Titanium dioxide photoinduced degradation of some pesticide/fungicide precursors

Five-membered nitrogen heterocycles (pyrrole, imidazole and 1,2,4-triazole) have been degraded using titanium dioxide and simulated solar radiation at pH = 8. The degradations followed a simple Langmuir-Hinshelwood mechanism. Accordingly, the adsorption equilibrium constants K of the heterocycles on...

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Bibliographic Details
Published in:Pest management science 2007-05, Vol.63 (5), p.491-494
Main Authors: Kuehr, I, Nunez, O
Format: Article
Language:English
Subjects:
1,2,4‐triazole
4-triazole
Adsorption
Biodegradation
Biological and medical sciences
catalysts
Chemical compounds
Control
Environmental Pollutants - chemistry
Environmental Pollutants - radiation effects
Environmental Restoration and Remediation - methods
Fundamental and applied biological sciences. Psychology
Fungal plant pathogens
fungicides
heterocyclic nitrogen compounds
Hydrogen-Ion Concentration
imidazole
imidazoles
Imidazoles - chemistry
Imidazoles - radiation effects
Kinetics
Langmuir-Hinshelwood
Pesticides
Pesticides - chemistry
Pesticides - radiation effects
photocatalysis
photolysis
Phytopathology. Animal pests. Plant and forest protection
pyrrole
pyrroles
Pyrroles - chemistry
Pyrroles - radiation effects
solar radiation
Titanium - chemistry
titanium dioxide
triazoles
Triazoles - chemistry
Triazoles - radiation effects
Ultraviolet Rays
wastewater treatment
water pollution
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Summary:Five-membered nitrogen heterocycles (pyrrole, imidazole and 1,2,4-triazole) have been degraded using titanium dioxide and simulated solar radiation at pH = 8. The degradations followed a simple Langmuir-Hinshelwood mechanism. Accordingly, the adsorption equilibrium constants K of the heterocycles on the titanium dioxide surface and the rate constants k of degradation of the heterocycle-catalyst adduct have been obtained experimentally. While the K values decrease with heterocycle pKa, the k values increase with increasing pKa. Therefore, apparently, the rate constant depends on the availability of the electron pair on nitrogen, but at the same time the electron pair repulsion induced by the negatively charged titanium dioxide surface at pH = 8 causes a reverse effect in the adsorption equilibrium constant. Only in the case of imidazole, where the adsorption equilibrium constant is low enough (K = 0.013 M-1), can the rate constant be approximated to a pseudo-first-order rate expression: k(obs) = Kk. In all other cases, k(obs) = Kk/(1 + K(heterocycle)).
ISSN:1526-498X
1526-4998
DOI:10.1002/ps.1355