Mechanism and Kinetics of Prothioconazole Photodegradation in Aqueous Solution.

This study investigated the effects of light source, pH value, and NO 3 - concentration on the photodegradation of prothioconazole in aqueous solution. The half-life ( t 1/2 ) of prothioconazole was 173.29, 21.66, and 11.18 min under xenon, ultraviolet, and high-pressure mercury lamps, respectively. At pH values of 4.0, 7.0, and 9.0 under a xenon lamp light source, the t 1/2 values were 693.15, 231.05, and 99.02 min, respectively. Inorganic substance NO 3 - clearly promoted the photodegradation of prothioconazole, with t 1/2 values of 115.53, 77.02, and 69.32 min at NO 3 - concentrations of 1.0, 2.0, and 5.0 mg L -1 , respectively. The photodegradation products were identified as C 14 H 15 Cl 2 N 3 O, C 14 H 16 ClN 3 OS, C 14 H 15 Cl 2 N 3 O 2 S, and C 14 H 13 Cl 2 N 3 based on calculations and the Waters compound library. Furthermore, density functional theory (DFT) calculations showed that the C-S, C-Cl, C-N, and C-O bonds of prothioconazole were the reaction sites with high absolute charge values and greater bond lengths. Finally, the photodegradation pathway of prothioconazole was concluded, and the variation in energy of the photodegradation process was attributed to the decrease in activation energy caused by light excitation. This work provides new insight into the structural modification and photochemical stability improvement of prothioconazole, which plays an important role in decreasing safety risk during application that will reduce the exposure risk in field environment.