In-situ formation of asymmetric thin-film, mixed-matrix membranes with ZIF-8 in dual-functional imidazole-based comb copolymer for high-performance CO₂ capture

Despite numerous studies on free-standing, mixed-matrix membranes (MMMs), the development of thin-film MMMs with high permeance is still an ongoing challenge. Here, the successful fabrication of ultra-high-permeance thin-film MMMs on a porous polymer substrate is described based on a highly porous zeolitic imidazole framework (ZIF-8) and a dual-functional imidazole-based comb copolymer. The copolymer of poly(vinyl imidazole)-poly(oxyethylene methacrylate) (PVI-POEM) is synthesized via free-radical polymerization, and it exhibits CO₂-philicity, strong adhesion, and good interactions with fillers. In contrast to commercial benchmark membranes such as Pebax, the use of the PVI-POEM comb copolymer results in significant improvement in the CO₂ permeance without significant loss of selectivity even at high ZIF-8 loadings and low thickness. It is attributed to the in-situ formation of inverse, asymmetric morphology of MMMs and partial infiltration of PVI-POEM chains into ZIF-8 particles. Optimization of the preparation process, such as ZIF-8 loading, substrate type, and coating layer thickness, leads to an extremely high CO₂ permeance of 4474 GPU with high CO₂/N₂ and CO₂/CH₄ ideal selectivities of 32.0 and 12.4, respectively, which is far beyond the current trade-off limit for membranes. The mechanism behind the exceptionally high CO₂ separation performance is delineated by exploring molecular dynamic simulation through morphology, structural, and energetic analyses.