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

Abstract Although proven to be promising for CO 2 capture from flue gas, maintaining superior separation efficiency of CO 2 ‐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 CO 2 from N 2 but also serves as reactive‐carriers toward CO 2 ‐facilitated diffusion. Relying on facilitated diffusion mechanism, the CO 2 /N 2 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 CO 2 /N 2 separation performance over a wide humidity range due to its intrinsic hydrophobicity, showing great promise in practical flue gas separation.