Molecular-level investigation of CO₂ absorption in deep eutectic solvents using molecular dynamics simulations and...

This work proposes to thoroughly assess the thermodynamic and kinetic performance of deep eutectic solvents (DESs) based on choline chloride (ChCl) for CO₂ immobilization in order to meet the urgent need for effective carbon capture technologies. Molecular dynamics (MD) simulations and the Conductor-like Screening Model for Real Solvents (COSMO-RS) were used to determine the solubility of CO₂ in three different DESs: ChCl-phenol, ChCl-diethylene glycol (DEG), and ChCl-triethylene glycol (TEG) at temperatures between 303 K and 323 K. The hydrogen bond acceptor (HBA) to hydrogen bond donor (HBD) mole ratios of 1 : 3 and 1 : 4 were chosen. The computational findings show that the ChCl-TEG system at a 1 : 4 molar ratio had the maximum CO₂ absorption capacity, with simulated solubilities of 0.0054, 0.0047, and 0.0043 at 303, 313, and 323 K, respectively. Henry's law constants predicted by the COSMO-RS model rise with temperature, indicating strong thermodynamic agreement with MD simulations. Three-dimensional spatial distribution functions define a site-specific solvation shell in which Cl^- anions and HBD preferentially coordinate equatorially around the central carbon atom of CO₂, whereas [Ch]⁺ cations are localized along the axial termini near the oxygen atoms. Furthermore, CO₂ diffusivity increases as temperature rises, demonstrating a common kinetic-thermodynamic trade-off. This computational study provides a definitive, molecular-level understanding of how the constituent cations, anions, and HBDs of DESs affect CO₂ absorption.