(185b) Understanding of in-Situ Growth of MOF in a Polymer Thin Film: Polyimide/ZIF-7 Mixed Matrix Membranes with Three Different Crystal Phases for Gas Separations

Polymer-modification-enabled in-situ metal-organic framework formation (PMMOF) is a paradigm-shifting fabrication method of polymer/MOF-based mixed matrix membranes (MMMs). However, a mechanism of in-situ growth of MOF nanoparticles inside polymers by PMMOF have not been unveiled so far. Herein, we carried out systematic investigations on the understanding of in-situ growth of ZIF-7 nanoparticles inside polymer (6FDA-DAM) by PMMOF. The resulting 6FDA-DAM/ZIF-7 MMMs by PMMOF exhibited an excellent adhesion and a uniform dispersion of fine-sized ZIF-7 nanoparticles (63.5 ± 11.7 nm) throughout the 6FDA-DAM matrix. The trace of the absorbed precursor content along PMMOF led to the interpretation of the PMMOF mechanism on the basis of the prepared ZIF-7 crystal phase diagram by varying the precursor concentrations. Estimated reaction conditions and plausible PMMOF mechanism enabled control over ZIF-7 crystal phase, yielding 6FDA-DAM/ZIF-7 MMMs with three different crystal phases: large pore ZIF-7, layered ZIF-7, and mixed phased ZIF-7. The resulting PMMOF ZIF-7 MMMs showed superior H₂/CO₂ separation performance compared with MMMs prepared by conventional blending methods. The understanding of the mechanism of in-situ growth of MOF crystals in a polymer by PMMOF highlights one formidable strategy in designing the future scale-up process and to enlarge PMMOF applying to various combinations of polymers and MOFs for MMMs.