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