NIPS-triggered in situ crystallization of ZIF-8/PES composite membranes for H2/CO2 separation

Gas separation using metal organic framework (MOF) membranes has attracted considerable attention in recent years. Despite the progress made, establishing thin, defect-free MOF layers within the porous polymer remains a significant challenge. In this study, a novel approach is reported for the preparation of ZIF-8/Polyethersulfone (ZIF-8/PES) composite membranes via non-solvent-induced phase separation (NIPS)-triggered in-situ crystallization strategy. In this method, PES serves as a solid solvent for Zn(NO 3 ) 2 . During the NIPS process, an asymmetric PES membrane with a skin layer, finger-like pores, and interconnected foam structures is formed. Concurrently, Zn(NO 3 ) 2 diffuses to the skin layer and reacts with 2-methylimidazole (2-MIM), yielding a dense ZIF-8 layer on the PES surface. The simultaneous nucleation and growth of ZIF-8 within the polymer create strong interfacial interactions at the organic-inorganic interface. These interactions improve the compatibility between ZIF-8 and the polymer matrix, reduce interfacial defects. As a result, the composite membrane exhibits enhanced mechanical stability. When the crystallization time is extended to 48 h, the thickness of the ZIF-8 layer reaches approximately 540 nm, and the membrane exhibits an H 2 /CO 2 selectivity of 72.3 ± 3.35 at 298 K. This study provides a facile and effective route for constructing thin MOF membranes on polymeric matrix for high-performance gas separation.