Interfacial Engineering of Nanofilm Composite Membranes for Enhanced CO₂ Capture

We wish to highlight a long-neglected issue in nanofilm composite (NFC) membranes for gas separation: selective nanofilms (<100 nm) exhibit markedly different gas separation properties from bulk films (>10 μm) due to nanoconfinement and interfacial interactions with substrates. We synthesize three series of poly(ethylene glycol) (PEG)-based copolymers with excellent intrinsic CO₂/N₂ separation properties. When they are fabricated into NFC membranes with selective layers of 15–95 nm, CO₂ permeability decreases dramatically owing to nanoconfinement and the affinity between the copolymers and dopamine-modified gutter layer, while CO₂/N₂ selectivity remains similar. For example, a copolymer (PEGDA5) synthesized from 95% PEG methyl ether acrylate (PEGMEA) and 5% PEG diacrylate (PEGDA) exhibits CO₂ permeability of 420 Barrer for bulk films but only 120 Barrer for a 95 nm layer. Nevertheless, the membrane exhibits CO₂ permeance of 1570 GPU and CO₂/N₂ selectivity of 52 at 25 °C, comparable to state-of-the-art membranes and surpassing Robeson’s upper bound. The nanoscale behaviors elucidated in this study should be useful for designing NFC membranes for important gas separations.