Photochromic property of ternary transition metal oxide nanocomposite prepared with co-solvated deep eutectic mixtures

The application of deep eutectic solvents (DES) in the synthesis of photochromic transition metal oxide (TMO)-based nanocomposites is gaining attention in recent years. In this study, DES-based on choline chloride and ethylene glycol (1:2) was prepared with the addition of different volume of water as co-solvent for the dissolution and preparation of ternary TMO nanocomposites at different temperatures. TGA showed a corresponding increase in weight loss as the volume of the co-solvent increases with a 10–22% loss in mass of the nanocomposites at > 432 °C. SEM images revealed an aggregated and clustered particle distribution, while the TEM revealed an uneven polyhedral-like shaped morphology. The nanocomposites exhibited fast photochromic response by a change from pale-yellow to light blue coloration after 5 s of irradiation with UV-light. The intensity of the coloration deepens after 180 s of irradiation due to the excitation of electrons from the valence band to the conduction band of the metallic systems via a synergistic electronic transition. The variable oxidation states of the individual metal oxides and their redox property inspired the fast fading in a dark oxygenated environment after 30 min, thus, rendering the material suitable for application in smart windows/glasses and color display devices.