High CO2 separation performance of amino acid ionic liquid-based double network ion gel membranes in low CO2 concentration gas mixtures under humid conditions

Liquid-crystalline nanostructured membranes for CO2 separation

We report herein that self-organized subnanoporous membranes prepared from ionic liquid-crystalline (LC) compounds exhibit CO2 separation properties (αCO2/N2 ≈ 60) in humid conditions. A bicontinuous cubic (Cubbi) LC film shows N2 barrier properties, whereas the CO2 permeability is kept as permeable.

Micro and Nanoporous Membrane Platforms for Carbon Neutrality: Membrane Gas Separation Prospects

Recently, carbon neutrality has been promoted as a potentially practical solution to global CO2 emissions and increasing energy-consumption challenges. Many attempts have been made to remove CO2 from the environment to address climate change and rising sea levels owing to anthropogenic CO2 emissions. Herein, membrane technology is proposed as a suitable solution for carbon neutrality. This review aims to comprehensively evaluate the currently available scientific research on membranes for carbon capture, focusing on innovative microporous material membranes used for CO2 separation and considering their material, chemical, and physical characteristics and permeability factors. Membranes from such materials comprise metal-organic frameworks, zeolites, silica, porous organic frameworks, and microporous polymers. The critical obstacles related to membrane design, growth, and CO2 capture and usage processes are summarized to establish novel membranes and strategies and accelerate their scaleup.

Aquatic Functional Liquid Crystals: Design, Functionalization, and Molecular Simulation

Aquatic functional liquid crystals, which are ordered molecular assemblies that work in water environment, are described in this review. Aquatic functional liquid crystals are liquid-crystalline (LC) materials interacting water molecules or aquatic environment. They include aquatic lyotropic liquid crystals and LC based materials that have aquatic interfaces, for example, nanoporous water treatment membranes that are solids preserving LC order. They can remove ions and viruses with nano- and subnano-porous structures. Columnar, smectic, bicontinuous LC structures are used for fabrication of these 1D, 2D, 3D materials. Design and functionalization of aquatic LC sensors based on aqueous/LC interfaces are also described. The ordering transitions of liquid crystals induced by molecular recognition at the aqueous interfaces provide distinct optical responses. Molecular orientation and dynamic behavior of these aquatic functional LC materials are studied by molecular dynamics simulations. The molecular interactions of LC materials and water are key of these investigations. New insights into aquatic functional LC materials contribute to the fields of environment, healthcare, and biotechnology.

Accelerated Oxidative Degradation of Phosphonium-Type Ionic Liquid with l-Prolinate Anion: Degradation Mechanism and CO2 Separation Performance

Amino acid ionic liquids (AAILs) are regarded as green alternatives to existing CO₂-sorptive materials because amino acids are readily available from renewable sources in large quantities. For widespread applications of AAILs, including direct air capture, the relationship between the stability of AAILs, especially toward O₂, and the CO₂ separation performance is of particular importance. In the present study, the accelerated oxidative degradation of tetra-n-butylphosphonium l-prolinate ([P₄₄₄₄][Pro]), a model AAIL that has been widely investigated as a CO₂-chemsorptive IL, is performed using a flow-type reactor system. Upon heating at 120-150 °C and O₂ gas bubbling to [P₄₄₄₄][Pro], both the cationic and anionic parts undergo oxidative degradation. The kinetic evaluation of the oxidative degradation of [P₄₄₄₄][Pro] is performed by tracing the decrease in the [Pro]^- concentration. Supported IL membranes composed of degraded [P₄₄₄₄][Pro] are fabricated, and the membranes retain CO₂ permeability and CO₂/N₂ selectivity values in spite of the partial degradation of [P₄₄₄₄][Pro].

Synthesis and performance evaluation of copper and magnesium-based metal organic framework supported ionic liquid membrane for CO2/N2 separation

The CO₂ emission is enhancing drastically because of the continuous emission from industries and transport sector. Although the CO₂ emission had decreased in the first half of 2020 by 8.8% due to COVID-19 restrictions however, it is again on the rise and it might exceed the estimated level in 2030. The current methods used for CO₂ separation have serious operational and environmental constraints. To overcome these problems we have devised a supported ionic liquid membrane (SILM) incorporated with the blend of bimetallic metal-organic framework (MOF) of copper and magnesium ions (Cu_xMg_x) and Trihexyltetradecylphosphonium chloride [P₆₆₆₁₄] [Cl] ionic liquid (IL). Cu_xMg_x MOF were synthesized and characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and energy dispersive X-ray analysis (EDX). Cu_xMg_x MOF with [P₆₆₆₁₄] [Cl] IL were immobilized on a flat sheet of polytetrafluoroethylene (PTFE) membrane. Single gas permeation tests of membranes loaded with 0.2/0.8 wt/wt% MOF/IL solution showed the highest CO₂ permeability of 2937 Barrer and CO₂/N₂ selectivity of 33.26. The performance of SILM was also investigated with different water loadings of (30 wt % and 50 wt %) in addition to MOF/IL solution and at different feed pressure varying from 0.5 to 2 bars. Membranes showed enhancement in CO₂ permeability to 3738 and 4628 Barrer whereas CO₂/N₂ selectivity decreased to 23.53 and 21.8 with membranes loaded with 30 and 50 wt % water, respectively, at a feed pressure of 2 bar. The gas permeation results show that the incorporation of Cu_xMg_x MOF with IL in polymeric membrane enhances the CO₂/N₂ separation under humid conditions but slightly decreases CO₂/N₂ selectivity with an increase in feed pressure. The SILM synthesized in this research is highly viable for industrial flue gases because of the incorporation of phosphonium-based ILs that have high thermal stability.

Technological advancements in the use of ionic liquid- membrane systems for CO2 capture from biogas/flue gas - A review

Carbon capture has become a very important method for curbing the problems associated with the release of carbon dioxide into the atmosphere, which in turn has detrimental effects on the planet and its inhabitants. Ionic liquids and membrane separation have been explored in this review paper as effective means of capturing carbon dioxide. An innovative approach to CO₂ capture is the use of Ionic liquids (ILs) since they exhibit certain significant traits such as good stability (thermal, mechanical and chemical), inflammability and high absorptive capacities. Ionic liquids (ILs) are widely regarded as nontoxic substances. Viscosity and thermal degradation of ILs at temperatures slightly above 100 °C are the major disadvantages of ILs. Membrane separation is a technique used for the effective separation of substances by materials bearing holes in a continuous structure. Membrane technology has gained significant improvements, over the years. Several ILs and membrane systems were considered in this work. Their weaknesses, strengths, permeability, selectivity, operating conditions and carbon capture efficiencies, were all highlighted in order to gain a good perspective on ways by which the individual systems can be improved upon. The study considered several polymer-Ionic liquid hybrid materials as viable options for CO₂ capture from a post-combustion process. Different ILs were scrutinized for possible integration in membranes by taking full advantage of their individual properties and harnessing their tune-able characteristics in order to improve the overall carbon capture performance of the system. Several options for improving the mechanical, chemical, and thermal stabilities of the hybrid systems were considered including the use of cellulose acetate membrane, nanoparticles (graphene oxide powder) alongside potential ionic liquids. Doping membranes with ILs and nanoparticulates such as graphene oxide serves as a potential method for enhancing the CO₂ capture of membranes and this review provides several evidences that serve as proofs for this concept.

Ionic Liquid Mixtures for Direct Air Capture: High CO2 Permeation Driven by Superior CO2 Absorption with Lower Absolute Enthalpy

This paper reports a series of liquid materials suitable for use as high-performance separation membranes in direct air capture. Upon mixing two ionic liquids (ILs), namely N-(2-aminoethyl)ethanolamine-based IL ([AEEA][X]) and 1-ethyl-3-methylimidazolium acetate ([emim][AcO]), the resulting mixtures with a specific range of their composition showed higher CO₂ absorption rates, larger CO₂ solubilities, and lower absolute enthalpies of CO₂ absorption compared to those of single ILs. NMR spectroscopy of the IL mixture after exposure to ¹³CO₂ allowed elucidation of the chemisorbed species, wherein [AEEA][X] reacts with CO₂ to form CO₂-[AEEA]⁺ complexes stabilized by hydrogen bonding with acetate anions. Supported IL membranes composed of [AEEA][X]/[emim][AcO] mixtures were then fabricated, and the membrane with a suitable mixing ratio showed a CO₂ permeability of 25,983 Barrer and a CO₂/N₂ selectivity of 10,059 at 313.2 K and an applied CO₂ partial pressure of 40 Pa without water vapor. These values are higher than those reported for known facilitated transport membranes.

Tough ion gels composed of coordinatively crosslinked polymer networks using ZIF-8 nanoparticles as multifunctional crosslinkers

Constructing crosslinked polymer networks via reversible interactions is a promising approach to recover the mechanical strength of damaged gels. In addition, by designing effective reversible crosslinks, the mechanical strength of the gel can be enhanced through energy dissipation based on the destruction of the crosslinks by an applied force. In this study, we introduced zeolitic imidazole framework-8 nanoparticles (ZIF-8 NPs), which acted as multifunctional crosslinkers, to provide multipoint coordination bonding with a poly(N,N-dimethylacrylamide)-based polymer network in a gel containing an ionic liquid. The mechanical strength of the gel increased with an increase in the content of ZIF-8 NPs up to 6 wt%. It was confirmed that the energy loaded onto the gel was dissipated through the desorption of the polymer network from the surface of the ZIF-8 NPs. Owing to the reversible destruction and reconstruction of the coordinative crosslinking between the polymer network and ZIF-8 NPs, the mechanical strength of the damaged gel was almost fully recovered through annealing.

Emerging iongel materials towards applications in energy and bioelectronics

In the past two decades, ionic liquids (ILs) have blossomed as versatile task-specific materials with a unique combination of properties, which can be beneficial for a plethora of different applications. The additional need of incorporating ILs into solid devices led to the development of a new class of ionic soft-solid materials, named here iongels. Nowadays, iongels cover a wide range of materials mostly composed of an IL component immobilized within different matrices such as polymers, inorganic networks, biopolymers or inorganic nanoparticles. This review aims at presenting an integrated perspective on the recent progress and advances in this emerging type of material. We provide an analysis of the main families of iongels and highlight the emerging types of these ionic soft materials offering additional properties, such as thermoresponsiveness, self-healing, mixed ionic/electronic properties, and (photo)luminescence, among others. Next, recent trends in additive manufacturing (3D printing) of iongels are presented. Finally, their new applications in the areas of energy, gas separation and (bio)electronics are detailed and discussed in terms of performance, underpinning it to the structural features and processing of iongel materials.

Recent Developments in High-Performance Membranes for CO2 Separation

In this perspective article, we provide a detailed outlook on recent developments of high-performance membranes used in CO₂ separation applications. A wide range of membrane materials including polymers of intrinsic microporosity, thermally rearranged polymers, metal–organic framework membranes, poly ionic liquid membranes, and facilitated transport membranes were surveyed from the recent literature. In addition, mixed matrix and polymer blend membranes were covered. The CO₂ separation performance, as well as other membrane properties such as film flexibility, processibility, aging, and plasticization, were analyzed.

The dynamic behavior and intrinsic mechanism of CO2 absorption by amino acid ionic liquids

Reducing carbon dioxide emissions is one of the possible solutions to prevent global climate change, which is urgently needed for the sustainable development of our society. In this work, easily available, biodegradable amino acid ionic liquids (AAILs) with great potential for CO₂ absorption in the manned closed space such as spacecraft, submarines and other manned devices are used as the basic material. Molecular dynamics simulations and ab initio calculations were performed for 12 AAILs ([P4444][X] and [P66614][X], [X] = X = [GLy]^-, [Im]^-, [Pro]^-, [Suc]^-, [Lys]^-, [Asp]^2-), and the dynamic characteristics and the internal mechanism of AAILs to improve CO₂ absorption capacity were clarified. Based on structural analysis and the analysis of interaction energy including van der Waals and electrostatic interaction energy, it was revealed that the anion of ionic liquids dominates the interaction between CO₂ and AAILs. At the same time, the CO₂ absorption capacity of AAILs increases in the order [Asp]^2- < [Suc]^- < [Lys]^- < [Pro]^- < [Im]^- < [Gly]^-. Meanwhile, the synergistic absorption of CO₂ by multiple-sites of amino and carboxyl groups in the anion was proved by DFT calculations. These findings show that the anion of AAILs can be an effective factor to regulate the CO₂ absorption process, which can also provide guidance for the rational and targeted molecular design of AAILs for CO₂ capture, especially in the manned closed space.

A Review on Ionic Liquid Gas Separation Membranes

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.

Facilitated Transport Membranes With Ionic Liquids for CO2 Separations

In recent years, significant development milestones have been reached in the areas of facilitated transport membranes and ionic liquids for CO2 separations, making the combination of these materials an incredibly promising technology platform for gas treatment processes, such as post-combustion and direct CO2 capture from air in buildings, submarines, and spacecraft. The developments in facilitated transport membranes involve consistently surpassing the Robeson upper bound for dense polymer membranes, demonstrating a high CO2 flux across the membrane while maintaining very high selectivity. This mini review focuses on the recent developments of facilitated transport membranes, in particular discussing the challenges and opportunities associated with the incorporation of ionic liquids as fixed and mobile carriers for separations of CO2 at low partial pressures (<1 atm).

Inorganic/organic nanocomposite ion gels with well dispersed secondary silica nanoparticles

We have previously reported tough inorganic/organic nanocomposite (NC) ion gels composed of silica particles and poly(N,N-dimethylacrylamide) (PDMAAm) networks and a large amount of ionic liquid. In this study, the network structure and toughening mechanism of NC ion gels were investigated. The NC ion gels showed characteristic mechanical properties; i.e. the stress was significantly increased at a highly elongated state. In addition, the NC ion gels showed an almost elastic mechanical property, which was completely different from that of our other developed inorganic/organic tough ion gels named double-network (DN) ion gels. It was found from structural observation that secondary silica nanoparticles dispersed well in the NC ion gel. It was also found that some of the secondary silica nanoparticles had a ring-like structure which would incorporate PDMAAm chains. From the silica particle content dependency on stress-strain curves of inorganic/organic NC ion gels, it was inferred that the secondary silica particles could serve as a movable cross-linker of PDMAAm chains in the NC ion gel.

Influence of Anion Structure on Thermal, Mechanical and CO2 Solubility Properties of UV-Cross-Linked Poly(ethylene glycol) Diacrylate Iongels

Iongel-based CO₂ separation membranes were prepared by fast (< 1 min) UV-initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of different ionic liquids (ILs) with the [C₂mim]⁺ cation and anions such as [TFSI]^-, [FSI]^-, [C(CN)₃]^- and [B(CN)₄]^-. The four ILs were completely miscible with the non-ionic PEGDA network. Transparent and free-standing iongels containing between 60 and 90 %wt of IL were obtained and characterized by diverse techniques (FTIR, TGA, DSC, DMTA, SEM, CO₂ solubility and pure gas permeability). The thermal and mechanical stability of the iongels, as well as CO₂ solubility, were found to be strictly dependent on the IL content and the anion's nature. The TGA results indicated that the iongels mostly follow the thermal profile of the respective neat ILs. The DMTA analysis revealed that the iongels based on fluorinated anions have higher storage modulus than those of cyano-functionalized anions. Conversely, the PEGDA-C(CN)₃ iongels presented the highest CO₂ solubility values ranging from 72 to 80 mmol/g. Single CO₂ permeabilities of 583 ± 29 Barrer and ideal CO₂/N₂ selectivities of 66 ± 3 were obtained with the PEGDA-70 C(CN)₃ iongel membrane. This work demonstrates that the combination of PEGDA with high contents of the best performing ILs is a promising and simple strategy, opening up new possibilities in the design of high-performance iongel membranes for CO₂ separation.

Energy dissipation via the internal fracture of the silica particle network in inorganic/organic double network ion gels

Inorganic/organic double network (DN) ion gels, which are composed of an inorganic silica particle network, an organic poly(N,N-dimethylacrylamide) (PDMAAm) network, and a large amount of ionic liquid, showed excellent mechanical strength of over 25 MPa compression fracture stress at an 80 wt% ionic liquid content. The excellent mechanical strength of these inorganic/organic DN ion gels was attributed to the energy dissipation of the inorganic/organic DN structure. It has been considered that the energy dissipation in inorganic/organic DN ion gels is caused by the internal fracture of the silica particle network, which is preferentially fractured by deformation. However, no studies aiming to investigate the internal fracture of the silica particle network in inorganic/organic DN ion gels have been conducted by direct approaches. In this study, the internal fracture of the silica particle network in the inorganic/organic DN ion gel was directly evaluated by a small angle X-ray scattering (SAXS) technique. The synchrotron SAXS measurements conducted under a uniaxial loading-unloading process demonstrated that the aggregation size of the silica particle network irreversibly decreased with uniaxial stretch. Based on these results, it was clarified that the energy dissipation of the inorganic/organic DN ion gels was attributed to the internal fracture of the silica particle network.

Rheology of Concentrated Polymer/Ionic Liquid Solutions: An Anomalous Plasticizing Effect and a Universality in Nonlinear Shear Rheology

An anomalous plasticizing effect was observed in polymer/ionic liquid (IL) solutions by applying broad range of rheological techniques. Poly(ethylene oxide)(PEO)/IL solutions exhibit stronger dynamic temperature dependence than pure PEO, which is in conflict with the knowledge that lower-Tg solvent increases the fractional free volume. For poly(methy methacrylate)(PMMA)/IL solutions, the subtle anomaly was detected from the fact that the effective glass transition temperature Tg,eff of PMMA in IL is higher than the prediction of the self-concentration model, while in conventional polymer solutions, Tg,eff follows the original Fox equation. Observations in both solutions reveal retarded segmental dynamics, consistent with a recent simulation result (Macromolecules, 2018, 51, 5336) that polymer chains wrap the IL cations by hydrogen bonding interactions and the segmental unwrapping delays their relaxation. Start-up shear and nonlinear stress relaxation tests of polymer/IL solutions follow a universal nonlinear rheological behavior as polymer melts and solutions, indicating that the segment-cation interaction is not strong enough to influence the nonlinear chain orientation and stretch. The present work may arouse the further theoretical, experimental, and simulation interests in interpreting the effect of complex polymer-IL interaction on the dynamics of polymer/IL solutions.

Protein-Rich Biomass Waste as a Resource for Future Biorefineries: State of the Art, Challenges, and Opportunities

Protein-rich biomass provides a valuable feedstock for the chemical industry. This Review describes every process step in the value chain from protein waste to chemicals. The first part deals with the physicochemical extraction of proteins from biomass, hydrolytic degradation to peptides and amino acids, and separation of amino acid mixtures. The second part provides an overview of physical and (bio)chemical technologies for the production of polymers, commodity chemicals, pharmaceuticals, and other fine chemicals. This can be achieved by incorporation of oligopeptides into polymers, or by modification and defunctionalization of amino acids, for example, their reduction to amino alcohols, decarboxylation to amines, (cyclic) amides and nitriles, deamination to (di)carboxylic acids, and synthesis of fine chemicals and ionic liquids. Bio- and chemocatalytic approaches are compared in terms of scope, efficiency, and sustainability.

Inorganic/Organic Double-Network Ion Gels with Partially Developed Silica-Particle Network

Tough inorganic/organic composite network gels consisting of a partially developed silica-particle network and a large amount of an ionic liquid, named micro-double-network (μ-DN) ion gel, are fabricated via two methods. One is a one-pot/one-step process conducted using a simultaneous network formation via sol-gel reaction of tetraethyl orthosilicate and free radical polymerization of N, N-dimethylacrylamide in an ionic liquid. When the network formation rates of the inorganic and organic networks are almost the same, the μ-DN structure is formed. The second method is simpler and involved the use of silica nanoparticles as the starting material. By controlling the dispersion state of the silica nanoparticles in an ionic liquid, the μ-DN structure is formed. In both μ-DN ion gels, silica nanoparticles partially aggregate and form network-like clusters. When a large deformation is induced in the μ-DN ion gels, the silica-particle clusters rupture and dissipate the loaded energy. The fracture stress and Young's modulus of the μ-DN ion gel increase as the size of the silica nanoparticles decreases. The increment in the mechanical strength would have been caused by the increase in the total van der Waals attraction forces and the total number of hydrogen bonding in the silica-particle networks.

Functionalized ionic liquid membranes for CO2 separation

It is imperative to develop efficient, reversible and economic technologies for separating CO₂ which mainly comes from flue gas, natural gas and syngas.