Degradation of boscalid by nitrogen-doped/undoped TiO2 and persulfate ions using different activation conditions and the identification of its main degradation products using LC/MS/MS

The degradation of boscalid (Bd) in an aqueous solution was studied using different oxidation systems, including the persulfate ion (PS), TiO2 (UT), N-TiO2 (NT) and mixtures of UT/PS and NT/PS under sunlight irradiation, in addition to using heat-activated (50 or 80 °C) PS ions. NT exhibited a higher percent Bd degradation than UT, which was explained by a higher surface area and a higher amount of anatase for NT. However, the NT/PS or UT/PS systems did not degrade Bd as much as PS alone under sunlight, which may be a result of interactions between the produced hydroxyl and sulfate radicals. Eventually, the highest Bd degradation was obtained by the activation of PS at 80 °C. However, the degradation of Bd by NT or UT in an aqueous solution containing MeOH was completely inhibited. MeOH is a scavenger for hydroxyl radicals, OH and the positive holes of activated catalysts. In addition, the PS system was influenced more than the UT/PS and NT/PS systems were in the presence of MeOH. This result can be explained by the facts that (i) MeOH scavenged more OH than SO4−, and (ii) more SO4− was present for the UT/PS and NT/PS systems than for the PS. Therefore, the NT/PS and UT/PS systems showed a higher percent Bd degradation in an aqueous solution containing MeOH than the PS system did. Eventually, an analysis of the Bd residues was carried out using LC/MS/MS, and the seven basic intermediates were identified.