Fabrication of Mixed-Metal ZIF-7 Membrane by the Self-Conversion of Hydroxy Double Salts for Gas Separation

Achieving the desired separation performance in membrane-based gas separation demands intricate manipulation of molecular structures. Constructing mixed-metal metal organic framework (MOF) membranes is an effective strategy to improve the gas separation performance due to the outstanding properties of mixed-metal MOFs materials in adsorption and separation fields. Herein, we proposed a novel solvent-vapor assisted space-confined transformation (SAST) strategy to fabricate a dense mixed-metal ZIF-7 membrane for the separation of H2 over CO2, N2, and CH4. The fabrication process includes the initial growth of hydroxy double salts (HDSs) on the tube, followed by the deposition of bIm ligand on the surface of HDSs intermediate and then the growth of the mixed-metal ZIF-7 membrane in the confined space under DMF solvent vapor. Compared to the traditional solvothermal methods, this synthesis process significantly reduces the usage of toxic organic solvents, thereby contributing to a more environmentally sustainable approach. The resulting mixed-metal ZIF-7 membrane shows outstanding gas separation performance with the H2/CO2 ideal separation selectivity as high as 42.8 and the H2 permeance of 1.89 × 10–7 mol·m–2·s–1·Pa–1. This method holds substantial potential in the production of mixed-metal MOF membrane for extensive applications in molecular sieving on a large-scale.