Current Status of Metal-Organic Framework Membranes for Gas Separations: Promises and Challenges

Metal-organic frameworks (MOFs) are hybrid organic-inorganic nanoporous materials that exhibit regular crystalline lattices with relatively well-defined pore structures. Chemical functionalization of the organic linkers in the structures of MOFs affords facile control over pore size and chemical/physical properties, making MOFs attractive for a variety of industrial applications including membrane-based gas separations. A wealth of reports exists discussing the synthesis and applications of MOFs; however, relatively few reports exist discussing MOF membranes. This disparity owes to challenges associated with fabricating films of MOF materials, including poor substrate-film interactions, moisture sensitivity, and thermal/mechanical instability. Since even nanometer-scale cracks and defects can affect the performance of a membrane for gas separation, these challenges are particularly acute for the fabrication of MOF membranes. Here, we review recent progress on MOF membranes with an emphasis on their fabrication techniques, challenges involved in membrane synthesis, reported strategies to address these challenges (issues), and gas separation performance. Finally, we conclude with our perspectives on future research directions in this area.