Understanding the interactions between CO2 and selected choline-based deep eutectic solvents using density functional theory

The interaction of CO2 with different deep eutectic solvents (DES) has been studied at the molecular level using density functional theory. Choline chloride and choline bromide were selected as the hydrogen bond acceptors (HBA); urea, ethylene glycol and glycerol were selected as the hydrogen bond donors (HBD). The type and intensity of interactions in DES and that between DES and CO2 molecules at various interaction sites as well as the quantification of short-range interactions has been studied using Bader's quantum theory of atoms in molecules (QTAIM). The distribution of electrostatic potential (ESP) charges during these interactions has been detailed using the Charges from ESP using a grid (CHELPG) scheme. The non -covalent interactions have been identified using the reduced density gradient (RDG) analysis. Strong van der Waals forces were observed to contribute in the formation of DES. The highest interaction energy of -10.65 kcal/mol was found between the DES2 that comprised of choline chloride and ethylene glycol in the molar ratio of 1:2 and the CO2. The results of this study show that both HBA and HBD affect the interaction between CO2 and DES. This study can contribute in designing more specific DES for CO2 capture and utilization.