Fabrication of Ultrathin Zeolitic Imidazolate Framework on Polymeric Hollow Fiber via Sequential Seed Layer Sputtering

초록

Zeolitic imidazolate framework-8 (ZIF-8), which is a subclass of metal organic frameworks (MOFs), has great potential for energy efficient gas separations of gas mixtures such as H2, CO￢2, C3H6 and C3H8. ZIF-8 membranes supported on porous polymeric hollow fibers have been studied owing to a high-packing density and surface-to-volume ratio. Currently, most of the ZIF-8 membranes grown on polymeric hollow fibers exhibit microscale thickness, and the fabrication of ZIF-8 thin film remains challenging although the exploitation of the thin film MOF is expected to impact the commercial applications. Herein, we report the growth of ultrathin ZIF-8 layer ( < 200 nm) on the porous polyamide-imide (PAI) hollow fiber surface. First, densely-packed ZnO layer was deposited on the PAI fiber using RF sputtering. Then, the ZnO-coated PAI fiber was exposed to solvothermal condition at 100 ℃, using 2-methylimidazole dissolved in methanol. We confirm the formation of continuous ZIF-8 thin film with < 200 nm thickness on top of the fiber surface. Detailed analysis on the relationship between the solvothermal conversion time and the ZIF-8 layer structure indicates that the incorporation of 2-mehtylimidazole occurs at the grain boundaries of pre-deposited ZnO crystal domains. These results suggest a viable approach to control the defect density of ultrathin ZIF-8 layers for user-programmable separation performance.