Structure of monoethanolamine based type III DESs: Insights from molecular dynamics simulations

Novel Deep Eutectic Solvents (DESs) have been developed with a wide-range of applications, including efficient CO₂ capture. Among several DESs, mixtures of methyltriphenylphosphonium bromide (MTPPBr) and mono ethanol amine (MEA) at molar ratios of 1:6, 1:7, and 1:8 have shown high CO₂ absorption capacity. Using molecular dynamics simulations, we herein systematically analyze the interactions occurring between MTPPBr and MEA at three molar ratios. The results, based on intermolecular energy, hydrogen bonds, and radial distribution functions, show that interaction energy between MTPP⁺ and Br⁻ ions is reduced by approximately 50% in the presence of MEA. Although the interactions between MTPP⁺ ions and MEA are strong, they are limited because of steric hindrance from the phenyl group. In addition, we observe strong hydrogen bonds between MEA and Br⁻ ions. The molecular interactions are further correlated to the observed decline in the melting point of the DESs, as compared to the individual components. The results taken together shed light on the formation of the DES and can provide guidelines for the methodical design of novel DESs.