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A B S T R A C TThe photocatalytic degradation of the insecticide methomyl in water using TiO 2 Merck Eusolex Ò T (anatase) under Osram ultra-vitalux Ò lamp light (315-400 nm, 300 W) was studied. The effect of the operational parameters, such as initial concentration of catalyst, initial methomyl concentration, initial salt concentration (NaCl), and pH, was studied. The optimal concentration of catalyst was found to be 2.0 g/L. Using the Langmuir-Hinshelwood mechanism as a base, a pseudo-first-order kinetic model was illustrated and the adsorption equilibrium constant and the rate constant of the surface reaction were calculated (K MT = 0.079 L/mg and k C = 0.134 mg/L min, respectively). The photodegradation rate was higher in acidic than in alkaline conditions. The presence of Cl -ions significantly affected the photodegradation of the pollutant. The rate of photodecomposition of methomyl was measured using UV spectroscopy and high performance liquid chromatography, while its mineralization was followed using ion chromatography and total organic carbon analysis. In addition, several photocatalysts were used: ZnO (Merck), TiO 2 P-25 (Degussa), TiO 2 Merck (anatase), and TiO 2 Merck R-706 (rutile), and were compared with TiO 2 Merck Eusolex Ò T (anatase).

Activities of two catalysts obtained from hydroxide and alkoxide precursors were correlated to their different structural and textural properties. Activity is mainly determined by the presence of active tetragonal phase, which is more stable at high temperatures in the catalyst of alkoxide origin than in one from hydroxide. An appropriate structure must be accompanied with beneficial pore structure, as is the case of mesopores of the catalyst from alkoxide. In the case of very small pores of the catalyst from hydroxide precursor, activity is negligible due to pores plugged by coke.