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A comprehensive overview of graphene-based membrane materials and its applications.
Two-Dimensional-Materials-Based Membranes An authoritative and up to date discussion of two-dimensional materials and membranes In Two-Dimensional-Materials-Based Membranes: Preparation, Characterization, and Applications, a team of distinguished chemical engineers delivers a comprehensive exploration of the latest advances in design principles, synthesis approaches, and applications of two-dimensional (2D) materials—like graphene, metal-organic frameworks (MOFs), 2D layered double hydroxides, and MXene—and highlights the significance and development of these membranes. In the book, the authors discuss the use of membranes to achieve high-efficiency separation and to address the challenges posed in the field. The book also discusses potential challenges and benefits in the future development of advanced 2D nanostructures, as well as their impending implementation in applications in the fields of energy, sustainability, catalysis, electronics, and biotechnology. Readers will also find: A thorough introduction to fabrication methods for 2D-materials-based membranes, including the synthesis of nanosheets, membrane structures, and fabrication methods Descriptions of three types of 2D-materials-based membranes: single-layer membranes, laminar membranes and mixed-matrix membranes Comprehensive discussions of 2D-materials-based membranes for water and ions separation, solvent-water separation and gas separation Explorations of transport mechanism of 2D-materials-based membranes for molecular separations Perfect for membrane scientists, inorganic chemists, and materials scientists, Two-Dimensional-Materials-Based Membranes will also earn a place in the libraries of chemical and process engineers in industrial environments.
Membrane-based filtration enables energy-efficient separations of solutes, solvents, or gases, benefiting a wide range of applications including water desalination, nanofiltration, hemodialysis, solvent-based separation, or natural gas purification. Semipermeable polymeric desalination membranes rely on solution-diffusion mechanism to separate water from salts, where selective transport of species arises from their solubility and diffusivity in polymer phase. Despite the remarkable progress in materials, structure, and separation process over the past few decades, today's membranes are subjected to intrinsic challenges ranging from resolving the trade-off between permeability and selectivity to maintaining robust operation with high stability and low fouling. Two dimensional materials have the potential to address some of the above challenges by offering a fundamentally new mechanism to control nanofluidic transport with sustainable nanoscale pores, thereby presenting a platform for next-generation reverse osmosis (RO) or nanofiltration (NF) membranes. Although theoretical investigations of great breadth and depth have been pursued to understand mass transport across the atomically thin materials, experimental efforts are required to engineer and tune nanopore structure in macroscopically large graphene membranes and understand the resulting transport characteristics. Moreover, the effects of interplay between graphene nanopore structure and porous support layer on membrane transport properties need to be considered to identify the structure-function relationship of the nanoporous graphene membranes. This thesis aims at controlling selective graphene nanopore structure for high permeability and selectivity and understanding the tunable membrane transport properties. A two-step process of ion bombardment and oxygen plasma is carried out to introduce a high density of nanopores in large-area graphene membranes. Pore creation parameters are thoroughly explored to investigate the influence on pore size and density. The resulting transport properties of graphene membranes can be tuned to achieve high permeance to water, comparable to that of NF membranes, and highly selective transport of monovalent ions over organic molecules. Nanopore structure introduced in graphene membranes is inspected to quantitatively relate the pore creation parameters with the resulting pore size distributions. A multiscale transport model is constructed to investigate the interplay between nanoporous graphene and support pores that governs osmotic water flux and diffusive solute transport. Internal concentration polarization of draw solutes estimated by the model suggests that achieving narrowly distributed graphene pores with minimal leakage is essential to optimal operation of high-flux asymmetric graphene membranes under forward osmosis. Sterically governed molecular assembly is explored to mitigate residual solute leakage across large, non-selective pores for enhanced membrane selectivity. High molecular weight polymers can electrostatically or covalently assemble across nanoscale defects of graphene to narrow down the effective pore size distribution, sterically and electrostatically hindering transport. Multi-step size-selective polyelectrolyte assembly enables >/=99% retention of divalent ions and organic molecules, promising the potential of graphene in desalination, nanofiltration or organic solvent nanofiltration (OSN). With experimental/theoretical means to characterize membrane structure and transport properties, this thesis forms the basis for regulating nanofluidic mass transport with tunable nanopores and developing atomically thin separation membranes with high selectivity and permeability.
This book covers newly emerging two-dimensional nanomaterials which have been recently used for the purpose of water purification. It focuses on the synthesis methods of 2D materials and answers how scientists/engineers/nanotechnologist/environmentalists could use these materials for fabricating new separation membranes and most probably making commercially feasible technology. The chapters are written by a collection of international experts ensuring a broad view of each topic. The book will be of interest to experienced researchers as well as young scientists looking for an introduction into 2D materials-based cross-disciplinary research.
Separation processes are found in many diverse applications, including health (drug purification, sterilization) and environment (CO2 capture, water treatment, resource recovery). Compared to thermal-based separation systems, membranes are modular and have the potential for more efficient separations without the need for extreme temperatures and large equipment. However, conventional polymeric membranes can suffer from fouling, poor stability at high temperatures and in harsh chemical environments, are subject to a permeability/selectivity trade-off, and it remains hard to precisely control and engineer their structures on the molecular level. These limitations call for the development of new membrane materials to yield significant performance improvements. The emergence of 2D nanomaterials allows for the creation of atomically thin membranes such as nanoporous graphene (NPG), and offers the opportunity to enhance chemical stability as well as increase both permeability and selectivity via significantly reducing membrane thickness and controlling the pore structure. Despite significant progress in theoretical and experimental work in the development of NPG membranes, challenges remain to be addressed for NPGs to be deployed, particularly in the control of leakages through defects, the limited experimentally-supported transport understanding, and the exploration and design of NPG systems for various health and environment applications. This thesis extends the theoretical understanding of transport across graphene composite membranes and demonstrates how differences in the scaling of transport rates with pore size for viscous flow, gas effusion, dilute solute diffusion, and ion transport, together with the interplay between graphene and support structure and selective pore size distribution, influence leakage and selectivity. This thesis also explores how non-linear current-voltage relationships can arise in ultra-thin membranes due to induced charge effects. These models enable us to estimate permeation rates without the need for computationally-intensive simulations. Furthermore, this thesis presents the application of NPG to hemodialysis, desalination, and ion separations. For dialysis, using system level modeling of the device and its interaction with the body, we show that current dialyzers are membrane mass-transfer limited for protein-bound uremic toxins (PBUTs), and establish performance targets for NPG membranes to enhance PBUT removal. These targets are translated to the novel design and fabrication of 2 an hierarchically-supported NPG composite membrane. We also investigate the desalination performance achievable by practical NPGs with pore size distributions and ways to surpass the polymeric permeability/selectivity trade-off limit, and develop a novel experimental/analysis procedure to study simultaneous ion transport across NPG and strategies to enhance selectivity for the recovery of rare earth elements.
Single-layer graphene membranes and other 2D membranes can realize very high gas permeation fluxes due to their atomic or unit cell thickness. Established modeling approaches for membrane transport consider transport through a finite and continuum thickness, and therefore they do not apply to the emerging field of 2D membranes, motivating the development of new theoretical treatments. In this thesis, I first developed an analytical theory for the transport of gases through single- layer graphene membranes, from the perspective of using pores in the graphene layer as a means for separation. I considered two pathways for the transport. The first being direct gas phase impingement on the pore, for which the large-pore separation factors are dictated by Knudsen selectivity, inversely proportional to the molecular weight; selectivity exceeding Knudsen is possible with smaller pores that reach a size commensurate with the size of the molecule, enabling separation by molecular sieving. The second pathway involves adsorption and transport on the graphene surface, similar to mechanisms in heterogeneous catalysis, which becomes more relevant for larger, strongly-adsorbing molecules. These models and pathways are applied for an estimate of a N2/H2 separation and as an explanation for results observed in the molecular dynamics literature. I applied our understanding of nanopore mechanisms and developed analysis of gas transport through graphene with approximately one selective nanopore etched into it, using experimental data from Bunch et al at Boston University for transport of He, H2 Ne, Ar, and CO2 through a small area graphene membrane with a single or few pores. The transport was measured by collaborators via monitoring the deflection of a graphene flake sealing a pressurized, 5[gamma]m diameter microcavity on the surface of a Si/SiO2 wafer. For this experimental system, I report on a mathematical formalism that allows one to detect and analyze stochastic changes in the gas phase fluxes from graphene membranes, extracting activation energies of pore rearrangements, 1.0 eV, and even identifying contributions from multiple, isolated pores.One opportunity that I identified is the use of a molecularly sized nanopore to 'direct write' the flux using a translatable platform. I performed an exploratory investigation of this concept of using a "nanonozzle," a nanometer scale pore that can deliver a flow of material locally, to grow nanoscale features. The model application was the growth of a graphene nanoribbon on a surface. I explored a variety of analytical mathematical models to understand the parameters and limitations of such a system. I developed a simple simulation of the nanoribbon growth and compared the results to the models for a range of parameters, considering the reasons for differences between the simulated and calculated results. This analysis provides considerations for the experimental design of such a system. Overall, the theories in this thesis and the analysis in they enable should aid the development of 2D membranes for separations applications and a novel direct write method for nanoscale patterning.
Current Trends and Future Developments on (Bio-) Membranes: Microporous Membrane and Membrane Reactors focuses on the structure, preparation, characterization and applications of microporous membranes and membrane reactors, including transport mechanisms through a range of microporous membranes. It is a key reference text for R&D managers who are interested in the development of gas separation and water/waste treatment technologies, but is also well-suited for academic researchers and postgraduate students working in the broader area of strategic material production, separation and purification. Users will find comprehensive coverage of current methods, their characterization and properties, and various applications in gas separation and water treatment. Reviews gas separation and water treatment processes and relates them to various applications Outlines the use of microporous membranes in gas separations and water treatment Introduces the various types of microporous membranes (graphene, polymeric, etc.) and their mechanism of action Provides simulation models of the various processes
Filtration membranes are required to be thin, robust, energy efficient, and accurate on selectivity. Graphene oxide (GO) is believed to be a potential next generation material for industrial membrane applications because of its unique properties such as strong mechanical strength, excellent aqueous solution processability, and great flexibility for membrane fabrication. Research on the transport models, the separation performance, and the functionalization of GO membranes has been developed. However, many mechanisms of mass transport through GO membranes still remain debatable. In this work, GO was synthesized, and then functionalized with linear amine-terminated poly(ethylene glycol) (PEG) and aluminum ions (Al). The fabrication and characterizations of GO, PEG-GO, and Al-GO membranes were demonstrated in this work. Water and water/ethanol binary mixture transport through GO, PEG-GO, and Al-GO membranes were studied to investigate the permeation and the rejection rates of solvents through GO-based membranes. The total volumetric flux of water/ethanol mixture through GO membranes was inversely proportional to the viscosity of the solvent mixtures. The steric hindrance effect and the interactions between the solvent molecules and the membrane surfaces dominated the rejection rate of ethanol through GO membranes. The functionalization of GO modified the pore size and the porosity of the membranes, resulting in faster permeation of solvents and reduced rejection rates of ethanol through PEG-GO and Al-GO membranes. Deformation of nanochannels within the functionalized GO membranes was observed when the membranes were operated under highly pressurized conditions. Diffusive transport of two charge equivalent and structurally similar ruthenium complex ions Ru(bpy)32+ and iv Ru(phen)32+ through GO, PEG-GO, and Al-GO membranes were also studied. Our data showed high similarity with the results reported previously in the literature, indicating that the GO and functionalized GO membranes used in this work were highly consistent. Due to the enlarged pore sizes and the reduced interactions between ions and the membrane surfaces, the flux of ions through PEG-GO membranes was 300% higher than that through GO membranes. In contrast, permeation of ions through Al-GO membranes was slower than that through GO membranes. The blocked nanopores and the electrostatic repulsion between the intercalated aluminum ions and complex ions were the main reasons for this observation. In addition, the main reason for the significant permeance difference between Ru(bpy)32+ and Ru(phen)32+ ions was confirmed as the steric hindrance effect. This work contributes to the basic research on GO membranes in potential applications. It can be beneficial to the academic laboratories for understanding the mechanism of mass transport through GO-based membranes. These new membrane materials could replace traditional membrane materials in many industrial applications in the future.
Comprehensive Membrane Science and Engineering, Second Edition, Four Volume Set is an interdisciplinary and innovative reference work on membrane science and technology. Written by leading researchers and industry professionals from a range of backgrounds, chapters elaborate on recent and future developments in the field of membrane science and explore how the field has advanced since the previous edition published in 2010. Chapters are written by academics and practitioners across a variety of fields, including chemistry, chemical engineering, material science, physics, biology and food science. Each volume covers a wide spectrum of applications and advanced technologies, such as new membrane materials (e.g. thermally rearranged polymers, polymers of intrinsic microporosity and new hydrophobic fluoropolymer) and processes (e.g. reverse electrodialysis, membrane contractors, membrane crystallization, membrane condenser, membrane dryers and membrane emulsifiers) that have only recently proved their full potential for industrial application. This work covers the latest advances in membrane science, linking fundamental research with real-life practical applications using specially selected case studies of medium and large-scale membrane operations to demonstrate successes and failures with a look to future developments in the field. Contains comprehensive, cutting-edge coverage, helping readers understand the latest theory Offers readers a variety of perspectives on how membrane science and engineering research can be best applied in practice across a range of industries Provides the theory behind the limits, advantages, future developments and failure expectations of local membrane operations in emerging countries