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
Résumé
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 degrees 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 degrees 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 center dot 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 center dot than
SO4 center dot-, and (ii) more SO4 center dot- 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. (C) 2015 Elsevier B.V. All rights
reserved.