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The photo-induced degradation of 3,6-dichloro-2-methoxybenzoic acid present at the trace level in aqueous solutions has been studied by comparing the UV photolytic treatment with the processes operating in the presence of either irradiated TiO2 aqueous suspensions and irradiated hydrogen peroxide. The efficiency of the treatments was evaluated by monitoring the kinetics of the primary degradation process, the chloride release and the DOC evolution. The identification of aromatic intermediates by means of GC-MS and LC-MS analysis evidenced a common degradation path for TiO2- and H2O2-mediated degradation, whereas the photolytic mechanism resulted quite different. The mixed TiO2-t-H2O2−UV treatment was found to exhibit the best performances.

The photocatalytic degradation of Monuron (3-(4-chlorophenyl)-1-1-dimethylurea) in aqueous TiO2 dispersions irradiated in the near-UV region has been investigated by using a Pyrex batch photoreactor. The Monuron and total organic carbon concentrations were determined; several reaction intermediates were also identified using HPLC. The influence on the degradation kinetics of the initial Monuron concentration, of the TiO2 concentration, and of the initial pH of dispersion was studied. A pseudo-first order kinetics of Langmuir-Hinshelwood type was found to satisfactorily describe the Monuron degradation. The mineralization of the pollutant was virtually complete in the 3–9 pH range while at pH = 1.0 and 11.0 only a partial mineralization was reached even after a long irradiation time. The quantum yield values of Monuron degradation were determined by measuring the photon flow transmitted by the dispersion and applying a macroscopic photon balance on the photoreactor. The quantum yields were found to increase by increasing the pH of the dispersion.