The field of metal–organic framework based mixed matrix membranes (M4s) is critically reviewed, with special emphasis on their application in CO2 capture during energy generation. After introducing the most relevant parameters affecting membrane performance, we define targets in terms of selectivity and productivity based on existing literature on process design for pre- and post-combustion CO2 capture. Subsequently, the state of the art in M4s is reviewed against these targets. Because final application of these membranes will only be possible if thin separation layers can be produced, the latest advances in the manufacture of M4 hollow fibers are discussed. Finally, the recent efforts in understanding the separation performance of these complex composite materials and future research directions are outlined.

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Metal–organic framework based mixed matrix membranes: a solution for highly efficient CO2 capture?

The latest developments in zeolite membranes are reviewed, with an emphasis on the synthesis techniques, including seed assembly and secondary growth methods. This review also discusses the current industrial applications of zeolite membranes, the feasibility of their use in membrane reactors and their hydrothermal stability. Finally, zeolite membranes are compared with metal–organic framework (MOF) membranes and the latest advancements in MOF and mixed matrix membranes are highlighted.

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Zeolite membranes – a review and comparison with MOFs

The separation and purification of light hydrocarbons (LHs) mixtures is one of the most significantly important but energy demanding processes in the petrochemical industry. As an alternative technology to energy intensive traditional separation methods, such as distillation, absorption, extraction, etc., adsorptive separation using selective solid adsorbents could potentially not only lower energy cost but also offer higher efficiency. The need to develop solid materials for the efficiently selective adsorption of LHs molecules, under mild conditions, is therefore of paramount importance and urgency. Metal-organic frameworks (MOFs), emerging as a relatively new class of porous organic-inorganic hybrid materials, have shown promise for addressing this challenging task due to their unparalleled features. Herein, recent advances of using MOFs as separating agents for the separation and purification of LHs, including the purification of CH4 , and the separations of alkynes/alkenes, alkanes/alkenes, C5 -C6 -C7 normal/isoalkanes, and C8 alkylaromatics, are summarized. The relationships among the structural and compositional features of the newly synthesized MOF materials and their separation properties and mechanisms are highlighted. Finally, the existing challenges and possible research directions related to the further exploration of porous MOFs in this very active field are also discussed.

Metal–Organic Framework Materials for the Separation and Purification of Light Hydrocarbons

A three-dimensional water-stable cationic metal-organic framework (MOF) pillared by a neutral ligand and with Ni(II)  metal nodes has been synthesized employing a rational design approach. Owing to the ordered arrangement of the uncoordinated tetrahedral sulfate (SO4 (2-) ) ions in the channels, the compound has been employed for aqueous-phase ion-exchange applications. The compound exhibits rapid and colorimetric aqueous-phase capture of environmentally toxic oxoanions (with similar geometries) in a selective manner. This system is the first example of a MOF-based system which absorbs both dichromate (Cr2 O7 (2-) ) and permanganate (MnO4 (-) ) ions, with the latter acting as a model for the radioactive contaminant pertechnetate (TcO4 (-) ).

A Water-Stable Cationic Metal-Organic Framework as a Dual Adsorbent of Oxoanion Pollutants.

Metal-organic framework-based heterogeneous catalysts for the conversion of C1 chemistry: CO, CO2 and CH4

A new class of metal-organic frameworks (MOFs) has been synthesized by ligand-functionalization strategy. Systematic studies of their adsorption properties were performed at low and high pressure. Importantly, when fluorine was introduced into the framework via the functionalization, both the framework stabilities and adsorption capacities towards H2/CO2 were enhanced significantly. This consequence can be well interpreted by theoretical studies of these MOFs structures. In addition, one of these MOFs TKL-107 was used to fabricate mixed matrix membranes, which exhibit great potential for the application of CO2 separation.

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Fluorous Metal-Organic Frameworks with Enhanced Stability and High H2/CO2 Storage Capacities

Organic donor-acceptor systems have attracted much attention due to their various potential applications. However, the rational construction and modulation of highly ordered donor-acceptor systems could be a challenge due to the complicated self-assembly process of donor and acceptor species. Considering the well-defined arrangement of species at the molecule level, a crystalline host-guest system could be an ideal platform for the rational construction of donor-acceptor systems. Herein, it is shown how the rational construction of highly tunable donor-acceptor materials can be achieved based on a crystalline host-guest platform. Within the well-established metal-organic framework NKU-111 as the crystalline host enabled by the relatively stable coordination-directed assembly, the introduction and arrangement of guest molecules in the crystals allow the rational construction of the NKU-111⊃guest donor-acceptor system. The donor-acceptor interaction in the systems can be readily modulated with different guest molecules, which can be justified by the well-demonstrated guest-dependent characteristics. Accordingly, the NKU-111⊃guest reveals highly tunable donor-acceptor properties such as charge-transfer-based emissions and electrical conductivity. This work indicates the potential of crystalline host-guest systems as an ideal platform for systematic investigations of donor-acceptor materials.

Rational Construction of Highly Tunable Donor–Acceptor Materials Based on a Crystalline Host–Guest Platform

Two new zinc MOFs with similar “pillar-layered” framework structures based on 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acid (H4bpta) and two different bipyridine pillar ligands, namely {[Zn4(bpta)2(4-pna)2(H2O)2]·4DMF·3H2O}n (1) and {[Zn2(bpta)(bpy-ea)(H2O)]·2DMF·H2O}n (2) (4-pna = N-(4-pyridyl)isonicotinamide and bpy-ea = 1,2-bis(4-pyridyl)ethane), have been synthesized and investigated with their CO2 adsorption properties. By analysis of the structure properties and the CO2 adsorption performances of these two MOFs, it was found that the introduction of polar acylamide groups via 4-pna resulted in 1 with enhanced CO2 capacity and CO2/CH4 selectivity at low pressure. In contrast, the framework of 2 shows flexible properties originating from the flexibility of the ethanediylidene group in the bpy-ea ligand, which benefits the sieve effect of pores to give higher CO2/CH4 selectivity at a relatively high pressure range.

Targeted Structure Modulation of “Pillar-Layered” Metal–Organic Frameworks for CO2 Capture

A novel “cage-in-cage” metal–organic framework based on nested cages originated from two-fold interpenetrated networks was reported, which indicates the potential of interpenetration in structure modulation of cage-based MOFs.

A unique “cage-in-cage” metal–organic framework based on nested cages from interpenetrated networks

The invention discloses a cadmium coordination polymer. The chemical formula of the cadmium coordination polymer is C60H36Cd3N12O17, 2,4,6-three(4-pyridyl) triazine serves as the main ligand of the cadmium coordination polymer, terephthalic acid serves as the auxiliary ligand of the cadmium coordination polymer, mixed liquor of N, N-dimethylformamide, ethyl alcohol and water serves as the solution, and accordingly a triple-interpenetrating three-dimensional 'tfz' topology network structure with an inner sealed hole is formed. The cadmium coordination polymer is prepared through the solvothermal method. The cadmium coordination polymer has the advantages that the coordination frame is high in thermal stability and water stability, and the light emitting performance of the cadmium coordination polymer can be controlled by packaging guest molecules with different functions. The manufacturing method of the cadmium coordination polymer has the advantages that the technology is simple in process and easy to apply, the crystal yield and purity are high, and the cadmium coordination polymer has good application prospect in the field of material science as an energy converter and a solid light-emitting material.

Zhi-Hong Xuan

Papers

Fluorous Metal-Organic Frameworks with Enhanced Stability and High H2/CO2 Storage Capacities

Rational Construction of Highly Tunable Donor–Acceptor Materials Based on a Crystalline Host–Guest Platform

Targeted Structure Modulation of “Pillar-Layered” Metal–Organic Frameworks for CO2 Capture

A unique “cage-in-cage” metal–organic framework based on nested cages from interpenetrated networks

Cadmium coordination polymer and preparation method and application thereof