Kinetics modeling and reaction mechanism of ferrate(VI) oxidation of benzotriazoles

• Published in: Water research (Oxford) Vol. 45; no. 6; pp. 2261 - 2269
• Main Authors: Yang, Bin, Ying, Guang-Guo, Zhang, Li-Juan, Zhou, Li-Jun, Liu, Shan, Fang, Yi-Xiang
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.03.2011; Elsevier
• Subjects: Applied sciences; Benzotriazoles; Buffers; Computer Simulation; Exact sciences and technology; Ferrate(VI); Iron - chemistry; Kinetics; Linear free-energy relationship; Linear Models; Mathematical models; Models, Chemical; Oxidants - chemistry; Oxidation; Oxidation-Reduction; Pollution; Rate constants; Reaction kinetics; Reaction mechanisms; Thermodynamics; Triazoles - chemistry; Waste water; Water treatment and pollution; Ferrate(VI); Oxidation; Kinetics; Linear free-energy relationship; Benzotriazoles; Aquatic environment; Kinetic model; Ultraviolet radiation; Decontamination; Reaction mechanism; Hydroxyl radicals; Waste water
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2011.01.022

Benzotriazoles (BTs) are high production volume chemicals with broad application in various industrial processes and in households, and have been found to be omnipresent in aquatic environments. We investigated oxidation of five benzotriazoles (BT: 1H-benzotriazole; 5MBT: 5-methyl-1H-benzotriazole; DMBT: 5,6-dimethyl-1H-benzotriazole hydrate; 5CBT: 5-chloro-1H-benzotriazole; HBT: 1-hydroxybenzotriazole) by aqueous ferrate (Fe(VI)) to determine reaction kinetics as a function of pH (6.0–10.0), and interpreted the reaction mechanism of Fe(VI) with BTs by using a linear free-energy relationship. The p K a values of BT and DMBT were also determined using UV–Visible spectroscopic method in order to calculate the species-specific rate constants, and they were 8.37 ± 0.01and 8.98 ± 0.08 respectively. Each of BTs reacted moderately with Fe(VI) with the k app ranged from 7.2 to 103.8 M −1s −1 at pH 7.0 and 24 ± 1 °C. When the molar ratio of Fe(VI) and BTs increased up to 30:1, the removal rate of BTs reached about >95% in buffered milli-Q water or secondary wastewater effluent. The electrophilic oxidation mechanism of the above reaction was illustrated by using a linear free-energy relationship between pH-dependence of species-specific rate constants and substituent effects (σ p). Fe(VI) reacts initially with BTs by electrophilic attack at the 1,2,3-triazole moiety of BT, 5MBT, DMBT and 5CBT, and at the N–OH bond of HBT. Moreover, for BT, 5MBT, DMBT and 5CBT, the reactions with the species HFeO 4 − predominantly controled the reaction rates. For HBT, the species H 2FeO 4 with dissociated HBT played a major role in the reaction. The results showed that Fe(VI) has the ability to degrade benzotriazoles in water. ► Fe(VI) has the ability to oxidize benzotriazoles (BTs) in water. ► The reactions with HFeO 4- predominantly controlled the removal rates. ► The removal rate of BTs reached >95% with the molar ratio of Fe(VI) and BTs up to 30:1.