Detection of active oxidative species in TiO2 photocatalysis using the fluorescence technique

The active oxidative species (mainly corresponding to hydroxyl radicals (·OH)) produced on TiO2 film photocatalyst in aerated aqueous solution have been quantitatively investigated by measuring the fluorescence derived by the reaction with either coumarin or terephthalic acid. Upon UV light illumination, coumarin in aqueous solution and terephthalic acid in NaOH solution were converted on the TiO2 film photocatalyst to highly fluorescent hydroxy products. Analysis of the resultant hydroxy compounds provides sensitive and specific monitoring of the generated active oxidative species. The rate of active species formation could be determined by the time dependence of the increase in concentration of the resultant hydroxy products. Using this fluorescence method, the effect of light intensity on the generation efficiency of active oxidative species was examined. The obtained results show that the efficiency of active oxidative species formation is constant at the UV intensity from 50 mu W cm-2 to 15 mW cm-2, which is consistent with the results for ·OH detection reported recently by the use of other techniques.