title: Effects of chloride ion on degradation of Acid Orange 7 by sulfate radical-based advanced oxidation process: implications for formation of chlorinated aromatic compounds.
abstract: Sodium chloride is a common salt used during textile wet processes. Here a dual effect of chloride (i.e. inhibitory and accelerating effect) on azo dye (Acid Orange 7, AO7) degradation in an emerging cobalt/peroxymonosulfate (Co/PMS) advanced oxidation process (AOP) was reported. Compared to OH-based AOPs, high concentrations of chloride (>5mM) can significantly enhance dye decoloration independent of the presence of the Co(2+) catalyst, but did greatly inhibit dye mineralization to an extent which was closely dependent upon the chloride content. Both UV-vis absorbance spectra and AOX determination indicated the formation of some refractory byproducts. Some chlorinated aromatic compounds, including 3-chloroisocoumain, 2-chloro-7-hydroxynaphthalene, 1,3,5-trichloro-2-nitrobenzene and tetrachlorohydroquione, were identified by GC-MS measurement in both Co/PMS/Cl(-) and PMS/Cl(-) reaction systems. Based on those experimental results, two possible branched (SO(4)(-)radical-based and non-radical) reaction pathways are proposed. This is one of the very few studies dealing with chlorinated organic intermediates formed via chlorine radical/active chlorine species (HOCl/Cl(2)) attack on dye compounds. Therefore, this finding may have significant technical implications for utilizing Co/PMS regent to detoxify chloride-rich azo dyes wastewater.
authors.affiliation: College of Environmental Science and Engineering, Donghua University, Shanghai, 201620, China.
authors.forename: Ruixia
authors.initials: R
authors.lastname: Yuan
authors.forename: Sadiqua N
authors.initials: SN
authors.lastname: Ramjaun
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.forename: Jianshe
authors.initials: J
authors.lastname: Liu
mesh_terms: D001391:Azo Compounds / Q000302:isolation & purification*; D001557:Benzenesulfonates / Q000302:isolation & purification*; D005609:Free Radicals; D008401:Gas Chromatography-Mass Spectrometry; D006841:Hydrocarbons, Aromatic / Q000032:analysis*; D006843:Hydrocarbons, Chlorinated / Q000032:analysis*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D012965:Sodium Chloride / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D001391:Azo Compounds; D001557:Benzenesulfonates; D005609:Free Radicals; D006841:Hydrocarbons, Aromatic; D006843:Hydrocarbons, Chlorinated; D013431:Sulfates; D014874:Water Pollutants, Chemical; D012965:Sodium Chloride; C014722:2-naphthol orange