A detailed study of physicochemical properties and microstructure of EmimCl-EG deep eutectic solvents: Their influence on SO2 absorption behavior

To get a better understanding of the effect of physicochemical properties and microstructure on SO2 absorption behavior of DESs with different molar ratios of EmimCl and EG (from 2:1 to 1:2), densities (ρ), viscosities (η), speeds of sound (u), refractive indices (nD), and thermal decomposition temperatures (Td) of EmimCl-EG DESs were measured and used to obtain the other derived properties, such as thermal expansion coefficient (αp) and activation energy for viscous flow (Eη). Moreover, FT-IR spectra and in situ variable-temperature NMR spectroscopy were employed to study the microstructures of DESs. Based on physicochemical and spectroscopic properties, the influence of the concentrations of EmimCl on the interactions in DESs was explored to be associated with their SO2 absorption behavior. The results show that the interactions between Emim+ and Cl− of EmimCl is gradually weakening with increasing the concentration of EG in DESs by forming of hydrogen bond interaction of OH⋯Cl−, resulting in a decrease of ρ, η, u, nD, and Td of DESs, and hindering the charge–transfer interaction of SO2 with Cl− and deceasing SO2 capture capacity. Moreover, the SO2 absorption capacity of DESs is proportional to their ρ and Eη, respectively.