Photocatalytic Degradation of Herbicide Quinmerac in Various Types of Natural Water
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The efficiency of the photocatalytic degradation of the herbicide quinmerac in aqueous TiO2 suspensions was examined as a function of the type of light source, TiO2 loading, pH, temperature, electron acceptors, and hydroxyl radical (•OH) scavenger. The optimum loading of catalyst was found to be 0.25 mg mL−1 under UV light at pH 7.2, with the apparent activation energy of the reaction being 13.7 kJ mol−1. In the first stage of the reaction, the photocatalytic degradation of quinmerac (50 μM) followed approximately a pseudo-first order kinetics. The most efficient electron acceptor appeared to be H2O2 along with molecular oxygen. By studying the effect of ethanol as an •OH scavenger, it was shown that the heterogeneous catalysis takes place mainly via •OH. The results also showed that the disappearance of quinmerac led to the formation of a number of organic intermediates and ionic byproducts, whereas its complete mineralization occurred in about 120 min. The reaction intermediates (7-chloro-3-methylquinoline-5,8-dione, three isomeric phenols hydroxy-7-chloro-3-methylquinoline-8-carboxylic acids, and 7-chloro-3-(hydroxymethyl)quinoline-8-carboxylic acid) were identified and the kinetics of their appearance/disappearance was followed by LC–ESI–MS/MS. Tentative photodegradation pathways were proposed and discussed. The study also encompassed the effect of quality of natural water on the rate of removal of quinmerac.
KeywordQuinmerac Herbicide Photocatalytic degradation Titanium dioxide Photocatalytic degradation pathways Natural water
This document has been produced with the financial assistance of the European Union (Project HU-SRB/0901/121/116 OCEEFPTRWR Optimization of Cost Effective and Environmentally Friendly Procedures for Treatment of Regional Water Resources). The contents of this document are the sole responsibility of the University of Novi Sad, Faculty of Sciences and can under no circumstances be regarded as reflecting the position of the European Union and/or the Managing Authority.
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