ZIF-8/graphene nanoribbon hybrid nanoplates for mixed-matrix membranes with enhanced CO2 separation performance

Abstract

Pore-tuned metal-organic frameworks (MOFs) have been extensively utilized for the development of mixed matrix membranes (MMMs). In this study, we synthesized a ZIF-8/graphene oxide nanoribbon (GONR) hybrid nanoplate and incorporated it into 6FDA-DAM-type polyimide polymers. The process began with the shear-induced assembly of graphene oxide nanoribbons (GONRs) into high-aspect-ratio nanosheets by extruding GONR dispersions through a micro-gap channel. During the subsequent solvothermal synthesis of ZIF-8, ZIF-8 nanoparticles were grown and densely intergrown within the GONR nanosheets, resulting in hybrid nanoplates with a thickness of several hundred nanometers. The resulting MMMs, containing 5 wt% of the ZIF-8/GONR hybrid filler, exhibited significantly enhanced CO₂ separation performance. They achieved a CO₂ permeability of 639 Barrer, with ideal selectivities of 19.3 for CO₂/N₂ and 31 for CO₂/CH₄. Unlike conventional ZIF-8-based MMMs showing limited improvement in CO₂ separation due to the larger and flexible aperture size (∼4 Å) of ZIF-8, the enhanced CO₂ selectivity is attributed to the GONR-induced pore tuning of ZIF-8. This tuning effectively narrows the aperture size, hindering the permeation of larger molecules and improving CO₂ selective permeation.