Amino Acid‐Decorated MOF Membranes Toward Facilitated CO₂ Separation Under Varying Humidities

Abstract Although proven to be promising for CO₂ capture from flue gas, maintaining superior separation efficiency of CO₂‐philic membranes under widely differing humidities remains highly challenging to date. Targeting high‐efficiency and humidity‐resistant flue gas separation, in this study, a multi‐scale structure optimization protocol is pioneered to fabricate highly (200)‐oriented 55 nm‐thick MIL‐140A membrane. On one hand, employing ʟ‐histidine as modulator retards crystallization kinetics and inhibits multilamellar‐stacking crystal growth, warranting formation of MIL‐140A nanosheets and ultrathin oriented membrane; on the other hand, bulky ʟ‐histidine segments coordinates in MIL‐140A framework not only induced distorted pore configuration toward precise discrimination of CO₂ from N₂ but also serves as reactive‐carriers toward CO₂‐facilitated diffusion. Relying on facilitated diffusion mechanism, the CO₂/N₂ selectivity of obtained MIL‐140A membrane reached 79.0 under high‐humid environments, which is 32.1% higher than that in dry environments; moreover, the membrane exhibited stable CO₂/N₂ separation performance over a wide humidity range due to its intrinsic hydrophobicity, showing great promise in practical flue gas separation.