Solvation Shell Anatomy of H₂S and CO Dissolved in Reline and Ethaline Deep Eutectic Solvents

Rising atmospheric concentrations of anthropogenic hydrogen sulfide (H₂S) and carbon monoxide (CO) as a result of industrialization have encouraged researchers to explore innovative technologies for capturing these gases. Deep eutectic solvents (DESs) are an alternative media for mitigating H₂S and CO emissions. Herein, we have employed ab initio molecular dynamics simulations to investigate the structures of the nearest-neighbor solvation shells surrounding H₂S and CO when they are dissolved in reline and ethaline DESs. We aim to delineate the structural arrangement responsible for favorable H₂S and CO capture by analyzing the key interactions between H₂S and CO solutes with various components of the DESs. We observe that in the reline-H₂S system, chloride and carbonyl oxygen of urea are found to have the closest distance interaction with hydrogen atoms of the H₂S solute. The sulfur atom of H₂S is found to be predominantly solvated by hydrogen and oxygen atoms of urea molecules and the hydroxyl hydrogen of choline cations. The chloride ions and ethylene glycol molecules predominantly govern the solvation of H₂S in the ethaline-H₂S system. In both the DESs, H₂S is solvated by the hydroxyl group of the choline cations rather than by their ammonium group. In the reline-CO system, all the atoms of urea along with chloride dominate the immediate solvation shell around CO. In the ethaline-CO system, hydroxyl oxygen and hydrogen atoms of ethylene glycol are found in the nearest solvation structure around CO. Both the DESs exhibit a stronger solvent-solute charge-transfer tendency toward the H₂S solute compared to CO.