Electrophoretic Nuclei Assembly for Crystallization of High‐Performance Membranes on Unmodified Supports

Metal–organic framework (MOF) films have recently emerged as highly permselective membranes yielding orders of magnitude higher gas permeance than that from the conventional membranes. However, synthesis of highly intergrown, ultrathin MOF films on porous supports without complex support-modification has proven to be a challenge. Moreover, there is an urgent need of a generic crystallization route capable of synthesizing a wide range of MOF structures in an intergrown, thin-film morphology. Herein, a novel electrophoretic nuclei assembly for crystallization of highly intergrown thin-films (ENACT) approach, that allows synthesis of ultrathin, defect-free ZIF-8 on a wide range of unmodified supports (porous polyacrylonitrile, anodized aluminum oxide, metal foil, porous carbon and graphene), is reported. As a result, a remarkably high H2 permeance of 8.3 × 10−6 mol m−2 s−1 Pa−1 and ideal gas selectivities of 7.3, 15.5, 16.2, and 2655 for H2/CO2, H2/N2, H2/CH4, and H2/C3H8, respectively, are achieved from an ultrathin (500 nm thick) ZIF-8 membrane. A high C3H6 permeance of 9.9 × 10−8 mol m−2 s−1 Pa−1 and an attractive C3H6/C3H8 selectivity of 31.6 are obtained. The ENACT approach is straightforward, reproducible and can be extended to a wide range of nanoporous crystals, and its application in the fabrication of intergrown ZIF-7 films is demonstrated.