Construction of a type II/III deep eutectic solvent/Pebax membrane for efficient CO₂ and N₂ separation: Unraveling the synergistic mechanism of multisite cooperation for enhanced CO2 transport

The demand for carbon dioxide separation in the industrial sector is growing rapidly, and the urgent need to curb carbon dioxide emissions has driven the development of membrane technology. Because deep eutectic solvent (DES) has a strong affinity for carbon dioxide, we embarked on the exploration of how the DES/Pebax mixed matrix membrane could enhance the efficiency of carbon capture. We prepared two types of DES: Type II (TBAB/PEG-400) and Type III (TBAB/PEG-400/ZnCl₂). When these DES were dispersed into Pebax-1657, the separation performance of the membrane was significantly improved. For the Type II DES/Pebax membrane, compared with the pure Pebax membrane, its CO₂ permeability has increased by 37.7% and its selectivity has improved by 54.1%. Subsequently, we introduced Zn²⁺ ions into the DES system, leveraging the π-complexation ability of metal ions to assist in enhancing the DES's carbon dioxide adsorption capacity. The CO₂ permeability of the Type III DES/Pebax membrane reaches 108.6 Barrer, and the CO₂/N₂ selectivity is 82.6. In order to gain a deeper understanding of the interaction mechanism between DES and CO₂ molecules, we conducted DFT calculations. For type II deep eutectic solvents (DESs), hydrogen bonding between TBAB and PEG modulates the overall charge distribution of PEG. The increased charge density on oxygen atoms subsequently enhances its CO₂ adsorption capacity. In Type III DES, Zn²⁺ exhibits a concentration-dependent dual effect. The results of this work imply that DES-incorporated membrane materials might possess certain application prospects in high-efficiency CO₂ separation, offering preliminary insights for advancing eco-friendly and innovative carbon capture technologies.