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Molecules 2017, 22(10), 1684; doi:10.3390/molecules22101684

Participation of the Halogens in Photochemical Reactions in Natural and Treated Waters

Department of Environmental Sciences, The Connecticut Agricultural Experiment Station, 123 Huntington St., P.O. Box 1106, New Haven, CT 06504-1106, USA
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Received: 18 September 2017 / Revised: 1 October 2017 / Accepted: 4 October 2017 / Published: 13 October 2017
(This article belongs to the Special Issue Photon-involving Purification of Water and Air)
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Abstract

Halide ions are ubiquitous in natural waters and wastewaters. Halogens play an important and complex role in environmental photochemical processes and in reactions taking place during photochemical water treatment. While inert to solar wavelengths, halides can be converted into radical and non-radical reactive halogen species (RHS) by sensitized photolysis and by reactions with secondary reactive oxygen species (ROS) produced through sunlight-initiated reactions in water and atmospheric aerosols, such as hydroxyl radical, ozone, and nitrate radical. In photochemical advanced oxidation processes for water treatment, RHS can be generated by UV photolysis and by reactions of halides with hydroxyl radicals, sulfate radicals, ozone, and other ROS. RHS are reactive toward organic compounds, and some reactions lead to incorporation of halogen into byproducts. Recent studies indicate that halides, or the RHS derived from them, affect the concentrations of photogenerated reactive oxygen species (ROS) and other reactive species; influence the photobleaching of dissolved natural organic matter (DOM); alter the rates and products of pollutant transformations; lead to covalent incorporation of halogen into small natural molecules, DOM, and pollutants; and give rise to certain halogen oxides of concern as water contaminants. The complex and colorful chemistry of halogen in waters will be summarized in detail and the implications of this chemistry for global biogeochemical cycling of halogen, contaminant fate in natural waters, and water purification technologies will be discussed. View Full-Text
Keywords: hydroxyl radical; sulfate radical; photocatalysis; atmospheric aerosols; reactive oxygen species; reactive halogen species; advanced oxidation processes; dissolved natural organic matter; halogenation; reclaimed waters hydroxyl radical; sulfate radical; photocatalysis; atmospheric aerosols; reactive oxygen species; reactive halogen species; advanced oxidation processes; dissolved natural organic matter; halogenation; reclaimed waters
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Yang, Y.; Pignatello, J.J. Participation of the Halogens in Photochemical Reactions in Natural and Treated Waters. Molecules 2017, 22, 1684.

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