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. TiO ₂ sols were prepared by the hydrolysis and condensation of titanium (IV) n-butoxide in wo-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 °C, the TiO ₂ particles turned polygonal in shape. The XRD pattern was sensitive to heat treatment. At a calcination temperature of 400 °C, only anatase phase was observed. As calcination temperature was increased to 700 °C, 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 °C. Simultaneously, the BET surface area recorded a decreased from 122 to 11.5 m² 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.