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

Highly hydrogen-permselective zeolitic imidazolate framework ZIF-8 membranes are prepared on coarse and macroporous Al 2 O 3 tubes through a repeated synthesis strategy for the separation of H 2 /CO 2, H 2 /CH 4 , and H 2 /C 3 H 8 mixtures. Since the amino-groups of 3-aminopropyltriethoxysilane (APTES) can coordinate to the free Zn 2+ 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 Al 2 O 3 tubes. The SEM and XRD characterizations indicate that a dense and phase-pure ZIF-8 membrane with a thickness of about 25.0   μm can be formed on the alumina tubes by microwave synthesis at 105   °C for 3   h, 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 H 2 /CO 2 , H 2 /CH 4 , H 2 /C 3 H 8 mixtures at 100   °C and 2   bar, the mixture separation factors of H 2 /CO 2 , H 2 /CH 4 , and H 2 /C 3 H 8 are 5.6, 44.0, 328.6, with a H 2 permeance of about 1.1   ×   10 −7   mol   m −2   s −1   Pa −1 , which is promising for potential applications in hydrogen purification and separation.