Studies on the photocatalytic activity of titanium dioxide

Abstract

A novel technique for determining the photoactivity of anatase and rutile forms of TiO₂ has been developed. This involves measurement of the rate of oxygen-uptake in the propan-2-ol/propanone dehydrogenation system, which is photocatalysed by TiO₂ particles maintained in suspension. The system has been studied under several experimental conditions, including the variation of incident light intensity and sample temperature. The effect of varying the alcohol concentration on the oxygen-uptake rate has been studied and, found to be related to the self-association properties of the alcohol, as determined from a series of NMR studies. In addition, strong organic bases have been shown to be effective in reducing the oxygen-uptake rate and a mechanism involving the blocking of surface sites on TiO₂ is proposed. The generation and participation H₂O₂ of in the alcohol to ketone conversion has been studied and, in particular, a technique has been developed to enable the luminescence, which has been observed to emanate from the vortex of the irradiated suspension, to be studied under various experimental conditions. This technique revealed the rapid nature of the interaction of H₂O₂ at the TiO₂ surface. The overall mechanism of the photocatalysed dehydrogenation is discussed in terms of two interdependent pathways: one involving oxygen, the other H₂O₂. Photoluminescence from dry, powdered samples of anatase and rutile has been observed at low temperatures upon excitation with a pulsed nitrogen laser. The decay kinetics of the photoluminesoence have been modelled via computer fitting techniques and the participation of two sets of trapping sites is postulated for anatase and rutile. The photophysical behaviour of benzophenone in poly(methylmethacrylate) films has been studied and a dual pathway for triplet deactivation, involving delayed fluorescence and triplet-triplet annihilation put forward.