Zeolitic imidazolate framework ZIF-8 films by ZnO to ZIF-8 conversion and their usage as seed layers for propylene-selective ZIF-8 membranes

Supported ZIF-8 films with varying microstructures are prepared by ZnO to ZIF-8 conversion reaction in a 2-methylimidazole ligand solution. The grain size and continuity of the films are controlled by manipulating two critical conversion parameters such as solvents and their blends, and temperature. The ZIF-8 films with varying microstructures are used as seed layers to synthesize propylene-selective ZIF-8 membranes. The propylene/propane separation performances are greatly affected by the seed layer microstructures. Non-continuous seed layers with compactly packed ZIF-8 nanocrystals tend to yield more propylene-selective membranes than those grown from continuous seed layers with larger grain size likely due to improved grain boundary structure. Furthermore, the membranes are mechanically stronger than those grown from conventional seed layers, which are obtained by dip-coating ZIF-8 nanocrystals on substrates, possibly owing to the presence of mechanical interlocks between the membranes and porous substrate network.