Metal−organic framework composite membranes: Synthesis and separation applications

Metal−organic framework (MOF) materials, which are built of metal ions or metal ion clusters bridged organic linkers, possess the well-defined pore structures, large surface area and extraordinary adsorption affinities. In recent years, MOF-based membranes have attracted large attention in separation applications due to their excellent performance. In respect to practical applications, the substrates and construction will greatly influence the industrial promotion and separation performance of the MOF-based membranes. Inorganic materials are the earliest substrates for continuous MOF membranes. Both the bare and modified substrates can be used for supporting the MOF membranes by changing the synthesis preparation process, such as solvothermal synthesis, interfacial synthesis and liquid phase epitaxy approach. In order to reduce the cost and enhance the processability of the MOF membrane, the polymer substrates can also be employed to obtain the continuous MOF membranes. Moreover, the hollow fiber substrates can provide the large membrane areas per volume. Since there is good compatibility between the MOFs and polymers, MOFs can also be employed as fillers to fabricate mixed matrix membranes. Those MOF-based membranes exhibit good performance in gas separation, pervaporation and nanofiltration. Therefore, this review gives an overview of the continuous MOF membranes supported by inorganic substrates and polymer substrates and the MOF-based mixed matrix membranes.