Ultra-Tuning of the Aperture Size in Stiffened ZIF-8_Cm Frameworks with Mixed-Linker Strategy for Enhanced CO2 /CH4 Separation

Abstract

ZIF-8 membrane has the potential for CO₂ /CH₄ separation based on size exclusion. But if traditionally prepared by solvothermal methods, it shows only negligible selectivity due to the linker mobility. Here, ≈500 nm-thin hybrid ZIF-7_x -8 membranes with suppressed linker mobility and narrowed window aperture are prepared by a fast current-driven synthesis (FCDS) within 20 min. The in situ electric field during FCDS allows the formation of stiffened ZIF-8_Cm as parent skeleton and the mixed-linker strategy is applied to narrow the aperture size simultaneously. The ZIF-7₂₂ -8 membrane shows significantly sharpened molecular sieving for CO₂ /CH₄ with a separation factor above 25, which soared tenfold compared with other unmodified ZIF-8 membranes. Additionally, the membrane shows exceptional separation performance for H₂ /CH₄ and CO₂ /N₂ , with separation factors of 71 and 20, respectively. After 180 h temperature swing operation, it still maintains the excellent separation performance.

Keywords: MOF membrane; fast current-driven synthesis; gas separation; mixed-linker; zeolitic imidazolate framework.