Solid-state chemistry of thermally induced yellow colouring in synthetic hydrous titanium oxide from TiCl3

Abstract

Calcination of hydrous titanium oxide (HTO) gel, synthesized by the hydrolysis of titanium(III) chloride (TiCl₃) in the presence of urea, produces a brilliant yellow powder when the pale blue HTO gel is heated at 400 °C in air. From the results of diffuse reflectance (DR) spectroscopy, thermogravimetry and/or differential thermal analysis. (TG/DTA) and electron paramagnetic resonance (EPR) spectroscopy, this colouring is attributed to the formation of thermally induced Ti⁴⁺ peroxide. The colour is lost and the superoxide radical anion is generated when the temperature is increased to 800 °C; this is accounted for by the thermal decomposition of the peroxide complex. The solid-state chemistry of the appearance and loss of the yellow colour is discussed along with results of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA).