High-performance composite membranes incorporated with carboxylic acid nanogels for CO₂ separation

Composite membranes were fabricated by incorporating carboxylic acid nanogels (CANs) into a Pebax MH 1657 matrix for potential applications in CO₂/CH₄ (or N₂) separation. CANs were synthesized by precipitation polymerization of N-isopropylacrylamide (NIPAM), acrylic acid (AA) monomer and N,N'-methylenebisacrylamide (BIS) crosslinker. The incorporation of CANs simultaneously tailored favorable water environment and increased CO₂ transport sites within the membranes. With increasing CANs loading, the homogeneously dispersed CANs in the Pebax matrix offered more favorable water environment and the additional carboxyl group sites for efficient CO₂ transport, thus constructing interconnected preferential CO₂ transport passageways. The Pebax-CANs-30 composite membrane exhibited the highest gas separation performance, with the CO₂/CH₄ and CO₂/N₂ selectivities of 33 and 85 respectively, and a CO₂ permeability of 2026 Barrer (1 Barrer=10^-10cm³ (STP) cm/(cm²scmHg), well surpassing the Robeson's upper bound limit reported in 2008. This effort will give rise to a new option to tailor water environment and increase CO₂ transport sites for fabricating high-performance CO₂ separation membranes.