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 hours, 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 hours with the roughness of almost 200nm 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 H 2 , CO 2 , N 2 , and CH 4 . High H 2 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 H 2 /CO 2 , H 2 /N 2 , and H 2 /CH 4 , respectively, proved the potential of this tubular membrane for the H 2 separation from the light gases, for the future studies.