Molecularly integrated polymer–MOF interfaces enable directional gas transport in oriented nanosheet mixed-matrix membranes

Constructing mixed-matrix membranes (MMMs) in which porous fillers effectively contribute to gas transport remains challenging, especially in highly permeable polymer matrices where gas diffusion is often dominated by the polymer phase or non-selective interface. Here we show interfacially integrated oriented MMMs based on homologous microporous polymer-grafted ZIF-8 nanosheets for CO 2 /CH 4 separation. Acyl chloride-functionalized PIM-1 was covalently grafted onto amino-functionalized ultrathin ZIF-8 nanosheets. This interlayer improves the compatibility between ZIF-8 nanosheets and the PIM-1 matrix while preserving the accessible nanopores of ZIF-8, enabling uniform nanosheet dispersion and preferential in-plane alignment during membrane fabrication. Structural characterizations and molecular simulations reveal an integrated filler–interlayer–matrix structure involving covalent bonding and polymer-chain inter-penetration, which suppresses non-selective gas transport and allows the oriented ZIF-8 nanosheets to contribute more effectively to diffusion-based molecular sieving. The optimized membrane with 40 wt% grafted nanosheets exhibits a CO 2 permeability of 5890 Barrer and CO 2 /CH 4 selectivity of 26.8 under mixed-gas conditions. Furthermore, the interpenetrated PIM interface improves aging resistance, allowing the membrane to retain 79.7% of its initial CO 2 permeability after 120 days. This work offers a practical interfacial engineering strategy for constructing high-loading oriented MOF nanosheet MMMs with enhanced selectivity and long-term stability.