Acidity Scale in a Choline Chloride- and Ethylene Glycol-Based Deep Eutectic Solvent and Its Implication on Carbon Dioxide Absorption

Abstract

An equilibrium acidity (pK a ) scale that comprises 16 Bronsted organic acids, including phenols, carboxylic acids, azoles, and phenylmalononitriles, was established in a choline chloride/EG-based deep eutectic solvent (DES) ([Ch][Cl]:2EG) by ultraviolet−visible (UV−Vis) spectroscopic methods. The established acidity scale spans about 6 pK units in the DES, which is similar to that for these acids in water. The acidity comparisons and linear correlations between the DES and other solvents show that the solvent property of [Ch][Cl]:2EG is quite different from those of amphiphilic protic and dipolar aprotic molecular solvents. The carbon dioxide absorption capabilities as well as apparent absorption kinetics for a series of anion-functionalized DESs ([Ch][X]:2EG) were measured, and the results show that the basicity of comprising anion [X] of choline salt is essential for the maximum carbon dioxide absorption capacity, i.e., a stronger basicity leads to a greater absorption capacity. The possible absorption mechanisms for carbon dioxide absorption in these DESs were also discussed based on the spectroscopic evidence.

Formation of choline salts and dipolar ions for CO2 reactive eutectic solvents

“…Contrary to our observations, Li et al 18 and Nie et al 19 reported the formation of [Ch] + [Im] − and [Ch] + [PhO] − , respectively, which we suspect to result from the high-water content. When the 1 H-NMR chemical shifts of the Ch ± ImH sample were probed after adding 10 wt% water, the H b′ peak associated with –NH⋯O − experienced an upfield shift from 9.85 ppm to 6.03 ppm as seen in Fig.…”

“…S16, ESI†). The contribution from [Im] − –CO 2 (C) is very small, even in the absence of EG, in contrast to the report by Nie et al 19 (Fig. S17, ESI†).…”

Structure, Microheterogeneity, and Transport Properties of Ethaline Decoded by X-ray/Neutron Scattering and MD Simulation

“…Ethaline is gaining significant attention in various technological applications due to its excellent electrical conductivity (0.763 S·m –1 ), biodegradability, low viscosity (48.1 mPa·s), low toxicity, and affordability . Ethaline offers a sustainable alternative to traditional organic solvents, which is finding applications in electrochemistry, biomass conversion, nanomaterial synthesis, and CO 2 capture …”

CO2 capture by imidazolium-based deep eutectic solvents: the effect of steric hindrance of N-heterocyclic carbenes

“…20–24 Anion-functionalized DESs exhibit promising chemisorption performances for CO 2 , 25–28 such as azolide-based DESs 29,30 and phenolate-based DESs. 31,32 The CO 2 capture mechanisms of anion-functionalized DESs present various reaction pathways depending on the structures of the components of the DESs. 8…”