Membranes with Molecular Gatekeepers for Efficient CO₂ Capture and H₂ Purification

The urgent need for CO₂ capture and hydrogen energy has attracted great attention owing to greenhouse gas emissions and global warming problems. Efficient CO₂ capture and H₂ purification with membrane technology will reduce greenhouse gas emissions and help reach a carbon-neutral society. Here, 4-sulfocalix[4]arene (SC), which has an intrinsic cavity, was embedded into the Matrimid membrane as a molecular gatekeeper for CO₂ capture and H₂ purification. The interactions between SC and the Matrimid polymer chains immobilize SC molecules into the interchain gaps of the Matrimid membrane, and the strong hydrogen and ionic bondings were able to form homogeneous mixed-matrix membranes. The incorporation of the SC molecular gatekeeper with exceptional molecular-sieving properties improved the gas separation performance of the mixed-matrix membranes. Compared with that of the Matrimid membrane, the CO₂ permeability of the Matrimid-SC-3% membrane increased from 16.75 to 119.78 Barrer, the CO₂/N₂ selectivity increased from 29.39 to 106.95, and the CO₂/CH₄ selectivity increased from 29.91 to 140.92. Furthermore, when the permeability of H₂ was increased to 172.20 Barrer, the H₂/N₂ and H₂/CH₄ selectivities reached approximately 153.75 and 202.59, respectively, which are far superior to those of most existing Matrimid-based materials. The mixed-matrix membranes also exhibited excellent long-term operation stability, with separation performance for several important gas pairs still overtaking the Robeson upper limit after aging for 400 days.