Membranes 329Jiangnan Shen, Lijing Zhu, Lixin Xue and Congjie Gao9.1 Introduction 3299.2 Most Recent Developments 3309.3 Liquid Membranes Based Separation Processes 330
9.3.1 Emulsionized Liquid Membranes 3309.3.2 Immobilized Liquid Membranes 3459.3.3 Applications of Immobilized Liquid Membranes 3489.3.4 Molten Salt Membranes 3499.3.5 Hollow Fiber Liquid Membranes 3499.3.6 Bulk Hybrid Liquid Membranes 354
9.3.6.1 Instruction 3549.3.6.2 Theoretical Aspects of Bulk Hybrid
Liquid Membranes 3549.3.6.3 Pertraction in a Multi-membrane
Hybrid System 356
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9.3.6.4 Applications 3589.3.6.5 Summary 359
9.3.7 Bulk Aqueous Hybrid Liquid Membranes 3609.3.7.1 Introduction 3609.3.7.2 Theoretical Aspects of Bulk Aqueous
Hybrid Liquid Membranes 3619.3.7.3 Applications 3639.3.7.4 Summary 364
9.3.8 Liquid Membranes in Gas Separation 3649.3.8.1 Introduction 3649.3.8.2 Separation Mechanism 3659.3.8.3 Materials for LM 367
9.3.9 Common Gas Separation Applications 3759.3.9.1 Carbon Dioxide Separation from
Various Gas Streams 3759.3.9.2 Sulfur Dioxide Separation from
Various Gas Streams 3769.3.9.3 Hydrogen Separation from
Various Gas Streams 3779.3.9.4 Olefin Separation 3779.3.9.5 Conclusion and Outlook 378
9.4 Conclusion 379References 379
10 Recent Progress in Separation Technology Based on Ionic Liquid Membranes 391M.J. Salar-García, V.M. Ortiz-Martínez, A. Pérez de los Ríos and F.J. Hernández-Fernández10.1 Introduction 39210.2 Ionic Liquid Properties 39310.3 Bulk Ionic Liquid Membranes 39510.4 Emulsified Ionic Liquid Membranes 39710.5 Immobilized Ionic Liquid Membranes 400
10.5.1 Supported Ionic Liquid Membranes 401 10.5.2 Polymer Ionic Liquid Inclusion Membranes 404 10.5.3 Polymeric Ionic Liquid Membranes 406 10.5.4 Membranes Based on Gelation of Ionic Liquids 407 10.5.5 Non-dispersive Solvent Extraction (NDSX)
and Pseudo-emulsion Hollow Fiber Strip Dispersion (PEHFSD) Based on Ionic Liquids 408
Contents xiii
10.6 Green Aspect of Ionic Liquids 41010.7 Conclusions 411Acknowledgments 411References 412
11 Membrane Distillation 419Mohammadali Baghbanzadeh, Christopher Q. Lan, Dipak Rana and Takeshi Matsuura11.1 Introduction 41911.2 Applications of Membrane Distillation Technology 42011.3 Different Kinds of Membrane Distillation
Configurations 422 11.3.1 Direct Contact Membrane
Distillation (DCMD) 422 11.3.2 Air Gap Membrane Distillation (AGMD) 423
11.3.2.1 Memstill and Aquastill 423 11.3.3 Permeate Gap Membrane Distillation (PGMD) 425 11.3.4 Sweep Gas Membrane Distillation (SGMD) 425 11.3.5 Vacuum Membrane Distillation (VMD) 426
11.3.5.1 Vacuum Gap Membrane Distillation (VGMD) 427
11.3.5.2 Memsys 428 11.3.5.3 Differences between VMD and
Pervaporation (PV) 42911.4 Distillation Membranes 432
11.4.1 MD Modules 432 11.4.1.1 Plate and Frame 432 11.4.1.2 Hollow Fiber 432 11.4.1.3 Tubular 433 11.4.1.4 Spiral Wound 433
11.4.2 Applicable Membranes for MD 434 11.4.2.1 Nanocomposite Membranes 434
11.4.3 Membrane Characteristics in MD 435 11.4.3.1 Liquid Entry Pressure
(Wetting Pressure) 435 11.4.3.2 Membrane Thickness 436 11.4.3.3 Porosity and Tortuosity 436 11.4.3.4 Mean Pore Size and Pore Size
Distribution 437 11.4.3.5 Thermal Conductivity 437 11.4.3.6 Membrane Fabrication 438
xiv Contents
11.5 Transport Phenomena in MD 439 11.5.1 Mass Transfer in MD 439 11.5.2 Heat Transfer in MD 443
11.5.2.1 Thermal Efficiency and Heat Loss 445 11.5.3 Temperature and Concentration Polarization 447 11.5.4 Fouling 448 11.5.5 Operating Parameters 449
11.5.5.1 Feed Temperature 449 11.5.5.2 Permeate Temperature 449 11.5.5.3 Feed Concentration 449 11.5.5.4 Feed Flow Rate 449 11.5.5.5 Air Gap Thickness 449 11.5.5.6 Membrane Properties 450
11.6 Conclusion 450References 450
12 Alginate-based Films and Membranes: Preparation, Characterization and Applications 457Jiwei Li and Jinmei He12.1 Introduction 45712.2 Recent Development 459
12.2.1 Cross-linking 460 12.2.2 Plasticizing 462 12.2.3 Blending 463 12.2.4 Compositing 465 12.2.5 Drying 467
12.3 Applications 468 12.3.1 Pharmaceutical and Medical Applications 468 12.3.2 Packaging Applications 470 12.3.3 Environmental Applications 472
12.4 Conclusion 473References 474
Index 491
Preface
Many recent research accomplishments in the area of polymer nanocom-posite membrane materials are summarized in this book, Nanostructured Polymer Membranes: Processing and Characterizations. State-of-the-art on membrane technology and chemistry and new challenges being faced in the field are discussed. Among the topics reviewed are characterization of membranes; current techniques for the processing and characterization of ceramic and inorganic polymer membranes; supramolecular membranes; organic membranes and polymers for removal of pollutants; membranes for CO2 separation; polymer nanomembranes; liquid membranes; separa-tion technology based on ionic liquid membranes; membrane distillation; and alginate-based membranes and films.
This book is intended to serve as a “one-stop” reference resource for important research accomplishments in the area of nanostructured poly-mer membranes and their processing and characterizations. It will be a very valuable reference source for university and college faculties, professionals, post-doctoral research fellows, senior graduate students, and researchers from R&D laboratories working in the area of polymer nanobased mem-branes. The various chapters are contributed by prominent researchers from industry, academia and government/private research laboratories across the globe and comprise an up-to-date record on the major findings and observations in the field.
Chapter 1 provides an overview of the techniques and processes detailed in later chapters, along with the state of art, new challenges and opportunities in the field. In chapter 2, principles and fundamentals of membrane separation are presented in addition to a description of differ-ent types of membrane processes (pressure-driven membrane methods and liquid membranes) and the chemical and physical methods for mem-brane modification. Chapter 3 provides fundamental ideas about all types of characterization techniques for polymer-based nanomembranes such as FTIR, Raman spectroscopy, X-ray spectroscopy, electron spectroscopy, atomic force microscopy mass spectrometry and surface hydrophilicity. The next chapter mainly concentrates on the preparation, characterization
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and applications of ceramic and inorganic polymer membranes. Chapter 5 gives an overview of supramolecular membranes, primarily focusing on polymeric membranes and mixed matrix membranes for gas separation applications. Other topics discussed in this chapter are membranes synthe-sized from self-assembly, hydrogen bonding, π-π stacking of block copoly-mer systems, small molecules, and nanoparticles; and a summary of recent research into gas membrane separations.
Chapter 6 explains organic membranes and polymers to remove pollut-ants. It provides fundamental aspects of membranes as well as processes, including membranes as electro-ultrafiltration, ultrafiltration coupled to ultrasound, flotation coupled to microfiltration, liquid-phase polymer-based retention and liquid surfactant membrane. The next chapter is essential for tracking the progress in membrane development. It is a com-prehensive review of recent studies in CO2 separation using different tech-nologies, CO2 permeation properties, and breakthroughs and challenges in developing efficient CO2 separation membranes. Chapter 8 reports the state-of-the-art on fabrication methods of polymeric nanomembranes according to their specific needs and illustrates the most useful materi-als, employing mostly glassy and rubbery polymers. Often, to enhance membrane properties or to prevent undesired behavior, the fabrication is followed by different kinds of surface treatments. The authors discuss recent investigations on mechanical, thermal and gas transport properties of nanomembranes that frequently reveal a different behavior with respect to the polymeric membranes of greater thickness. The next chapter pres-ents an introduction to liquid membrane separation techniques such as emulsion liquid membranes, immobilized liquid membranes, salts liquid membranes, hollow fiber contained liquid membranes, bulk hybrid liquid membranes and bulk aqueous hybrid liquid membranes. The author of this chapter also discusses the theory behind liquid membranes, along with their material design, preparation, performance and stability, and their applications in the separation and removal of metal cations from a range of diverse matrices, gas separation, etc.
Chapter 10 provides an overview of the recent progress in separation technology based on ionic liquid membranes; moreover, it covers issues relevant to this technology such as methods of preparation, mechanisms of transport, stability and fields of application. Chapter 11 on membrane dis-tillation provides comprehensive coverage of both the fundamentals and recent developments associated with the application, process design, and membrane fabrication in this field. The final chapter provides a comprehen-sive overview of general properties, recent developments, and applications of alginate-based films and membranes. Sodium alginate is water-soluble,
Preface xvii
nontoxic, biocompatible, biodegradable, reproducible, and can yield coher-ent films or membranes upon casting or solvent evaporation.
In conclusion, the editors would like to express their sincere gratitude to all the contributors of this book, whose excellent support made the suc-cessful completion of this venture possible. We are grateful to them for the commitment and sincerity they showed towards their contributions. Without their enthusiasm and support, the compilation of a book would not have been possible. We would like to thank all the reviewers who have taken their valuable time to make critical comments on each chap-ter. We also thank the publisher, John Wiley and Sons Ltd. and Scrivener Publishing, for recognizing the demand for a book on the increasingly important area of Nanostructured Polymer Membranes Processing and Characterization and handling such a new project, which many other pub-lishers have yet to address.
Visakh. P. M. Olga NazarenkoSeptember 2016
1
Visakh P.M. and Olga Nazarenko (eds.) Nanostructured Polymer Membranes: Volume 1, (1–26) © 2017 Scrivener Publishing LLC
1
Processing and Characterizations: State-of-the-Art and New Challenges
Visakh. P. M.
Research Assistant, Department of Ecology and Basic Safety, Tomsk Polytechnic University, Tomsk, Russia
AbstractA brief account of various topics concerning the processing and characterization of nanostructured polymer membranes is presented in this chapter. The different topics that are discussed include membrane technology and chemical character-ization of membranes; ceramic and inorganic polymer membranes preparation, characterization and applications; supramolecular membranes synthesis and characterizations; organic membranes and polymers to remove pollutants; mem-branes for CO2 separation; polymer nanomembranes; liquid membranes; recent progress in separation technology based on ionic liquid membranes; membrane distillation; and preparation, characterization and applications of alginate-based membranes and films.
Keywords: Nanostructured polymer membranes, membrane processing, membrane characterizations, supramolecular membranes, organic membranes, liquid membranes, separation technology, ionic liquid membranes
1.1 Membrane: Technology and Chemistry
Membranes are used in a broad range of applications such as protein frac-tionation, purification of drugs, separation of gaseous mixtures, sample simplification in analytical procedures, production of ultrapure water and
Corresponding author: [email protected]
2 Nanostructured Polymer Membranes: Volume 1
wastewater treatment, among others [1–5]. The membrane can be defined as a selective barrier that allows some species to permeate the barrier while retaining others. Membrane can be symmetric or asymmetric membrane according to their macroscopic configuration. Thus, asymmetric mem-branes consist of two layers; the top one is a very thin dense layer and is commonly called the skin layer or active layer and determines the perme-ation properties. In particular, separation methods directed by pressure can be categorized into four major membrane processes: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) [6, 7]. Liquid membrane processes are commonly identified as three main con-figuration types: bulk liquid membrane, surfactant liquid membrane (or emulsion liquid membrane) and supported liquid membrane. Membranes can be referred to as porous and dense, and this first classification permits defining the two main mass transport models through the membranes. In membrane processes, the retained or rejected species accumulate near the membrane surface and as a consequence concentration polarization is produced.
According to the transport mechanisms, the separation methods by liquid membrane can be divided into six basic mechanisms of transport: simple transport, simple transport with chemical reaction in strip solution, facilitated transport, coupled counter-transport, coupled co-transport and active transport. The range of materials used for nanofiltration and reverse osmosis membranes is much smaller than that used for microfiltration and ultrafiltration, and is limited to polymers. Membrane material is required to be resistant to operation conditions and suitable for specific applica-tion. In many cases, additives are added to membrane phase during the fabrication to increase the permeability or reduce the fouling. Inorganic membranes have high selectivity and high permeability as well as ther-mal, chemical and mechanical stability but the cost of these are very high in comparison with polymer membranes. Organic and inorganic mem-branes can be modified for different applications by changes in the mate-rial chemical properties or by changes of pore size [8]. The above can be accomplished using methods such as chemical oxidation, incorporation of additives into the membrane matrix, plasma treatment, classical organic reactions, polymer grafting, interpenetrating polymer network, surfactant modification, self-assembly of the nanoparticles, among others [9].
Plasma surface treatment usually refers to a plasma reaction that either results in modification of the molecular structure of the surface, or atomic substitution. For example, simple inert gas [10], nitrogen, or oxygen plas-mas have been used to increase the surface hydrophilicity of membranes [11], and ammonia plasmas have successfully yielded functionalized
Processing and Characterizations 3
polysulfone membranes [12]. There are several potential advantages for the use of enzymes in membrane modification. Currently, the pressure-driven membrane processes are widely used in water treatment, biotechnology, food industry, medicine, and other fields [13].
One of the main problems arising from the operation of the membrane units is membrane fouling, which seriously hampers the applications of membrane technologies [14]. New membrane modification methods have been proposed, including the modification of membrane surfaces via microswelling for fouling control in drinking water [15], hydrogel surface modification of reverse osmosis membranes [16], modification of Nafion membrane using fluorocarbon surfactant for all vanadium redox flow batteries [17], modification of ultrafiltration membranes via interpen-etrating polymer networks for removal of boron from aqueous solution [18], among others.
1.2 Characterization of Membranes
Membrane morphology characterization is one of the indispensable com-ponents of the field of membrane research. Physical and chemical properties of membranes can be characterized with different laboratory techniques. Several microscopic techniques, both electronic as scanning and transmis-sion electron microscopies, and atomic, as atomic force microscopy, have been used to analyze the pore structure and pore size distribution of the membrane. Microscopy methods, including scanning electron microscopy (SEM), transmission electron microscopy (TEM) or atomic force micros-copy (AFM), are the most direct methods to characterize the membrane pore structure. SEM can be used in various pore size characterization stud-ies to visually inspect pore sizes and shapes. The AFM has proven itself to be a useful and versatile tool in the field of surface characterization. Porometry measurements can also give information about the pore size distribution (PSD) of membrane surface area [19].
Gas adsorption is one of the most popular methods and is generally used for the surface characterization and structural properties of porous materials, allowing the determination of their surface area, pore volume, pore size distribution and adsorption energy distribution of polymer membranes. One of the most promising methods is permporometry, where a mixture of non-condensable gas and condensable vapor is fed to a porous membrane and the permeation rate of non-condensable gas is measured [20]. Fourier transform infrared (FTIR) spectroscopy is widely used in structural characterization of membrane surfaces. With
4 Nanostructured Polymer Membranes: Volume 1
recent advances in the technology, the instrument has become simpli-fied and some of the problems are reduced [21]. Raman spectroscopy technique usually employs a laser source and the scattered light and analyzes in terms of wavelength, intensity and polarization. Raman scat-tering is capable of detecting elastic vibrations of an entire nanoparticle, therefore Raman scattering is good for detecting nanoparticles on the membrane surface [22].
Energy-dispersive X-ray spectroscopy (EDS) analysis can be helpful for both membrane characterization and foulant characterization. For exam-ple, Sile-Yüksel et al. [23] used EDS analysis to determine the location of silver nanoparticles in different polymer membrane matrix. Corneal et al. [24] coated tubular ceramic membranes with manganase oxide nanopar-ticles. They examined the coating layer using SEM-EDS. With the help of EDS analysis they observed that the manganase oxide nanoparticles were not just successfully placed on the surface but also penetrated the membrane matrix. Soffer et al. [25] used EDS analysis to show colloidal iron fouling on ultrafiltration membrane surface. Long-term fouling of a reverse osmosis membrane was examined by Melián-Martel et al. [26]. The measuring method must be adapted according to charge places whether it is on the surface or inside the pores.
1.3 Ceramic and Inorganic Polymer Membranes: Preparation, Characterization and Applications
Liquid electrolytes are liquid state electrolyte used to conduct the elec-tricity. However, these conventional liquid electrolytes possess several dis advantages such as leakages of corrosive solvent and harmful gas, elec-trolytic degradation of electrolyte, formation of lithium dendrite growth, poor dimensional and mechanical stabilities, slow evaporation due to the gel state of polymer electrolyte, low safety performances, narrow potential window, poor interfacial stability and reduction in thermal, electrical and electrochemical stabilities as well [27]. Ionic liquids also offer some fasci-nating advantages, such as excellent chemical, thermal and electrochemi-cal stabilities, high ionic conductivity due to high ion concentration, good oxidative stability and superior ion mobility as well as high cohesive energy density [28].
Krawiec et al. found that the particle size of filler is a vital parameter to govern the conductivity of the polymer electrolytes. They reported that the conductivity of nanosized Al2O3 added polymer electrolytes was higher about an order of magnitude that that of micrometer-sized Al2O3. High
Processing and Characterizations 5
surface area to volume ratio of nanoparticles has become a driving force in the development of nanotechnology in various research fields, especially in materials science. The small particle size of the fillers can improve the homogeneity in the sample and its electrochemical properties [29]. The higher conductivity of nanoscale filler compared to micro-sized filler is also attributed to the rapid formation of the space charge region between the grains [30].
Mica plays a role in reducing resin costs, enhancing processability and dissipating heat in exothermic thermosetting reaction. Other par-ticulate fillers, such as graphite, carbon black, and aluminium flakes, are used to reduce mold shrinkage or to minimize the electrostatic charging. Electrochemical devices, especially batteries, show a wide range of elec-trical and electronic applications. These devices can not only be applied in portable electronic and personal communication devices, such as lap-tops, mobile phones, MP3 players, and PDAs, but also in hybrid electrical vehicles (EVs) and start–light–ignition (SLI), which serves as a traction power source for electricity [31]. The properties of the final alumina depend on the crystalline structure, morphology and microstructure of the polymorph. Therefore, many attempts have been studied with respect to their transformation mechanisms, changes in porosity, specific surface area, surface structure, chemical reactivity and the defect crystal structure of polymorph [32].
1.4 Supramolecular Membranes: Synthesis and Characterizations
Supramolecular chemistry has typically been focused within the inor-ganic field, with our understanding of porous silicas [33] leading to break-throughs in electrochemical energy storage. New approaches have been designed and investigated to improve the membranes performance; this involves the incorporation of porous composite materials. Metal-organic frameworks (MOFs) are a class of supramolecular coordination polymers that have emerged in the literature over two decades ago, when they could be identified by single-crystal X-ray crystallo graphy [34–38].
The MOF structures are obtained by a self-assembling process start-ing from metal ions that assemble together with linker molecules. MOFs are successfully synthesized from solvothermal reactions with metal and organic building blocks which are dissolved in organic solvents and heated up to 130 °C. In addition to the conventional heating used for sol-vothermal reactions, MOFs can be synthesized using electrochemistry,
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mechanochemistry and ultrasonic methods. Because MOFs can reversibly absorb carbon dioxide gas, they are promising materials for the selective capture of carbon from the atmosphere and flue gas. The large quadru-pole moment of carbon dioxide molecules causes them to interact with the framework, increasing the uptake of the gas over other inert adsorbents such as zeolites. Polycrystalline thin films are made from direct synthesis where a bare substrate is used with the appropriate mother growth solution for the given MOF, heat treated as required for solvothermal synthesis. The method involves the metal and organic linker crossing a porous membrane and crystallizing at the interface [39].
Zeolites are widely used in industry for water purification, adsorbents, catalysts and gas separations. They are naturally found but can also be synthesized to incorporate a range of small inorganic and organic species. Supramolecular chemistry describes chemical systems comprising a num-ber of assembled molecular subunits or components arranged in spatial organizations using noncovalent bonding like hydrogen bonding, metal coordination, and hydrophobicity. The first part of this chapter will focus on supramolecular chemistry concepts in polymeric membranes, followed by a short discussion on how metal coordination and host-guest chemistry play important roles in mixed-matrix membranes. Membranes fabricated via supramolecular chemistry are rarely reported for gas separations, and are more common for liquid separation or purification and filtration mem-branes. Polytrimethylsilylpropyne (PTMSP) membranes operate as size-selective membranes. Meanwhile, when PTMSP membranes are used to isolate hydrocarbons from mixtures containing condensable hydro carbon vapors and permanent gases, these membranes operate in the reverse-selective mode [40]. Despite its unique property of high hydrocarbon/gas selectivity and permeability, PTMSP has apparently found no industrial applications. This is due in part to PTMSP being highly soluble in liquid hydrocarbons [41, 42].
Additive incorporation into polymer matrices remains one of the most common ways in which supramolecular chemistry is observed in mem-branes. For example, Merkel et al. reported that the incorporation of non-porous fumed silica nanoparticles into a PTMSP polymer matrix enhanced gas permeability [43]. Schmidt et al. used a bottom-up approach to form supramolecular nanofibers inside a scaffold to prepare stable polymer-microfiber/supramolecular-nanofiber composites for filter applications [44]. Upon solvent evaporation, and filtration over commercial microfil-tration syringes, three-dimensional supramolecular networks were formed within cellulose acetate membranes that are suitable for inexpensive and fast water separations.
Processing and Characterizations 7
1.5 Organic Membranes and Polymers to Remove Pollutants
A membrane is a thin planar structure or interphase that separates two phases and permits mass transfer between the phases. Membranes can be classified into two main groups: (1) biological membranes and (2) artificial or synthetic membranes. The polymer membranes are the main type of membranes in the market because polymeric materials are easier to pro-cess and less expensive [45, 46].
The separation of various components of a mixture is related directly to their relative transport rate within the membrane, which is determined by their diffusivity and solubility in the membrane material. Ultrafiltration membranes are used in electrodialysis pretreatment, electrophoretic paint, cheese whey treatment, juice clarification recovery of textile sizing agents, separation of oil/water emulsion, water treatment, and reverse osmosis pretreatment. The permeate is the portion of the fluid that has passed through the membrane and the retentate, or concentrate, is the portion con-taining the constituents that have been rejected by the membrane [47–49].
For a membrane separation method to be denominated as a hybrid separation method, changes beyond the simple incorporation of a dif-ferent configuration or the simple change in a sequence in a separation line should be incorporated. The main disadvantage of flotation lies in the fact that the removal efficiency may be reduced if some of the undesired substances are not sufficiently hydrophobic, thus remaining in the bulk dispersion or solution [50]. Consequently, in the flotation coupled with microfiltration, the solid particles are partially removed by flotation, while clean water is obtained from the membrane module. Fewer solid particles remaining in the dispersion are then deposited on the membrane’s surface, resulting in decreased membrane fouling [51, 52]. Fouling has a direct impact on operating costs because a large part of the energy consumption is required to overcome fouling resistance and for periodic cleaning opera-tions [53]. Geckeler et al. carried out the first experimental advances and analytical applications related with this technique [54–56]. Later, many research groups worked on the evaluation and description of retention properties of different water-soluble polymers (WSPs) for environmental and analytical applications [57–65].
One of the most promising techniques used is the application of sepa-ration methods based on the membrane process [66, 67]. Membrane fil-tration easily allows this separation by means of the method known as the LPR technique [68–75]. Among these methods, the membranes are
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the most promising for the enrichment of several ions from solution and their separation, especially where very low arsenic is required. The value of retention in the system with regenerated cellulose membrane is different than that reported in the literature where poly(ethersulfone) membrane was used as a filter [76]. At the present time, new research is being directed at improving the properties of the membranes, which are being modified to be an active component during the separation process. Thus, modifica-tion of the membrane is not only directed at permeability or antifouling properties.
1.6 Membranes for CO2 Separation
Numerous methods have been used for the separation of CO2. These methods include adsorption with porous solids (e.g., activated carbon and zeolites), amine absorption cryogenic separation and membrane-based separations [77, 78]. Adsorption technology is also being used for CO2 separation using different types of adsorbents. The low energy consumption and environment friendly nature was the main reason and focus of a large number of research studies on membrane technology [79]. Membranes (which generally consist of a semipermeable, thin, polymeric film) allow selective and specific permeation of some molecules while retaining others [80, 81].
Permeability and selectivity are the two main criteria that must be achieved in a good membrane. Membrane systems give reductions of over 70% in size and about 66% in weight compared to conventional separa-tion columns [82]. The highpurity CO2 separation may require numerous membranes with different characteristics, due to their limited ability to achieve high degrees of gas separation [83]. Gas separation membranes use the differences in partial pressure as their driving force for separation [84]. One component dissolves into the membrane, diffusing through the membrane before passing to the other side in the final stage [85].
Most of the research studies in membrane gas separation have been car-ried out on nonporous (dense) polymeric membranes. These membranes play an important role in gas separation. Different types of polymers have been used to develop dense polymeric membranes for CO2 separation from different gases, including polyimides, polysulfones, cellulose, and polycarbonates. Polyamides are one of the most extensively investigated polymeric materials for membrane gas separation since they possess very high CO2 permeability, mainly those incorporating the group 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane (6FDA). Polyimides have become
Processing and Characterizations 9
widely used membrane materials for gas and vapor separation due to their excellent thermal, chemical and mechanical stability in addition to their high gas separation. Polysulfone (PSF) is considered to be one of the most widely studied polymeric membrane material for CO2 separation for sev-eral gas streams [86, 87].
Gas permeation properties of PSF blends have been extensively investi-gated because of their low cost, chemical stability and mechanical strength [88]. Mixed-matrix membranes (MMMs), or composite membranes, are well-known in polymeric membranes development for gas separation. These membranes incorporate an inorganic material in the form of micro- or nanoparticles, hence combining the ease of polymer processing with the efficient gas permeation of a molecular sieve [89, 90]. Incorporating an inorganic material into a polymeric membrane can serve as a molecular sieve that enhances the gas permeance through the membrane or as a bar-rier that reduces the gas permeability [91].
Guo and coworkers prepared polysulfone-based mixed-matrix mem-branes (MMMs) incorporated with amine-functionalized titanium-based metal organic framework. One of the growing processes in the develop-ment of membrane science is the supported ionic liquid membranes (SILMs) technology. Due to their special properties, e.g., high thermal and chemical stability and low vapor pressure, ILs have become an ideal alter-native to conventional organic solvents in a wide range of chemical applications at lab scale, such as separation and purification and chemical catalysis [92–97].
1.7 Polymer Nanomembranes
To cite some of the most recent examples of polymeric nanostructured nanomembranes, researchers have found that they may act as molecular sieves [98] or humidity sensors in optical microcavity [99]; others have found large applicability in advanced biomedical applications [100]. Watanabe et al. found that polystyrene (PS) is not a satisfactory material to build robust nanomembrane with big size because it is not tough enough [101], thus suggesting that PS is not a suitable material for nanomembranes. A semiconducting polythiophene derivative like poly(3-thiophene methyl acetate) (P3TMA) has been blended with poly(tetramethylenesuccinate) (PE44) [102] or with thermoplastic polyurethane (TPU) [103] in order to fabricate robust biodegradable nanomembranes for tissue engineering.
Poly(diallyldimethyl-ammonium chloride) (PDMADMAC) and poly(styrenesulfonate) (PSS) [104] have been used to control the gas
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permeability of polymeric nanomembranes. Thanks to its biocompatibility and biodegradability, poly(lactic acid) (PLA) in the form of nanosheets, has been proposed as a physical barrier against burn wound infec-tion [105], for sealing operations in surgery [106], and for cell adhesion [46, 107]. Polysaccharide nanomembrane with a thickness of 75 nm is suit-able for repairing a visceral pleural defect without any loss of respiratory functions of the lung [108], and the same polymer is used together with a poly(vinylacetate) (PVAc) to sandwich tetracycline antibiotics against bacterial infection, to form an antibiotic-loaded nanosheet [109].
Mixed-matrix membranes (MMMs) consist of a mixture of rubbery or glassy polymer with inorganic materials like zeolites [110], carbon molec-ular sieves [111], or nanoparticles [112]. Yin et al. [113] summarized the scientific and technological advances in developing nanocomposite mem-branes for water treatment, including ultrathin films. Recent studies have revealed that the incorporation of small amounts of a dense monolayer of planar graphene oxide in polyelectrolyte nanomembranes significantly enhances their mechanical properties [114]. The surface of the substrate has to be ideally flat to fabricate membranes with uniform thickness, in particular where it is necessary to transfer it from a soft support as in [115]. Freestanding nanoscale membranes with outstanding mechanical charac-teristics, made with polyelectrolyte multilayers (PEM) with a central inter-layer containing gold nanoparticle, have been built combining spin coating with layer-by-layer (LbL) assembly [116]; graphene oxide layers have also been incorporated into the same previous multilayers fabricated in LbL assembly via Langmuir-Blodgett (LB) deposition. Evans et al. [117] synthe-sized conducting polymer nanocomposite film in a vacuum chamber oven following vapor phase polymerization (VPP) technique, and Fabretto et al. [118] investigated the influence of the VPP parameters on the dynamics of the polymerization process for use in large-scale electrochromic devices. Angelova et al. [119] presented a modular scheme to efficiently fabricate carbon nanomembranes utilizing a three-step procedure: deposition of self-assembled monolayer of polyaromatic molecules on solid substrate followed by electron irradiation to induce two-dimensional crosslinking, and transfer on the final support.
We should point out that the depth of surface plasma modification ranges from a few microns down to a few nanometers [120] depending on plasma energy. Recently, great attention has been devoted to the perfor-mance of polymeric nanomembranes with micro- or nanoporous struc-ture. The LbL technique allows the fabrication of conjugated microporous nanomembranes with tunable selectivity and permeability. Zhou et al. tar-geted their attention on developing a thin composite polymer membrane
