Surface area and porosity in obliquely grown photocatalytic titanium dioxide for air purification

Process parameters affecting the photocatalytic performance of thin films of titanium dioxide were investigated. Nanorods of titanium dioxide were grown using the technique of oblique angle deposition to create porous films of high surface area. The surface area of the films was measured as a function of deposition angle using krypton gas adsorption and compared with the photocatalytic activity of the films. The maximum surface area achieved was 148 m2/g for films deposited at a 70° angle. A gas chamber outfitted with a volatile organic compound sensor was constructed to monitor the breakdown of isobutylene test gas. The reaction rate, normalized by the film thickness, increased with measured surface area, as expected. Annealing the deposited films was required for best performance, and annealing times of only 3 min were sufficient to maximize the reaction rate, with longer times resulting in a decrease in activity. The annealing environment was not a factor. Nitrogen worked as well as oxygen. The films w...