Theoretical and experimental photodegradation of Phosmet via oxidation techniques in the presence of aqueous TiO2suspension

This study is conducted with the aim to analyze the reaction kinetics of Phosmet with the OH radical, and to determine its mechanism. Due to the lack of experimental evidence of radical intermediate products occurring during the reactions, the theoretical stage has been quite informative. In this study, in order to theoretically determine all probable reaction paths, geometric optimization of the reactants and transition state complexes was conducted using DFT/B3LYP/6-31G(d) basic set of Quantum Mechanical Density Functional Theory (DFT). As a result of the calculations, the energy values at ground state, and rate constant and activation energies (Ea) at transition state (TS) of the probable reaction paths were determined. And finally, the primary intermediate products were found out by the determination of the atom where the OH radicals attach, and the hydrogen atoms they had removed. The reaction mechanism was clarified through the determination of the intermediate products. Since the reactions of pesticides with OH radical are important both in terms of water purification and atmospheric chemistry, the calculations were carried out in gaseous phase and also at aqueous phase by modelling the solvent impact. In the experimental stage, the degradation reactions under UV-light impact of the pesticide, chosen as pollutant, in aqueous TiO2 suspensions, were analyzed. At the end of this research, the optimum photocatalyst amount and TiO2 concentration were determined. The degradation rates were determined, the impact of the initial concentration was analyzed, and the reaction products were identified. © 2021 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria