title: Effects of chloride ions on bleaching of azo dyes by Co2+/oxone reagent: kinetic analysis.
abstract: Orange II (Org II), one of the most common used azo dyes, was taken as a model to investigate the effects of chloride ion on dye decoloration in cobalt/peroxymonosulfate (Co/PMS) system. A significant decrease in the rate of Org II decoloration was observed upon addition of Cl(-) (0.05-10mM), but further addition of Cl(-) (>50mM) apparently accelerated dyes degradation. This dual effect of chloride on dyes bleaching was also observed as other halide ions (e.g. Br(-), I(-)) or other azo dyes were present in Co/PMS system. In the Co-free PMS solutions, the observed first-order rate constant always exponentially increased with the chloride content. The reactive chlorine species generated from chloride oxidation by PMS should be responsible for this non-radical mechanism for dye decoloration, however, these rapid decoloration of Org II as chloride ion was present, did not readily lead to much mineralization. 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. zhaohuiwang@dhu.edu.cn
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.forename: Ruixia
authors.initials: R
authors.lastname: Yuan
authors.forename: Yaoguang
authors.initials: Y
authors.lastname: Guo
authors.forename: Lei
authors.initials: L
authors.lastname: Xu
authors.forename: Jianshe
authors.initials: J
authors.lastname: Liu
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D001557:Benzenesulfonates / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry; D003116:Color; D004396:Coloring Agents / Q000737:chemistry*; D007220:Industrial Waste / Q000517:prevention & control; D007700:Kinetics; D013464:Sulfuric Acids / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D001557:Benzenesulfonates; D002712:Chlorides; D004396:Coloring Agents; D007220:Industrial Waste; D013464:Sulfuric Acids; D014874:Water Pollutants, Chemical; D003035:Cobalt; C048813:potassium peroxymonosulfuric acid; C014722:2-naphthol orange