Degradation and mineralization of sulcotrione and mesotrione in aqueous medium by the electro-Fenton process: a kinetic study
2012
Murati, Minir | Oturan, Nihal | Aaron, Jean-Jacques | Dirany, Ahmad | Tassin, Bruno | Zdravkovski, Z. | Oturan, Mehmet A.
INTRODUCTION: The degradation and mineralization of two triketone (TRK) herbicides, including sulcotrione and mesotrione, by the electro-Fenton process (electro-Fenton using Pt anode (EF-Pt), electro-Fenton with BDD anode (EF-BDD) and anodic oxidation with BDD anode) were investigated in acidic aqueous medium. METHODS: The reactivity of both herbicides toward hydroxyl radicals was found to depend on the electron-withdrawing effect of the aromatic chlorine or nitro substituents. The degradation of sulcotrione and mesotrione obeyed apparent first-order reaction kinetics, and their absolute rate constants with hydroxyl radicals at pH 3.0 were determined by the competitive kinetics method. RESULTS AND DISCUSSION: The hydroxylation absolute rate constant (k abs) values of both TRK herbicides ranged from 8.20 × 108 (sulcotrione) to 1.01 × 109 (mesotrione) L mol−1 s−1, whereas those of the TRK main cyclic or aromatic by-products, namely cyclohexane 1,3-dione , (2-chloro-4-methylsulphonyl) benzoic acid and 4-(methylsulphonyl)-2-nitrobenzoic acid, comprised between 5.90 × 108 and 3.29 × 109 L mol−1 s−1. The efficiency of mineralization of aqueous solutions of both TRK herbicides was evaluated in terms of total organic carbon removal. Mineralization yields of about 97–98% were reached in optimal conditions for a 6-h electro-Fenton treatment time. CONCLUSIONS: The mineralization process steps involved the oxidative opening of the aromatic or cyclic TRK by-products, leading to the formation of short-chain carboxylic acids, and, then, of carbon dioxide and inorganic ions.
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