Transport and Energetics of Carbon Dioxide in Ionic Liquids at Aqueous Interfaces

A major hurdle in utilizing carbon dioxide (CO₂) lies in separating it from industrial flue gas mixtures and finding suitable storage methods that enable its application in various industries. To address this issue, we utilized a combination of molecular dynamics simulations and experiments to investigate the behavior of CO₂ in common room-temperature ionic liquids (RTIL) when in contact with aqueous interfaces. Our investigation of RTILs, [EMIM][TFSI] and [OMIM][TFSI], and their interaction with a pure water layer mimics the environment of a previously developed ultrathin enzymatic liquid membrane for CO₂ separation. We analyzed diffusion constants and viscosity, which reveals that CO₂ molecules exhibit faster mobility within the selected ILs compared to what would be predicted solely based on the viscosity of the liquids using the standard Einstein-Stokes relation. Moreover, we calculated the free energy of translocation for various species across the aqueous-IL interface, including CO₂ and HCO₃^-. Free energy profiles demonstrate that CO₂ exhibits a more favorable partitioning behavior in the RTILs compared to that in pure water, while a significant barrier hinders the movement of HCO₃^- from the aqueous layer. Experimental measurement of the CO₂ transport in the RTILs corroborates the model. These findings strongly suggest that hydrophobic RTILs could serve as a promising option for selectively transporting CO₂ from aqueous media and concentrating it as a preliminary step toward storage.