The photoassisted oxidation of a dilute aqueous solution of 2-chlorophenol (2-CP) was investigated, over a heterogeneous catalyst of TiO 2 (anatase), in an annular photocatalytic reactor. The effects of some physical and chemical parameters such as 2-CP concentration, catalyst concentration, dissolved oxygen concentration, pH, temperature, and absorbed light intensity were studied in order to optimize the process. The experiment, carried out in the presence of electron scavengers such as metallic ions, shows that the reaction rate is significantly higher than that obtained when oxygen is used alone. The results obtained in this study have led us, on the basis of experimentally determined adsorption, to propose a kinetic approach in which the rate-determining step is the reaction of OH • radicals, identified by a spin trapping technique (EPR), with adsorbed 2-CP. A kinetic model proposed was based on a Langmuir type adsorption involving a competition between solvent and substrate with a supplementary assumption that the further oxygen adsorption sites were different from those of 2-CP and the oxygen adsorption obeys the Freundlich isotherm. This model is able to justify the observed dependence of the pollutant disappearance rate on dissolved 2-CP concentration, oxygen partial pressure, and absorbed light intensity.

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