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

초록

Y Zeolitic imidazolate framework-8 (ZIF-8), a subclass of metal-organic frameworks (MOFs), has excellent potential for diverse applications such as gas separation, catalysis, and electronics. Fabrication of the thin film ZIF-8 crystals on the porous polymer substrate in a hollow fiber configuration promises an enhanced functionality. Despite the recent progress in the fabrication of ultrathin ZIF-8 composite layered structures, conformal growth of a ZIF-8 crystal on the porous hollow fiber polymeric substrate remains challenging because it requires an elaborate ZnO seeding process. Herein, we report the growth of an ultrathin ZIF-8 layer (<300 nm) on the surface of a porous polyamide-imide (PAI) hollow fiber. A densely packed ZnO seed layer was uniformly deposited on the PAI fiber via sequential two-step radio frequency sputtering. The ZnO layer was subsequently converted to ZIF-8 using 2-methylimidazole under solvothermal conditions. Conversion time-dependent analysis confirms that the conversion from ZnO to ZIF-8 thin film follows the heterogeneous crystal nucleation and growth kinetics. A conversion mechanism based on the Zn2+ ion diffusion through the ZnO grain boundaries is proposed. These results suggest a viable approach to deposit a uniform seed layer on the topographically nonflat (e.g., cylinder) substrate for the multivalent functional MOF-polymer composite structure.

키워드