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.