Polyimide-based mixed matrix membranes incorporated with g-C3N4 nanosheets for efficient helium enrichment

Membrane separation offers an efficient and energy-saving process for extracting rare helium from natural gas. Among them, mixed matrix membranes (MMMs) containing two-dimensional (2D) materials are considered potential gas separation membranes. Herein, 2D g-C₃N₄ nanosheets with nanoporous structure are incorporated into the polyimide (PI) matrix to prepare MMMs for efficient He separation. The incorporated g-C₃N₄ nanosheets generate additional gas transport and sieving channels in MMMs. As a result, the PI/g-C₃N₄ MMM comprising 0.5 wt% g-C₃N₄ nanosheets exhibits a He/CH₄ selectivity of 160.4 with He permeability of 40.7 Barrer, which are 2.0 and 3.2 times higher than the pure PI membrane, respectively. Moreover, the membrane also shows good stability at elevated temperatures or a continuous 150 h long-term operation. Therefore, the remarkable gas separation performance and excellent stability make the membrane promising for gathering helium from natural gas.