Self-supported membranes fabricated by a polymer‒hydrogen bonded network with a rigidified MOF framework

Mixed matrix membranes (MMMs) combine the advantages of porous fillers and polymer membranes, endowing them with potential applications in gas separation. Due to their high porosity and defined pore sizes, metal‒organic frameworks (MOFs) have been extensively investigated as MMM fillers. However, the frameworks of many MOFs are flexible, which may limit selectivity. Here, hydrogen bonding between polyimide (PI) and flexible MIL-53(Al) with large pore size (M53-L) is utilized to rigidify the framework in a series of PI/M53-L MMMs. The high pore volume and large pore size of rigid M53-L increased the affinity of CO2 with hydroxy groups, leading to higher separation performance than the pure PI membrane. The separation performance of PI/M53-L MMMs exceeds the Robeson 2008 upper bounds for both CO2/N2 and CO2/CH4. We propose a method of utilizing hydrogen bonds to rigidify flexible MOF frameworks to prepare self-supported MMMs, providing a strategy for the application of flexible MOFs in gas separation.