Development of Hollow Fiber Membranes Functionalized with Ionic Liquids for Enhanced CO2 Separation

The combination of CO2-selective ionic liquids (ILs) with block copolymers, such as Pebax 1657, has demonstrated an enhancement of the gas separation capabilities of polymeric membranes. In the current work, the development of composite membranes by applying a thin, concentrated selective layer made of Pebax/imidazolium-based ionic liquids (ILs) is presented. The objective of the experiments was to determine the optimized IL loading and investigate how the alteration of the anion impacts the properties of the membranes. Two membrane configurations have been studied: coated flat sheet membranes, supported on a porous poly(ether sulfone) (PES) layer, as well as composite hollow fiber membranes, supported on commercial polypropylene (PP) hollow fibers. Coated hollow fiber composites were fabricated using a continuous coating method, offering a straightforward scalability in the manufacturing process. The determined mechanical pressure stability of hollow fiber composites reached up to 5 bar, indicating their potential for various industrial gas separation applications. It was found that the Pebax 1657-based coating containing 40 wt % [C6mim][NTf2] yielded membranes with the best gas separation properties, for both the coated flat sheet and the hollow fiber configurations. The CO2 permeance of hollow fibers reached 23.29 GPU, whereas the CO2/N2 ideal selectivity stood at 8.7, suggesting the necessity of the further enhancement of the coating technique, which can be achieved, for example, through application of multiple coatings. Nonetheless, the superior ideal selectivity of the CO2/CO separation, reaching 12.44, gave a promising outlook for further novel membrane applications, which involve the separation of the aforementioned gases.

Temperature Responsive Copolymers Films of Polyether and Bio-Based Polyamide Loaded with Imidazolium Ionic Liquids for Smart Packaging Applications

Temperature-responsive materials are highly interesting for temperature-triggered applications such as drug delivery and smart packaging. Imidazolium Ionic Liquids (ILs), with a long side chain on the cation and a melting temperature of around 50 °C, were synthetized and loaded at moderate amounts (up to 20 wt%) within copolymers of polyether and a bio-based polyamide via solution casting. The resulting films were analyzed to assess their structural and thermal properties, and the gas permeation changes due to their temperature-responsive behavior. The splitting of FT-IR signals is evident, and, in the thermal analysis, a shift in the glass transition temperature (Tg) for the soft block in the host matrix towards higher values upon the addition of both ILs is also observed. The composite films show a temperature-dependent permeation with a step change corresponding to the solid-liquid phase change in the ILs. Thus, the prepared polymer gel/ILs composite membranes provide the possibility of modulating the transport properties of the polymer matrix simply by playing with temperature. The permeation of all the investigated gases obeys an Arrhenius-type law. A specific permeation behavior, depending on the heating-cooling cycle sequence, can be observed for carbon dioxide. The obtained results indicate the potential interest of the developed nanocomposites as CO₂ valves for smart packaging applications.

Aminosilane-Functionalized Zeolite Y in Pebax Mixed Matrix Hollow Fiber Membranes for CO2/CH4 Separation

Due to their interfacial defects between inorganic fillers and polymer matrices, research into mixed matrix membranes (MMMs) is challenging. In the application of CO₂ separation, these defects can potentially jeopardize the performance of membranes. In this study, aminosilane functionalization is employed to improve the nano-sized zeolite Y (ZeY) particle dispersion and adhesion in polyether block amide (Pebax). The performance of CO₂/CH₄ separation of Pebax mixed matrix composite hollow fiber membranes, incorporated with ZeY and aminosilane-modified zeolite Y (Mo-ZeY), is investigated. The addition of the zeolite filler at a small loading at 5 wt.% has a positive impact on both gas permeability and separation factor. Due to the CO₂-facilitated transport effect, the performance of MMMs is further improved by the amino-functional groups modified on the ZeY. When 5 wt.% of Mo-ZeY is incorporated, the gas permeability and CO₂/CH₄ separation factor of the Pebax membrane are enhanced by over 100% and 35%, respectively.

Pebax® 2533/PVDF thin film mixed matrix membranes containing MIL-101 (Fe)/GO composite for CO2 capture

MIL-101 (Fe) and MIL-GO composites were successfully synthesized and used as fillers for the preparation of Pebax® 2533/PVDF thin film MMMs for CO2/N2 separation. The defect-free Pebax® 2533/PVDF thin film MMMs were fabricated by casting the Pebax solution containing fillers on the PVDF support. The presence of GO nanosheets in the reaction solution did not destroy the crystal structure of MIL-101 (Fe). However, the BET surface area and total pore volume of MIL-GO decreased dramatically, comparing with MIL-101 (Fe). The incorporation of MIL-GO-2 into Pebax matrix simultaneously increased the CO2 permeability and the CO2/N2 ideal selectivity of Pebax® 2533/PVDF thin film MMMs mainly owing to the porous structure of MIL-GO-2, and the tortuous diffusion pathways created by GO nanosheets. MMMs containing 9.1 wt% MIL-GO-2 exhibited the highest CO2 permeability equal to 303 barrer (1 barrer = 10-10 cm3 (STP) cm cm-2 s-1 cmHg-1) and the highest CO2/N2 ideal selectivity equal to 24. Pebax-based MMMs containing composite fillers showed higher gas separation performance than the Pebax-based MMMs containing single filler (GO or MOFs). Therefore, the synthesis and utilization of 3D@2D composite filler demonstrated great potential in the preparation of high-performance MMMs for gas separation processes.

Ionic Liquid-Based Polymer Nanocomposites for Sensors, Energy, Biomedicine, and Environmental Applications: Roadmap to the Future

Current interest toward ionic liquids (ILs) stems from some of their novel characteristics, like low vapor pressure, thermal stability, and nonflammability, integrated through high ionic conductivity and broad range of electrochemical strength. Nowadays, ionic liquids represent a new category of chemical-based compounds for developing superior and multifunctional substances with potential in several fields. ILs can be used in solvents such as salt electrolyte and additional materials. By adding functional physiochemical characteristics, a variety of IL-based electrolytes can also be used for energy storage purposes. It is hoped that the present review will supply guidance for future research focused on IL-based polymer nanocomposites electrolytes for sensors, high performance, biomedicine, and environmental applications. Additionally, a comprehensive overview about the polymer-based composites' ILs components, including a classification of the types of polymer matrix available is provided in this review. More focus is placed upon ILs-based polymeric nanocomposites used in multiple applications such as electrochemical biosensors, energy-related materials, biomedicine, actuators, environmental, and the aviation and aerospace industries. At last, existing challenges and prospects in this field are discussed and concluding remarks are provided.

Pebax-Based Composite Membranes with High Transport Properties Enhanced by ZIF-8 for CO2 Separation

A series of mixed matrix membranes containing poly (ether-block-amide) Pebax 1657 as matrix and polyethylene glycol (PEG) and Zeolitic Imidazolate Framework-8 (ZIF-8) as additives, were prepared and tested for CO₂ separation. The membranes were prepared by solvent evaporation method and were characterized by TGA, DSC, SEM, and gas permeation measurements. The effects of PEG and its molecular weight, and the percentage of ZIF-8 into Pebax matrix were investigated. The results showed that the addition of PEG to Pebax/ZIF-8 blends avoid the agglomeration of ZIF-8 particles. A synergic effect between PEG and ZIF was particularly observed for high ZIF-8 content, because the initial permeability of pristine Pebax was multiplied by three (from 54 to 161 Barrers) while keeping the CO₂ selectivity (α_CO2/N2 = 61, α_CO2/CH4 = 12 and α_CO2/O2 = 23). Finally, the mechanism of CO₂ transport is essentially governed by the solubility of CO₂ into the membranes. Therefore, this new Pebax/PEG/ZIF-8 system seems to be a promising approach to develop new selective membranes for CO₂ with high permeability.

Mixed-Matrix Membranes Based on Polyetherimide, Metal–Organic Framework and Ionic Liquid: Influence of the Composition and Morphology on Gas Transport Properties

In this work, membranes based on polyetherimide (PEI), a ZIF-8 metal–organic framework and 1-ethyl-methylimidazolium tetrafluoroborate ionic liquid (IL) were prepared. IL and ZIF-8 contents amounting to 7 wt% and 25 wt%, respectively, were investigated. CO₂, He and H₂ transport properties of PEI/IL/ZIF-8 membranes were compared to those obtained for the respective PEI/ZIF-8 and PEI/IL systems. Membranes’ gas permeability and selectivity are discussed as a function of the membrane composition and morphology, and they were assessed in relation to existing experimental and theoretical data from the literature. Promising gas transport properties were obtained using the appropriate combination of ZIF-8 and IL amounts in the PEI matrix. Indeed, an increase in the CO₂ permeability coefficient by a factor of around 7.5 and the He and H₂ permeability coefficients by a factor of around 4 was achieved by adding 7 wt% IL and 10 wt% ZIF-8 to the PEI matrix. Moreover, diffusion was evidenced as a governing factor in the studied membrane series.

The State-of-the-Art Functionalized Nanomaterials for Carbon Dioxide Separation Membrane

Nanocomposite membrane (NCM) is deemed as a practical and green separation solution which has found application in various fields, due to its potential to delivery excellent separation performance economically. NCM is enabled by nanofiller, which comes in a wide range of geometries and chemical features. Despite numerous advantages offered by nanofiller incorporation, fabrication of NCM often met processing issues arising from incompatibility between inorganic nanofiller and polymeric membrane. Contemporary, functionalization of nanofiller which modify the surface properties of inorganic material using chemical agents is a viable approach and vigorously pursued to refine NCM processing and improve the odds of obtaining a defect-free high-performance membrane. This review highlights the recent progress on nanofiller functionalization employed in the fabrication of gas-separative NCMs. Apart from the different approaches used to obtain functionalized nanofiller (FN) with good dispersion in solvent and polymer matrix, this review discusses the implication of functionalization in altering the structure and chemical properties of nanofiller which favor interaction with specific gas species. These changes eventually led to the enhancement in the gas separation efficiency of NCMs. The most frequently used chemical agents are identified for each type of gas. Finally, the future perspective of gas-separative NCMs are highlighted.

Poly(ethylene glycol) Diacrylate Iongel Membranes Reinforced with Nanoclays for CO2 Separation

Despite the fact that iongels are very attractive materials for gas separation membranes, they often show mechanical stability issues mainly due to the high ionic liquid (IL) content (≥60 wt%) needed to achieve high gas separation performances. This work investigates a strategy to improve the mechanical properties of iongel membranes, which consists in the incorporation of montmorillonite (MMT) nanoclay, from 0.2 to 7.5 wt%, into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) network containing 60 wt% of the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][TFSI]). The iongels were prepared by a simple one-pot method using ultraviolet (UV) initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) and characterized by several techniques to assess their physico-chemical properties. The thermal stability of the iongels was influenced by the addition of higher MMT contents (>5 wt%). It was possible to improve both puncture strength and elongation at break with MMT contents up to 1 wt%. Furthermore, the highest ideal gas selectivities were achieved for iongels containing 0.5 wt% MMT, while the highest CO2 permeability was observed at 7.5 wt% MMT content, due to an increase in diffusivity. Remarkably, this strategy allowed for the preparation and gas permeation of self-standing iongel containing 80 wt% IL, which had not been possible up until now.

Graphene oxide loaded fibrous matrixes of polyether block amide (PEBA) elastomer as an adsorbent for removal of cationic dye from wastewater

Novel highly porous nanoparticle materials are increasingly being applied in adsorption processes, but they need to be supported by robust matrixes to maintain their functionality. We present a study of hosting graphene oxide (GO) particles on polyether block amide (PEBA) melt electrospun fibers and applying such composite matrix to the adsorption of the cationic dye (crystal violet) from water. Various amounts of GO (from 0.5 to 2.0%) were mixed into pure PEBA and electrospun by melt electrospinning obtaining micro fibrous matrixes. These were characterized for morphology (SEM), chemical composition (FTIR), crystallinity (XRD), and wetting behavior (WCA). The increasing amount of GO adversely affected fiber diameter (reduced from 13.18 to 4.38 μm), while the hydrophilic properties (Water contact angle decrease from 109 to 76°) and overall dye adsorption was increased. Efficient adsorption has been demonstrated, reaching approximately 100 % removal efficiency using a 2% GO composite matrix at a dose of 40 mg/l and pH of 10. Further increase of GO concentration in polymer is not feasible due to instability in the electrospinning process.

Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part I: Membrane Synthesis and Characterization

In this work, polymeric membranes functionalized with ionic liquids (ILs) and exfoliated graphene nanoplatelets (xGnP) were developed and characterized. These membranes based on graphene ionanofluids (IoNFs) are promising materials for gas separation. The stability of the selected IoNFs in the polymer membranes was determined by thermogravimetric analysis (TGA). The morphology of membranes was characterized using scanning electron microscope (SEM) and interferometric optical profilometry (WLOP). SEM results evidence that upon the small addition of xGnP into the IL-dominated environment, the interaction between IL and xGnP facilitates the migration of xGnP to the surface, while suppressing the interaction between IL and Pebax^®1657. Fourier transform infrared spectroscopy (FTIR) was also used to determine the polymer-IoNF interactions and the distribution of the IL in the polymer matrix. Finally, the thermodynamic properties and phase transitions (polymer-IoNF) of these functionalized membranes were studied using differential scanning calorimetry (DSC). This analysis showed a gradual decrease in the melting point of the polyamide (PA6) blocks with a decrease in the corresponding melting enthalpy and a complete disappearance of the crystallinity of the polyether (PEO) phase with increasing IL content. This evidences the high compatibility and good mixing of the polymer and the IoNF.

Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part II: Gas Separation Properties toward Fluorinated Greenhouse Gases

Membrane technology can play a very influential role in the separation of the constituents of HFC refrigerant gas mixtures, which usually exhibit azeotropic or near-azeotropic behavior, with the goal of promoting the reuse of value-added compounds in the manufacture of new low-global warming potential (GWP) refrigerant mixtures that abide by the current F-gases regulations. In this context, the selective recovery of difluorometane (R32, GWP = 677) from the commercial blend R410A (GWP = 1924), an equimass mixture of R32 and pentafluoroethane (R125, GWP = 3170), is sought. To that end, this work explores for the first time the separation performance of novel mixed-matrix membranes (MMMs) functionalized with ioNanofluids (IoNFs) consisting in a stable suspension of exfoliated graphene nanoplatelets (xGnP) into a fluorinated ionic liquid (FIL), 1-ethyl-3-methylpyridinium perfluorobutanesulfonate ([C2C1py][C4F9SO3]). The results show that the presence of IoNF in the MMMs significantly enhances gas permeation, yet at the expense of slightly decreasing the selectivity of the base polymer. The best results were obtained with the MMM containing 40 wt% IoNF, which led to an improved permeability of the gas of interest (PR32 = 496 barrer) with respect to that of the neat polymer (PR32= 279 barrer) with a mixed-gas separation factor of 3.0 at the highest feed R410A pressure tested. Overall, the newly fabricated IoNF-MMMs allowed the separation of the near-azeotropic R410A mixture to recover the low-GWP R32 gas, which is of great interest for the circular economy of the refrigeration sector.

Impacts of Multilayer Hybrid Coating on PSF Hollow Fiber Membrane for Enhanced Gas Separation

One of the most critical issues encountered by polymeric membranes for the gas separation process is the trade-off effect between gas permeability and selectivity. The aim of this work is to develop a simple yet effective coating technique to modify the surface properties of commonly used polysulfone (PSF) hollow fiber membranes to address the trade-off effect for CO₂/CH₄ and O₂/N₂ separation. In this study, multilayer coated PSF hollow fibers were fabricated by incorporating a graphene oxide (GO) nanosheet into the selective coating layer made of polyether block amide (Pebax). In order to prevent the penetration of Pebax coating solution into the membrane substrate, a gutter layer of polydimethylsiloxane (PDMS) was formed between the substrate and Pebax layer. The impacts of GO loadings (0.0–1.0 wt%) on the Pebax layer properties and the membrane performances were then investigated. XPS data clearly showed the existence of GO in the membrane selective layer, and the higher the amount of GO incorporated the greater the sp2 hybridization state of carbon detected. In terms of coating layer morphology, increasing the GO amount only affected the membrane surface roughness without altering the entire coating layer thickness. Our findings indicated that the addition of 0.8 wt% GO into the Pebax coating layer could produce the best performing multilayer coated membrane, showing 56.1% and 20.9% enhancements in the CO₂/CH₄ and O₂/N₂ gas pair selectivities, respectively, in comparison to the membrane without GO incorporation. The improvement is due to the increased tortuous path in the selective layer, which created a higher resistance to the larger gas molecules (CH₄ and N₂) compared to the smaller gas molecules (CO₂ and O₂). The best performing membrane also demonstrated a lower degree of plasticization and a very stable performance over the entire 50-h operation, recording CO₂/CH₄ and O₂/N₂ gas pair selectivities of 52.57 (CO₂ permeance: 28.08 GPU) and 8.05 (O₂ permeance: 5.32 GPU), respectively.

Poly[3-ethyl-1-vinyl-imidazolium] diethyl phosphate/Pebax® 1657 Composite Membranes and Their Gas Separation Performance

Poly(ionic liquid)s are an innovative class of materials with promising properties in gas separation processes that can be used to boost the neat polymer performances. Nevertheless, some of their properties such as stability and mechanical strength have to be improved to render them suitable as materials for industrial applications. This work explored, on the one hand, the possibility to improve gas transport and separation properties of the block copolymer Pebax® 1657 by blending it with poly[3-ethyl-1-vinyl-imidazolium] diethyl phosphate (PEVI-DEP). On the other hand, Pebax® 1657 served as a support for the PIL and provided mechanical resistance to the samples. Pebax® 1657/PEVI-DEP composite membranes containing 20, 40, and 60 wt.% of PEVI-DEP were cast from solutions of the right proportion of the two polymers in a water/ethanol mixture. The PEVI-DEP content affected both the morphology of the dense membranes and gas transport through the membranes. These changes were revealed by scanning electron microscopy (SEM), time-lag, and gravimetric sorption measurements. Pebax® 1657 and PEVI-DEP showed similar affinity towards CO2, and its uptake or solubility was not influenced by the amount of PIL in the membrane. Therefore, the addition of the PIL did not lead to improvements in the separation of CO2 from other gases. Importantly, PEVI-DEP (40 wt.%) incorporation affected and improved permeability and selectivity by more than 50% especially for the separation of light gases, e.g., H2/CH4 and H2/CO2, but higher PEVI-DEP concentrations lead to a decline in the transport properties.

A New Industrial Technology for Mass Production of Graphene/PEBA Membranes for CO2/CH4 Selectivity with High Dispersion, Thermal and Mechanical Performance

Polyether block amide (PEBA) nanocomposite membranes, including Graphene (GA)/PEBA membranes are considered to be a promising emerging technology for removing CO2 from natural gas and biogas. However, poor dispersion of GA in the produced membranes at industrial scale still forms the main barrier to commercialize. Within this frame, this research aims to develop a new industrial approach to produce GA/PEBA granules that could be used as a feedstock material for mass production of GA/PEBA membranes. The developed approach consists of three sequential phases. The first stage was concentrated on production of GA/PEBA granules using extrusion process (at 170-210 °C, depending on GA concentration) in the presence of Paraffin Liquid (PL) as an adhesive layer (between GA and PEBA) and assisted melting of PEBA. The second phase was devoted to production of GA/PEBA membranes using a solution casting method. The last phase was focused on evaluation of CO2/CH4 selectivity of the fabricated membranes at low and high temperatures (25 and 55 °C) at a constant feeding pressure (2 bar) using a test rig built especially for that purpose. The granules and membranes were prepared with different concentrations of GA in the range 0.05 to 0.5 wt.% and constant amount of PL (2 wt.%). Also, the morphology, physical, chemical, thermal, and mechanical behaviors of the synthesized membranes were analyzed with the help of SEM, TEM, XRD, FTIR, TGA-DTG, and universal testing machine. The results showed that incorporation of GA with PEBA using the developed approach resulted in significant improvements in dispersion, thermal, and mechanical properties (higher elasticity increased by ~10%). Also, ideal CO2/CH4 selectivity was improved by 29% at 25 °C and 32% at 55 °C.

Organic-inorganic hybrids for CO2 sensing, separation and conversion

Motivated by the air pollution that skyrocketed in numerous regions around the world, great effort was placed on discovering new classes of materials that separate, sense or convert CO₂ in order to minimise impact on human health. However, separation, sensing and conversion are not only closely intertwined due to the ultimate goal of improving human well-being, but also because of similarities in material prerequisites -e.g. affinity to CO₂. Partly inspired by the unrivalled performance of complex natural materials, manifold inorganic-organic hybrids were developed. One of the most important characteristics of hybrids is their design flexibility, which results from the combination of individual constituents with specific functionality. In this review, we discuss commonly used organic, inorganic, and inherently hybrid building blocks for applications in separation, sensing and catalytic conversion and highlight benefits like durability, activity, low-cost and large scale fabrication. Moreover, we address obstacles and potential future developments of hybrid materials. This review should inspire young researchers in chemistry, physics and engineering to identify and overcome interdisciplinary research challenges by performing academic research but also - based on the ever-stricter emission regulations like carbon taxes - through exchanges between industry and science.