Metal-organic framework-graphene oxide composites: A facile method to highly improve the CO2 separation performance of mixed matrix membranes

Abstract

Mixed matrix membranes (MMMs) were fabricated by incorporating ZIF-8@GO into Pebax matrix to improve CO2 separation performance. The ZIF-8@GO played multiple roles in enhancing membrane performance. First, the high-aspect ratio GO nanosheets in polymer matrix increased the length of the tortuous path of gas diffusion, restricting the diffusion of larger molecules and favoring the diffusion of small molecules with less resistance, which enhanced the diffusivity selectivity. Second, the inherent high permeability of ZIF-8 with ultra-microporosity was anticipated to optimize fractional free volume and enhance the gas permeability and solubility selectivity of MMMs. The MMMs doped with ZIG-8@GO had better gas separation performance than those doped with only ZIF-8 or GO. The membrane containing 6wt% of ZIF-8@GO (Peabx/ZIF-8@GO-6) exhibited the optimum performance with a CO2 permeability of 249 Barrer and a CO2/N2 selectivity of 47.6. Compared with the pure Pebax membrane, the CO2 permeability and CO2/N2 selectivity of the Pebax/ZIF-8@GO-6 MMMs were increased by 191% and 174%, respectively. The strategy of growing ZIFs on GO may provide an effective method to further develop MMMs performance through the modification of ZIFs on existing fillers which had larger adsorption differences to specific gases.