Scalable affinity-driven nanofilm nanocomposite membranes for CO₂/N₂ separation

Mixed-matrix materials (MMMs) that combine the excellent processability of polymers with the superior molecular separation capabilities of metal-organic frameworks (MOFs) have demonstrated excellent gas separation performance in freestanding films (>10 μm). However, fabricating them into defect-free nanofilm nanocomposite (NFN) membranes on a large scale remains challenging due to interfacial incompatibility between polymers and MOF nanoparticles (NPs). Herein, we have successfully developed NFN membranes via roll-to-roll coating with MMMs (70 - 200 nm) comprising amorphous poly(ethylene oxide) ( a PEO), polyethylene glycol dimethyl ether (PEGDME, 240 Da), and UiO-66-NH₂ NPs (45-85 nm), enabled by the strong hydrogen bonds between the two matrices and between the nanofilms and dopamine-modified substrates, as well as the rubbery nature of a PEO and PEGMEA. Interestingly, nanoconfinement significantly reduces intrinsic gas permeability in the selective nanofilms, and adding UiO-66-NH₂ NPs disproportionately enhances gas permeance. For example, adding 40 mass% PEGDME to a PEO enhances CO₂ permeance from 630 to 1090 GPU and slightly decreases CO₂/N₂ selectivity from 53 to 46; incorporating 10 mass% UiO-66-NH₂ further increases CO₂ permeance to 3700 GPU and CO₂/N₂ selectivity to 57, surpassing Robeson's upper bound and state-of-the-art membranes. This affinity-driven approach to designing high-performance NFN membranes is versatile and well-suited for developing next-generation membranes for practical separations.