Balancing the Crystallinity and Film Formation of Metal–Organic Framework Membranes through In Situ Modulation for Efficient Gas Separation

Polycrystalline metal–organic framework (MOF) layers hold great promise as molecular sieve membranes for efficient gas separation. Nevertheless, the high crystallinity tends to cause inter‐crystalline defects/cracks in the nearby crystals, which makes crystalline porous materials face a great challenge in the fabrication of defect‐free membranes. Herein, for the first time, we demonstrate the balance between crystallinity and film formation of MOF membrane through a facile in situ modulation strategy. Monocarboxylic acid was introduced as a modulator to regulate the crystallinity via competitive complexation and thus concomitantly control the film‐forming state during membrane growth. Through adjusting the ratio of modulator acid/linker acid, an appropriate balance between this structural “trade‐off” was achieved. The resulting MOF membrane with moderate crystallinity and coherent morphology exhibits molecular sieving for H 2 /CO 2 separation with selectivity up to 82.5.