Covalent-Linking-Enabled Superior Compatibility of ZIF-8 Hybrid Membrane for Efficient Propylene Separation.

The interface is a critical issue for metal-organic-framework hybrid membranes in propylene separation. Here, a covalent-linking strategy is reported for strikingly reinforcing the interfacial compatibility in a ZIF-8-based membrane. A functionalized ZIF-8 material named ZIF-8-CN is synthesized using the mixed-ligand approach. ZIF-8-CN has an identical crystalline structure to ZIF-8, and the 4,5-dicyanoimidazole ligand is available for further functionalization. Covalent linkage of ZIF-8-CN with PIM-1 is driven by the thermal reaction of the cyano groups on both entities, which strengthens the filler-polymer connection in the ZIF-8-CN@tPIM-1 membrane. ZIF-8-CN@tPIM-1 exhibits remarkably enhanced propylene permeation property with C H /C H selectivity of ≈28, which is 350% and 180% higher than those on non-treated ZIF-8-CN/PIM-1 and non-functionalized ZIF-8@tPIM-1, respectively. Additionally, ZIF-8-CN@tPIM-1 shows the highest C H permeability of ≈370 Barrer among all relevant ZIF-8 membranes. This strategy opens an avenue for precise interface engineering in membranes and the resultant high performance is appealing in the propylene separation industry.