Enhancing CO₂ Oversaturation in the Confined Water Enables Superior Gas Selectivity of 2D Membranes

Due to the global demands on carbon neutralization, CO₂ separation membranes, particularly those based on two-dimensional (2D) materials, have attracted increasing attention. However, recent works have focused on the chemical decoration of membranes to realize the selective transport, leading to the compromised stability in the presence of moisture. Herein, we develop a series of 2D capillaries based on layered double hydroxide (LDH), graphene oxide, and vermiculite to enhance the oversaturation of CO₂ in the confined water for promoting the membrane permselectivity. By employing the dielectric spectroscopy as a probe to unveil oversaturation, the dissolved CO₂ can be enhanced by up to ten times facilitated by water confined in the 2D capillary, particularly constructed by the LDH, endowing the uprise of CO₂/N₂ separation factor by 43 times. Therefore, our work opens an avenue to the future design of selective membranes by modulating the confined water beyond chemical modification.