Solar photodegradation of pesticides in water by sodium decatungstate

Solar photodegradation in aqueous solutions of phenol, 4-chlorophenol, 2,4- dichlorophenol, bromoxynil, atrazine, imidachloprid and oxamyl, in the pres ence of two photocatalysts titanium dioxide TiO2 and sodium decatungstate N a4W10O32 is reported. TiO2 appears to be the most efficient photocatalyst c oncerning the rate of photodegradation and mineralization of the pure compo unds. However, when the pesticides are used in formulated solutions, the de catungstate anion becomes as efficient or even more efficient than TiO2. Th e mechanism of the photodegradation in the presence of Na4W10O32 is investi gated by nanosecond flash-photolysis experiments, and is compared to the on e proposed for TiO2. The difference of reactivity between the two photocata lysts is accounted by the different primary processes of the mechanisms. Th e formulation effect is investigated with two model surfactants SDS and Tri ton X100, and 2-chlorophenol as a model pesticide. (C) 1999 Elsevier Scienc e B.V. All rights reserved.