Synthesis and characterization of a computationally predicted redox and radiation stable deep eutectic solvent

Abstract

• DFT calculations towards finding suitable HBD and HBA for the formation of redox and radiation stable DES. • Phase diagram to depict the molar ratio of the constituents in the new DES. • Stabilization energy calculation of the predicted new DES. • Experimental synthesis and characterization of the DES predicted from computational calculations. • Radiation stability study and by-product analysis of the as synthesized DES under gamma irradiation. A redox and radiation stable DES has been predicted based on the fundamental electronic properties such as energy gap, ionization potential and electron affinity computed applying suitable density functionals in combination with 6-311++G(d,p) set of atomic basis functions. A selected series of optimized hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) has been screened using density functional theory (DFT). The long range corrected density functionals; ωB97XD and LC-BLYP are found to be cost effective and appropriate towards orbital energy gap calculations of such systems. Choline acetate and malonic acid appeared to be the most appropriate combination among those studied for formation of a chemical and radiation stable DES. Theoretically constructed phase diagram using Gibbs free energy minimization technique is applied to suggest the eutectic point and eutectic composition of the recommended DES. Stabilization energy calculations following electronic structure support the phase diagram data denoting formation of a stable eutectic with 1:2 stoichiometry. Density, viscosity, differential scanning calorimetry (DSC) and Fourier transform infra-red (FTIR) experiments have been carried out with this synthesized DES. Measured glass transition temperature (−75 °C) is observed to be lower than the theoretical eutectic point (−40 °C) indicating strong interspecies interaction within the medium. Experimental FTIR analysis gives an idea of the type and number of H-bonds present within the DES whereas computationally optimized 1:2 geometry identifies the specific H-bonds along with their distances. Irradiation of this new DES has been conducted at a constant dose of 100 kGy to observe the extent of degradation. UV–Vis and FTIR analysis does not denote generation of any new species within the liquid phase upon irradiation, however the yields of the gaseous by-products have been quantified by Gas Chromatography (GC).