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  • Kinetic studies of the reaction between pesticides and hydroxyl radical generated by laser flash photolysis.

Kinetic studies of the reaction between pesticides and hydroxyl radical generated by laser flash photolysis.

Journal of the science of food and agriculture (2015-05-15)
Fábio Gozzi, Silvio C Oliveira, Renato F Dantas, Volnir O Silva, Frank H Quina, Amilcar Machulek
RESUMO

Due to contamination of the environment by pesticides and their mishandling, there is the need for treatment of contaminated sites and correct disposal of materials containing them. Thus, studies with advanced oxidation processes are expanding and can determine the rate constant of the hydroxyl radical with organic compounds of great importance in environmental contamination. In this context, the use of laser flash photolysis has been shown to be viable for the determination of these constants. The reaction rate constants of different pesticides with HO(•) in degassed acetonitrile have been determined. They were 1.6 × 10(9)  M(-1)  s(-1), 0.6 × 10(9)  M(-1)  s(-1), 1.2 × 10(9)  M(-1)  s(-1), 2.4 × 10(9)  M(-1)  s(-1) and 2.2 × 10(9)  M(-1)  s(-1) for the pesticides carbaryl, propoxur, fenoxycarb, ethoxysulfuron and chlorimuron-ethyl, respectively. These values are about an order of magnitude smaller than the diffusion controlled rate and correlate with the relative rates of disappearance of the pesticides in the photo-Fenton reaction in water. The correlation of the relative rate constants determined by laser flash photolysis with the relative rates of photo-Fenton degradation of the pesticides is compelling evidence for the participation of the hydroxyl radical in the degradation of these pesticides in the latter system.

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Sigma-Aldrich
trans-Stilbene, 96%
Sigma-Aldrich
Pyrvinium pamoate salt hydrate, ≥98% (HPLC)
Supelco
Ethoxysulfuron, PESTANAL®, analytical standard
Supelco
Propoxur, PESTANAL®, analytical standard