Enhanced CO₂ Separation by Functionalized g-C₃N₄ Nanosheets as Composite Filler to Fabricate Mixed Matrix Membranes

Membrane separation technology has become a very effective separation technology for CO2 reduction, saving about 90% of energy consumption. However, the CO2 separation performance of gas separation membranes is limited by the “trade-off” between permeance and selectivity in the separation process. Herein, g-C3N4-GO/Pebax-1657 MMMs (mixed matric membranes) were prepared by a solution casting method by combining graphene oxide (GO) nanosheets with g-C3N4 nanosheets as composite fillers, and the membrane possesses excellent thermal stability and mechanical properties. Among them, GO nanosheets containing abundant functional groups were used to repair nonselective defects in g-C3N4 nanosheets (amide bonds were formed between them). The prepared g-C3N4-GO0.30/Pebax MMM possesses excellent CO2 separation performance (CO2 permeance of 815.11 GPU and selectivity of 48.37 for CO2/N2 separation; CO2 permeance of 737.99 GPU and selectivity of 44.94 for CO2/CH4 separation). This study provides theoretical and experimental guidance for the design and preparation of a practical CO2 separation membrane.