An approach to estimating photocatalytic activity of TiO2 suspension by monitoring dissolved oxygen and superoxide ion on decomposing organic compounds

We proposed a novel method to analyze photocatalytic reaction of TiO2 suspension by measuring the consumption process of dissolved oxygen (DO). The decay rates for DO consumption could be analyzed with Langmuir–Hinshelwood (L–H) kinetics as the effects of reactants such as ethanol and iso-propanol. Two parameters in the L–H kinetics, the maximum consumption rate rmax and adsorption equilibrium constant KD were obtained. The rate constants, kt and kp, which express O2 consumption and O2 reproduction, respectively, could be estimated from dependence of rmax on excitation intensity. Participation of O2− in the decomposition of alcohols was examined by measuring the amount of O2−. An increase of O2− concentration was observed by the addition of a small amount of the reactants, and a decrease was observed for the reactant concentration of more than few mM. Based on these results, we analyzed the DO consumption process and suggested the applicability that the DO consumption efficiency can be used as a relative photonic efficiency to compare the differences in the photocatalytic activities and in the stabilities of reactants.