EPD method of seeding nano ZnO followed by CVD of organo-linker; a step by step method for synthesis of ZIF-8 thin layer on tubular α-alumina

Abstract

In this work, a step by step approach consisting of electrophoretic deposition (EPD) followed by chemical vapor deposition (CVD) was employed to synthesize a uniform film of zeolitic imidazole framework-8 (ZIF-8) on the outer surface of the porous α-alumina tube. Upon providing conductivity to the alumina substrate, thin polypyrrole (Ppy) film was coated on its surface and the electrical conductivity of α-alumina was increased to 1 S/cm. Then, ZnO nanoparticles were deposited by the EPD method, using 50 V during 20 min, to supply localized nucleation sites for ZIF-8 layer formation. Thereafter, the outer surface of the ZnO seeded surface was exposed to the organo-linker (2- methylimidazole) vapors sublimated at 160 °C in an autoclave, at different contact times of 1, 3.5, and 7 h, respectively. The impact of the contact time was studied on the thickness and quality of the formed layers by characterization methods of XRD, HR-SEM, EDX, elemental mapping, FTIR, and AFM analyses. According to XRD and EDX analyses, the synthesized ZIF-8 layer during 3.5 h with the roughness of almost 200 nm possessed the highest uniformity, adhesion, and degree of conversion of parent ZnO to ZIF-8. Finally, the fabricated layer was examined to the permeation tests of pure gases of H2, CO2, N2, and CH4. High H2 permanence of up to 7.6*10−8 mol m−2. pa−1. s−1 and ideal selectivities of 5.24, 3.04, and 3.3 for H2/CO2, H2/N2, and H2/CH4, respectively, proved the potential of this tubular membrane for the H2 separation from the light gases, for the future studies.