Sub-nano porous graphene-based membranes enabled by in-situ-grown ZIF-8 for enhanced CO2 capture

Graphene oxide (GO) membranes hold promise for selective CO2 adsorption over N2 due to their carboxyl groups, making them attractive for flue gas CO2 capture. However, challenges such as limited carboxyl content, flexible nanosheets, and dense layer stacking hinder their N2/CO2 gas selectivity, pressure resistance, and permeability. In this study, we introduce a specific sub-nanometer framework structure within GO membranes by in-situ growing ZIF-8 nanocrystals. This novel approach, achieved through simultaneous infiltration of zinc nitrate and 2-methylimidazole precursors on both sides of the membrane, enhances CO2 capture and pressure resistance capabilities of resulting ZIF-8@GO composite membranes. Additionally, the incorporation of carboxylated wrinkled graphene (WG) and ethylenediamine (EDA) cross-linking agent molecules improves CO2 capture capability and introduces reinforced porous structures to enhance permeability. Experimental results demonstrate remarkable permeability, selectivity, and pressure resistance of the prepared ZIF-8@EDA-GO/WG composite membranes. Under a gas pressure of 0.2 MPa, permeability reaches 1850 GPU, with theoretical selectivity for N2/CO2 single gas and separation factors for mixed gases of 18.3 and 32.3, respectively, surpassing conventional GO membranes (3 GPU, 1.1, and 1.2). Even under elevated air pressure conditions (1.2 MPa), the composite membranes maintain a theoretical selectivity of 13.4. Our CO2 capture membrane design strategy not only advances the development of functional membranes but also contributes to mitigating CO2 emissions from flue gas, thereby combating global warming.