Synthesis of nano-sheets seeds for secondary growth of highly hydrogen permselective ZIF-95 membranes

Recently, more and more attentions have been focused on the preparation of metal-organic framework (MOF) membranes for gas or liquid separations. However, it is rather difficult to prepare a dense MOF membrane by a direct solvothermal synthesis route because of poor heterogeneous nucleation of MOF on the native ceramic support surface. Chemical modifications or seeds coating are usually carried out to promote nucleation and growth of MOF membranes. In this work, we report the synthesis of ZIF-95 nano-sheets as seeds for secondary growth of highly hydrogen permselective ZIF-95 membranes. Under the action of the vacuum force, the ZIF-95 seeds in the colloidal suspensions are attracted and transported onto the whole area of the support surface continuously and uniformly, thus forming a continuous and uniform ZIF-95 seeding layer, which is helpful to promote the nucleation and growth of ZIF-95 membranes. After solvothermal synthesis at 120 °C for 48 h, a well-intergrown ZIF-95 membrane was formed on the seeding support surface. Attributing to a preferentially affinity to CO₂ and a narrow pore size of ~0.37 nm, the developed ZIF-95 membrane shows high hydrogen permselectivity for the separation H₂ from other large molecules. At 200 °C and 1 bar, the mixture separation factors of H₂/CO₂, H₂/N₂, and H₂/CH₄ are 41.6, 36.8, and 40.3, respectively, with H₂ permeances over 1.7 × 10⁻⁷ mol m⁻² s⁻¹·Pa⁻¹.