Sol-gel preparation and photocatalysis of titanium dioxide

Titanium dioxide (TiO2) is extensively used as a photocatalyst due to the strong oxidizing power of its holes, high photostability and redox selectivity. In the present work, the microstructural and chemical properties of TiO2, obtained by a sol-gel procedure, were investigated. TiO2 sols were prepared by the hydrolysis and condensation of titanium (IV) n-butoxide in iso-propyl alcohol. The particle dimensions and morphology of the product were examined by transmission electron microscopy (TEM), the crystal structure by X-ray diffraction (XRD) and chemical state was identified by electron spectroscopy for chemical analysis. The titania particles in the initial sol was elliptical in shape. Upon annealing at 400 degreesC, the TiO2 particles turned polygonal in shape. The XRD pattern was sensitive to heat treatment. At a calcination temperature of 400 degreesC, only anatase phase was observed. As calcination temperature was increased to 700 degreesC, the rutile phase became the major constituent of TiO2. The XRD data also showed that the crystal size of TiO2 increased from 4 to 35 nm as the temperature was increased to 700 degreesC. Simultaneously, the BET surface area recorded a decreased from 122 to 11.5 m(2) g(-1). To examine the photocatalytic activity of the as-prepared TiO2, the photodecomposition of salicylic acid was carried out. It was found that the anatase phase dominated the salicylic acid decomposition under the experimental conditions. A plausible explanation correlating the photocatalytic activity and the TiO2 preparation conditions is discussed. (C) 2004 Published by Elsevier B.V.