Modification of ZIF-8 membranes by atomic layer deposition for high propylene/propane selectivity

Zeolitic-imidazolate framework (ZIF-8) membranes have great potential to separate propylene/propane gas mixtures. Our recent work demonstrated that an excellent propylene/propane separation factor is obtained with a silicalite-seeded ZIF-8 membrane. However, the separation performance was limited due to non-selective defects in the ZIF-8 membranes that adversely affected the membrane separation performance. To further improve membrane performance, zinc oxide (ZnO) was atomically deposited on the synthesized ZIF-8 membrane surface using atomic layer deposition (ALD). ZnO ALD helped to minimize surface defects and inter-crystalline gaps of the membrane and improved the propylene/propane separation factor while maintaining the propylene permanence. After ZnO ALD treatment, ZIF-8 membranes showed significant improvement of the propylene/propane separation factor from 141 to 264, but at the expense of the propylene permeance with a ∼10% reduction. The improvement is likely due to defects healing on the ZIF-8 membrane surface via ZnO ALD. The resulting ZIF-8 membranes were characterized by XRD, XPS, BET, and SEM.