Research into extended porous materials such as metal-organic frameworks (MOFs) and porous organic frameworks (POFs), as well as the analogous metal-organic polyhedra (MOPs) and porous organic cages (POCs), has blossomed over the last decade. Given their chemical and structural variability and notable porosity, MOFs have been proposed as adsorbents for industrial gas separations and also as promising filler components for high-performance mixed-matrix membranes (MMMs). Research in this area has focused on enhancing the chemical compatibility of the MOF and polymer phases by judiciously functionalizing the organic linkers of the MOF, modifying the MOF surface chemistry, and, more recently, exploring how particle size, morphology, and distribution enhance separation performance. Other filler materials, including POFs, MOPs, and POCs, are also being explored as additives for MMMs and have shown remarkable anti-aging performance and excellent chemical compatibility with commercially available polymers. This Review briefly outlines the state-of-the-art in MOF-MMM fabrication, and the more recent use of POFs and molecular additives.

Metal–organic frameworks (MOFs), as porous fillers possessing molecular sieving properties, have been combined with polymers to give mixed-matrix membranes (MMMs) with enhanced separation performance. This field of research has produced a large number of different membranes, and many MOF/polymer combinations have been tested and reported to show potential application to industrial gas separation. Although MOFs have been proposed as novel additives with high porosity and tunable pore size, which were supposed to outperform other porous fillers, due to restrictions in separation performance of the filler and challenges concerning the compatibility of polymer and MOF, only a small fraction of these works report both improved permeability and selectivity. In this review these challenges are set into the context of MOF synthesis and membrane fabrication by the choice of appropriate polymer/MOF combinations, utilization of the MOF functional sites, modification of the MOF surface chemistry or pore texture and size, and also targeted influence of the size and shape of the filler particles. The effect of the highlighted MOF additives on the gas separation performance is analyzed and discussed by comparison of the gas permeability and selectivity. This emphasizes strategies by which high performing MMMs can be achieved through accessing the full potential of the porous MOF fillers.

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Die Forschung zu ausgedehnten porösen Materialien wie Metall‐organischen und porösen organischen Gerüstverbindungen (MOFs und POFs) sowie den analogen Metall‐organischen Polyedern (MOPs) und porösen organischen Käfigen (POCs) hat sich im letzten Jahrzehnt stark entwickelt. Mit ihrer chemischen und strukturellen Vielfalt und bemerkenswerten Porosität wurden MOFs als neue Adsorbentien für industrielle Gastrennungen und als vielversprechende Füllstoffkomponenten für leistungsstarke gemischt(Mixed)‐Matrix‐Membranen (MMMs) vorgeschlagen. Die Forschung in diesem Bereich konzentrierte sich auf die Verbesserung der chemischen Kompatibilität der MOFs mit der Polymerphase durch sinnvolle Funktionalisierung der organischen MOF‐Linker, auf die Modifizierung der MOF‐Oberflächenchemie und in jüngster Zeit auf Untersuchungen, wie Partikelgröße, ‐morphologie und ‐verteilung die Trennleistung erhöhen. Andere Füllstoffmaterialien, wie POFs, MOPs und POCs, werden ebenfalls als Additive für MMMs untersucht und zeigen eine bemerkenswerte Wirkung gegen Polymeralterung und ausgezeichnete chemische Kompatibilität mit handelsüblichen Polymeren. Dieser Aufsatz gibt einen Überblick zum Stand der Technik im MOF‐MMM‐Aufbau und zu aktuellen Anwendungen von porösen organischen Gerüsten und molekularen Additiven für MMMs.

The synthesis of the isostructural MOF-5 analogue 3D-[Co4(μ4-O)­(Me2pzba)3] with the bi- or mixed-functional pyrazolate-carboxylate linker was improved by the use of microwave heating instead of previously described conventional thermal heating, giving a higher yield at drastically shorter reaction time with nearly doubled BET surface area, smaller size, and less aggregation. The significantly increased air/moisture stability of [Co4(μ4-O)­(Me2pzba)3] compared to MOF-5 made the Co-MOF amenable for the preparation of moisture-tolerant [Co4(μ4-O)­(Me2pzba)3]/Matrimid mixed-matrix membranes (MMMs) without the use of inert conditions. Uniformly embedding of the small metal–organic framework (MOF) particles was achieved in the polymer, without aggregation and with good MOF–polymer compatibility. [Co4(μ4-O)­(Me2pzba)3]/Matrimid MMMs exhibited an improved CO2/CH4 separation performance over neat Matrimid membranes with an increase in mixed-gas selectivity from 41 for Matrimid to 60 for the 24 wt % MMM at 3 bar transmembrane pressure, which is also higher than reported for moisture-sensitive MOF-5/Matrimid MMMs (maximal S = 45).