Decorating Zn-MOF-74 on ZIF-8 to Increase Gas Transport and Plasticization Resistance in Mixed-Matrix Membranes

Abstract

The rational interfacial design of MOF–polymer mixed-matrix membranes (MMMs) is essential for achieving both high gas-separation performance and long-term stability. Conventional functional group-tethering methods improve MOF–polymer compatibility but involve complex synthesis and are difficult to generalize. Herein, we report a facile ligand-exchange strategy to decorate ZIF-8 nanoparticles with Zn-MOF-74 using 2,5-dihydroxyterephthalic acid (DHTA), creating nanoparticles with hydroxyl-rich ligand groups and open metal sites inherent to the Zn-MOF-74 characteristics that form strong interactions with the 6FDD polyimide matrix. This interfacial engineering not only enhances the mechanical and physicochemical stability of the MMM but also increases pore window size and gas sorption sites. As a result, 20 wt% Zn-MOF-74@ZIF-8/6FDD MMMs exhibit greatly improved gas permeabilities (H₂: 627 Barrer; CO₂: 463 Barrer) compared to pristine 6FDD membranes (H₂: 106 Barrer; CO₂: 116 Barrer) while maintaining excellent high-pressure CO₂ plasticization resistance.