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Application of Fenton ‐Based Reactions for Treating Dye Wastewaters: Stability of Sulfonated Azo Dyes in the Presence of Iron(III)
Author(s) -
MacKay Allison A.,
Pignatello Joseph J.
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20010919)84:9<2589::aid-hlca2589>3.0.co;2-c
Subject(s) - chemistry , benzenesulfonic acid , perchlorate , sulfonate , hydrogen peroxide , chromophore , inorganic chemistry , hydrolysis , orange g , chloride , nuclear chemistry , sodium , photochemistry , organic chemistry , catalysis , ion
Fenton ‐ and photo‐assisted Fenton advanced oxidation processes generate reactive oxygen species from hydrogen peroxide and are candidates for the remediation of dye wastewaters. The purpose of this study was to investigate interactions of iron (III) with hydroxyazo dyes. The o ‐hydroxyazo dyes Acid Orange 7 (AO7; 4‐[(2‐hydroxynaphthalen‐1‐yl)azo]benzenesulfonic acid sodium salt) and Acid Orange 10 (AO10; 7‐hydroxy‐8‐(phenylazo)naphthalene‐1,3‐disulfonic acid disodium salt) represent dyes allegedly able to chelate Fe III through the chromophore. The p ‐hydroxyazo dye Acid Orange 20 (AO20; 4‐[(4‐hydroxynaphthalen‐1‐yl)azo]benzenesulfonic acid sodium salt) represents an analogous structure that is unable to chelate Fe III due to the position of the OH group. Reactions were carried out at pH 2 – 3 in perchlorate or chloride media in the absence of peroxide. No evidence was found by UV/VIS spectroscopy for complexation of Fe III by the o ‐hydroxyazo chromophore. Instead, Fe III apparently coordinated or formed an ion pair with the sulfonate group, and, when only one sulfonate group was present ( i.e. , AO7), the dye formed a co‐precipitate with iron(III) hydrous oxides and perchlorate ion. Dye precipitation was seeded by colloidal iron hydrolysis product nuclei. By contrast, the p ‐hydroxyazo dye (AO20) was rapidly oxidized by iron(III). The net Fe 2+ /oxidized AO20 ratio was 2 : 1, and a minor yield of 1,4‐naphthoquinone was obtained. The major initial oxidation product, which was not identified, formed a reversible complex with Fe 2+ . Results of this study indicate that the effectiveness of Fenton ‐based methods for treating certain azo dyes that form insoluble ferric salts may be compromised by removal of the catalyst from solution. However, the degradation of certain other azo dyes might be assisted by direct thermal oxidation by iron(III).