Composition–property relationships of choline based eutectic solvents: impact of the hydrogen bond donor and CO2 saturation

Abstract

Eutectic solvents are tunable for targeted applications through the functional groups in their hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) components, as well as the HBA : HBD composition ratio. This study examines the properties of choline-based eutectics containing imidazole, phenol, pyrrole-2-carbonitrile, and 1,2,4-triazole HBAs, and ethylene glycol, 1,2-propylene glycol, and ethanolamine HBDs. The viscosity, conductivity, degree of hydrogen bonding, thermal stability, and solvatochromic properties are examined as a function of HBA, HBD, and the composition. These studies revealed a predominant dependence of physical properties on the HBD and determined that the strong hydrogen bonding in phenol and imidazole-based systems lead to higher viscosities and lower conductivities – critical parameters for CO₂ capture and electrochemical conversion. The developed eutectic solvents were further evaluated in terms of their CO₂ capture capacities and electrochemical stabilities. Solvatochromic properties were found to correlate with CO₂ capacities, demonstrating the tunability of these solvents for CO₂ capture. The quantitative structure–property relationship (QSPR) analysis demonstrated the ability to predict viscosities and CO₂ capture capacities (<25% deviation) through a multi linear regression method utilizing five molecular descriptors. This work highlights the role of functionalized HBAs and HBDs in the physical, thermal, and electrochemical properties of eutectic solvents as they relate to CO₂ capture and electrochemical processes.