Surfactant-mediated and wet-impregnation approaches for modification of ZIF-8 nanocrystals: Mixed matrix membranes for CO2/CH4 separation

ZIF-8 nanocrystals were synthesized in the presence of cetyltrimethylammonium bromide, as a cationic surfactant, (ZIF-8@CTAB) and then modified by iron promoter (ZIF-8@Fe-CTAB) through a wet impregnation process. Self-assembly of surfactant in the synthesis route changed morphology of ZIF-8 nanocrystals from rhombic dodecahedron (RD) to truncated rhombic dodecahedron (TRD). The structural modifications significantly changed the adsorption properties of the nanocrystals for CO2 and CH4, so that ZIF-8@Fe-CTAB nanocrystals provided the highest CO2/CH4 adsorption selectivity (∼19) compared to values have ever been reported in the literature. The nanocrystals were also employed for preparation of mixed matrix membranes (MMMs) using Matrimid®5218 as the polymeric matrix. Investigation of gas transport properties of the MMMs confirmed promising separation performance of ZIF-8@Fe-CTAB nanocrystals for CO2/CH4 separation.