Ammonia-mediated fabrication for ZIF-8 membranes: modulation, characterization and H2/CO2 separation performance

A continuous and dense ZIF-8 membrane was successfully synthesized on α-Al 2 O 3 supports via a combined approach of ammonia modulation and solvothermal synthesis. A unique synergistic promoting effect between ammonia solution and ZnO nanoarrays was identified through comparative investigation of ammonia and ethylenediamine as alkaline additives. The as-prepared membranes were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), and scanning electron microscopy (SEM). Experimental results demonstrated that ammonia facilitates rapid conversion of the ZnO interlayer, shortens crystallization time, and mitigates intracrystalline defects, while an appropriate increase in 2-methylimidazole (2-MIM) concentration enhances ZIF-8 crystal growth and crystallization—collectively ensuring membrane continuity and denseness. Gas separation performance tests indicated that when the 2-MIM concentration was 0.05 mol·L −1 with ammonia addition, the ZIF-8 membrane exhibited a substantially high H 2 /CO 2 selectivity of 15.04, exceeding the corresponding Knudsen diffusion selectivity. This study effectively enhances the structural integrity and separation performance of ZIF-8 membranes.