Evidence of superoxide radical formation in the photodegradation of pesticide on the dye modified TiO2 surface using visible light

Degradation of a pesticide (atrazine) in air-equilibrated aqueous mixture has been achieved on the surface of TiO2 semiconductor modified with thionine and eosin Y by using visible light. Under 5 h of irradiation with a 150 W xenon lamp, appreciable degradation of atrazine has been observed. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO2 conduction band and formation of reactive O-2(.-)/HO2. radicals is proposed for the degradation of the pesticide to carbon dioxide. Formation of O-2(.-) radical has been evidenced by using a chemiluminescent probe, luminol. (C) 2004 Published by Elsevier B.V.