Supported titanium dioxide (TiO2) was investigated for the photodegradation of the insecticide fenamiphos in water. The photocatalyst was immobilised on borosilicate glass plates and the kinetics of degradation were studied in a stirred tank reactor under UV irradiation. Two types of TiO2, for example, Millennium PC500 (100% anatase) and Degussa P25 (80% anatase, 20% rutile), were used. Their activities have been based on the rates of insecticide disappearance. Experiments were investigated to evaluate the effect of pH and initial concentrations of fenamiphos as well as catalyst doses on the photocatalytic degradation of fenamiphos. Kinetic parameters were experimentally determined and an apparent first-order kinetic was observed. For photolysis process of fenamiphos, two photoproducts were identified and characterized using high performance liquid chromatography/mass spectrometry (HPLC/MS). The plausible mechanism of photolysis involved is the oxidation of sulfonamide group. In presence of photocatalyst TiO2, photodegradation was observed. Under identical conditions, Degussa P25 shows higher photocatalytic activity in regard to PC500 Millennium and complete degradation was observed after 180？min. 1. Introduction In recent years, novel methods for water, soil, and air purification have been developed including chemical, electrochemical, and photochemical processes [1–4]. Indeed, photocatalytic degradation has been shown to be a promising technology for the treatment of water contaminated with organic and inorganic pollutants [1, 2]. Furthermore, photocatalysis has been reported to be effective for the degradation of persistent organic pollutants, such as pesticides, exhibiting chemical stability and resistance to natural biodegradation in water [5–11]. Using titanium dioxide as photocatalyst has been extensively investigated as an alternative physical-chemical process for decontamination of water pollution. Thus, the use of UV energy and TiO2 as semiconductor either in suspension or immobilized on a thin layer can completely degrade or mineralize organic pollutants [12–17]. The Degussa P25 TiO2-type is a commercially available powder preparation and has emerged as the research standard in the field of photocatalysis. However, since the final filtration of titania powders in suspension for the release of cleaned water and the recovery of the catalysts is a tedious process, titania has been successfully deposited on different supports [18–24]. The pesticide selected here is fenamiphos (ethyl 4-methylthio-m-tolyl isopropylphosphoramidate) which is a
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