Evidence of Direct Dissolution of CO₂ into the Ionic Liquid [C₄min] [NTf₂] during Their Initial Interaction

Ionic liquids (ILs) are known for their high ability to capture CO₂. However, the mechanism of CO₂ solubility into ILs during their initial interaction remains controversial. In this study, we analyzed the initial dissolution of CO₂ into an IL 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ([C₄min] [NTf₂]) by measuring its solubility using a combination of a molecular beam and a flowing liquid jet sheet beam (FJSB) and the King and Wells method (KW method). The temperature dependence of the initial dissolution probability indicates that the solubility of CO₂ in the IL [C₄min] [NTf₂] increases with increasing temperature. This result is not consistent with what has been reported in an equilibrium state. The initial dissolution probability was well-fitted by the Vogel-Fulcher-Tammann (VFT) equation, which describes the dynamical cage structure in IL systems. We also find that the initial dissolution probability was correlated to the cage lifetime and correlation length. The simple model of CO₂ dissolution into an IL with the cage model was implemented to explain the experimental results in this study. Our results indicate that the initial dissolution of CO₂ into the IL corresponds to a direct solution and not an uptake process.