Bleaching and photobleaching of Orange II within seconds by the oxone/Co2+ reagent in Fenton-like processes

Abstract

Accelerated bleaching, photobleaching and mineralization of the non-biodegradable azo-dye, Orange II, was observed with oxone in solutions with Co 2+ -ions. The bleaching rate of Orange II in the dark was found to follow a first-order kinetics with respect to [Co 2+ ] with a rate constant of 20 M −1 s −1 . Fitting of the Orange II photobleaching experimental points in the presence of the Co 2+ /oxone reagent was carried out and followed the trend known for reactions presenting a chain radical branched mechanism. The photobleaching trace could be fitted by a single mathematical expression with an error <5% with respect to the experimental data. The bleaching trace observed for the Orange II solution in the dark followed zero-order decay kinetics. In a typical run, Orange II (0.20 mM or TOC 30 mg C/l) in the presence of oxone and Co 2+ was bleached under visible light within ∼15 s. The Co 2+ -ion concentrations necessary to catalyze the Orange II mineralization by oxone was observed to be ∼100 times lower than the oxone concentration. A 100% TOC decrease, under visible light irradiation, was attained for an Orange II (0.2 mM) solution in the presence of Co 2+ -ions (0.06 mM) and oxone (20 mM) within times ∼70 min for solutions purged with oxygen. Under visible light irradiation, Orange II mineralization in the presence of O 2 involves the photo-dissociation of reaction intermediates leading to organic peroxides in the second step of the mineralization process.

Accelerated photodegradation (minute range) of the commercial azo-dye Orange II mediated by Co3O4/Raschig rings in the presence of oxone

“…1-4 show the effect of light being absorbed by Orange II producing the charge transfer with Co 3 O 4 /RR transfer noted in Eq. (1) below leading to the unstable cation Orange II •+ [10][11][12][13]. Eqs.…”

“…This support was selected since: (a) it resists the attack of the highly oxidative radicals generated by the oxone decomposition catalyzed by Mn 2+ or Cu 2+ [10,11], (b) it also resists he decomposition of oxone recently reported by Co 2+ -ions [12,13] and (c) provides a large surface area in the reactor to induce accelerated Orange II decomposition. The short photodiscoloration times attained in the minute range are impressive compared with times needed by the TiO 2 /RR photocatalyst to degrade organic compounds under similar experimental conditions irradiation [7][8][9].…”

An Investigation of the Mn3O4/graphite Oxide Catalytic Oxidation of NO in Waste Gas

“…Oxone (2KHSO 5 ·KHSO 4 ·K 2 SO 4 ) has peroxymonosulfate (PMS) as its active species. These chemical oxidants can be further activated in several ways (heat, transition metals, or UV) to genertate sulfate radicals (SO 4 -) [1][2][3][4] . More specifically, PMS with transition metals such as Mn(II), Mn(III), Co(II), Ru(III), and Fe(II) could form sulfate radicals as the major oxidizing species [1] .…”

Detoxification of diluted azo-dyes at biocompatible pH with the oxone/Co2+ reagent in dark and light processes

“…The observed kinetics was drastically accelerated when Co 2+ -ions mediate the photocatalysis under daylight irradiation. In the presence of Co 2+ -ions, oxone has been reported [5][6][7]9] to generate a variety of highly oxidative sulphate radicals in aqueous solution.…”

“…Oxone is an oxidant used in organic synthesis, analytical chemistry, catalysis and degradation of organic pollutants [3][4][5][6][7][8][9]. The redox potential of the radical generated by oxone [5,10,11], HSO 5 − → HO • + SO 4 •− , E 0 = 1.82 eV is higher than the potential of the radicals generated by H 2 O 2 (H 2 O 2 → 2HO • , E 0 = 1.76 eV when used as the oxidant in dark or in the light activated decomposition of dyes and organic compounds.…”