Porous Organic Cage Membranes for Efficient CO₂ Capture

While membrane technology represents a promising approach for postcombustion carbon capture, its widespread application remains hindered by the permeability-selectivity trade-off and operational instability. Porous organic cages (POCs), as soluble discrete molecules, enable molecular-level mixing with polymer matrices, substantially minimizing interfacial defects and thereby enhancing gas selectivity. Herein, we present a molecular engineering strategy by integrating 2,5-dihydroxyterephthalaldehyde-tris(2-aminoethyl)amine cage (2,5-DHA-TAEA cage) into the polymer of intrinsic microporosity-1 (PIM-1), utilizing molecular cages that feature a precise 3.6 Å window─effectively intermediate between CO₂ and N₂ kinetic diameters. Combined with surface hydroxyl polar sites, this unique architecture establishes a synergistic "confinement sieving-polarity adsorption" mechanism. This dual functionality empowers the resulting composite membrane to achieve exceptional performance, delivering CO₂ permeability of 4690.8 Barrer and CO₂/N₂ selectivity of 35.6 under single-gas conditions, surpassing the 2019 Robeson upper bound. Significantly, under simulated flue gas conditions (CO₂/N₂: 50/50 v/v), the optimized PIM-POC-5 wt % exhibited 115% and 145% enhancements in CO₂ permeability and CO₂/N₂ selectivity, respectively, compared to the pure PIM-1. Furthermore, stability was demonstrated under high pressure (20 bar), elevated temperature (100 °C), and 120-day aging. This work provides a versatile strategy for designing stable, high-performance separation membranes for sustainable carbon capture.