Angstrom‐Scale Defect‐Free Crystalline Membrane for Sieving Small Organic Molecules

Crystalline membranes, represented by the metal-organic framework (MOF) with well-defined angstrom-sized apertures, have shown great potential for molecular separation. Nevertheless, it remains a challenge to separate small molecules with very similar molecular size differences due to angstrom-scale defects during membrane formation. Herein, a stepwise assembling strategy is reported for constructing MOF membranes with intrinsic angstrom-sized lattice aperture lattice to separate organic azeotropic mixtures separation. The membrane is synthesized by redesigning the metal source, which reduces the coordination reaction rate to avoid cluster-missing defects. Then, extra ligands are introduced to overcome the coordination steric hindrance to heal the linker-missing defects. Ultralow-dose transmission electron microscopy is used to realize a direct observation of the angstrom-scale defects. For separating the challenging methanol-containing ester or ether azeotropic mixtures with molecular size difference as small as <1 Å, the angstrom-scale defect-free MOF membrane exhibits an outstanding flux of ≈3700 g·m^-2h^-1 and separation factor of ≈247-524, far beyond the upper-bound of state-of-the-arts membranes. This study offers a feasible strategy for precisely constructing angstrom-confined spaces for diverse applications (e.g., separation, catalysis, and storage).