Hydroxyl-Functionalized Ultrathin Covalent Organic Framework Membrane for Fast H₂/CO₂ Separation

Utilization of covalent organic frameworks (COFs) as membrane materials presents a promising approach to addressing the permeation-selection trade-off problem. However, the pore dimensions of COF membranes are considerably larger than those of CO2 molecules, which constrains the efficacy in H2/CO2 separation. This study presents a novel strategy for H2/CO2 separation by modifying the pore walls of a COF membrane. DHTA-Hz, which contains hydroxyl (−OH) functional groups, selectively adsorbs CO2, confining it within the channels while permitting H2 to permeate with minimal resistance. Despite having a pore size of 0.84 nm, the membrane exhibits a remarkable H2/CO2 selectivity of 10.8 and outstanding H2 permeability of 1921 GPU. The overall performance exceeds the Robeson upper bound, highlighting the potential for efficient gas separation. Theoretical simulations validate the effectiveness of this pore-wall adsorption strategy, offering innovative insights into the design of COF membranes for enhanced gas separation.