Pristine Polymeric Membranes Research Articles

Advancements in Mixed-Matrix Membranes for Various Separation Applications: State of the Art and Future Prospects

Integrating nanomaterials into membranes has revolutionized selective transport processes, offering enhanced properties and functionalities. Mixed-matrix membranes (MMMs) are nanocomposite membranes (NCMs) that incorporate inorganic nanoparticles (NPs) into organic polymeric matrices, augmenting mechanical strength, thermal stability, separation performance, and antifouling characteristics. Various synthesis methods, like phase inversion, layer-by-layer assembly, electrospinning, and surface modification, enable the production of tailored MMMs. A trade-off exists between selectivity and flux in pristine polymer membranes or plain inorganic ceramic/zeolite membranes. In contrast, in MMMs, NPs exert a profound influence on membrane performance, enhancing both permeability and selectivity simultaneously, besides exhibiting profound antibacterial efficacy. Membranes reported in this work find application in diverse separation processes, notably in niche membrane-based applications, by addressing challenges such as membrane fouling and degradation, low flux, and selectivity, besides poor rejection properties. This review comprehensively surveys recent advances in nanoparticle-integrated polymeric membranes across various fields of water purification, heavy metal removal, dye degradation, gaseous separation, pervaporation (PV), fuel cells (FC), and desalination. Efforts have been made to underscore the role of nanomaterials in advancing environmental remediation efforts and addressing drinking water quality concerns through interesting case studies reported in the literature.

BiOCl-PVDF nanofibrous membrane for synergic oil-water separation and degradation of dye

Polymeric membranes have garnered remarkable attention, attributed to the significant breakthrough in the filtration of oily wastewater. However, the major setbacks of pristine polymeric membranes include susceptibility to fouling and chemical instability. Addressing such issues, this work focusses in the modification of polymer membranes using a metal oxyhalide, such as Bismuth oxychloride (BiOCl). This modification not only enhances water purification capabilities but also strengthens the membrane, protecting it from environmental deterioration and extending its lifespan. BiOCl was integrated into an electrospun pristine nanofibrous polymeric membrane using hydrothermal technique. The synthesized membrane matrix displayed superhydrophilicity and underwater superoleophobicity, effectively separating oil-in-water mixtures and emulsions. Moreover, BiOCl was effectively utilized to assess organic pollutant adsorption and degradation through photocatalysis. In addition, the membrane exhibited exceptional recyclability and withstood harsh conditions, contributing to its mechanical stability. The numerous advantages, enhance the effectiveness of BiOCl modified membrane in water pollution remediation.

Quantum dot- β-Cyclodextrin nanofiller decorated thin film nanocomposite membrane for removal of cationic and anionic dyes from aqueous solution

Graphene oxide quantum dots (GOQDs) are finding tremendous attention as nanofillers in separation processes owing to their excellent chemical and mechanical robustness. GOQDs-functionalized thin film nanocomposite (TFN) membranes were fabricated via low pressure mediated interfacial polymerization (IP) over a polysulfone support, where β-Cyclodextrin (β-CD) was taken as an aqueous monomer with a fractional amount of GOQDs and tetraethylenepentamine (TEPA) as the organic monomer. The resultant TFN membranes showed improved hydrophilicity over its pristine polymeric analogue. The best performing membrane was obtained for MPG2, which had a mass loading of 3 % of β-CD, 0.3 % of TEPA and 0.4 % of GOQD during the interfacial polymerization. The membrane showed pure water flux that was two fold higher than that of the pristine polymeric membrane, with a dye rejection of 99.6 % for congo red and 96 % for methyl blue. This excellent rejection for the anionic dye can be attributed to the Donnan exclusion imparted by the negative charges on the membrane surface. The salt rejection properties of the membranes were also analyzed and the MPG2 membrane exhibited a high rejection rate of 96 % and 99.1 % for the salt containing Cl− and NO3− ions, respectively.

Dormancy and double-activation strategy for construction of high-performance mixed-matrix membranes.

Mixed-matrix membranes (MMMs) have the potential for energy-efficient gas separation by matching the superior mass transfer and anti-plasticization properties of the fillers with processability and scaling up features of the polymers. However, construction of high-performance MMMs has been prohibited due to low filler-loading and the existence of interfacial defects. Here, high MOF-loaded, i.e., 55 wt %, MMMs are developed by a 'dormancy and double-activation' (DDA) strategy. High MOF precursor concentration suppresses crystallization in the membrane casting solution, realizing molecular level mixing of all components. Then, the polymeric matrix was formed with uniform encapsulation of MOF nutrients. Subsequently, double-activation was employed to induce MOF crystallization: the alkali promotes MOFs nucleation to harvest small porous nanocrystals while excessive ligands activate the metal ions to enhance the MOFs conversion. As such, quasi-semi-continuous mass transfer channels can be formed in the MMMs by the connected MOFs nanocrystals to boost the gas permeability. The optimized MMM shows significantly ameliorated CO2 permeability, i.e., 2841 Barrer, five-fold enhancement compared with pristine polymer membrane, with a good CO2 /N2 selectivity of 36. Besides, the nanosized MOFs intensify their interaction with polymer chains, endowing the MMMs with good anti-plasticization behaviour and stability, which advances practical application of MMMs in carbon capture.

Dormancy and double‐activation strategy for construction of high‐performance mixed‐matrix membranes

AbstractMixed‐matrix membranes (MMMs) have the potential for energy‐efficient gas separation by matching the superior mass transfer and anti‐plasticization properties of the fillers with processability and scaling up features of the polymers. However, construction of high‐performance MMMs has been prohibited due to low filler‐loading and the existence of interfacial defects. Here, high MOF‐loaded, i.e., 55 wt %, MMMs are developed by a ‘dormancy and double‐activation’ (DDA) strategy. High MOF precursor concentration suppresses crystallization in the membrane casting solution, realizing molecular level mixing of all components. Then, the polymeric matrix was formed with uniform encapsulation of MOF nutrients. Subsequently, double‐activation was employed to induce MOF crystallization: the alkali promotes MOFs nucleation to harvest small porous nanocrystals while excessive ligands activate the metal ions to enhance the MOFs conversion. As such, quasi‐semi‐continuous mass transfer channels can be formed in the MMMs by the connected MOFs nanocrystals to boost the gas permeability. The optimized MMM shows significantly ameliorated CO2 permeability, i.e., 2841 Barrer, five‐fold enhancement compared with pristine polymer membrane, with a good CO2/N2 selectivity of 36. Besides, the nanosized MOFs intensify their interaction with polymer chains, endowing the MMMs with good anti‐plasticization behaviour and stability, which advances practical application of MMMs in carbon capture.

A novel ternary mixed‐matrix membrane comprising Pebax‐1657, [HMIM][NTf2] IL, and Al2O3 nanoparticles for efficient CO2 separation

AbstractAn innovative technique to efficiently remove CO2 involves introducing a third component with a positive affinity with CO2 into a binary mixed‐matrix membrane (MMM) and eliminating interfacial defects in its structure. In this research, novel ternary MMMs (TMMMs) were synthesized by embedding 1–Hexyl–3–methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf2]) ionic liquid (IL) and aluminum oxide (γ–Al2O3) nanoparticles into poly (ether‐block‐amide) (Pebax‐1657) matrix for enhancing CO2 removal from light gases. FESEM, DSC, ATR‐FTIR, and XRD analyses were used to evaluate the fabricated MMMs structurally. The permeation tests of gases (CH4, N2, and CO2) through prepared membranes were conducted at 25°C and 4, 6, 8, and 10 bar pressures. In accordance with the permeation outcomes, the ternary MMMs exhibited enhanced CO2 separation performances compared to the unloaded polymeric membrane. Also, the optimized MMM comprising 10 wt.% of the IL and 6 wt.% of the nanoparticles obtained a CO2 permeability of 173.90 Barrer, as well as CO2/N2 and CO2/CH4 selectivities of 77.98 and 24.29 at 10 bar and 25°C, which are higher by about 51%, 23%, and 22%, respectively than those of the pristine polymeric membrane. Based on these results, the prepared membrane appears to be a promising choice for separating CO2 from light gases.

Hydrogen recovery from industrial waste streams using Matrimid®/ZIF mixed matrix membranes

This work reports the performance of Mixed Matrix Membranes (MMMs) for hydrogen purification. ZIF-8 and ZIF-90 Zeolitic Imidazole Frameworks (ZIFs) have been used as additives to improve the separation performance of the pristine Matrimid® polymeric membrane. The good interfacial contact and distribution of the filler along the membrane have been determined by electronic microscopy and the comparison of the membrane's performance is done in terms of hydrogen permeability and selectivity from industrial waste streams. The results showed that MMMs almost double H2 permeability (50 Barrer) and increase H2 selectivity (H2/CO2: ≈4.3, H2/N2: ≈35, H2/CO: ≈41, H2/CH4: ≈36) compared to the pristine polymeric membrane. Finally, the influence of the feed composition (by means of binary and multicomponent mixtures) and temperature (30, 50 and 80 °C) as operating variables has been analysed. The permeability was stable in the wide range of feed compositions while the increase in temperature resulted in lower selectivity and higher permeability.

Preparation and Characterization of PVDF-TiO2 Mixed-Matrix Membrane with PVP and PEG as Pore-Forming Agents for BSA Rejection.

Polymeric membranes offer straightforward modification methods that make industry scaling affordable and easy; however, these materials are hydrophobic, prone to fouling, and vulnerable to extreme operating conditions. Various attempts were made in this study to fix the challenges in using polymeric membranes and create mixed-matrix membrane (MMMs) with improved properties and hydrophilicity by adding titanium dioxide (TiO2) and pore-forming agents to hydrophobic polyvinylidene fluoride (PVDF). The PVDF mixed-matrix ultrafiltration membranes in this study were made using the non-solvent phase inversion approach which is a simple and effective method for increasing the hydrophilic nature of membranes. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) as pore-forming chemicals were created. Pure water flux, BSA flux, and BSA rejection were calculated to evaluate the mixed-matrix membrane's efficiency. Bovine serum albumin (BSA) solution was employed in this study to examine the protein rejection ability. Increases in hydrophilicity, viscosity, and flux in pure water and BSA solution were achieved using PVP and PEG additives. The PVDF membrane's hydrophilicity was raised with the addition of TiO2, showing an increased contact angle to 71°. The results show that the PVDF-PVP-TiO2 membrane achieved its optimum water flux of 97 L/(m2h) while the PVDF-PEG-TiO2 membrane rejected BSA at a rate greater than 97%. The findings demonstrate that use of a support or additive improved filtration performance compared to a pristine polymeric membrane by increasing its hydrophilicity.

Polymeric membranes functionalized with nanomaterials (MP@NMs): A review of advances in pesticide removal

The excessive contamination of drinking water sources by pesticides has a pernicious impact on human health and the environment since only 0.1% of pesticides is utilized effectively to control the and the rest is deposited in the environment. Filtration by polymeric membranes has become a promising technique to deal with this problem; however, the scientific community, in the need to find better pesticide retention results, has begun to meddle in the functionalization of polymeric membranes. Given the great variety of membrane, polymer, and nanomaterial synthesis methods present in the market, the possibilities of obtaining membranes that adjust to different variables and characteristics related to a certain pesticide are relatively extensive, so it is expected that this technology will represent one of the main pesticide removal strategies in the future. In this direction, this review focused on, - the main characteristics of the nanomaterials and their impact on pristine polymeric membranes; - the removal performance of functionalized membranes; and - the main mechanisms by which membranes can retain pesticides. Based on these insights, the functionalized polymeric membranes can be considered as a promising technology in the removal of pesticides since the removal performance of this technology against pesticide showed a significant increase. Obtaining membranes that adjust to different variables and characteristics related to a certain pesticide are relatively extensive, so it is expected that functionalized membrane technology will represent one of the main pesticide removal strategies in the future.

Ultra-permeable intercalated metal-induced microporous polymer nano-dots rooted smart membrane for environmental remediation

Energy efficient CO2 separation using ultrathin smart membranes must possess efficient permeation performance, higher surface area and hydrostatic stability at industrially relevant high pressures. However, ultrathin membranes are susceptible to lower surface area, plasticization and swelling which reduces the performance at higher pressure under humidified conditions. This paper evaluates the routes for the potential intercalated effect of metal-induced microporous polymers (MMPs) dots into a cellulose-based polymer matrix to enhance promising properties, including the surface area, CO2 permeation performance, plasticization resistance and hydrostatic stability of ultrathin smart membranes at high pressure. The MMP dots-rooted smart membrane demonstrated 55 nm thickness of ultrathin selective layer with a higher surface of 220 cm2. The enhancement of CO2 permeability from 14.1 to 108.9 Barrer and CO2/CH4 ideal selectivity from 11.8 to 31.1 was observed due to the integration of MMP dots into the cellulose polymer. This result could be due to enhancement of nitrogen lone pair electron interactions with CO2 followed by amines group which improved the CO2 adsorption on the membrane surface. The MMP dots-rooted membrane demonstrated plasticization resistance up to 26 bar pressure, as compared to a pristine polymer membrane which is a percentage increase of 160% under humidified conditions. The resulting ultrathin smart membrane exhibited stable performance for a duration of 200 h under humidified conditions which confirmed the higher hydrostatic stability of the membrane. These findings confirmed the potential of MMP dots materials for the development of an industrial scale CO2 separation process using intercalated membranes.

Facile manufacture of COF-based mixed matrix membranes for efficient CO2 separation

• In situ bottom-up growth strategy is proposed to manufacture 2D-COF-based MMMs. • The new method allows the favorable reduction of COF pore sizes. • MMMs contain uniformly distributed COFs and feature good interfacial compatibility. • MMM shows a 185.9% increase in permeability and a 32–77% enhancement in selectivity compared with pristine polymer membranes. Mixed-matrix membranes containing covalent-organic frameworks (COFs) and polymer phase hold great promise for effective and economical CO 2 separation due to the robust and tunable porous framework structures of COFs. However, the pore sizes of most reported COFs are larger than gas molecules. Meanwhile, the undesired COF aggregation impedes the preparation of continuous and defect-free membranes. Herein, we describe a new strategy for the facile manufacture of 2D-COF based mixed-matrix membranes via in situ “bottom-up” growth approach which involved the admixing of COF precursors with PEO monomers at the molecular level in a solvent-free system. Free radical polymerization allowed the formation of polymer membranes containing well-dispersed COF precursors. The 2D-COFs with uniform distributions were further generated via the covalent linkages of precursors within the cross-linked polymer network under microwave assisted Zincke reaction. The resulting mixed-matrix membrane exhibited a remarkable permeability of 803.9 barrer for CO 2 and selectivities of 61.4, 19.8, 15.0 for CO 2 /N 2 , CO 2 /CH 4 , CO 2 /H 2 , respectively, exceeding the known upper-bound limits reported for polymer membranes. Meanwhile, the membranes displayed a one-month stability confirming its exceptional long-term operational stability and great potential for industrial gas separations.

Homoporous hybrid membranes containing metal-organic cages for gas separation

Hybridization of porous fillers and polymers is an effective strategy for fabricating composite membranes, affording synergic properties contributed by every single component. However, it has high requirements on the dispersivity of porous fillers and compatibility between porous fillers and the polymeric matrix. Herein, we report the fabrication of homoporous hybrid membranes (HHMs) by chemically cross-linking polymerizable metal-organic cages (MOCs) with polymeric precursors via UV-induced polymerization. The polymerizable MOC molecules, synthesized by heterogeneous postassembly modification, are soluble in polymeric precursors and can be cross-linked with in-situ formed polymeric matrix at a molecular-level dispersivity. The cross-linking between MOCs and polymeric matrix can improve the interfacial compatibility and enhance the thermal stability of the membranes. Compared with the pristine polymeric membrane, the HHM with 1 wt% of MOC loading shows an enhanced CO2 permeability (338 Barrer) and a comparable CO2/CH4 selectivity (16.7) due to the increased CO2 solubility and diffusivity with the addition of MOCs. This strategy inspires the design of hybrid membranes with uniform yet tunable pore sizes for efficient molecular separations.

Mitigating the Agglomeration of Nanofiller in a Mixed Matrix Membrane by Incorporating an Interface Agent.

Nanodiamonds (ND) have recently emerged as excellent candidates for various applications including membrane technology due to their nanoscale size, non-toxic nature, excellent mechanical and thermal properties, high surface areas and tuneable surface structures with functional groups. However, their non-porous structure and strong tendency to aggregate are hindering their potential in gas separation membrane applications. To overcome those issues, this study proposes an efficient approach by decorating the ND surface with polyethyleneimine (PEI) before embedding it into the polymer matrix to fabricate MMMs for CO2/N2 separation. Acting as both interfacial binder and gas carrier agent, the PEI layer enhances the polymer/filler interfacial interaction, minimising the agglomeration of ND in the polymer matrix, which is evidenced by the focus ion beam scanning electron microscopy (FIB-SEM). The incorporation of PEI into the membrane matrix effectively improves the CO2/N2 selectivity compared to the pristine polymer membranes. The improvement in CO2/N2 selectivity is also modelled by calculating the interfacial permeabilities with the Felske model using the gas permeabilities in the MMM. This study proposes a simple and effective modification method to address both the interface and gas selectivity in the application of nanoscale and non-porous fillers in gas separation membranes.

Mixed Matrix Membranes Based on Fluoropolymers with m- and p-Terphenyl Fragments for Gas Separation Applications.

Novel mixed matrix membranes (MMMs) based on fluoropolymers with m- and p-terphenyl fragments and NaX zeolites were prepared. The fluoropolymers were synthesized by a one-pot, room-temperature, metal-free superacid-catalyzed stoichiometric and nonstoichiometric step polymerization of 2,2,2-trifluoroacetophenone with two multiring aromatic nonactivated hydrocarbons (p-terphenyl and m-terphenyl). MMMs were characterized by scanning electron microscopy (SEM) and infrared (Fourier transform infrared (FTIR)) spectroscopy and used in gas permeability tests. SEM analysis showed interfacial voids in MMMs prepared in N-methyl-2-pyrrolidone (NMP), The interfacial adhesion in the polymer–zeolite system was considerably improved when chloroform was used as a solvent. Permeability coefficients for pristine polymer membranes were 1.3-fold higher in CHCl3 than in NMP for p-terphenyl fragment and 2.0 times higher in NMP than in CHCl3 for the polymer with m-terphenyl fragment. The incorporation of NaX zeolites in the polymeric matrices improved the gas permeability coefficients compared to the pristine membranes. The effects of polymer architecture, casting solvent, and interaction between the organic matrix and the inorganic particles on the gas separation performance of the developed MMMs were investigated.

Constructing Strong Interfacial Interactions under Mild Conditions in MOF-Incorporated Mixed Matrix Membranes for Gas Separation.

Although mixed matrix membranes (MMM) possess remarkably improved gas separation performance compared to traditional polymeric membranes, membrane stability including CO2 plasticization and aging is still a serious issue due to the existence of interfacial defects. In this work, we report an efficient and less destructive route to cross-link the MOFs/polyimide (PI) MMM, where amine group-functionalized MOF (NH2-UiO-66) nanoparticles are thermally cross-linked with a carboxylic acid-functionalized PI (COOH-PI) matrix to form an amide bond at the interface at 150 °C under vacuum condition. Such a chemical cross-linking strategy conducted at a relatively mild condition improves membrane stability greatly while ensuring that the membrane structure is not destroyed. The resulting cross-linked MMM achieves enhanced mechanical strength with higher Young's modulus than a pristine polymer membrane. The CO2 antiplasticization pressure of the MMM after cross-linking is enhanced by 200% from ∼10 to >30 bar and the CO2 permeability of MMM only drops slightly from 995 to 735 Barrer after 450 days. At the same time, the separation performance of H2/CH4 gas pair surpasses the 2008 upper bound and that of CO2/CH4 gas pair nearly approaches the 2008 upper bound. The cross-linking strategy used herein provides a feasible and effective route for improving membrane stability and membrane performance in the MMM system for gas separation.

Cross-Linked Mixed-Matrix Membranes Using Functionalized UiO-66-NH2 into PEG/PPG-PDMS-Based Rubbery Polymer for Efficient CO2 Separation.

Mixed-matrix membranes (MMMs) with an ideal polymer-filler interface and high gas separation performance are very challenging to fabricate because of incompatibility between the fillers and the polymer matrix. This work provides a simple technique to prepare a series of cross-linked MMMs (xMMM@n) by covalently attaching UiO-66-NB metal-organic frameworks (MOFs) within the PEG/PPG-PDMS copolymer matrix via ring-opening metathesis polymerization and in situ membrane casting. The norbornene-modified MOF (UiO-66-NB) is successfully copolymerized and dispersed homogeneously into a PEG/PPG-PDMS matrix because of very fast polymer formation and strong covalent interaction between MOFs and the rubbery polymer. A significant improvement in gas permeability is achieved in membranes up to a 5 wt % MOF loading compared to the pristine polymer membrane without affecting selectivity. The CO2/N2 separation performance of xMMM@1, xMMM@3, and xMMM@5 with 1, 3, and 5 wt % MOF loading, respectively, surpassed Robeson's 2008 upper bound. In addition, the best performing membrane, xMMM@3 (PCO2 = 585 Barrer and CO2/N2 ∼53), approaches the 2019 upper bound, indicating that the cross-linked MMMs (xMMM@n) are very promising for CO2 separation from flue gas. The experimental results of our study were evaluated and are supported by theoretical data obtained using the Maxwell model for MMMs. Moreover, the developed MMMs, xMMM@ns, displayed outstanding antiplasticization performance at pressures of up to 25 atm and very stable antiaging performance for up to 11 months with good temperature switching behaviors.

Roll-to-roll atomic layer deposition of titania coating on polymeric separators for lithium ion batteries

Atomic layer deposition (ALD) on flexible substrates has rarely been demonstrated using roll-to-roll (R2R) coating configuration. We develop R2R ALD technique to uniformly coat TiO2 layer on the porous polyethylene (PE) separators for Li-ion batteries (LIBs). The R2R ALD method using titanium isopropoxide and water as the precursors enables a precise control over the growth of TiO2 nanolayer on PE separators. The TiO2-coated separators remarkably improve the LIB performance, as compared to the LIBs utilizing pristine polymeric membranes. The TiO2 deposition also enhances the thermal and dimensional stability, through forming a stabilizing and robust skeleton within the polymeric matrix. Accordingly, the TiO2 layers play a critical role in boosting the LIB performance, via increasing the ionic conductivity, decreasing high-frequency impedance, and enhancing the electrolyte wettability. Ultimately, the application of ceramic nanocoating on the PE-based porous separators results in improved safety, higher energy density, and excellent cycleability during high-temperature and long-duration cycling of LIBs. Thus, the TiO2-coated separators can be easily adopted to replace the commercially available separators due to excellent performance and reduced cost of manufacturing. The production rate of the ceramic separators can reach as high as 2.4 m min−1 fulfilling the requirements of the industrial and large-scale production.

Can flexible framework fillers keep breathing in mixed matrix membranes to enhance separation performance?

With porous materials acting as fillers, mixed matrix membranes (MMMs) can significantly enhance the separation performance of corresponding pristine polymeric membranes. This improvement mainly ascribes to the high selectivity of porous fillers. However, it is unclear whether those porous fillers, especially flexible metal organic framework (fMOF) fillers, can keep their extraordinary target-responded selectivity in confined space of membranes. To illustrate, a full-atomic-molecular dynamic simulation was carried out to explore the flexibility of the ZIF-7-NH2 fMOF in the confined pores produced by the random distribution of Pebax chains. Significantly, not only the “Induced-Fit Suction” deformation of ZIF-7-NH2 by the n-butanol molecule still kept unchanged, but also the Pebax chains could induce benzene rings of ZIF-7-NH2 to flip over, facilitating the “gate-opening” effect. Inevitably, the experimentally produced ZIF-7-NH2/Pebax MMMs exhibited excellent butanol/water separation performance through the pervaporation, that the n-butanol permeability and the separation factor were as high as 3.59 × 10−6 g−1m−1h−1Pa−1 and 18.8 for a 5 wt% n-butanol feed solution at 40 °C, which was 150% and 160% higher than the pristine Pebax membrane, respectively. To the best of our knowledge, it was the highest separation permeability among all the reported Pebax-based membranes. This work provided a clear evidence why and how fMOFs exhibit the deformation in MMMs for the first time, which helps to design task-specific MMMs by incorporating highly selective fMOFs.

Metal Organic Framework - Based Mixed Matrix Membranes for Carbon Dioxide Separation: Recent Advances and Future Directions.

Gas separation and purification using polymeric membranes is a promising technology that constitutes an energy-efficient and eco-friendly process for large scale integration. However, pristine polymeric membranes typically suffer from the trade-off between permeability and selectivity represented by the Robeson's upper bound. Mixed matrix membranes (MMMs) synthesized by the addition of porous nano-fillers into polymer matrices, can enable a simultaneous increase in selectivity and permeability. Among the various porous fillers, metal-organic frameworks (MOFs) are recognized in recent days as a promising filler material for the fabrication of MMMs. In this article, we review representative examples of MMMs prepared by dispersion of MOFs into polymer matrices or by deposition on the surface of polymeric membranes. Addition of MOFs into other continuous phases, such as ionic liquids, are also included. CO2 separation from hydrocarbons, H2, N2, and the like is emphasized. Hybrid fillers based on composites of MOFs with other nanomaterials, e.g., of MOF/GO, MOF/CNTs, and functionalized MOFs, are also presented and discussed. Synergetic effects and the result of interactions between filler/matrix and filler/filler are reviewed, and the impact of filler and matrix types and compositions, filler loading, surface area, porosity, pore sizes, and surface functionalities on tuning permeability are discoursed. Finally, selectivity, thermal, chemical, and mechanical stability of the resulting MMMs are analyzed. The review concludes with a perspective of up-scaling of such systems for CO2 separation, including an overview of the most promising MMM systems.

Development of high performance amine functionalized zeolitic imidazolate framework ( ZIF ‐8)/cellulose triacetate mixed matrix membranes for CO 2 / CH 4 separation

High cost and complex fabrication process of inorganic membranes and lower position of pristine polymeric membranes in the Robeson upper bound curve urged the researchers to develop mixed matrix membranes (MMMs). Cellulose acetate being most commercially used polymer, dominates the market of CO2 separation mainly because of low cost and environmental friendly resource. In the present study, MMMs consists of amine functionalized zeolitic imidazolate framework (NH2-ZIF-8) and cellulose triacetate were fabricated for the first time. NH2-ZIF-8 was used as a filler because the pore size of ZIF-8 is between the kinetic diameter of separating gases (CO2 and CH4). Moreover, NH2 group attached on the surface of ZIF-8 has affinity with condensable gases like CO2. Morphology, crystallinity, tensile strength and functional groups of fabricated membranes were investigated using different analytical techniques. Results revealed that the increase of feed pressure has increased CO2 permeability and decreased permselectivity. However, improvements in gas separation performance were observed with the addition of nanofiller. Best position in Robeson's upper bound curve at 4 bar was obtained with 10 wt% loading with CO2 permeability and CO2/CH4 permselectivity of 218 barrer and 13.84, respectively. The improvement in the gas separation performance with loading is attributed to the increased diffusion coefficients as well as solubility coefficients, which was increased to 33% and 3.8%, respectively.