Development and applications of eutectic liquids

The chapter is concluded with multi-technique studies on zinc oxide speciation in deep eutectic solvents, with the aim to elucidate the dissolution mechanism. Two plausible mechanisms are proposed, but unfortunately these studies remained inconclusive.<br><br>Studies described in Chapters 2 and 3 led to the conclusion that the components of the archetypical deep eutectic system, choline chloride and urea, are neither uniquely suited for metal oxide dissolution, nor particularly inclined to form deep eutectic solvents, which motivated the search for alternatives (Chapter 4).

Seeking a more thermally stable alternative to urea, with improved affinity to metals, several approaches were investigated, combining choline chloride with various hydrogen bond donors: imidazole (N-donor), thioureas (5-donors) and various carboxylic acids. However, the most interesting systems given their low viscosity and hydrophobic nature were prepared by completely abandoning choline chloride, and moving onto a non-ionic hydrogen bond acceptor, trioctylphosphine oxide (TOPO).<br><br>An in-depth study into the first TOPO-based eutectics is presented in Chapter 5, which combines a physical chemistry investigation into the TOPO-phenol system and preliminary studies into its applications for extraction of uranyl from aqueous media.