(705f) Tailoring Ultramicropores in Hybrid Carbon Molecular Sieve Membranes to Achieve High H2 Selectivity

Porous carbon materials with tunable pore structures have attracted substantial attention for membrane separation. Particularly, carbon molecular sieve (CMS) membranes with micropores (7 to 20 â„«) that promote gas transport and ultramicropores (7 to 20 â„«) derived from controlled pyrolysis of polymer precursors that confer strong size-sieving ability, have emerged for gas pair separation, including CO₂/CH₄, olefin/paraffin. However, rare CMS membranes have high selectivity for H₂/gas separation due to small molecular size of H₂. Here, we report advanced CMS membranes derived from a supramolecular mixed matrix network (SMMN) with high H₂ selectivity against other gases including CO₂, N₂, CH₄, and C₂H₆. Specifically, ZIF-8/polybenzimidazole (PBI) SMMN containing crystalline ZIF-8 and amorphous Zn/imidazole coordination on PBI chains was prepared via the in-situ ZIF-8 growth in PBI. With porous ZIF-8 promoting gas transport and Zn/imidazole coordination cross-linking PBI chains and then enhancing size-sieving ability, ZIF-8/PBI SMMN displayed both increased H₂ permeability and H₂/CO₂ selectivity. Then, the SMMN was carbonized from 400 to 900 ℃. Compared to PBI/CMS prepared at same temperatures, SMMN/CMS films exhibit both higher H₂ permeability and selectivity, even far surpassing Robeson’s upped bounds 2008. It can be attributed to Particularly, SMMN/CMS carbonized at 900 ℃ exhibited H₂/CO₂ selectivity of 220 at 70 ℃, higher than those of other leading membrane materials. This study opens up a new approach to design advanced CMS materials for H₂ separation and other applications.