Abstract: The adsorption behavior and photooxidation kinetics of OH－ at TiO2 thin film electrodes in solution of alcohols have been studied by electrochemical measurements. The results show that the adsorption model of OH－ on TiO2 surface corresponds to the Langmuir isotherm and under high enough applied bias potential the photooxidation kinetics can be described by Langmuir-Hinshelwood expression. Hydroxide ions are regarded to be the reactant with photogenerated holes and adsorbed water could not be captured by the holes and, consequently, the photocurrent is proportional to the density of OH－ adsorbed on TiO2 surface under the condition of high enough light intensity. In solution with high content of alcohols, the recombining reaction between radical and photogenerating electron can hardly occur, where the rate-limiting step is the formation of photo-driven OH• radical.

Key words: Hydroxide ion, TiO₂ thin film, Photooxidation kinetic, Langmuir isotherm