Theoretical and experimental photodegradation of organophosphorus and carbamate pesticides with advanced oxidation techniques in the precence of aqueous TiO2 suspensions

In this study, in order to analyse the Organophorous (OP), and Carbamate (CB) pesticides and to determine the kinetics of their reactions with OH radical (.OH), analyses were conducted with Phosmet, Azamethiphos, Coumaphos and Temephos as organophosphorous pesticides, along with Methiocarb, Carbofuran and Pirimicarb compounds as carbamate pesticides. The initial geometry of reactants were primarily determined theoretically. In order to determine all the probable reaction paths, geometric optimizations of reactants were carried out using quantum mechanical Density Functional Theory DFT/B3LYP/6-31G(d) basic set. Since the reaction of the pesticides with OH radicals is essential in terms of both water purification and the chemistry of the atmosphere, calculations were done in gaseous phase as well as in aqueous phase via modelling the solvent impact. The decomposition reaction was estimated with the help of the calculated energy values for each molecule. In the experimental step of aqueous suspensions of TiO2, degradation reactions of the chosen pesticides under UV light were analysed. The optimum photocatalyst amount for the studied pesticides were determined, and TiO2 concentration amount in all experiments was identified. After the determination of degradation speed, the impact of the initial concentration was analysed. The reaction of pesticides with the OH radical, are the most dominant ones among all dissipation reactions in the atmosphere. Due to the intermediate products occurring in the reactions not being able to be determined, the conclusion was drawn through the comparison of theoretical and experimental results. As a result of the research, the reaction mechanisms of OH radical in the atmosphere and in waters were clarified, and the reaction products were determined.