Phase Transformation of Hydrothermally Synthesized Nanoparticle TiO2: from Anatase to Rutile Nanorods
Mild hydrothermal hydrolysis of TiCl4 produces nanorods of the rutile phase of titanium dioxide in high yield, while in the presence of organic acids (citric, acetic, D-tartaric and benzoic acids) anatase is the only product. The effect of these organic acids on the products of the hydrolysis reaction as well as the reaction kinetics of the hydrolysis reaction were studied using X-ray powder diffraction and scanning electron microscopy. These studies confirmed that the anatase phase, stabilized by the organic acid, is the kinetically produced product. In addition, in the absence of any organic acids, the conversion of anatase to rutile occurred in two steps (rate constants 0.046 ± 0.025 min–1 and 0.0013 ± 0.0002 min–1). The first step entailed a relatively rapid reaction corresponding to the conversion of anatase nanoparticles to rutile nanoparticles, while the second slower reaction converted the remaining anatase material into rutile titania nanorod clusters. A mechanism is proposed for the reaction and compared with other literature proposals.
KEYWORDS: Nanostructures, crystallization, powder diffraction.