Adsorption-enhanced carbon membranes derived from copolyimide for ultrafast subangstrom discriminating CO₂ separation

Carbon membranes are emerging as a versatile platform for the selective separation of gas mixtures with similar molecular sizes. Here, a high-performance carbon membrane is developed from an asymmetric, rigid copolyimide precursor via a precisely controlled carbonization process. Membranes carbonized at 800°C exhibit exceptional CO₂ separation performance, with CO₂ permeabilities up to 15,700 barrer and CO₂/N₂ and CO₂/CH₄ selectivities of 63 and 52, respectively—surpassing the 2019 upper bounds. Molecular dynamic simulations, in conjunction with in situ thermogravimetric analysis-mass spectroscopy and thermogravimetric analysis-Fourier transform infrared spectroscopy, reveal the evolution of a bimodal carbon matrix with micropores (7 to 20 angstroms) and ultramicropores (4 to 7 angstroms). Gas transport is dominated by synergistic adsorption-selective and molecular sieving mechanisms, enabling subangstrom discrimination between CO₂ and larger gases. This work demonstrates a facile, tunable strategy to engineer carbon membranes with outstanding CO₂ separation capabilities, offering previously unexplored opportunities for energy-efficient gas separation processes in industrial applications.