Precursor-chemistry engineering toward ultrapermeable carbon molecular sieve membrane for CO2 capture

Carbon capture is an important strategy and is implemented to achieve the goals of CO₂ reduction and carbon neutrality. As a high energy-efficient technology, membrane-based separation plays a crucial role in CO₂ capture. It is urgently needed for membrane-based CO₂ capture to develop the high-performance membrane materials with high permeability, selectivity, and stability. Herein, ultrapermeable carbon molecular sieve (CMS) membranes are fabricated by pyrolyzing a finely-engineered benzoxazole-containing copolyimide precursor for efficient CO₂ capture. The microstructure of CMS membrane has been optimized by initially engineering the precursor-chemistry and subsequently tuning the pyrolysis process. Deep insights into the structure-property relationship of CMSs are provided in detail by a combination of experimental characterization and molecular simulations. We demonstrate that the intrinsically high free volume environment of the precursor, coupled with the steric hindrance of thermostable contorted fragments, promotes the formation of loosely packed and ultramicroporous carbon structures within the resultant CMS membrane, thereby enabling efficient CO₂ discrimination via size sieving and affinity. The membrane achieves an ultrahigh CO₂ permeability, good selectivity, and excellent stability. After one month of long-term operation, the CO₂ permeability in the mixed gas is maintained at 11,800 Barrer, with a CO₂/N₂ selectivity exceeding 60. This study provides insights into the relationship between precursor-chemistry and CMS performance, and our ultrapermeable CMS membrane, which is scalable using thin film manufacturing, holds great potential for industrial CO₂ capture.