Exploring the potential energy surface of nCO₂ (n = 1–5) capture by imidazole-and fluorine-based ionic liquids: A DFT study

One of the reasons for global warming is the rising of greenhouse gasses causing the planet's temperature to increase; among these gases, CO₂ accounts for 80%. For this reason, it is essential to contemplate environmentally sustainable alternatives for CO₂ capture and storage, such as the use of ionic liquids (ILs), which represent an excellent option due to their high affinity for CO₂. This theoretical study considered ILs based on imidazole ([bmim]⁺ and [emim]⁺) and fluorinated ([TFSI]^- and [PF6]^-) dimers, thorough exploration of the potential energy surfaces of nCO₂[bmim]⁺[PF6]⁻, nCO₂[emim]⁺[TFSI]⁻, nCO₂[bmim]⁺[PF6]⁻ and nCO₂[emim]⁺[TFSI]⁻ molecular clusters, n = 1–5, by using a stochastic SnippetKick searching algorithm. Followed by the optimisation of the molecular cluster geometries using Density Functional Theory (DFT) calculations to describe the effect of physisorption of up to five CO₂ in ILs. It was revealed an aggregation of CO₂ molecules between the imidazole ring and the anion, mainly surrounding [TFSI]^- or [PF6]^-, in the form of an orbital in putative global minimum-energy structures, which allows a higher CO₂ physisorption. Finally, a detailed analysis of the thermodynamic properties and intermolecular interactions between ILs and CO₂ molecules was performed with different approximations of the electron density scalars. Overall, this confirms the use of the ILs studied to capture CO₂ efficiently.