Preparation and Gas Permeability of ZIF-7 Membranes Prepared via Two-step Crystallization Technique

Continuous and dense ZIF-7 membranes were successfully synthesized on <TEX>α-Al₂O₃</TEX> porous substrate via two-step crystallization technique. ZIF-7 seeding layer was first deposited on porous <TEX>α-Al₂O₃</TEX> 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 <TEX>α-Al₂O₃</TEX> substrate, respectively. As a result, a continuous and defect-free ZIF-7 membrane layer can be prepared on porous <TEX>α-Al₂O₃</TEX> 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 <TEX>H₂</TEX>, <TEX>O₂</TEX>, <TEX>CH₄</TEX> or <TEX>CO₂</TEX> was conducted based on our prepared ZIF-7 membrane. The ZIF-7 membrane exhibited excellent H2 molecular sieving properties due to its suitable pore aperture and defect-free membrane layer.