Highly hydrogen-permselective zeolitic imidazolate framework ZIF-8 membranes prepared on coarse and macroporous tubes through repeated synthesis

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Highly hydrogen-permselective zeolitic imidazolate framework ZIF-8 membranes are prepared on coarse and macroporous Al2O3 tubes through a repeated synthesis strategy for the separation of H2/CO2, H2/CH4, and H2/C3H8 mixtures. Since the amino-groups of 3-aminopropyltriethoxysilane (APTES) can coordinate to the free Zn2+ centers and thus bind the growing nano-crystals directly, the nucleation and growth of well intergrown ZIF-8 membranes could be promoted through a repeated synthesis of the ZIF-8 layer on APTES-modified macroporous Al2O3 tubes. The SEM and XRD characterizations indicate that a dense and phase-pure ZIF-8 membrane with a thickness of about 25.0μm can be formed on the alumina tubes by microwave synthesis at 105°C for 3h, and no cracks, pinholes or other defects were observed in the membrane layer. The ZIF-8 membranes were evaluated in single gas permeation and mixed gas separation. Attributed to the preferential adsorption affinity and capacity as well as a highly porous structure with nano-sized channels, the ZIF-8 membrane displays a high hydrogen permselectivity. For the separation of equimolar H2/CO2, H2/CH4, H2/C3H8 mixtures at 100°C and 2bar, the mixture separation factors of H2/CO2, H2/CH4, and H2/C3H8 are 5.6, 44.0, 328.6, with a H2 permeance of about 1.1×10−7molm−2s−1Pa−1, which is promising for potential applications in hydrogen purification and separation.