Carbon Dioxide Formation From Organic Solutes in Aqueous Suspensions of Ultraviolet-Irradiated TiO₂. Effect of Solute Concentration

Abstract

The oxidation of a number of aromatic compounds to carbon dioxide by exposure to near U.V. light in aqueous titanium dioxide suspensions has been studied as a function of the solute concentration. In most, the dependence of the rate of CO₂ formation follows the simple Langmuir expression:

R(CO₂)=k₁k₂[s]/(1+k₁[s])

The rate is essentially independent of concentration above 200 µM and becomes progressively more dependent on the concentration as it decreases. Changes in the mineralization rate are most clearly reflected in k₂, the parameter determined by the limiting rate at high concentrations. A consequence of the dependence is that total mineralization is strictly never achieved but is approached asymptotically at extended illumination times. The expression and parameters are given which enable the prediction of the extent of mineralization over a wide range of concentrations. The solutes studied were benzene, benzoic acid, benzoate ion, salicylate ion, phenol, chlorobenzene , aniline, anilinium ion, nitrobenzene, chloroform and formic acid. It was confirmed that pH and oxygen concentration affect the rate of carbon dioxide formation but, in the photochemical reactor used, the rate was not significantly affected by the amount of TiO₂ suspended for loadings from 0.05 to 0.40 g per 400 ml.