Locking Metal–Organic Framework Linkers to Mesoporous Nanosheets via π–π Conjugation for Gas Separation

Metal–organic framework (MOF) membranes show great potential for efficient molecular separation. However, the framework flexibility from linker rotation causes the fluctuation of windows and changes in sieving properties. In this study, we report locking the linkers of zeolitic imidazolate framework (ZIF) membranes to mesoporous graphene oxide nanosheets by strong π–π conjugation for stiffening transport pathways and boosting gas-sieving performance. Comprehensive experiments, characterizations, and density functional theory simulations demonstrate that the π–π interaction exists between the linker rings of ZIFs and the aromatic rings of nanosheets, thereby suppressing linker rotation and inducing window shrinkage. Moreover, because nanosheets offer nucleation sites and nanoconfined growth regions, the ultrathin membranes with different ZIF types can be deposited on both flat and hollow fiber polymeric substrates in scalability. Since π–π stacking inhibits linker rotation and narrows windows, preferential crystallization repairs non-selective voids, and in-plane porosity of nanosheets facilitates mass transfer processes, the linker-locked membranes with a thickness of 50 nm exhibit H2/CO2 selectivity up to 43.7 and H2 permeance of 3120 gas permeation units, exceeding most MOF–polymer membranes. These generally applicable concepts provide effective routes to adjust the pore structure and framework flexibility of MOFs and to design high-performance ultrathin membranes for molecular separations.