Results of the destruction of organic solutes in a simple, thin film Ti02 reactor are described. The reactor was illuminated with a 20-W blacklight UV fluorescent tubeand the aqueous stream containing the organic solute flowed past the stationary photocatalyst. In the continuous recirculation mode, the destructionrate of each solute obeyed approximately first-order kinetics. The reaction rate constant decreased with increasing solute concentration. The times for 50% destruction of 500 cm3 of 10 µ solutions of each of the solutes salicylic acid, phenol, 2-chlorophenol, 4-chlorophenol, benzoic acid, 2-naphthol, naphthalene, and fluorescein were 7.1, 7.2, 8.2, 8.7, 6.9, 8.5, 4.3, and 6.4 min, respectively. It was found that the observed apparent first-order dependence and the change in rate constant with concentration could be explained in terms of the integrated form of the Langmuir adsorption isotherm. A markeddependence of the destruction rate on flow rate was observed and an expression developed which allows the calculation of the destruction curve with good precision at any soluteconcentration and flow rate. A corresponding curve was observed for the formation of carbon dioxide from salicylic acid solution. It was shown that hydroxylation of the aromatic ring to give salicylic acid is a minor reaction path in the destruction of benzoic acid. The maximum quantum yieldfor the destruction of salicylic acid at 25 C was found to be 0.022. The activation energy for the photooxidation of salicylic acid was determined to be 11.0±0.8 kj mor1 11. introduction

Many organic compounds are decomposed in aqueous solution in the presence of titanium dioxidepowder illuminated with near-UV light1-6 and there is interest in this process as a means of purifying water. 7" 16 Although phenols are formed as inter-mediate compounds in the process, 17" 20 these and other organic compounds including chlorinated organic compounds have been