title: [Kinetics modeling and reaction mechanism of ferrate(VI) oxidation of triclosan].
abstract: Triclosan (TCS) is a broad-spectrum antibacterial agent widely used in many personal care products. We investigated oxidation of TCS by aqueous ferrate Fe(VI) to determine reaction kinetics, interpreted the reaction mechanism by a linear free-energy relationship, and evaluated the degradation efficiency. Second-order reaction kinetics was used to model Fe (VI) oxidation of TCS, with the apparent second-order rate constant (k(app)) being 531.9 L x (mol x s)(-1) at pH 8.5 and (24 +/- 1) degrees C. The half life (t1/2) is 25.8 s for an Fe( VI) concentration of 10 mg x L(-1). The rate constants of the reaction decrease with increasing pH values. These pH-dependent variations in k(app) could be distributed by considering species-specific reactions between Fe(VI) species and acid-base species of an ionizable TCS. Species-specific second-order reaction rate constants, k, were determined for reaction of HFeO4(-) with each of TCS's acid-base species. The value of k determined for neutral TCS was (4.1 +/- 3.5) x 10(2) L x (mol x s)(-1), while that measured for anionic TCS was (1.8 +/- 0.1) x 10(4) L x (mol x s)(-1). The reaction between HFeO4(-) and the dissociated TCS controls the overall reaction. A linear free-energy relationship illustrated the electrophilic oxidation mechanism. Fe (VI) reacts initially with TCS by electrophilic attack at the latter's phenol moiety. At a n[Fe(VI)]: n(TCS) > 7: 1, complete removal of TCS was achieved. And lower concentration of the humic acid could enhance the k(app) of Fe( VI) with TCS. In conclusion, Fe(VI) oxidation technology appears to be a promising tool for applications of WWTPs effluents and other decontamination processes.
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China. ppyangbin@163.com
authors.forename: Bin
authors.initials: B
authors.lastname: Yang
authors.forename: Guang-Guo
authors.initials: GG
authors.lastname: Ying
authors.forename: Jian-Liang
authors.initials: JL
authors.lastname: Zhao
mesh_terms: D000891:Anti-Infective Agents, Local / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D017680:Potassium Compounds / Q000737:chemistry; D014260:Triclosan / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D000891:Anti-Infective Agents, Local; D058085:Iron Compounds; D017680:Potassium Compounds; D014874:Water Pollutants, Chemical; C017311:ferrate ion; C044384:potassium ferrate; D014260:Triclosan; D007501:Iron