Preparation of Ni-MOF-74 membrane for CO2 separation by layer-by-layer seeding technique

Continuous and defect-free Ni-MOF-74 membranes were prepared on α-alumina support via a layer-by-layer seeding technique followed by secondary growth crystallization. The seeded supports were examined by SEM–EDX and AFM which evidenced that a uniform and compacted seeding layer can be formed on porous substrate surface through four alternated immersion cycles. Then Ni-MOF-74 seeding layer can grow into continuous Ni-MOF-74 membranes under optimal synthesis solution conditions. The as-synthesized Ni-MOF-74 membranes were characterized by XRD, SEM, BET and TGA. The continuous and crack-free membranes can be synthesized based on comparatively more concentrated solution and yet excessively concentrated solution is disadvantageous to obtain the uniform and defect-free membranes. Gas permeation properties of the membranes were investigated for small gases such as H2, N2, CH4 and CO2. Compared with other gases, Ni-MOF-74 membrane exhibits the stronger adsorption affinity to CO2 and thus the permeation of CO2 through Ni-MOF-74 membrane is dominated by surface diffusion. The high H2/CO2 ideal selectivity can be obtained for Ni-MOF-74 membranes.

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► Ni-MOF-74 seeding layer on α-alumina supports is coated by layer-by-layer method.
► Secondary crystallization is used to grow Ni-MOF-74 membrane.
► Synthesis solution with optimized concentration is essential for crack-free membrane.
► Ni-MOF-74 membrane exhibits stronger adsorption affinity to CO2 over other gases.
► High H2/CO2 ideal selectivity can be obtained for Ni-MOF-74 membranes.