Deep eutectic solvents: structure, solvation, and synthesis

Authors: Oliver Hammond (University of Bath)
Co-authored by industrial partner: No

Type: Thesis

State: Published (Approved)
Published: June 2019
Diamond Proposal Number(s): 15194

Abstract: Deep Eutectic Solvents (DES) are a recently-discovered category of potentially more sustainable alternative solvents. They are liquid eutectics formed upon the combination of various precursors, normally organic halide salts and neutral species. The most common DES is a 1:2 mixture of choline chloride:urea. DES are beginning to be used as non-aqueous alternative solvents for a variety of processes, such as synthesis of small molecules and materials, and electrodeposition. For the successful development and implementation of DES as a drop-in green solvent, it is important to build a strong fundamental understanding of the structure and properties. This will aid in the realisation of DES as ‘task-specific’ solvents which can be rationally tuned to fit the application of interest. There are several fundamental issues presently impeding the progression of the field of DES. Firstly, due to their similar properties and designer nature, DES are often presented as a sub-category of ionic liquids (ILs) though the combination of ionic and molecular species will yield a more structurally complex system, with contributions from electrostatic forces as well as H-bonding. In this thesis the structure of various DES has been explored primarily using neutron diffraction and atomistic modelling studies. These works showed evidence for a disordered and extensive H-bond network in the liquid rather than extensive ion complexation, which has important consequences for the design of chemical processes using DES. Overall, this thesis is a coherent body of independent systematic investigations into the solvent structure and solvation behaviour of DES, and synthesis of nanoparticles with wide-reaching environmental applications. We have built further upon the fundamental understanding of DES and have drawn comparison between systematic structural observations and the performance of DES in relevant applications. It is hoped that these findings will help with the onward development of DES as alternative solvents for efficient and sustainable future industrial technologies, which can make the world a cleaner place.

Journal Keywords: Deep eutectic solvents; Neutron scattering; Nanomaterials; Liquid structure

Subject Areas: Chemistry

Instruments: I20-EDE-Energy Dispersive EXAFS (EDE) , I20-Scanning-X-ray spectroscopy (XAS/XES) , I22-Small angle scattering & Diffraction

Other Facilities: ESRF; MAX IV