INNOVATIVE APPROACHES FOR THE PHOTOCATALYTICDEGRADATION OF PESTICIDES

Mono- and tri-vanadium-substituted Keggin-type heteropolyoxoanions [SiW12O40]4- and[PW12O40] 4- were evaluated as photocatalysts for the photodegradation of three hazardous food pesticides: Atrazine, Chlorpyrifos and Dieldrin. Kinetic experiments were performed under UV irradiation at 254nm. The degradation of each pesticide was assessed by investigating its disappearance with time using High Performance Liquid Chromatography c o n n e c t e d to an Ultra-Violet s p e c t r o p h o t ome t e r d e t e c t o r (HPLC-UV). The photocatalytic degradation of the three pesticides exhibited first order kinetics. It was found that the introduction of vanadium addenda atoms into the Keggin-type polyoxometalates decrease the degradation rate for the photocatalytic transformation of each pesticide as well as the degradation percentage. This effect was significantly related to the number of vanadium metal ions substituting the tungsten addenda atoms. As a general trend, the photocatalytic efficiency of {XVW11} was better than that of {XV3W9}. A marked drop was noticed in the photocatalytic degradation of Atrazine. 90% of Atrazine was decomposed in the presence of [a-SiW12O40] 4- at a rate of 1 ppm/min whereas the degradation percentage decreased to 5 5 % i n t h e presence of [a-SiVW11O40] 5- at a decreased rate of 0.7 ppm/min