KINETIC-STUDIES USING THE QUARTZ MICROBALANCE TECHNIQUE ON THE PHOTOREDUCTION OF POLYANILINE FILM CONTAINING TIO2 PARTICLES

The photoreduction behavior of polyaniline films containing TiO2 parti cles (PANI + TiO2 films) in methanol solution has been studied using t he quartz crystal microbalance (QCM) technique. When a protonated PANI + TiO2 film in an oxidized state is illuminated in the presence of me thanol, the amount of electrolyte anions included in the film as charg e compensators decreases monotonically with illumination time. Illumin ation of a deprotonated form in an oxidized state of the film results in incorporation of the electrolyte anions into the film at an initial stage, but the incorporated anions are eliminated from the film on fu rther illumination. These results support the reaction mechanism of th e photoreduction of the PANI + TiO2 film which has been proposed previ ously: positive holes generated in illuminated TiO2 oxidize methanol, resulting in protons which protonate the deprotonated polyaniline such that the electrochemically inactive film becomes electrochemically ac tive and is then reduced by photoexcited electrons. The rates of the p hotoreduction, protonation and deprotonation of the PANI + TiO2 film w ere evaluated by analyzing transient changes in the QCM signals caused by the illumination. The rates of both protonation and photoreduction of the film were proportional to the illumination intensity, whereas no appreciable influence was observed for the deprotonation reaction o f the protonated polyaniline.