Photocatalytic Oxidation of Chlorophenols in Single-Component and Multicomponent Systems

The photocatalytic oxidation of single-component and multicomponent systems consisting of chlorophenols in aqueous TiO₂ suspension was investigated using long, medium, and short wavelength UV radiation. In the single-component experiments, 2-chlorophenol (2-CP), 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol, and 4-chloro-3-methylphenol (4-Cl-3-MP) were found to degrade at the same rate. The rate of mineralization of 4-Cl-3-MP was higher than that of the others. Power law kinetic models for the temporal prediction of the degradation and mineralization profiles fitted the experimental results well for the single-component systems. The application of these models to represent the simultaneous oxidation of a binary mixture of 2-CP and 4-Cl-3-MP was examined for several equimolar and nonequimolar mixtures. Competitive inhibition kinetics were observed. Under equimolar feed conditions the rates of degradation of the total mixture were comparable to those for single-component systems and could be represented well by the model developed for single-component systems. When one of the two substrates was in excess, the overall oxidation kinetics were controlled by that substrate and the system could therefore be treated as a single-component system.