Continuous and dense ZIF-7 membranes were successfully synthesized on α-Al 2 O 3 porous substrate via two-step crystallization technique. ZIF-7 seeding layer was first deposited on porous α-Al 2 O 3 substrate by in-situ low temperature crystallization, and then ZIF-7 membrane layer can be grown through the secondary high-temperature crystallization. Two synthesis solutions with different concentration were used to prepare ZIF-7 seeding layer and membrane layer on porous α-Al 2 O 3 substrate,

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... pectively. As a result, a continuous and defect-free ZIF-7 membrane layer can be prepared on porous α-Al 2 O 3 substrate, as confirmed by scanning electron microscope. XRD characterization shows that the resulting membrane layer is composed of pure ZIF-7 phase without any impurity. A single gas permeation test of H 2 , O 2 , CH 4 or CO 2 was conducted based on our prepared ZIF-7 membrane. The ZIF-7 membrane exhibited excellent H 2 molecular sieving properties due to its suitable pore aperture and defect-free membrane layer.