PHOTOOXIDATIVE DEGRADATION OF THE PESTICIDE PERMETHRIN CATALYZED BY IRRADIATED TIO2 SEMICONDUCTOR SLURRIES IN AQUEOUS-MEDIA

The organochlorine pesticide permethrin can be photodegraded into Cl- and CO2 with TiO2 semiconductor catalyst. The aromatic moiety in permethrin is easily cleaved approximately via apparent first-order kinetics. The aromatic ring opening rate (1.73 x 10(-3) min-1) is nearly identical with the dechlorination rate (1.82 x 10(-3) min-1). The presence of the TiO2 catalyst, UV irradiation and oxygen gas are essential for photo-oxidation at a reasonable rate. The insoluble permethrin (in water) can be efficiently photodegraded in a TiO2 slurry of hexane-water mixture under solar exposure with high conversion (more than 90%), even at high concentration (17 000 ppm), in 8 h on a sunny day. The hydrophobic TiO2 catalyst (T-805) modified by octyltrimethoxyl silane gives more effective photocatalytic activity than the naked TiO2 (P-25).