Improved H₂/CO₂ separation performance on mixed-linker ZIF-7 polycrystalline membranes

Membrane-based hydrogen purification has been considered to be a promising alternative because of its low energy consumption, ease of operation, and cost effectiveness. Amino-functionalized ZIF-7 (ZIF-7-NH₂) is an attractive candidate for membrane gas separation due to the maintenance of pore-opening structure after total removal of guest molecules (DMF). In this work, ZIF-7-NH₂ membrane with improved both H₂ permeance and H₂/CO₂ selectivity than reported mono-ligand ZIF-7 membrane was first prepared. Several activation process for ZIF-7-NH₂ membranes to opening the pores were investigated. It was found that the coating of a Pebax®1657 layer on the surface of ZIF-7-NH₂ membrane is crucial for preventing the formation of cracks during pore-activation procedure. The permeance of H₂ and separation factor for H₂/CO₂ binary mixtures were improved to ∼ 1 × 10⁻⁷ mol/m² s Pa and ∼19, respectively. The separation performance was very close to the upper bound for inorganic microporous membranes. Furthermore, the improved hydrothermal stability on ZIF-7-NH₂ materials endows the membrane is highly potential for hydrogen purification.