Abstract
Metal-organic frameworks (MOFs) are promising materials for gas separation membranes. However, the framework flexibility affects their molecular-sieving properties. Herein, we restrict the flexibility of zeolitic imidazolate framework-7 (ZIF-7) by controlling its phase transition in mixed-matrix membranes (MMMs), relying on the so-called "space-confinement effect" of a novel thermosetting polymer, poly 2,2'-(p-oxydiphenyl)-5,5'-bibenzimidazole (OPBI) polymer. Compared with the pure OPBI membrane, the optimized membranes containing 30 wt % ZIF-7 with a narrow-pore (np) phase (ZIF-7-II) exhibited a significant improvement in H2/CO2 separation, e.g., the H2/CO2 ideal selectivity increased ∼2.8 times, surpassing the state-of-the-art upper bound of polymeric membranes and exhibited excellent stability at increased pressure and temperature (8 bar, 180 °C).
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