title: The mode of action of sodium hypochlorite in the decolorization of azo dye orange II in aqueous solution.
abstract: The effect of sodium hypochlorite (NaOCl) on the decolorization of azo dye orange II (4-[(2-hydroxy-1-naphthalenyl) azo]-benzenesulfonic acid, monosodium salt) in aqueous solution was studied as a function of pH. The first-order rate constant of color reduction (k) was evaluated from the curve of color reduction in the initial stage of decolorization. The k values increased with increasing the pH from 5.4 to 9.3 and the NaOCl concentration from 2.82 × 10(-4) M to 1.13 × 10(-3) M. It was found that k depended on the concentration of OCl(-), but not on HOCl. On the other hand, k decreased markedly at pHs more than 10, depending on pH. This suggested that the reactivity of the orange II molecule with OCl(-) decreased probably due to the competitive action of the hydroxide ion under alkaline conditions. It could be concluded that controlling the solution pH and the OCl(-) concentration was indeed a key factor determining the rate of decolorization of orange II in aqueous solution.
authors.affiliation: Industrial Technology Center of Okayama Prefecture, Okayama, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Urano
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fukuzaki
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D001557:Benzenesulfonates / Q000737:chemistry*; D003116:Color; D004202:Disinfectants / Q000737:chemistry*; D015394:Molecular Structure; D012973:Sodium Hypochlorite / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry
chemical_list: D001391:Azo Compounds; D001557:Benzenesulfonates; D004202:Disinfectants; D012996:Solutions; D012973:Sodium Hypochlorite; C014722:2-naphthol orange