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A mechanistic study on photocatalysis by thiapyrylium salts. Photodegradation of dimethoate, alachlor and pyrimethanil under simulated sunlight

Paper ID Volume ID Publish Year Pages File Format Full-Text
46139 46430 2012 6 PDF Available
Title
A mechanistic study on photocatalysis by thiapyrylium salts. Photodegradation of dimethoate, alachlor and pyrimethanil under simulated sunlight
Abstract

Photodegradation of dimethoate, alachlor, and pyrimethanil using a thiapyrilium salt (TPTP+) as photocatalyst was performed under simulated sunlight. The photocatalyst removes preferentially pyrimethanil (45% after 60 min of irradiation), followed by dimethoate (20%) and alachlor (13%). In the three cases, an important to moderate decrease of the fluorescence intensity upon addition of the pollutants was observed. The active participation of the singlet excited state in the photodegradation of the pollutants was demonstrated; the corresponding dynamic quenching rate constants were found to be 1.9 × 1010 M−1 s−1 (pyrimethanil), 6.7 × 109 M−1 s−1 (dimethoate) and 9.1 × 109 M−1 s−1 (alachlor). Moreover, a decrease in the signal corresponding to the triplet excited state was observed immediately after the laser pulse; again a good correlation was observed between the missing fraction of triplets and the photodegradation rates under solar light. Detection of TPTP+, the reduced species derived from the photocatalyst, as well as Rehm–Weller calculations on the free energy changes, strongly support an electron transfer mechanism occurring from the singlet excited state.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights▸ Photodegradation of the title pesticides occurs using a thiapyrilium salt (TPTP+). ▸ The photoreactivity order is: pyrimethanil > dimethoate > alachlor. ▸ Formation of TPTP+/pesticide complexes is involved in photodegradation. ▸ Quenching of TPTP+ singlet excited state by pesticides leads to photodegradation. ▸ A correlation exists between the missing fraction of triplets and photoreactivity.

Keywords
Pesticides; Fluorescence; Laser flash photolysis; Quenching; Singlet excited state; Triplet
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A mechanistic study on photocatalysis by thiapyrylium salts. Photodegradation of dimethoate, alachlor and pyrimethanil under simulated sunlight
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volumes 123–124, 23 July 2012, Pages 208–213
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us