Mixed matrix membranes incorporating amino-functionalized ZIF-8-NH₂ in a carboxylic polyimide for molecularly selective gas separation

Mixed matrix membranes (MMMs) combine the advantages of polymers and inorganic materials and demonstrate higher gas permeability than polymeric membranes, which, however, face the challenge of incompatible interface ascribed to the intrinsically different nature of the polymer and inorganic phase. To overcome this hurdle, herein, co-polyimide (6FBDA) was designed with carboxylic side groups to enhance the interfacial compatibility with amino-functionalized MOF(ZIF-8-NH2) via intensive pi-pi stacking and hydrogen bonds. The imidazole units in 6FBDA resemble ZIF-8-NH2 ligands and promote pi-pi stacking of polymer and MOF while the carboxylic moieties establish hydrogen bonds with the amino ligands of ZIF-8-NH2, significantly improving the interfacial compatibility of polymer and MOF. The defect-free MMMs with 50 wt% MOF loading demonstrate a CO2 and H-2 permeability of 80.8 Barrer and 127.5 Barrer, respectively, with a CO2/CH4 and H-2/CH4 selectivity of 89.4 and 141.7, respectively, exceeding 2008 Robeson upper bounds. The experimental concept of this work opens a door for fabricating molecularly selective gas separation membranes with prospects for energy-efficient CO2 capture and hydrogen separations.