Mechanism of clomazone photocatalytic degradation: hydroxyl radical, electron and hole scavengers

• Published in: Reaction kinetics, mechanisms and catalysis Vol. 115; no. 1; pp. 67 - 79
• Main Authors: Abramovic, Biljana, Despotovic, Vesna, Sojic, Daniela, Fincur, Nina
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-06-2015
• Subjects: Catalysis; Chemistry; Chemistry and Materials Science; Degradation; Industrial Chemistry/Chemical Engineering; Pathways; Photocatalysis; Photodegradation; Physical Chemistry; Radicals; Reaction kinetics; Scavengers; Titanium dioxide; Photocatalytic degradation; TiO; Hydroxyl radical, electron and hole scavenger; Clomazone; Degussa P25
• ISSN: 1878-5190; 1878-5204
• DOI: 10.1007/s11144-014-0814-z

The role of
•
OH radicals (adsorbed and free) and valence band holes as primary oxidants in the photodegradation of clomazone in UV-illuminated TiO
2
suspension was investigated. Significant inhibition of the photodegradation of clomazone in the presence of NaI (hole and surface
•
OH scavenger) suggesting that the surface degradation mechanism played a crucial role rather than the bulk degradation pathway. Also, less impact of
tert
-butanol on the photodegradation indicated that free
•
OH radicals were not majorly involved in the photodegradation process of clomazone. On the other hand, when the surface is covered by fluoride, it was concluded that the kinetic pathways for reaction with subsurface holes and with free
•
OH in solution are predominant. The LC–ESI–MS/MS analyses of the irradiated solution of clomazone in the presence of NaF indicated formation of the same intermediates when free
•
OH played a crucial role in mechanism instead of surface
•
OH radicals. Besides, molecular oxygen, H
2
O
2
, KBrO
3
, and (NH
4
)
2
S
2
O
8
are generally used as electron scavengers in heterogeneous photocatalytic reactions. It was found that the addition of electron scavengers such as H
2
O
2
, KBrO
3
, and (NH
4
)
2
S
2
O
8
has resulted in higher pollutant degradation rate compared to molecular oxygen alone.