Gas Separation Performance Of Mixed Matrix Membranes Research Articles

Synergistic improvement in gas separation performance of MMMs by porogenic action and strong molecular forces of ZIF-93

In the present study, ZIF-93 metal–organic frameworks were prepared. N2 adsorption tests revealed that the particle size, specific surface area, and pore size of ZIF-93 were 30 nm–45 nm, 869.40 m2/g, and 0.36 nm, respectively. Pebax-based mixed matrix membranes (MMMs) were prepared using ZIF-93 as the filler. The pore diameters of ZIF-93 lied between the kinetic diameters of CO2 and N2; thus, its pore structure provided a fast transfer channel for CO2 and increased the permeability of the membrane. Further, X-ray diffraction showed that the membrane became denser upon introducing ZIF-93 because of the formation of a bridging structure between the Pebax molecular chains and ZIF-93. A denser stacking by moving the Pebax molecular chains closer to each other effectively bettered the CO2 selectivity of the mixed matrix membrane. The test results showed that when the ZIF-93 loading was 10 wt%, the CO2 permeability was 84.85 barrer and the CO2/N2 selectivity was 65.76 at 0.4 MPa, which are 51.57 % and 65.50 % higher than those of the pure Pebax membrane, respectively. When the feed pressure was increased to 0.8 MPa, the CO2 permeability was 94.5 barrer and the CO2/N2 selectivity is 87.5, which are 51.57 % and 65.50 % higher compared with those of the pure Pebax membrane, in order. The membrane performance significantly exceeded that of the 2008 Robeson curve.

Nanocomposite membranes comprising covalent organic framework and polymer of intrinsic microporosity for efficient CO2 separation

The fabrication of new mixed-matrix membranes (MMMs) with superior gas permeability and selectivity are highly sought for industrial development of membrane separation technology for CO2 capture. This study reports improvement in CO2 permeability and selectivity by employing porous covalent organic framework (COF-TpPa-1). Herein, we report a novel PIM-1 doped with COF-TpPa-1 in various concentrations ranging from 0 to 10 wt% to prepare COF-TpPa-1/PIM-1 MMMs. Good compatibility between COF-TpPa-1 particles and PIM-1 matrix rendered an ideal interfacial morphology. The MMMs composed of 7 wt% COF-TpPa-1 exhibit a CO2 permeability of 6336 Barrer with an enhancement of 104 % compared to pristine sample and CO2/N2 ideal selectivity 20.1 among five tested compositions. The CO2 permeability of COF-TpPa-1 7 wt% doped membrane was 88 % more than pristine PIM-1 after 30 days aging, while CO2/N2 selectivity was well maintained, coupled with excellent anti-plasticization and mixed-gas separation properties. The overall gas separation performance of MMMs exceeds the Robeson Upper bound (2008) for CO2/N2 and O2/N2. The measured experimental permeability exhibited excellent agreement with the Singh thermal conductivity model at low loading (<5 wt%). This work provides a potential approach to fabricate PIM-1-based high performance MMMs with COF fillers for efficient CO2 separation.

Graphene-Oxide-Modified Metal-Organic Frameworks Embedded in Mixed-Matrix Membranes for Highly Efficient CO2/N2 Separation.

MOF-74 (metal-organic framework) is utilized as a filler in mixed-matrix membranes (MMMs) to improve gas selectivity due to its unique one-dimensional hexagonal channels and high-density open metal sites (OMSs), which exhibit a strong affinity for CO2 molecules. Reducing the agglomeration of nanoparticles and improving the compatibility with the matrix can effectively avoid the existence of non-selective voids to improve the gas separation efficiency. We propose a novel, layer-by-layer modification strategy for MOF-74 with graphene oxide. Two-dimensional graphene oxide nanosheets as a supporting skeleton creatively improve the dispersion uniformity of MOFs in MMMs, enhance their interfacial compatibility, and thus optimize the selective gas permeability. Additionally, they extended the gas diffusion paths, thereby augmenting the dissolution selectivity. Compared with doping with a single component, the use of a GO skeleton to disperse MOF-74 into Pebax®1657 (Polyether Block Amide) achieved a significant improvement in terms of the gas separation effect. The CO2/N2 selectivity of Pebax®1657-MOF-74 (Ni)@GO membrane with a filler concentration of 10 wt% was 76.96, 197.2% higher than the pristine commercial membrane Pebax®1657. Our results highlight an effective way to improve the selective gas separation performance of MMMs by functionalizing the MOF supported by layered GO. As an efficient strategy for developing porous MOF-based gas separation membranes, this method holds particular promise for manufacturing advanced carbon dioxide separation membranes and also concentrates on improving CO2 capture with new membrane technologies, a key step in reducing greenhouse gas emissions through carbon capture and storage.

PEO-based mixed matrix membranes containing N-doped microporous carbon microparticles for enhanced CO2/N2 separation

As a promising strategy to reduce greenhouse gas emissions, carbon dioxide capture from industrial and power plants has been proposed. Due to its advantages of low consumption and a modest environmental impact, membrane technology has been widely used in the gas separation process. Advanced porous fillers can be successfully added into the polymer matrix to create mixed matrix membranes (MMMs) with simple processing and applicable gas separation performance. The high porosity and stability of microporous carbon materials make them desirable for use in the gas separation process. Herein, N-doped microporous carbon microparticles (NMCP) were successfully synthesized and incorporated into UV crosslinked polyethylene oxide (XLPEO) matrix membranes. Fast CO2 transport channels are created in MMMs by rationally constructing NMCP fillers with ultra-micropores (∼0.53 nm), high-content heteroatoms (N, 13.94%), and two-dimensional morphology. The relationship between the structure of the NMCP samples and the gas separation performance of MMMs was discussed. Additionally, tests were conducted on the effects of NMCP loading, operating conditions, and long-term stability of NMCP/XLPEO membranes. NMCP/XLPEO membranes with a 2.5 wt% NMCP loading displayed a CO2 permeability of 606 Barrer and a CO2/N2 selectivity of 56.4, approaching the 2019 upper bound. This work offers a novel perspective to build fast gas transport channels in porous carbon-based MMMs for carbon capture.

Investigation of the effect of functionalized carbon nanotube and graphene oxide in guar gum‐based mixed matrix membrane for gas separation application

AbstractThe present study deals with preparing mixed matrix membranes (MMMs), a new polysaccharide‐based natural polymer used as a matrix with functionalized carbon nanotubes (FCNTs) and graphene oxide (GO) used as an inorganic filler. This work identified the effect of the inorganic fillers (FCNTs or GO) with naturally occurring polymer for gas separation. The incorporation of fillers improves the gas separation performance of MMMs. In GG/FCNTs MMMs, the selectivities of CO2/N2 and CO2/H2 were enhanced by 55.24% and 57.89%, respectively. Moreover, in GG/GO MMMs, the selectivities of CO2/N2 and CO2/H2 were improved by 99.50% and 50%, respectively. The membrane was characterized by scanning electron microscopy (SEM) and Fourier‐transform infrared spectroscopy (FTIR). The SEM analysis of GG/GO MMMs reveals layered structure, and GG/FCNTs MMMs create passages to transport gases. The Universal testing machine (UTM) is used to analyze the mechanical properties of pristine and modified membranes.

Introducing defect-engineering 2D layered MOF nanosheets into Pebax matrix for CO2/CH4 separation

The layered Ni-MOF nanosheets (Ni-NS) with defective structure were used as fillers to prepare mixed matrix membranes (MMMs) for CO2 separation. In this work, the defect structure of Ni-MOF nanosheets was manipulated by adjusting the molar ratio of metal source to organic linker (RM/L), and the influence of defects at the Ni-MOF nanocrystal on the gas separation performance of MMMs was investigated. The characterization of filler and membranes showed that Ni-MOF nanosheets with defective structure could improve the gas separation performance mainly through the enlarged pore size and the increased adsorption sites. Compared with the Ni-NS-2 with complete crystal structure, the Ni-NS-8 with defective structure showed better interfacial compatibility with poly(ether-block-amide) (Pebax® MH 1657) matrix. The Pebax/Ni-NS-8-6 MMM showed the best CO2/CH4 separation performance. The CO2 permeability and CO2/CH4 selectivity were 436.1 Barrer and 33.1, which were 115% and 18% higher than those of pure Pebax membrane, respectively. The results showed that defect-engineering in MOF nanocrystals was an important strategy to optimize the gas separation performance of 2D MOF-based MMMs.

Visualization of the gas permeation in core–shell MOF/Polyimide mixed matrix membranes and structural optimization based on finite element equivalent simulation

Core-shell MOFs recently have suggested the greater potential on gas separation of mixed matrix membranes (MMMs) than the single MOFs. In this work, two core–shell MOFs (ZIF-67@ZIF-8 (ZIF-67@8) and ZIF-8@ZIF-67 (ZIF-8@67)) with adverse structure were specially designed to explore what structure is more conducive to gas separation of MMMs. Moreover, a simplified equivalent simulation based on electrical conductivity of Maxwell model was adopted to predict the gas permeability and the internal gas permeation behavior for core–shell MOF based MMMs. The simulation exhibited the better predicted results than the Felske model and revealed the gas transport pathway. As a result, ZIF-67@8 based MMM with the shell-dependent transport and a thin interlayer had the highest H2 permeability of 224 Barrer and H2/CH4 separation factor of 76.7, which are 180% and 24% higher than neat PI, respectively. Finally, core–shell MOFs based MMMs also showed the lower temperature dependence of permeation for N2 and CH4 compared to pure PI. This work provides a unique method to investigate how core–shell structure affects the gas separation performance of MMMs, especially for equivalent simulation, which not only is proved to play as an efficient tool to predict the gas permeability, but also exhibits a great potential on investigation of gas transport pathway for the further structural optimization.

MOF/Polymer Mixed-Matrix Membranes Preparation: Effect of Main Synthesis Parameters on CO2/CH4 Separation Performance.

Design and preparation of mixed-matrix membranes (MMMs) with minimum defects and high performance for desired gas separations is still challenging as it depends on a variety of MMM synthesis parameters. In this study, 6FDA-DAM:DABA based MMMs using MOF-808 as filler were prepared to examine the impact of multiple variables on the preparation process of MMMs, including variation in polymer concentration, filler loading, volume of solution cast per membrane area, solvent type used and solvent evaporation rate, and to identify their impact on the CO2/CH4 separation performance of these membranes. Solvent evaporation rate proved to be the most critical synthesis parameter, directly influencing the performance and visual appearance of the membranes. Although less dominantly influencing the MMM performance, polymer concentration and solution volume also had an important role via control over the casting solution viscosity, particle agglomeration, and particle settling rate. Among all solvents studied, MMMs prepared with chloroform led to the best performance for this polymer-filler system. Chloroform-based MMMs containing 10 and 30 wt.% MOF-808 showed 73% and 62% increase in CO2 permeability, respectively, without a decrease in separation factor compared to unfilled membranes. The results indicate that enhanced gas separation performance of MMMs strongly depends on the cumulative effect of various synthesis parameters rather than individual impact, thus requiring a system-specific design and optimization.

Mixed Dimensional Nanostructure (UiO-66-Decorated MWCNT) as a Nanofiller in Mixed-Matrix Membranes for Enhanced CO2 /CH4 Separation.

Mixed-matrix membranes (MMMs) with combination of two distinct dimensional nanofillers (such as 1D-3D, 2D-3D, or 3D-3D, etc.) have drawn special attention for gas separation applications due to their concerted effects on gas permeation and mechanical properties. An amine-functionalized 1D multiwalled carbon nanotube (NH2 -MWCNT) with exceptional mechanical strength and rapid gas transport was crosslinked with an amine-functionalized 3D metal-organic framework (UiO-66-NH2 ) with high CO2 affinity in a Schiff base reaction. The resultant crosslinked mixed-dimensional nanostructure was used as a nanofiller in a polysulfone (PSf) polymer matrix to explore the underlying synergy between 1D and 3D nanostructures on the gas separation performance of MMMs. Cross-sectional scanning electron microscopy and mapping revealed the homogenous dispersion of UiO-66@MWCNT in the polymer matrix. The MMM containing 5.0 wt. % UiO-66@MWCNT demonstrated a superior permeability 8.3 Barrer as compared to the 4.2 Barrer of pure PSf membrane for CO2 . Moreover, the selectivity (CO2 /CH4 ) of this MMM was enhanced to 39.5 from the 28.0 observed for pure PSf under similar conditions of pressure and temperature.

Gas separation performance of MMMs containing (PIM-1)-functionalized GO derivatives

A strategy to reduce the physical aging in PIM-1 membranes by incorporating novel functionalized graphene oxide (GO) fillers is reported. PIM-1 was covalently attached both to as-synthesized GO and to GO reacted with (3-aminopropyl)triethoxysilane (APTS-GO), leading to homogeneous dispersion of the nanofillers in the mixed matrix membranes (MMMs). It was found that the aging rate decreases with increasing content of (PIM-1)-functionalized GO, as evidenced by the smaller decrease in gas permeability over time. The best performance was achieved by a membrane containing 10 wt% of (PIM-1)-functionalized APTS-GO. This membrane maintains 85% of the initial CO2 permeability after 150 days (drop of only 310 Barrer), which represents about nine-fold less CO2 permeability drop as compared to pure PIM-1.

Effect of Nafion and APTEOS functionalization on mixed gas separation of PEBA-FAU membranes: Experimental study and MD and GCMC simulations

Many of the mixed matrix membranes (MMMs) face the challenge of fillers agglomeration. In this paper, the gas separation performance of MMMs based on poly (ether-block-amide) (PEBA, 60 wt% PEO and 40 wt% PA6) filled with different functionalized zeolite faujasite (FAU, X-type) fillers was investigated. To improve the interfacial adherence of the fillers with PEBA chains, Nafion® and 3-aminopropyl triethoxysilane (APTEOS) were used as sulfonic acid and aminosilane functionalizing agents, respectively. Different physicochemical and morphological characterizations such as XRD, FTIR, SEM, AFM, thermal, and mechanical tests were used to characterize the prepared membranes. The prepared membranes were evaluated for single gas and mixed gas separation performances. The results showed that CO2 permeability reached to 110 and 122 Barrer for sulfonic acid- and amine-FAU (1 wt%) filled PEBA, respectively. In addition, amine-MMM (1 wt%) had better performance for CO2/N2 selectivity (117), while SO3-MMM (1 wt%) showed higher CO2/CH4 selectivity (31) due to their intrinsic properties. Molecular simulation was also carried out to study the structural and transport properties of the fabricated membranes. The solubility and diffusivity of CO2, CH4, and N2 gas molecules were studied by Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods, respectively. The acquired results revealed that experimental and simulation data were consistent in approach.

Intensification of O2/N2 separation by novel magnetically aligned carbonyl iron powders /polysulfone magnetic mixed matrix membranes

In this research, novel magnetic mixed matrix membranes (MMMs) are developed using polysulfone (PSf) containing of carbonyl iron powders (CIPs) for oxygen/nitrogen separation. In order to create preferential permeation pathways for oxygen across the MMMs, the membrane formation is accomplished with the aid of an external magnetic field. The required magnetic force to control particle dispersion within the membrane is simulated using ANSYS Maxwell software. Scanning electron microscopy images reveal that CIPs are aligned in the membrane matrix according to the direction of applied magnetic field; while successful synthesis of magnetic membranes is confirmed by vibrating sample magnetometer. In addition, a novel gas permeation unit is constructed to investigate the effect of CIP loading (1−10 wt.%) on the gas separation performance of MMMs in the presence of various magnetic fields. The magnetic field -aligned CIP/PSf membranes present higher permeability and lower selectivity than both un-aligned CIP/PSf and neat PSf membranes. In addition, O2 permeability and (O2/N2) selectivity of magnetic field -aligned CIP/PSf membranes are considerably improved by applying the magnetic field during permeation tests. In the presence of 570 m T magnetic field, O2 permeability and selectivity of MMMs containing 10 wt.% CIP improved by 436 % and 41 % respectively, compared to the pure PSf membrane.

Perspective of mixed matrix membranes for carbon capture

Polymeric membrane-based gas separation has found wide applications in industry, such as carbon capture, hydrogen recovery, natural gas sweetening, as well as oxygen enrichment. Commercial gas separation membranes are required to have high gas permeability and selectivity, while being cost-effective to process. Mixed matrix membranes (MMMs) have a composite structure that consists of polymers and fillers, therefore featuring the advantages of both materials. Much effort has been made to improve the gas separation performance of MMMs as well as general membrane properties, such as mechanical strength and thermal stability. This perspective describes potential use of MMMs for carbon capture applications, explores their limitations in fabrication and methods to overcome them, and addresses their performance under industry gas conditions.

The beneficial impacts of functional groups of CNT on structure and gas separation properties of PEBA mixed matrix membranes

Incompatibility between filler and polymer chains accompanied by particle agglomeration has a detrimental effect on the performance of mixed matrix membranes (MMMs). To obviate intermolecular forces of different additives, functional groups (-COOH, –NCO, and –NH2) were grafted on the surface of multi-walled carbon nanotubes (MWCNTs) which were then incorporated as fillers in the poly(ether-block-amide) (PEBA) polymeric matrix in the range of 0.1–1 wt% loading. CO2 permeability and ideal CO2/N2 and CO2/CH4 selectivity of MMMs was compared with the neat membrane, and the results revealed favorable enhancement and surpassed CO2/N2 Robeson's upper bound under 4–10 bar in the range of 15–55 °C. Mixed gas separation performance of MMMs, which is of vital importance in industrial applications, was also investigated. The results indicate that MWCNT-NCO created superior grafts with the polymer chains, and MMMs with this additive had a better gas separation performance with high mechanical and thermal stability.

Amino-silane-grafted NH2-MIL-53(Al)/polyethersulfone mixed matrix membranes for CO2/CH4 separation.

Mixed-matrix membranes (MMMs) are promising candidates for carbon dioxide separation. However, their application is limited due to improper dispersion of fillers within the polymer matrix, poor interaction of fillers with polymer chains, and formation of defects and micro-voids at the interface of both phases, which all result in the decline of the gas separation performance of MMMs. In this work, we present a new method to overcome these challenges. To this end, a series of MMMs based on polyethersulfone (PES) as the continuous polymer matrix and MIL-53-derived MOFs as the dispersed filler were prepared. FTIR-ATR, XRD, TGA, FESEM, and N2 adsorption/desorption analyses were employed to characterize the structural properties of the synthesized nanoparticles. The obtained results indicated that 3-aminopropyltriethoxysilane (APTES) molecules were successfully attached onto the surface of NH2-MIL-53(Al). Morphological characterization by FESEM and energy dispersive X-ray mapping (EDX) showed that desirable distribution within the whole membrane thickness, suitable nanoscale dispersion, and excellent interface were achieved by using amino-silane-grafted NH2-MIL-53(Al) (A-MIL-53(Al)) nanoparticles. The permeation results indicated that the permeability of two gases and the ideal CO2/CH4 selectivity enhanced by increasing the concentration of MOFs. In particular, comparing the experimental gas separation results of A-MMM-10 with those of pure PES membrane showed an 84% increase in the CO2 permeability and a 70% increase in CO2/CH4 selectivity. These results suggest that post-synthetic modification of MOF nanoparticles and strong interfacial adhesion between functionalized nanoparticles and polymer matrix could be a useful method to eliminate interfacial voids and improve gas separation efficiency.

High nanoparticles loadings mixed matrix membranes via chemical bridging-crosslinking for CO2 separation

Under high nanoparticles loadings, the gas separation performance mixed matrix membranes (MMMs) could be limited by the inferior compatibility between polymer and nanoparticles. Herein, we utilized a “bridging-crosslinking” method to connect the polymer and nanoparticles via macromolecule. Specially, the poly(vinylamine) (PVAm) and UIO-66-NH2 nanoparticles were bridging-crosslinked by using poly(ethylene glycol) diglycidyl ether (PEGDE) to achieve high nanoparticles loadings. By this way, even though the nanoparticles loadings attained 28.5 wt%, the incorporated nanoparticles still showed good dispersion in coating solution without sedimentation for one week. According to the gas permeation test, the fabricated MMMs with amounts of functional groups via “bridging-crosslinking” method displayed excellent gas separation performance and good long-term stability under the simulated flue gas. For CO2/N2 (15/85) mixed gas, the MMMs can achieve a high CO2 permeance of 1295 GPU and CO2/ N2 selectivity of 91 at 0.3 MPa. For CO2/CH4 (10/90) mixed gas and CO2/H2 (40/60) mixed gas, the gas separation performance of MMMs was investigated.

Effective enhancement of gas separation performance in mixed matrix membranes using core/shell structured multi-walled carbon nanotube/graphene oxide nanoribbons

Novel core/shell structured multi-walled carbon nanotube/graphene oxide nanoribbons (MWCNT@GONRs) nanohybrids were successfully prepared using a modified chemical longitudinal unzipping method. Subsequently, the MWCNT@GONRs nanohybrids were used as fillers to enhance the gas separation performance of polyimide based mixed matrix membranes (MMMs). It is found that MMMs concurrently exhibited higher gas selectivity and higher gas permeability compared to pristine polyimide. The high gas selectivity could be attributed to the GONRs shell, which provided a selective barrier and large gas adsorbed area, while the high gas permeability resulted from the hollow structured MWCNTs core with smooth internal surface, which acted as a rapid transport channel. MWCNT@GONRs could be promising candidates to improve gas separation performance of MMMs due to the unique microstructures, ease of synthesis and low filling loading.

Mixed-matrix membranes incorporated with porous shape-persistent organic cages for gas separation

There has been much recent interest in the use of porous materials derived from self-assembling, shape-persistent organic cages due to their solubility and easy post-synthetic modification. Herein we report the preparation of novel mixed-matrix membranes (MMMs) employing the porous organic cage Noria and its derivatives Noria-Boc and Noria-COtBu as the fillers, and a fluorine containing polyimide, 6FDA-DAM, as the polymeric matrix. The physical structures and properties of Noria and its derivatives were measured and investigated. Noria with substituents of Boc (cleaved by thermal treatment during the process of membrane fabrication) and COtBu groups tend to show much better compatibility with polyimide than Noria itself, resulting in homogeneous dispersion of nanoaggregates and fine adhesion between the two phases in the derived Noria/6FDA-DAM and Noria-COtBu/6FDA-DAM MMMs. Gas permeation tests revealed that Noria and Noria-COtBu nanoparticles have different effect on gas separation performance of MMMs. The introduction of Noria into 6FDA-DAM tends to enhance CO2/CH4 selectivity and thus improve its gas separation properties, though a decrease in the observed permeability could be observed. In contrast, the introduction of Noria-COtBu with higher surface area and larger pores tends to increase the free volume and gas permeability of MMMs. These results show that both the morphology and the gas separation properties of MMMs could be tuned by tailoring the structures of porous organic cages.

Particle-Size Effects on Gas Transport Properties of 6FDA-Durene/ZIF-71 Mixed Matrix Membranes

A series of 6FDA-Durene-ZIF71 mixed matrix membranes (MMMs) comprising three different ZIF-71 particle sizes (i.e., 30, 200, and 600 nm) have been fabricated to investigate the effects of particle size on the gas separation performance of MMMs. Compared to MMMs containing ZIF-71 particle size > 200 nm, ZIF-71 embedded MMMs with particle sizes of ≤ 200 nm exhibited significantly enhanced gas separation performance. The O2 and N2 permeability of MMMs comprising ZIF-71 with particle sizes ≤ 200 nm have higher permeability than the predicted ones using the Maxwell model. By considering the inefficiently packed polymer chain and the sieve-in-a-cage phenomena, the modified Maxwell model displayed comparable permeability over the experimental results suggesting the nonideal nature of MMMs. For the first time, it was found that 200 nm ZIF-71 generated the best MMM for gas separation, particularly for H2/CH4 systems. Therefore, a trade-off between ZIF-71 particle size vs gas separation performance must be taken in...

Improving Gas Separation Performance of Poly(vinylidene fluoride) Based Mixed Matrix Membranes Containing Metal–Organic Frameworks by Chemical Modification

In this study, poly(vinylidene fluoride) (PVDF) was modified by a mixture of KOH and KMNO4 in order to effect HF elimination. During this reaction, some functional groups were created in the PVDF structure. The metal–organic frameworks, MIL-53(Al) and NH2-MIL-35(Al), were embedded in modified PVDF (M-PVDF) to fabricate mixed matrix membranes (MMMs). Different characterization techniques such as FT-IR, XRD, SEM, DSC, TGA, and contact angle tests have been implemented to identify the prepared membranes. Pure and mixed (1:1) CO2 and CH4 were used to test gas separation performance of MMMs. CO2 permeance was increased for pure M-PVDF membrane compared with the pristine PVDF by 31.2%. Upon 10 wt % loading of MIL-53(Al) and NH2-MIL-35(Al) in M-PVDF, CO2 permeability increased 104.33% and 80.02% relative to the unfilled M-PVDF. The highest CO2/CH4 ideal selectivity and separation factor of 43.9 and 42.65, respectively, were reported for NH2-MIL-35(Al)/M-PVDF with 10 wt % loading. These improvements could be attr...