Photocatalytic degradation of the fungicide Fenhexamid in aqueous TiO(2) suspensions: identification of intermediates products and reaction pathways |
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Authors: | Lambropoulou D A Konstantinou I K Albanis T A Fernández-Alba A R |
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Institution: | a Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece b Department of Environmental and Natural Resources Management, University of Ioannina, Agrinio 30100, Greece c Department of Chemistry, University of Ioannina, Ioannina 45110, Greece d Department of Analytical Chemistry, University of Almeria, 04120 Almeria, Spain |
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Abstract: | Liquid-chromatography interfaced with time-of-flight mass spectrometry (LC-TOF/MS) was used to separate and characterize the transformation products arising from TiO2-photocatalytic degradation of the fungicide Fenhexamid (FEX) in aqueous solution under simulated solar irradiation. Prior to identification, irradiated solutions of FEX (10 mg L−1) were concentrated by solid-phase extraction. Assignments of the mass spectra ions were aided by elemental composition calculations, comparison of structural analogues and available literature, and acquired knowledge regarding mass spectrometry of related heterocyclic compounds. The primary transformation intermediates identified were hydroxyl and/or keto-derivatives. Several positional isomers are typically produced as a consequence of the non-selectivity of the OH radical attack. Moreover, products resulted from the cleavage of the amide and NH dichlorophenol bonds were formed. Finally, cyclic - benzod]oxazole intermediates are also formed through an intramolecular photocyclization process and cleavage of halogen - carbon bond. In the case of the hydroxy and/or keto-derivatives, the generic fragmentation scheme obtained from the interpretation of the ESI-TOF-MS data cannot be diagnostic to precisely localize the position of the entering substituent on the FEX molecule, and thus to characterize all its possible oxygenated derivatives by assigning a plausible structure with confidence. On the basis of identified products different pathways of photocatalytic degradation of FEX were proposed and discussed. |
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Keywords: | Fenhexamid LC-TOF/MS Pesticides Photocatalysis TiO2 Transformation products |
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