Fillers In Mixed Matrix Membranes Research Articles

In situ growth of covalent organic framework on graphene oxide nanosheet enable proton-selective transport in flow battery membrane

Perfluorosulfonic acid (PFSA) is the most widely used membrane material for all-vanadium redox flow batteries (VRFB). However, severe vanadium ion permeation of PFSA membranes remains to be solved. In this work, a series of PFSA-based composite membranes are prepared by introducing two-dimensional continuous covalent organic framework (COF) to achieve enhanced performance. Two dimensional continuous Schiff base network-type COFs (GO/SNW) are synthesized by using the two-dimensional multi-functionalized surface of graphene oxide (GO) as a reaction site. Compared to the original form of agglomerated particles, two-dimensional continuous structure obtained a larger vanadium resistance area. Comparing to conventional PFSA membranes, the special pores of COF have a size sieving mechanism for selectively proton transfer, leading to simultaneously enhancement of proton conductivity and vanadium barrier property. VRFB assembled with PFSA-GO/SNW-7 showed high Coulombic efficiency (CE: 97.47%–98.18 % VS PFSA: 80.73%–91.92 %) and energy efficiency (EE: 93.04%–85.71 % VS PFSA: 77.53%–81.78 %) at 40–120 mA cm−2. In addition, there is no significant decrease in the efficiency of battery assembled with PFSA-GO/SNW-7 after 800 cycle (than 650 h) tests. This work provides a new direction in the design of fillers for mixed matrix membranes.

Synergistic effect of combining UiO-66 nanoparticles and MXene nanosheets in Pebax mixed-matrix membranes for CO2 capture

The use of membrane-based gas separation has garnered significant interest owing to its cost-effectiveness, outstanding performance and positive environmental impact. The performance of gas separation membranes can be considerably enhanced by mixed-matrix membranes (MMMs), but poor interactions between additives and membrane matrix and the agglomeration of highly incorporated fillers in MMMs limit the benefits of overcoming tradeoff effect. Therefore, the regulation of the state of fillers in membrane matrix is a crucial indicator in the development of MMMs. In this study, MXene (Ti3C2Tx) nanosheets and UiO-66 nanoparticles were prepared and used as fillers, in combination with a Pepax-1657 matrix, to synthesize MMMs for CO2-gas separation. As-prepared MMMs were used for the separation; the large pores (0.5–0.6 nm) of UiO-66 served as a highway to enhance CO2 permeability, and MXene nanosheets were used as selective channels to achieve high selectivity via the terminal polar surface groups of MXene. The combination of UiO-66 and MXene not only enhanced the selectivity, but also increased the solubility and diffusivity via selective CO2 adsorption and the tortuous pathway provided by MXene nanosheets. As a result, adding MXene and UiO-66 to Pebax helped MMMs overcome the tradeoff effect. MMMs loaded with 10 wt% MXene/UiO-66 exhibited a CO2 permeability coefficient of 214.6 Barrer and an ideal CO2/N2 selectivity coefficient of 102. Dual filler-containing MMMs showed enhanced CO2 permeability coefficient and CO2/N2 selectivity in comparison to pristine Pebax and individual nanofiller-added membranes. In this study, the combination of 2D MXene and UiO-66 nanoparticles exerted a synergistic effect in improving the CO2 separation efficiency of MMMs. This research provides a novel route for fabricating high-performance MMMs in the separation of CO2.

Comparison of the effect of topology type and linker composition of zeolitic imidazolate framework fillers on the performance of mixed matrix membranes in CO2/N2 separation

Mixed matrix membranes (MMMs) combine the high separation performance of porous materials with the processibility of polymers and so possess potential for carbon capture from CO2-containing gas streams. Zeolitic imidazolate frameworks (ZIFs) are promising candidates as molecular-sieve fillers in MMMs due to their tunability and ease of synthesis. We have compared four ZIFs, all as nanoparticles of similar sizes (ca. 400 nm), as MMM fillers, to investigate the effects of ZIF structure and chemistry on MMM performance of pure gas (CO2, N2) permeation under the same conditions. The chosen ZIFs include two that exhibit strong CO2 adsorption (hybrid ZIF-7/COK-17 and ZIF-94) and two that have higher pore volumes but weaker CO2 interactions (ZIF-8 and a hybrid ZIF-11/ZIF-71). The hybrid ZIF-7/COK-17 and ZIF-94 are structurally related to ZIF-7 (rhombohedral sod topology) and ZIF-8 (cubic sod), respectively, via partial or complete substitution of benzimidazole or 2-methylimidazole by 4,5-dichloroimidazole or 4-methyl-5-imidazolecarboxaldehyde, while the hybrid ZIF-11/ZIF-71 has the rho topology but the same composition as the ZIF-7/COK-17 hybrid. In the first part of the comparative study, MMMs based on two types of commercial polymers, Matrimid®5218 and PEBAX-MH1657, were prepared containing the ZIF-7/COK-17 hybrid and also with ZIF-94. ZIF-94 shows much better compatibility with the polymers, forming homogeneous dispersions at all loadings attempted (≤35 % wt%) whereas the hybrid shows inhomogeneity above 12 wt% in each case. At 12 wt% loading, both fillers show an increase in CO2 permeability at 1.2 bar and 293 K compared to the pure membrane (in PEBAX, this increases from 49.5 to 60 and 68 Barrer) which is the result of increased solubility compensating for decreased diffusivity, and this improvement in permeability continues to increase at the higher levels of loading possible with ZIF-94. ZIF-7/COK-17 in PEBAX show higher selectivity, achieving a calculated CO2/N2 selectivity up to 70. Further investigation of CO2 and N2 permeation on MMMs with the four ZIFs at 12 wt% in PEBAX-MH1657 showed a clear distinction between the ZIF-94 and ZIF-7/COK-17 MMMs (which show higher membrane solubilities but lower diffusivities) compared to ZIF-8 and ZIF-11/ZIF-71 MMMs. At the loading chosen, the CO2 permeability increase achieved by the four ZIFs over PEBAX-MH1657 increases in the order ZIF-11/-71, ZIF-7-COK-17 (ca. 60 Barrer) < ZIF-94 (68) < ZIF-8 (81), reflecting the complex interplay between CO2 solubility (increasing with interaction strength) and diffusivity (increasing with available cage and window size). The calculated CO2/N2 selectivity is highest for the hybrid ZIF-7/COK-17 membrane (70), which is attributed to molecular sieving effects in the rhombohedral sod structure.

ZIF-8 modified with 2-undecylimidazolate as filler for mixed matrix membranes for CO2 separation

A novel modification of zeolitic imidazolate framework-8 with 2-undecylimidazolate was explored to enhance its hydrophobicity and improve its compatibility with polymer PIM-1 when incorporated as a filler in mixed matrix membranes.

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.

Thin selective layered mixed matrix membranes (MMMs) with defective UiO-66 induced interface engineering toward highly enhanced pervaporation performance

The thin selective layer in mixed matrix membranes (MMMs) with high pervaporation performance is in high demand because of their high productivity. However, it has been limited because of the defective interface of sieving fillers in MMMs and the instability to permeate molecules, resulting in instability and degradation in the membrane state and pervaporation performance. Herein, we synthesized defective UiO-66 (DUiO66) by controlling the concentration of the reactants and then analyzed the characteristics of the defects. We confirmed that defects of the missing linker are induced in its structure, and DUiO66 (1.324) has a higher defect density than conventional UiO66 (1.064). Those led to the highly enhanced interface of DUiO66 with polyvinyl alcohol (PVA) matrix and water solvent, resulting in mechanical stability and a uniformed thin selective layer. Crosslinked thin-layered PVA MMMs with DUiO66 (XPDUiO66) were applied to the flat-sheet type and hollow fiber type membranes and then examined for the pervaporation performance to separate IPA/water solution (mainly 80/20 and 90/10 (w/w)). The thin-layered flat type and hollow fiber type XPDUiO66 revealed a dramatic increase in flux by 5.6 and 5.0 times compared to the free-standing type MMM while almost maintaining selectivity. Notably, the flat-sheet type XPDUiO66-2 increased around 606% and 1,664% in PSI relative to XPVA at a feed solution of 80/20 and 90/10 (w/w) IPA/water, respectively. The current work offers significant findings on the relationship between defective MOF-applied MMMs and pervaporation performance.

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.

The Difference in Performance and Compatibility between Crystalline and Amorphous Fillers in Mixed Matrix Membranes for Gas Separation (MMMs).

An increasing number of high-performing gas separation membranes is reported almost on a daily basis, yet only a few of them have reached commercialisation while the rest are still considered pure research outcomes. This is often attributable to a rapid change in the performance of these separation systems over a relatively short time. A common approach to address this issue is the development of mixed matrix membranes (MMMs). These hybrid systems typically utilise either crystalline or amorphous additives, so-called fillers, which are incorporated into polymeric membranes at different loadings, with the aim to improve and stabilise the final gas separation performance. After a general introduction to the most relevant models to describe the transport properties in MMMs, this review intends to investigate and discuss the main advantages and disadvantages derived from the inclusion of fillers of different morphologies. Particular emphasis will be given to the study of the compatibility at the interface between the filler and the matrix created by the two different classes of additives, the inorganic and crystalline fillers vs. their organic and amorphous counterparts. It will conclude with a brief summary of the main findings.

Improved CO2/N2 separation performance by relatively continuous and defect-free distribution of IL-encapsulated ZIF-67 in ion gel membranes

Metal-organic frameworks (MOFs), as a typical type of porous materials, are widely used as fillers in mixed matrix membranes (MMMs) to enhance the gas separation performance. However, non-selective interface defects are prone to appear in MMMs under high MOF loading conditions, meanwhile, the discontinuous dispersion of MOF particles in polymeric matrices makes the gas molecules diffuse along the MOF-polymer-MOF intersection path and difficult to achieve efficient molecular transfer. These factors greatly compromise the ability of MOF to enhance membrane separation performance. Herein, the [C5min][BF4] encapsulated ZIF-67 (IL@ZIF) composites were embedded into the defect-free IL/Pebax ion gel matrix to form a mixed matrix ion gel membrane without interface defects. On the basis of good interfacial compatibility, the relatively continuous and highly selective CO2 transmission channels were constructed via increasing the filler loading up to 80 wt%. In this context, the typical IL@ZIF/IL/Pebax membrane with 80 wt% IL content and 70 wt% IL@ZIF doping amount exhibits a CO2 permeability of 408.2 Barrer and CO2/N2 selectivity of 97.2, surpassing the latest upper line. This work may have high reference value in the construction and preparation of MOF-based MMMs with high performance in gas separation.

A new class of fillers in mixed matrix membranes: Use of synthetic silico-metallic mineral particles (SSMMP) as a highly selective component for CO2/N2 separation

Membrane-based CO2 separation technology is a promising technology with low operating and energy costs and high scalability. This work describes the influence of synthetic silico-metallic mineral particles (SSMMP) and SSMMP/ionic liquids (IL) associated with polysulfone (PSF) to produce new mixed matrix membranes (MMM) for post-combustion technology. SSMMP is the precursor of synthetic talc undergoing no hydrothermal process resulting in a low-cost, energy-demanding, and CO2-free emission material due to its synthesis process. SSMMP have many reactive OH groups free on their surface making this material ideal to be compatibilized in a polymeric matrix. IL was immobilized in SSMMP to further improve CO2 affinity. As far as we know, this is the first time this material has been used to obtain MMMs. MMMs were prepared with concentrations of 0.5, 1, 2 and 3 wt% of fillers via melting solution and solvent evaporation. The obtained MMMs were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) with elemental mapping, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Permeability analyses were carried out at 25 °C and 0.4 MPa. The addition of pristine SSMMP and SSMMP/Im(nBu)Tf2N improved membrane selectivity decreasing the permeability for the majority of tested filler content. When using SSMMP/Im(nBu)I to obtain MMMs a different behavior was observed decreasing selectivity (except for MMM with 2% (w/w) of filler) and increasing permeability in all studied concentrations. The best result was obtained for sample SSMMP/Im(nBu)Tf2N (2% w/w) achieving a selectivity of 71.9, four times higher than pristine polysulfone membrane.

Aligned Metal–Organic Framework Nanoplates in Mixed‐Matrix Membranes for Highly Selective CO2/CH4 Separation

Abstract2D metal–organic frameworks are attractive filler in mixed matrix membranes (MMMs) due to the high aspect ratio and contact opportunity at the filler–polymer interface. However, their alignment in polymer matrix remains a challenge to fully play their functions. Herein, to our best knowledge, for the first time, the facile synthesis of KAUST‐7‐NH2 (KAUST, King University of Science and Technology) nanoplate is reported with 1D channels with an aspect ratio greater than 30. The nanoplates are incorporated and aligned in the 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride‐2,4‐diaminomesitylene (6FDA‐DAM) polymer matrix under the shear force with a filler loading up to 50 wt%. The large difference in adsorption abilities between CO2 and CH4 from the (001)‐oriented KAUST‐7‐NH2 nanoplate‐based MMMs and the favorable interaction at the filler–polymer interface contribute to the excellent CO2/CH4 separation performance. The resultant membranes show CO2/CH4 selectivity with 66.2% enhancement (surpassed 2008 Robeson upper bound), antiplasticization up to 17 bar, and long‐term stability up to 240 h indicating its good potential for natural gas treatment.

Mixed-matrix membranes containing zero-dimension porphyrin-based complex for propylene/propane separation

The membrane-based technology for propylene/propane (C3H6/C3H8) separation is very promising due to its low-energy separation process with high effectiveness. Herein, we propose a new type of mixed-matrix membranes (MMMs) containing zero-dimension non-porous porphyrin-based complex (M-TMCPP, M = Zn2+, Cd2+, Ni2+) with coordinatively unsaturated metal sites. Density functional theory calculation results show that M-TMCPP can form π complexation with C3H6 and facilitate C3H6 molecule through membranes. Different from porous nanofillers, M-TMCPP exhibits zero-dimension non-porous molecular structure and can be dissolved in solvent at molecular lever under low concentration. Benefiting from the favorable interaction between C3H6 with metal sites and the uniform distribution of M-TMCPP particles and/or even independent M-TMCPP molecules in polymer, the porphyrin-based complexes are used as nanofillers in fluorinated polyimide (6FDA-DAM). The prepared MMMs exhibit an extraordinary C3H6/C3H8 ideal selectivity of up to 45.6 with a high C3H6 permeability of 70.3 Barrer, far surpassing the previously reported 6FDA-based polyimide MMMs and polymeric membranes. Membrane performances of three different M-TMCPP MMM were studied and the gas transportation mechanism was evaluated. This work provides a new conceptual approach of using non-porous zero-dimensional complexes with coordinatively unsaturated sites as fillers in mixed matrix membranes, which not only can accomplish olefin/alkane separation with ultrahigh performance, but also indicates its high potential for feasible usage.

Rational Design of Mixed Matrix Membranes Modulated by Trisilver Complex for Efficient Propylene/Propane Separation.

The application of membrane-based separation processes for propylene/propane (C3 H6 /C3 H8 ) is extremely promising and attractive as it is poised to reduce the high operation cost of the established low temperature distillation process, but major challenges remain in achieving high gas selectivity/permeability and long-term membrane stability. Herein, a C3 H6 facilitated transport membrane using trisilver pyrazolate (Ag3 pz3 ) as a carrier filler is reported, which is uniformly dispersed in a polymer of intrinsic microporosity (PIM-1) matrix at the molecular level (≈15nm), verified by several analytical techniques, including 3D-reconstructedfocused ion beam scanning electron microscropy (FIB-SEM) tomography. The π-acidic Ag3 pz3 combines preferentially with π-basic C3 H6 , which is confirmed by density functional theory calculations showing that the silver ions in Ag3 pz3 form a reversible π complex with C3 H6 , endowing the membranes with superior C3 H6 affinity. The resulting membranes exhibit superior stability, C3 H6 /C3 H8 selectivity as high as ≈200 and excellent C3 H6 permeability of 306 Barrer, surpassing the upper bound selectivity/permeability performance line of polymeric membranes. This work provides a conceptually new approach of using coordinatively unsaturated 0D complexes as fillers in mixed matrix membranes, which can accomplish olefin/alkane separation with high performance.

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.

Preparation of Mixed Matrix Membranes Containing COF Materials for CO&lt;sub&gt;2 &lt;/sub&gt;Removal from Natural Gas/Review

Gas separation membranes are one of the most important processes in purifying natural gas. CO2 reduction of natural gas is essential for purifying the gas and increasing its calorific value. A covalent organic framework (COF) has been developed as a filler in mixed-matrix membranes (MMM) to separate gases. COF materials were chosen because of their economical rate, good thermal and chemical stability, and flexible microporous structure. Mixed matrix membranes (MMMs) have received significant interest for their improved permeability and selectivity in natural gas purification. The results of using COF combined with other chemicals added to MMM. It has been observed that CO2 permeability increases as the COF content in the MMM increases, which enhances the gas-separation performance of the MMM. This review evaluated and analyzed the current scientific and the technical breakthroughs in developing MMMs, especially the unique type of organic fillers, which has been the basis of numerous new research for CO2 separation.

Nanoengineered ZIF fillers for mixed matrix membranes with enhanced CO2/CH4 selectivity

Zeolitic-imidazolate frameworks (ZIFs) are considered as promising nanoporous solids for the development of membranes with exceptional gas separation properties. In this work, we show how molecular-scale modifications can lead to ZIF variants, which can greatly enhance the CO2/CH4 separation performance of mixed-matrix membranes (MMMs) when used as additives. First the permeabilities of CO2 and CH4 in ZIF-8 are estimated with the help of molecular simulations. Based on these results and a macroscopic model, the performance of MMMs with ZIF-8 as fillers is deduced. The validity of this approach is confirmed through experiments by developing flat-sheet ZIF-8 based nanocomposite membranes with two typical polymers (rubbery Pebax® MH1657 and glassy 6FDA-DAM) having different permeability properties. In a subsequent step, we design computationally new ZIF crystals, by changing the original metal, organic linker and functional group of ZIF-8, and the CO2/CH4 separation performance of MMMs with the new ZIF variants is predicted. Our results reveal that some of these MMMs exhibit an unprecedented CO2/CH4 separation performance, which surpasses any reported MMM and is directly attributed to the enhanced sieving capacity of the modified ZIF fillers. In conclusion, this work highlights the effectiveness of ZIF nanoengineering as a means to develop highly selective CO2 membranes.

Front Cover: CO2 Separation by Imide/Imine Organic Cages (Chem. Eur. J. 49/2022)

CO2 capture and clean energy production technologies are stirring increasing interest due to the visible effects of global warming on our planet. In the background is a picture of a small lake in Lombardy, Italy, as it appeared in 2018. Novel imide/imine cages have shown promising results in the selective separation of CO2 from N2 and CH4 under vacuum swing adsorption conditions. The cages have also been successfully tested as fillers in mixed-matrix membranes. More information can be found in the Research Article by J. C. Jansen, M. Carta, V. Amendola et al. (DOI: 10.1002/chem.202201631).

CO2 Separation by Imide/Imine Organic Cages.

Invited for the cover of this issue are the groups of Valeria Amendola at the University of Pavia, Mariolino Carta at the University of Swansea, and Johannes C. Jansen at the CNR-ITM. The image depicts one of the novel imide/imine organic cages that were employed as fillers in mixed-matrix membranes for the selective separation of CO2 from N2 and CH4 . Read the full text of the article at 10.1002/chem.202201631.

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.

Cr-based MOF/IL composites as fillers in mixed matrix membranes for CO2 separation

New composite materials made of bromide-based ionic liquids (ILs) and metal–organic framework (MOF) MIL-101(Cr) were produced using two different ILs. The powdered composites [PMIM][Br]@MIL-101(Cr) and [BMIM][Br]@MIL-101(Cr) were rigorously characterized, and it was confirmed that both ILs were incorporated into the MOF structure. Single-component CO2 and N2 adsorption–desorption isotherms for the pristine MIL-101(Cr) and [BMIM][Br]@MIL-101(Cr), at 303 K and up to 10 bar, showed that the composite has lower gas adsorption capacity and selectivity when compared with the pristine MOF due to the IL incorporation. Mixed Matrix membranes (MMMs) were prepared by the solvent evaporation method, using Matrimid®5218 as the polymeric matrix, and MIL-101(Cr) and [email protected](Cr) composites as fillers with different loadings (10, 20 and 30 wt%). All prepared membranes were dense, except for the Matrimid®5218/[PMIM][Br]@MIL-101(Cr) ones, and their mechanical properties were improved by the presence of the IL in the composite fillers. Single-gas permeation experiments with CO2 and N2 were performed at 303 K for the Matrimid®5218/MIL-101(Cr) and Matrimid®5218/[BMIM][Br]@MIL-101(Cr) membranes, as the Matrimid®5218/[PMIM][Br]@MIL-101(Cr) showed voids. Independently of the filler percentage, the Matrimid®5218/MIL-101(Cr) membranes showed superior CO2 permeability than the Matrimid®5218/[BMIM][Br]@MIL-101(Cr) ones. In every case, the best CO2/N2 selectivity was achieved with a 20 wt% of filler loading, which indicates the existence of an optimum loading that yields the best membrane separation performance.