Alumina hollow fiber supported ZIF-7 membranes: synthesis and characterization

ZIF-7 membrane has been prepared on the outer surface of alumina hollow fibers by the solvothermal synthesis. The synthesis conditions, including reaction temperature, time, and solution concentration, are investigated. At the reaction temperature of 100 degrees C for 8 h, microsized ZIF-7 crystals are grown on the outer surface of the hollow fibers. A continuous and dense ZIF-7 membrane with a thickness of about 5 microm is obtained after twice crystallization at 100 degrees C for 8 h. The gas separation test indicates the as-prepared ZIF-7 membranes have intercrystalline defects as the H2/N2 ideal selectivity is less than the Knudsen diffusion. After post-modification with beta-cyclodextrin aqueous solution, the micropore defects of ZIF-7 membrane is significantly reduced and the membrane has H2/N2 ideal selectivity of 3.9. The gas permeances for H2 and N2 are almost constant from room temperature to 150 degrees C for the ZIF-7 hollow fiber membranes before and after beta-cyclodextrin modification.