Towards a better understanding of the reactive species involved in the photocatalytic degradation of sulfaclozine

The photocatalytic degradation of sulfaclozine on TiO2 suspensions under UV light was investigated and a complete degradation of 88 mu M of sulfaclozine was obtained after 60 min. The addition of isopropanol (500 mM), methanol (500 mM), and ICI (10 mM) to the system inhibited the degradation of sulfaclozine c.a 60%, 85% and 95% respectively, which allowed us to conclude that (OH)-O-center dot radicals, valence-band holes and electrons could intervene in the degradation of sulfaclozine. The second order rate constant of the reaction between sulfaclozine and (OH)-O-center dot radicals was determined by a competitive kinetics method and a value of (7.2 x 10(9) M-1 s(-1)) was obtained. HPLC/DAD and LC-MS/MS analysis were used to identify and follow the appearance and disappearance of sulfaclozine as well as its intermediates. Twelve main intermediates were identified from the photocatalytic degradation of sulfaclozine on TiO2 suspensions. The comparison of the evolution of those intermediates with and without the addition of methanol showed that the quantity of eight intermediates decreased in the presence of methanol, one intermediate was observed to show an increase, while three others maintained the same amount. These results helped us to propose a tentative mechanism of degradation including (OH)-O-center dot radicals, holes, superoxide radicals and electrons attack. In addition, TOC monitoring and mineralization during the photocatalytic degradation of sulfaclozine showed the release of almost all chlorides and the existence of the nitrogen atoms in molecular form even after 180 min of irradiation. (C) 2015 Elsevier B.V. All rights reserved.