Nano-MnO2-mediated transformation of triclosan with humic molecules present: kinetics, products, and pathways

Nano-MnO2-mediated transformation of triclosan with humic molecules present: kinetics, products,... It has been shown that manganese dioxide (MnO2) can mediate transformation of phenolic contaminants to form phenoxyl radical intermediates, and subsequently, these intermediates intercouple to form oligomers via covalent binding. However, the reaction kinetics and transformation mechanisms of phenolic contaminants with humic molecules present in nano-MnO2-mediated systems were still unclear. In this study, it was proven that nano-MnO2 were effective in transforming triclosan under acidic conditions (pH 3.5–5.0) during manganese reduction, and the apparent pseudo first-order kinetics rate constants (k = 0.0599–1.5314 h−1) increased as the pH decreased. In particular, the transformation of triclosan by nano-MnO2 was enhanced in the presence of low-concentration humic acid (1–10 mg L−1). The variation in the absorption of humic molecules at 275 nm supported possible covalent binding between humic molecules and triclosan in the nano-MnO2-mediated systems. A total of four main intermediate products were identified by high-resolution mass spectrometry (HRMS), regardless of humic molecules present in the systems or not. These products correspond to a suite of radical intercoupling reactions (dimers and trimers), ether cleavage (2,4-dichlorophenol), and oxidation to quinone-like products, triggered by electron transfer from triclosan molecules to nano-MnO2. A possible reaction pathway in humic acid solutions, including homo-coupling, decomposition, oxidation, and cross-coupling, was proposed. Our findings provide valuable information regarding the environmental fate and transformation mechanism of triclosan by nano-MnO2 in complex water matrices. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environmental Science and Pollution Research Springer Journals

Nano-MnO2-mediated transformation of triclosan with humic molecules present: kinetics, products, and pathways

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Publisher
Springer Journals
Copyright
Copyright © 2018 by Springer-Verlag GmbH Germany, part of Springer Nature
Subject
Environment; Environment, general; Environmental Chemistry; Ecotoxicology; Environmental Health; Atmospheric Protection/Air Quality Control/Air Pollution; Waste Water Technology / Water Pollution Control / Water Management / Aquatic Pollution
ISSN
0944-1344
eISSN
1614-7499
D.O.I.
10.1007/s11356-018-1637-7
Publisher site
See Article on Publisher Site

Abstract

It has been shown that manganese dioxide (MnO2) can mediate transformation of phenolic contaminants to form phenoxyl radical intermediates, and subsequently, these intermediates intercouple to form oligomers via covalent binding. However, the reaction kinetics and transformation mechanisms of phenolic contaminants with humic molecules present in nano-MnO2-mediated systems were still unclear. In this study, it was proven that nano-MnO2 were effective in transforming triclosan under acidic conditions (pH 3.5–5.0) during manganese reduction, and the apparent pseudo first-order kinetics rate constants (k = 0.0599–1.5314 h−1) increased as the pH decreased. In particular, the transformation of triclosan by nano-MnO2 was enhanced in the presence of low-concentration humic acid (1–10 mg L−1). The variation in the absorption of humic molecules at 275 nm supported possible covalent binding between humic molecules and triclosan in the nano-MnO2-mediated systems. A total of four main intermediate products were identified by high-resolution mass spectrometry (HRMS), regardless of humic molecules present in the systems or not. These products correspond to a suite of radical intercoupling reactions (dimers and trimers), ether cleavage (2,4-dichlorophenol), and oxidation to quinone-like products, triggered by electron transfer from triclosan molecules to nano-MnO2. A possible reaction pathway in humic acid solutions, including homo-coupling, decomposition, oxidation, and cross-coupling, was proposed. Our findings provide valuable information regarding the environmental fate and transformation mechanism of triclosan by nano-MnO2 in complex water matrices.

Journal

Environmental Science and Pollution ResearchSpringer Journals

Published: Mar 10, 2018

References

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