(502j) 6FDA-DAM/ZIF-7 Mixed-Matrix Membranes: Exploring in-Situ Formation of ZIF-7 Phases in Confined Polymer and Their Gas Separation Performances

Recently our group has reported polymer-modification-enabled in-situ metal-organic framework formation (PMMOF) for scalable fabrication of polymer/MOF mixed-matrix membranes (MMMs). The PMMOF can be potentially a paradigm-shifting preparation method by enabling in-situ formation of ZIF fillers in modified polymer matrices, leading to fabrication of asymmetric membranes with submicron-thick selective filler containing skin layers. In order to improve MMM formation by the PMMOF, it is of critical importance to elucidate the actual reaction conditions for in-situ formation of MOFs in confined polymer free volumes, which are expected to be different from those in a bulk solution. ZIF-7 that enables to transform into three different crystal phases (large-pore ZIF-7, layered ZIF-7, and mixed-phased ZIF-7) was a suitable material to explore actual reaction conditions of PMMOF with their high selectivity for light gas separations. In this presentation, we plan to present our efforts to understand in-situ confined formation of ZIF-7 phases inside polymer (6FDA-DAM) by PMMOF. The reaction conditions of ZIF-7 in the polymer free volume were deduced based on a bulk-phase ZIF-7 phase diagram constructed by varying ZIF-7 precursor concentrations and ratios. Based on the understanding of reaction conditions, ZIF-7 crystal phases formed inside polymer during the PMMOF process were controlled, yielding 6FDA-DAM/ZIF-7 MMMs with three different crystal phases. ZIF-7 phases had significant effects on the gas transport of MMMs with layered ZIF-7 fillers exhibiting the highest performance enhancement for H₂/CO₂ separation. Furthermore, the MMMs by the PMMOF showed superior H₂/CO₂ separation performance compared with other MMMs prepared by conventional blending methods.