Metal-organic Frameworks Fillers Research Articles

Self-Sorting of Interfacial Compatibility in MOF-Based Mixed Matrix Membranes.

Metal-organic framework (MOF)-based mixed matrix membranes (MMMs) have shown great promises to overcome the performance upper limit of polymeric membranes for various gas separation processes. However, the gas separation properties of the MMMs largely depend on the MOF-polymer interfacial compatibility which is a metric difficult to quantify. In most cases, whether a MOF filler and a polymer matrix make a good pair is not revealed until the gas transport experiments are performed. This is because there is a lack of characterization techniques to directly probe the MOF-polymer interfacial compatibility. In this work, we demonstrate a self-sorting method to rank the interface compatibility among several MOF-polymer pairs. By mixing one MOF with two polymers in an MMM, the demixing of two polymers will form two polymer domains. The MOF particles will preferably partition into the "preferred" polymer domain due to their higher interfacial affinity. By scanning different polymer pairs, a rank of MOF-polymer interfacial compatibility from high to low can be obtained. Moreover, based on this ranking, it was also found that a highly compatible MOF-polymer pair suggested by this method also corresponds to a more predictable MMM gas separation performance.

Design of Mixed-Matrix MOF Membranes with Asymmetric Filler Density and Intrinsic MOF/Polymer Compatibility for Enhanced Molecular Sieving.

The separation of high-value-added chemicals from organic solvents is important for many industries. Membrane-based nanofiltration offers a more energy-efficient separation than the conventional thermal processes. Conceivably, mixed-matrix membranes (MMMs), encompassing metal-organic frameworks (MOFs) as fillers, are poised to promote selective separation via molecular sieving, synergistically combining polymers flexibility and fine-tuned porosity of MOFs. Nevertheless, conventional direct mixing of MOFs with polymer solutions results in underutilization of the MOF fillers owing to their uniform cross-sectional distribution. Therefore, in this work, a multizoning technique is proposed to produce MMMs with an asymmetric-filler density, in which the MOF fillers are distributed only on the surface of the membrane, and a seamless interface at the nanoscale. The design strategy demonstrates five times higher MOF surface coverage, which results in a solvent permeance five times higher than that of conventional MMMs while maintaining high selectivity. Practically, MOFs are paired with polymers of similar chemical nature to enhance their adhesion without the need for surface modification. The approach offers permanently accessible MOF porosity, which translates to effective molecular sieving, as exemplified by the polybenzimidazole and Zr-BI-fcu-MOF system. The findings pave the way for the development of composite materials with a seamless interface.

Fabrication of Metal-Organic Framework-Based Mixed-Matrix Membranes by "Soft Spray" Technique.

Metal-organic framework (MOF)-based mixed-matrix membranes (MMMs) represent a class of composite membranes that seamlessly integrate the properties of MOF fillers and polymer matrix into a hybrid system and have been widely used in countless advanced technologies. However, there remains a need for scalable and simple manufacturing techniques that can fabricate a MOF-based MMM with uniform dispersion. Herein, a series of MMMs with well-dispersed MOFs are constructed by a soft spray technique. In brief, by uniformly spraying metal ions onto the surface of a mixed solution containing polyvinylpyrrolidone (PVP) and organic ligands, a free-standing MMM is synthesized at the miscible liquid-liquid interface, facilitated by the dual function of metal ions. Moreover, soft spray technology can also introduce multifunctional materials into the MMM to customize performance. We have successfully introduced carbon black into a MOF-based MMM by soft spray, resulting in MMMs with excellent photothermal effects. The resulted MOF-based MMM exhibits favorable catalytic performance in the condensation reaction of benzaldehyde with primary amines, and the MOF-based MMM modified with carbon black significantly boosts the endothermic CO2 conversion. The work opens a new avenue for the development of MOF-based MMMs with a promising future.

A series of formic acid MOFs/polylactic acid blending composites with the improved dielectric performance in Co(II) systems

In order to improve the limited compatibility of existing polymer/ceramic dielectric composites and further enhance the energy storage density, MOF/polymer composite dielectrics have been explored, which exhibit good compatibility to the polymer matrix from abundant organic groups of the inorganic–organic hybrid metal-organic framework (MOF) fillers. However, they still lack a clear composition–structure–property rule, and the precise design of MOF fillers and polymer matrix becomes a prominent problem in these composites due to the diversity of the metal ions and the organic groups. Thus, in this paper, we present a series of formic acid MOFs/polylactic acid dielectric composites in which ferroelectric formic acid MOFs, namely PDLLA/[NH[Formula: see text](CH[Formula: see text])[Formula: see text]NH[Formula: see text]][M[Formula: see text](HCOO)[Formula: see text]][Formula: see text] and PDLLA/[CH[Formula: see text]NH[Formula: see text]][M[Formula: see text](HCOO)[Formula: see text]][Formula: see text], in which the formic acid MOFs are with different structures and different metal ions as fillers, including [NH3(CH[Formula: see text]NH3][MII(HCOO)3]2 (namely MOF–Co (M [Formula: see text] Co), MOF–Mg(M [Formula: see text] Mg), MOF–Mn (M [Formula: see text] Mn), with 1, 4-butanediamine ion as guest) and [CH3NH3][M[Formula: see text](HCOO)3]2 (namely MOF–Co[Formula: see text] (M = Co), MOF–Ni[Formula: see text] (Ni), with methylamine ion as guest). The composition and morphology of composite films were characterized by XRD, IR, SEM, DSC and UV, respectively, while the dielectric characterizations of the composites including the dielectric permittivity, the dielectric loss, the breakdown field strength and the energy density were also performed. The composition–structure–property relationships were also investigated including the influence of MOF content and MOF category. With the introduction of MOFs, the dielectric constant of the polylactic acid substrate was improved slightly while the breakdown field strength can be improved in some systems. Interestingly, the Co(II)-containing formic acid MOF has advantages over other formic acid MOFs with similar structure for the enhancement of the dielectric constant and breakdown field strength. Also, in some composite films with methylamine ion guest MOF fillers and low-MOF content (MOF–Co[Formula: see text] (1 vol.%) and MOF–Ni[Formula: see text] (1 vol.%)), the breakdown electric field enhanced significantly and further led to improved energy storage density which was about 43% higher than that of the polylactic acid matrix. The possible reason is that in these composites, the orientation of C–H bonds of MOFs seems more beneficial to the formation of hydrogen bonds between the carboxyl group of formic acid and the polylactic acid matrix. These relationships obtained from formic acid MOFs/polylactic acid composites are valuable to the design of high-performance polymer/MOF energy storage composites and may be a new perspective to the practical use of ferroelectric MOFs.

Metal-organic framework-based mixed matrix membranes for gas separation: Recent advances and opportunities

The demand for carbon dioxide (CO2) emission mitigation has driven the scientific community to develop a viable strategy. Gas separation technology are considered as the most promising and effective carbon capture approach. The utility of mixed-matrix membranes (MMMs) for selective gas separation has prompted a paradigm shift from conventional methods towards more efficient and sustainable processes. Metal-organic frameworks (MOFs), with high porosity, surface area, and structural tunability, are identified as suitable fillers in MMMs. Their application in carbon capture and gas separation processes could significantly reduce greenhouse gas emissions while maintain cost-effectiveness. Herein, this review presents the latest scientific and technological advancements in several types of representative MOF fillers, including Zeolitic Imidazolate Frameworks (ZIFs), Materials of Institute Lavoisier (MILs), University of Oslo (UiO), and Hong Kong University of Science and Technology (HKUST-1). It also highlights the current challenges associated with MOF fillers and outlines potential research opportunities for future improvements in the performance of MOF-based MMMs.

ZIF-8 nanoplate/6FDA-DAM membrane for hydrogen extraction from propane dehydrogenation process

High-aspect ratio materials can enhance gas separation performance compared to low-aspect ratio materials when incorporated into a polymer matrix to form mixed matrix membranes (MMMs). However, the filler shape effect on various properties of MMMs was not thoroughly discussed. Herein, we fabricated a mixed matrix membrane with two different shapes of metal-organic framework (MOF) and examined the MOF filler shape effect on mechanical, thermal, and gas separation properties. Zeolitic imidazolate framework-8 nanoplates (NZIF-8) were synthesized by conversion method with an aspect ratio of 20. Isotropic ZIF-8 particles (IZIF-8) were also synthesized, and both fillers were hybridized with a 6FDA-DAM (PI) polymer. 20 wt% NZIF-8/PI membrane exhibited high mechanical properties of 0.282 GPa for hardness and 3.5 GPa for modulus, which is higher than that of IZIF-8/PI membranes. The membrane was stable in high temperatures which is comparable to the pristine PI membrane, showing long-term thermal stability at 300 °C. Furthermore, high aspect ratio fillers allowed significant enhancement in hydrogen separation performance, showing hydrogen permeability of around 1800 Barrer with hydrogen/propane selectivity of 260 at 20 wt% ZIF-8 nanoplate loading, which is much enhanced than the membrane with isotropic ZIF-8 particles. The separation performances were consistent in ternary mixture separation under different conditions. These highly stable and selective properties can be promising for hydrogen extraction from the propane dehydrogenation process.

Influence of polymer modification on intra-MOF self-diffusion in MOF-based mixed matrix membranes

Mixed-matrix membranes (MMMs) represent a promising membrane type for gas and liquid separations. Such membranes can be formed by dispersing crystals of metal–organic frameworks (MOFs) in polymers. For liquid separations, crosslinked polymers are desirable because crosslinking reduces polymer dilation and plasticization effects by liquid sorbates. However, polymer crosslinking processes can unfavorably change transport and related structural properties of MOF fillers. In this work, 13C pulsed field gradient (PFG) NMR was used to investigate possible changes in intra-MOF self-diffusion of p-xylene and o-xylene after MMM polymer crosslinking. The studied MMMs were formed by dispersing MOF crystals of the type ZIF-71 in Torlon (a poly(amide-imide)) or Matrimid (a polyimide) polymers. The reported PFG NMR data indicate that the polymer crosslinking process used does not influence the intra-ZIF diffusivities when all effects on these diffusivities that are related to diffusing molecules crossing over the crystal boundaries or reflected away from these boundaries are removed. In contrast, these data show that the crosslinking process resulted in a significant decrease of the effective size of ZIF-71 crystals inside the studied MMMs, especially in the ZIF-71/Matrimid MMM. This crystal size decrease is attributed to a partial degradation of the ZIF-71 crystals inside the MMMs due to the crosslinking process. This conclusion was found to be in agreement with the results of electron microscopy analysis. PFG NMR studies and data analysis similar to those presented here can be used for quantifying any types of MOF crystal degradation inside MOF-based MMMs.

Single-atom electrocatalyst and gel polymer electrolyte boost the energy density and life of aluminum-sulfur batteries

Aluminum-sulfur (Al-S) batteries are regarded as a desirable candidate for large-scale energy storage because of their high energy density and abundant natural resources of electrode materials. To address the critical issues of low discharge voltage and rapid capacity decay in Al-S batteries, here an electrocatalyst-assisted gel-polymer electrolyte (GPE)-based Al-S battery is fabricated using platinum nanoparticles decorated platinum/nitrogen co-doped graphene (PtNG) as sulfur host for positive electrode and metal-organic frameworks (MOF) filled GPE (MOF@GPE) as solid electrolyte. Pt-based active sites derived from Pt nanoclusters’ surface and atomically dispersed Pt-N2 chemical bonds in PtNG can catalyze the decomposition of sulfur and polysulfides in the electrochemical process, greatly accelerating the sulfur redox kinetics. Furthermore, the MOF fillers in MOF@GPE electrolyte significantly inhibit the shuttle effect of polysulfides, efficiently improving the utilization of sulfur. Consequently, the established Al-S battery delivers a specific capacity of 1009 mAh g−1 with a discharge plateau of ∼0.95 V, along with a capacity retention of 65% after 300 cycles, revealing ultrahigh energy density and long cycle life. Such a strategy of combining electrocatalyst and MOF-based gel electrolyte affords a fresh plateau for promoting the rechargeable ability of Al-S batteries, advancing remarkable routes for achieving efficient and stable energy storage devices.

Computational Investigation of Dual Filler-Incorporated Polymer Membranes for Efficient CO2 and H2 Separation: MOF/COF/Polymer Mixed Matrix Membranes.

Mixed matrix membranes (MMMs) composed of two different fillers such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) embedded into polymers provide enhanced gas separation performance. Since it is not possible to experimentally consider all possible combinations of MOFs, COFs, and polymers, developing computational methods is urgent to identify the best performing MOF-COF pairs to be used as dual fillers in polymer membranes for target gas separations. With this motivation, we combined molecular simulations of gas adsorption and diffusion in MOFs and COFs with theoretical permeation models to calculate H2, N2, CH4, and CO2 permeabilities of almost a million types of MOF/COF/polymer MMMs. We focused on COF/polymer MMMs located below the upper bound due to their low gas selectivity for five industrially important gas separations, CO2/N2, CO2/CH4, H2/N2, H2/CH4, and H2/CO2. We further investigated whether these MMMs could exceed the upper bound when a second type of filler, a MOF, was introduced into the polymer. Many MOF/COF/polymer MMMs were found to exceed the upper bounds showing the promise of using two different fillers in polymers. Results showed that for polymers having a relatively high gas permeability (≥104 barrer) but low selectivity (≤2.5) such as PTMSP, addition of the MOF as the second filler can have a dramatic effect on the final gas permeability and selectivity of the MMM. Property-performance relations were analyzed to understand how the structural and chemical properties of the fillers affect the permeability of the resulting MMMs, and MOFs having Zn, Cu, and Cd metals were found to lead to the highest increase in gas permeability of MMMs. This work highlights the significant potential of using COF and MOF fillers in MMMs to achieve better gas separation performances than MMMs with one type of filler, especially for H2 purification and CO2 capture applications.

A roadmap to enhance gas permselectivity in metal-organic framework-based mixed-matrix membranes.

Performing gas separation at high efficiency with minimum energy input and reduced carbon footprint is a major challenge. While several separation methods exist at various technology readiness levels, porous membrane-based separation is considered as a disruptive technology. To attain sustainability and required efficiency, different approaches of membrane design have been explored. However, the selectivity-permeation trade-off and membrane aging have restricted further advancement. In this regard, a new generation composite made of organic polymers and metal-organic framework (MOF) fillers shows substantial promise. Organic polymer matrix allows easy processibility, but it has poor permselectivity for gas molecules. Metal-organic frameworks are excellent sieving materials; however, they suffer from poor processibility issues. A combination of these two components makes an ideal sieving membrane, which can potentially outnumber the existing energy intensive distillation strategies. In this perspective, we have discussed key indices that regulate gas permselectivity by a careful selection of the existing literature. While the target gas flux and selectivity values have been a part of many previous reviews and articles, we have presented a concise discussion on the interface design of the MOF-polymer membrane, morphology, and orientation control of MOF fillers in the matrix. Following this, a future roadmap to overcome challenges related to MOF-polymer interfacial defects is outlined.

Enhanced compatibility and selectivity in mixed matrix membranes for propylene/propane separation

AbstractMixed matrix membranes (MMMs) based on metal–organic framework (MOF) have great promising application in separation of gas mixtures. However, achieving a good interfacial compatibility between polymer and MOF is not straightforward. In this work, focusing on one of the most challenging olefin/paraffin separations: propylene/propane (C3H6/C3H8), we demonstrate that modification of the MOF filler via dopamine polymerization using a double solvent approach strongly improves interfacial compatibility. The resulting membranes show an outstanding separation performance and long‐term stability with propylene permeability nearly 90 Barrer and propylene/propane selectivity close to 75. We anticipate that similar MOF modification strategies may help solve the problem of interface defects in the manufacture of MMMs and be extended to other porous fillers.

Submicron-thick, mixed-matrix membranes with metal-organic frameworks for CO2 separation: MIL-140C vs. UiO-67

High-performance thin-film mixed-matrix membranes (MMMs) were prepared using two types of zirconium-based metal-organic frameworks (MOFs), MIL-140C and UiO-67; both were dispersed in a polymer matrix for CO2 separation. A poly(glycidyl methacrylate-co-poly(oxyethylene methacrylate) (PGO) copolymer was synthesized via one-pot free-radical polymerization and used as an adhesive matrix to allow intimate interfacial contact with the MOF fillers, resulting in 600 nm-thick defect-free MMMs with uniform dispersion. Both fillers comprise the same building blocks but have different pore sizes, structures, and particle morphologies. The pores of UiO-67 are 3D cage-like with a polyhedral morphology and were larger than the 1D channel-like pores of MIL-140C, having a rod-like morphology. The use of two fillers led to different degrees of polymer infiltration into the MOF pores, resulting in different CO2 separation performances. Overall, the MMMs with MIL-140C showed greater CO2/N2 and CO2/CH4 selectivities than those with UiO-67 because of the well-defined micropores resulting from mild polymer infiltration and structural advantages such as a high aspect ratio. The best separation performance was achieved at 20% of MIL-140C loading (CO2 permeance of 1768 GPU and CO2/N2 selectivity of 38), lying in the commercial criteria required for post-combustion CO2 capture.

A comparison of shear‐mixing and solvent‐induced on phase behavior, thermal and dielectric properties of PVDF‐HFP/MOF composites

AbstractThe effects of processing techniques significantly alter on the electroactive β‐phase, thermal, and dielectric behavior of polymer composites. The metal–organic framework filler (C3N2H5)(Mg(HCOO)3), HImMg is prepared and introduced into poly(vinylidenefluoride‐co‐hexafluoropropylene) (PVDF‐HFP) matrix using two distinguished methods: melt‐mixing and solution‐casting methods. The processing conditions are important in determining the dominant phase in PVDF‐HFP. As a result of solvent‐induced crystallization, the β‐phase content of solution‐cast composites containing 10% HImMg is 22% higher than that of melt‐mixed composites. In both methods, the nucleating effect of HImMg particles increases the overall crystallinity of the polymer matrix and enhances the dielectric constant in composite films by improving the interfacial and dipolar polarization. Furthermore, the melt‐mixed composites with 7 wt% HImMg demonstrate the highest dielectric constant of 17.8 at 1 kHz, showing an enhancement of 59% compared with that of pristine PVDF‐HFP. Meanwhile, the dielectric loss is suppressed at 0.083. These findings suggest the possibility of enhancing composites' electroactive phase and dielectric properties without mechanical stretching or a large electrical field.

Activated metal-organic frameworks (a-MIL-100 (Fe)) as fillers in polymer electrolyte for high-performance all-solid-state lithium metal batteries

As a common filler in polymer electrolytes, Metal-organic frameworks (MOFs) has been studied extensively in recent years. In this study, we propose a novel solid composite electrolytes (SCEs) based on PEO/LiTFSI/a-MIL-100 (Fe)/PVDF by using a straightforward solution-casting method. Unactivated and activated MIL-100 (Fe) (a-MIL-100 (Fe)) as the fillers were compared, and the interactions of functional groups of unactivated MIL-100 (Fe) and a-MIL-100 (Fe) with anions of electrolyte salts through Lewis acid-base interaction are studied with density functional theory (DFT) calculations. The influences of different a-MIL-100 (Fe) contents on electrochemical performances were also examined. The Li/SCEs/LiFePO4 cell displayed high average discharge capacities of 161.8 mAh g−1, 166.8 mAh g−1, 158.9 mAh g−1, 146.2 mAh g−1 and 92.6 mAh g−1 at the rate of 0.1, 0.2, 0.5, 1 and 2 C at 60 ℃, respectively, without liquid electrolytes. This work might provide new insight into the role of activated MOFs fillers in polymer electrolytes.

Surface modification of bilayer structure on metal-organic frameworks towards mixed matrix membranes for efficient propylene/propane separation

Rational matching of filler-matrix in mixed matrix membranes (MMMs) is crucial but challenging for highly efficient gas separation. Herein, we propose a bilayer structure modification strategy on metal-organic frameworks (MOFs) to design various MOF-based MMMs for efficient propylene/propane separation. The octadecylphosphonic acid-lecithin-cholesterol bilayer structure grafted onto the surface of MOFs strengthens their sieving capacity under the premise of maintaining good interfacial compatibility, and promotes the formation of holes in the cross-linked poly(ethylene oxide) (XLPEO) polymer matrix. This allows for the simultaneous enhancement of gas permeability (∼266 Barrer) and C3H6/C3H8 selectivity (40.5). We briefly investigated the effect of the modified bilayer structure on the gas separation performance. More importantly, this constructing strategy is also effective for other MOF fillers in MMMs; thus this design of bilayer modification at a molecular level opens new insights into optimizing MOF-based MMMs in the challenging olefin/paraffin separation.

Gel-to-crystal route towards MOF-mixed MOF-matrix membranes

Metal-organic framework (MOF) membranes attract intensive attention for precisely molecular sieving. It is of greatly scientific interest to adjust transport property of MOF membranes. Inspired by formation and separation mechanisms of mixed matrix membranes (MMMs), in this study, we report a kind of MOF-mixed MOF-matrix membranes (M5), which consist of dispersed MOF fillers and continuous MOF matrixes and combine different features of two MOFs. A simple, controllable, and versatile gel-to-crystal methodology, similar to solvent-evaporation induced phase-inversion of polymer-based membranes and performed by precursor coating and thermally treating crystallization, is proposed to construct M5. The incorporated MOF fillers can improve membrane crystallization and have good compatibility toward MOF matrixes. As an example, because of UiO-66-NH2 filler has larger aperture than ZIF-8 matrix, the prepared M5 shows enhanced permeability while invariable selectivity compared with the pure one.

Poly(ionic liquid)-Functionalized UiO-66-(OH)2: Improved Interfacial Compatibility and Separation Ability in Mixed Matrix Membranes for CO2 Separation

Incorporating porous materials into a polymeric matrix to produce mixed matrix membranes (MMMs) usually offers the combined properties of each component. However, it requires efficient dispersity of porous materials in a polymeric matrix and good compatibility between them. To enhance the compatibility, we report an approach by covalent grafting of poly(ionic liquid) (PIL) brushes on the surface of metal–organic framework (MOF) UiO-66-(OH)2. Benefiting from the surface grafted PIL brushes, the as-synthesized UiO-66-(OH)2@PIL shows an improved dispersity in the solvent media and Pebax matrix due to the hydrophilicity of PIL and the formed hydrogen bonds between the MOF fillers and Pebax matrix. The obtained UiO-66-(OH)2@PIL-based MMMs manifest simultaneously increased selectivity and permeability for CO2/N2 separation, with the best performance at 20 wt % of loading (CO2 permeability of 132 Barrer and CO2/N2 separation factor of 71). This work highlights the efficiency of MOF functionality to achieve enhanced interfacial compatibility and membrane separation performance.

Engineering nanocomposite metal-phenolic network membranes with hollow MOFs via in-situ etching for High-efficiency organic solvent nanofiltration

Organic solvent nanofiltration (OSN), as an emerging membrane separation technology, holds great potential in pharmaceutical and chemical applications. However, the development of such a promising technology is severely retarded by the trade-off between permeability and selectivity. Herein, we report a novel thin-film nanocomposite (TFN) membrane by incorporating hollow metal-organic frameworks (MOFs) into the metal-phenolic network (MPN) selective layer for highly efficient OSN. This nanocomposite selective layer is fabricated via an aqueous deposition of tannic acid (TA) and FeII ions with MOFs, during which the MOFs are in-situ etched to a hollow structure. Attributed to the extra transfer channels provided by hollow MOFs, the methanol permeance of the TFN membranes increases to 24.7 L·m-2·h-1·bar-1, exhibiting an improvement of 270% compared with the membranes without MOFs (9.1 L·m-2·h-1·bar-1). Meanwhile, the coordination interaction between TA and metal centers in MOFs endows excellent interfacial compatibility between MPN matrix and MOF fillers, guaranteeing a defect-free selective layer and thus high rejection for small organic molecules (>99% for Alcian blue). Furthermore, various MOFs, including ZIF-67, prussian blue (PB), and MIL-53(Al), are also employed to fabricate MPN/MOF nanocomposite membranes, proving the availability and universality of this facial aqueous deposition strategy. Additionally, we also take deep insight into the mechanism of in-situ etching based on the density functional theory (DFT) calculation to pave the way for the fabrication of TFN membranes with other hollow nanofillers. This work provides a sufficient strategy for the design and construction of novel highly efficient OSN nanocomposite membranes with excellent permeability and retention performance.

MOF-based MMMs breaking the upper bounds of polymers for a large variety of gas separations

• Permeabilities of CO 2 , CH 4 , N 2 , O 2 , H 2 , and He gases were reported for 5599 MOFs. • 181,249 types of MOF/polymer MMMs were studied for 11 different gas separations. • A large number of MOF/polymer MMMs exceeded the upper bounds of polymers. • A guideline was provided for selection of the best MOF-polymer combinations. Mixed matrix membranes (MMMs) are a strong alternative to the conventional polymeric membranes which suffer from a trade-off between selectivity and gas permeability. Considering the existence of a large number of metal–organic frameworks (MOFs) and polymers, computational screening of MOF/polymer MMMs is strongly desired to explore their upper limits in various gas separation processes before experimental efforts. In this work, we computed permeability of CO 2 , CH 4 , N 2 , O 2 , H 2 , and He gases in 5599 metal organic frameworks (MOFs) using atomically-detailed simulations and then assessed performances of >180,000 different MOF/polymer MMMs for 11 different gas separations He/H 2 , He/N 2 , He/CH 4 , N 2 /CH 4 , H 2 /N 2 , H 2 /CH 4 O 2 /N 2 , CO 2 /N 2 , CO 2 /CH 4 , H 2 /CO 2 , He/CO 2 . Our results revealed that many MOF/polymer MMMs exceed the upper bounds due to their high gas permeability and/or selectivity. The impact of MOFs on the separation performances of polymers was examined to provide guidelines for the best MOF-polymer pairing for a variety of gas separations. Data showed that using MOFs as fillers significantly improves the permeability of CO 2 , CH 4 , N 2 , O 2 , H 2 , and He gases in 41 different types of polymers without changing their selectivities. Many MOFs offer a great opportunity for MMM applications by improving both the permeability and selectivity of polymers such as of Teflon AF-2400 for N 2 /CH 4 , PTMSP-co(95/5) for H 2 /CH 4 , PTMSDPA for O 2 /N 2 and PTMSP for CO 2 /CH 4 separations. The best MOF fillers leading to MMMs with exceptional selectivities were found to have narrow pores and low porosities. These results will contribute to directing the experimental efforts to the best MOF/polymer MMM materials for numerous industrially important gas separation applications.

Nanofibrous membranes comprising intrinsically microporous polyimides with embedded metal–organic frameworks for capturing volatile organic compounds

Here, we report the fabrication of nanofibrous air-filtration membranes of intrinsically microporous polyimide with metal–organic frameworks (MOFs). The membranes successfully captured VOCs from air. Two polyimides with surface areas up to 500 m2 g−1 were synthesized, and the impact of the porosity on the sorption kinetics and capacity of the nanofibers were investigated. Two Zr-based MOFs, namely pristine UiO-66 (1071 m2 g−1) and defective UiO-66 (1582 m2 g−1), were embedded into the nanofibers to produce nanocomposite materials. The nanofibers could remove polar formaldehyde and non-polar toluene, xylene, and mesitylene from air. The highest sorption capacity with 214 mg g−1 was observed for xylene, followed by mesitylene (201 mg g−1), toluene (142 mg g−1), and formaldehyde (124 mg g−1). The incorporation of MOFs drastically improved the sorption performance of the fibers produced from low-surface-area polyimide. Time-dependent sorption tests revealed the rapid sequestration of air pollutants owing to the intrinsic porosity of the polyimides and the MOF fillers. The porosity allowed the rapid diffusion of pollutants into the inner fiber matrix. The molecular level interactions between VOCs and polymer/MOFs were clarified by molecular modeling studies. The practicality of material fabrication and the applicability of the material were assessed through the modification of industrial N95 dust masks. To the best of our knowledge, this is the first successful demonstration of the synergistic combination of intrinsically microporous polyimides and MOFs in the form of electrospun nanofibrous membranes and their application for VOC removal.