PHOTOCATALYTIC DEGRADATION OF 2-CHLOROPHENOL IN TIO2 AQUEOUS SUSPENSION - MODELING OF REACTION-RATE

The photoassisted oxidation of a dilute aqueous solution of 2-chloroph enol (2-CP) was investigated, over a heterogeneous catalyst of TiO2 (a natase), in an annular photocatalytic reactor. The effects of some phy sical and chemical parameters such as 2-CP concentration, catalyst con centration, dissolved oxygen concentration, pH, temperature, and absor bed Light intensity were studied in order to optimize the process. The experiment, carried out in the presence of electron scavengers such a s 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 adso rption, to propose a kinetic approach in which the rate-determining st ep is the reaction of OH. radicals, identified by a spin trapping tech nique (EPR), with adsorbed 2-CP. A kinetic model proposed was based on a Langmuir type adsorption involving a competition between solvent an d substrate with a supplementary assumption that the further oxygen ad sorption sites were different from those of 2-CP and the oxygen adsorp tion 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 Fight intensi ty.