2D Nanosheets and Their Composite Membranes for Water, Gas, and Ion Separation.

Two‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.

Membrane–based gas separation has become an important research field for sustainable energy and environmental applications. Gas separation is one of the key steps in refineries and other gas‐related industries. Over the last two decades, the research on extended porous organic and inorganic materials such as zeolites, metal–organic frameworks (MOFs), covalent–organic frameworks (COFs), and their hybrids has increased continuously. These materials have garnered significant interest due to their structural flexibility and pronounced porosity, which offer excellent potential for gas adsorption and separation processes in industrial settings. As such, this review has aimed to provide an in‐depth analysis of the recent developments in MOFs, COFs, and MOF–COF hybrid‐based membranes for gas separation, highlighting their potential for practical industrial applications. It also offers a comprehensive understanding of some of the most critical and advanced materials used in gas separation compared to common polymers. In addition, membranes' concepts, efficiency, and cost‐effectiveness are discussed in detail.

Design and application of metal–organic framework membranes for gas and liquid separations

A review of polymeric composite membranes for gas separation and energy production

The phenomenon of melting in metal-organic frameworks (MOFs) has recently garnered attention. Crystalline MOF materials can be transformed into an amorphous glassy state through melt-quenching treatment. The resulting MOF glass structure eliminates grain boundaries and retains short-range order while exhibiting long-range disorder. Based on these properties, it emerges as a promising candidate for high-performance separation membranes. MOF glass membranes exhibit permanent and accessible porosity, allowing for selective adsorption of different gas species. This review summarizes the melting mechanism of MOFs and explores the impact of ligands and metal ions on glassy MOFs. Additionally, it presents an analysis of the diverse classes of MOF glass composites, outlining their structures and properties, which are conducive to gas adsorption and separation. The absence of inter-crystalline defects in the structures, coupled with their distinctive mechanical properties, renders them highly promising for industrial gas separation applications. Furthermore, this review provides a summary of recent research on MOF glass composite membranes for gas adsorption and separation. It also addresses the challenges associated with membrane production and suggests future research directions.

There are many membrane technology related books the publication collection, but this book gathered the up to-date knowledge sharing with technology experts around the world on the application of nanocomposite membrane in water and gas separation. This book consists of 510 pages and 19 chapters in this first edition covering the recent progress and development of the novel nanocomposite membrane and the prospect in various application. Each chapter starts with the preliminary introduction of the topics followed by the in-depth discussion and the concluded remarkably.Chapter 1 and 2 discussed the overview of the nanocomposite membranes in membrane technologies, recent advancement of the materials used and fabrication techniques. Chapter 3 and 5 provide an insight in the selection of polymeric materials, fillers and metal oxides for the fabrication of nanocomposite membrane. This chapter also carefully examined the formation of nanocomposite layers on the membrane by various techniques such as coating, grafting and self-assembly. Chapter 4 overview the heat, mass and charge transfer across the membrane with detailed explanation of the transport phenomenon involved in both porous and non-porous membrane. Chapter 6 to 9 addressed the development of the advanced nanocomposite membranes with detailed discussion on the incorporation of carbon-based nanomaterials (CNTs and GO), molecular sieving nanomaterials (zeolite and MOF), electrospun nanofibrous materials and biomimicking nanomaterials in the nanocomposite membrane. These chapters also discussed the fabrication and coating method of this materials onto the membrane and its effect on both physical and chemical properties of the nanocomposite membranes.Chapter 10 to 13 described the prospect of the nanocomposite membrane in water treatment by various separation techniques such as pressure-driven membrane processes, osmotic-driven membrane processes, membrane distillation and electrodriven membrane processes. These chapters highlighted the application of nanocomposite membranes with different separation processes in the water treatment application with the discussion on the effects of the operation parameter and the current performance of the membranes in respective processes. Chapter 14 to 17 focussed on the application of nanocomposite membrane in various gas separation in natural gas treatment, nitrogen and oxygen enrichment, recovery of hydrogen and production of syngas and gas separation by membrane contactors. These chapter summarized the results demonstrated by the membrane in gas separation and the identification of the challenges faced by the nanocomposite membrane. The last two chapters of the book addressed the outlook of the nanocomposite membrane with thorough examination of the operational and environmental challenges faced for the feasibility of commercialization.This book intended to capture the recent advancement of the nanocomposite membrane in terms of fabrication and its performance in water and gas separation that contributed to the sustainability of membrane technology in the future. More than 50 membrane experts from various countries contributed to this book, providing an insight of nanocomposite membrane which is still inscrutable for many in the separation field. This book will be the vital reference for the researchers, students, membrane technologist, membrane manufacturer or marketeers.

Ionic liquids have attracted the attention of the industry and research community as versatile solvents with unique properties, such as ionic conductivity, low volatility, high solubility of gases and vapors, thermal stability, and the possibility to combine anions and cations to yield an almost endless list of different structures. These features open perspectives for numerous applications, such as the reaction medium for chemical synthesis, electrolytes for batteries, solvent for gas sorption processes, and also membranes for gas separation. In the search for better-performing membrane materials and membranes for gas and vapor separation, ionic liquids have been investigated extensively in the last decade and a half. This review gives a complete overview of the main developments in the field of ionic liquid membranes since their first introduction. It covers all different materials, membrane types, their preparation, pure and mixed gas transport properties, and examples of potential gas separation applications. Special systems will also be discussed, including facilitated transport membranes and mixed matrix membranes. The main strengths and weaknesses of the different membrane types will be discussed, subdividing them into supported ionic liquid membranes (SILMs), poly(ionic liquids) or polymerized ionic liquids (PILs), polymer/ionic liquid blends (physically or chemically cross-linked ‘ion-gels’), and PIL/IL blends. Since membrane processes are advancing as an energy-efficient alternative to traditional separation processes, having shown promising results for complex new separation challenges like carbon capture as well, they may be the key to developing a more sustainable future society. In this light, this review presents the state-of-the-art of ionic liquid membranes, to analyze their potential in the gas separation processes of the future.

Membranes are widely used in industrial separation processes, particularly for gas separation and desalination processes. To develop membrane materials with improved permeability, selectivity can achieve more energy-efficient membrane separations and reduce costs. Since composite membranes offer improved performance, the aim of this research is to develop polymer-based composite membranes with improved performance for gas separation and water desalination applications. First, in order to obtain a composite membranes with high chlorine tolerance, a carbonaceous poly(furfuryl alcohol) (PFA) composite membrane was synthesized at a low temperature carbonation by formation and post-treatment of a thin PFA layer on porous polymer substrates. The carbonaceous PFA membrane exhibits high selectivity and excellent chemical stability in seawater desalination. The low-temperature carbonization method developed in this study is promising for developing a wide range of other carbonaceous polymer composite membranes for water desalination. Next, in order to apply PFA to other applications, understanding the effects of polymerization conditions on the properties of the PFA composite membrane is required. The PFA membrane was fully characterized in terms of microstructure and separation properties. Suitable synthesis conditions for the preparation of PFA composite membranes with smooth surfaces and uniform structure were (1) FA/ H2SO4 molar ratios: 74-300, (2) polymerization temperatures: 80-100°C and (3) solvents: ethanol and acetone. The preparation conditions were also optimized. The PFA composite membrane prepared with a FA/ H2SO4 molar ratio of 250, a polymerization temperature of 80°C and with ethanol as the solvent exhibited the highest H2/N2 ideal selectivity (αH2/N2=24.9), and a H2 permeability of 206 Barrers. This work led to a better understanding of the effect of the preparation procedures on the membrane performance. In order to investigate the effects of the incorporation of molecular sieve nanoparticles on the membrane structure and membrane performance, silicalite-poly(furfuryl alcohol) (PFA) mixed matrix composite membranes were successfully synthesized based on the best synthesis condition obtained previously. The silicalite-PFA mixed matrix composite membrane with 20% w/w silicalite loading had a high ideal selectivity (αo2/N2= 3.5 and αco2/N2= 5.4) and a good permeability (Po2= 821.2, Pco2= 1263.7, PN2= 233.3 Barrers) at room temperature. This membrane can be a good candidate for oxygen enrichment applications. Finally, in order to investigate the effects of the incorporation of silicalite nanocrystals on the desalination property of polyamide membranes, silicalite nanocrystals were also incorporated into polyamide matrix to synthesize silicalite-polyamide mixed matrix membranes. With an increase in the loading of silicalite nanocrystals, the water flux of silicalite-polyamide mixed matrix composite membranes increased whereas the salt selectivity significantly decreased. The silicalite-polyamide mixed matrix composite membrane prepared from TMC-hexane with 0.5% (w/v) silicalite had water flux of 2.7×10-6 m3/m2·s and NaCl rejection of 50% at a feed pressure of 34.5 bar which 2000 ppm salt solution was used as the feed. The silicalite-polyamide mixed matrix composite membrane is promising for developing high water flux composite membranes for water desalination. In this research, composite membranes with improved permeability, selectivity and chemical resistance were successfully synthesized for desalination and gas separation. For desalination, carbonaceous PFA composite membranes with high chlorine tolerance and silicalite-PA mixed matrix composite membranes with high salt rejection and water flux were successfully obtained. For gas separation, an optimized composite membranes PFA synthesis condition was found and silicalite-PFA mixed matrix composite membranes with high O2/N2 separation were successfully synthesized.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Chapter 8 - Toward Sustainable Chemical Processing With Graphene-Based Materials

Currently, graphene oxide (GO) has attracted widespread attention as a new membrane material owing to its unique properties, such as fast water transport, selective gas or ion separation properties, and proton conduction. While most carbon nanomaterials have been used for reinforcements to improve conventional membrane materials via mixing, GO can be easily prepared as a freestanding membrane from aqueous solution, which provides great benefit for easy membrane formation and also lots of permeation measurements. Differing from other membrane materials, GO membranes use tunable slit-like pores between layered GO sheets for molecular or ionic separations, and such pore width can be controllable by the degree of oxidation, amount of intercalated water and further functionalization. As such, GO and its functionalized derivatives have been prepared as various membrane forms, and many intriguing, selective transport properties have been found, which can be regarded as promising membrane materials for a wide variety of membrane applications such as gas separation, water purification and fuel cell membranes. This chapter will cover the state of the art of GO membranes and their promising membrane applications, and also provide material guidelines for future research directions suitable for practical membrane applications.

The various aspects concerned with society as a whole, such as energy utilization, industrial manufacturing and environmental protection have a close relation to the discipline of adsorption, separation and purification of gases. Explicitly, the storage of methane and hydrogen is vital for the prevalent use of clean energy; carbon dioxide separation is important in terms of the increased greenhouse effect; storage and separation of toxic gases, viz., ammonia and carbon monoxide, are significant for regulation of pollution and for production of industrial chemicals. In comparison to classical porous adsorbents (e.g., activated carbon, zeolite and silica-based systems), the intriguing structural features of metal-organic frameworks (MOFs) such as porous nature, enormous surface area, adaptable pore dimensions and flexible functionality enable such materials to exhibit great prospects in the area of storage as well as separation of gas. In this chapter, we hope to throw some light on some current developments in the field of storage, separation, and purification of gases by using some benchmark and currently developed MOFs. The chemical characteristics of MOFs that are desired for storage and separation of various gases will also be emphasized in this work. In a nutshell, a major emphasis on the current status of energy-related gases like hydrogen (H2) and methane (CH4), separation of various gases and removal of some toxic gases like nitrogen dioxide (NO2), ammonia (NH3), sulfur dioxide (SO2), and particulate matter are reviewed.

2D Materials Membranes are discussed by Guest Editor Zhiyong Tang in his Editorial for this special issue.

Membranes with well-defined pore structure which have thin active layers may be promising materials for efficient gas separation. Graphene oxide (GO) materials have potential applications in the field of membrane separation. Here we describe a strategy for the construction of ultra-thin and flexible HKUST-1@GO intercalated membranes, where HKUST-1 is a copper-based metal–organic framework with coordinatively unsaturated metal sites, with simultaneous and synergistic modulation of permeance and selectivity to achieve high H2/CO2 separation. CuO nanosheets@GO membranes are fabricated layer-by-layer via repeated filtration cycles, then transformed to HKUST-1@GO membranes upon in situ reaction with linkers. The HKUST-1@GO membranes show enhanced performance for gas separation of H2/CO2 mixture. The number of filtration cycles is optimized to obtain H2 permeance of 5.77 × 10−7 mol m−2 s−1 Pa−1 and H2/CO2 selectivity of 73.2. Our work provides a facile strategy for the construction of membranes based on metal–organic frameworks and GO, which may be applied in the preparation of flexible membranes for gas separation applications.

Two-dimensional membranes are considered as the most energy-efficient alternatives to various traditional separation processes. To date, atomically thin hexagonal boron nitride, covalent organic frameworks, graphene, graphene oxide, transition metal carbides and nitrides, layered double hydroxide, transition metal dichalcogenides (TMDCs), and metal-organic frameworks have been extensively investigated for high-performance lamellar membranes, which is due to their tunable physicochemical properties, single-layered structure, and in-plane pore structure. This comprehensive review summarizes the different fabrication methods of TMDC-based membranes and introduces the recent modification strategies to improve their microstructural properties. TMDCs-based membranes for wastewater treatment, desalination, proton exchange, gas separation, and energy devices are extensively discussed. Finally, we highlight the current engineering hurdles and suggest research directions for improving the separation efficiency, stability, and permeability of these membranes.