Synthesis and Characterisation of Metal Oxide Nanostructures Using Choline/Linear Alkyl Carboxylate Deep Eutectic Solvents

Abstract

The synthesis of YBa2Cu3O7−x (YBCO or 123) was carried out via the use of a variety of deep eutectic solvents (DESs), all formed by the interaction of choline hydroxide (as the cation source) and alkyl carboxylic acids with CnH2n+1 ranging from n = 2 to n = 10, namely acetic acid, propionic acid, butyric acid, pentanoic acid, nonanoic acid, and decanoic acid, as providers of the anion, all prepared in equimolar solutions. The behaviour of the synthetic media and the resulting morphology displayed by the crystallite product, using different molar ratios of DESs (X):1 YBaCu metal nitrates mixes, with x values of 20 ≤ x ≤ 60, is also reported. Synthetic performance results show a tendency to generate higher total phase percentage of the desired crystal with the increase of the alkyl chain length of the carboxylic acid up to butyric acid (92% belonging to the metal oxide), after which no enhancement was observed. Furthermore, the synthetic performance of the remaining, i.e., DES formed with pentanoic acid to decanoic acid, displayed a constant decay in total desired phase percentage belonging to the metal oxide. Morphological results were also analysed for all DESs (X):1 YBaCu metal nitrates mixes, with x values of 20 ≤ x ≤ 60. Well defined plate-like particles were generally observed however, in some cases fused plate-like particles of significantly bigger size were observed.