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Degradation of azo dyes in aqueous solution by H2O2/Fe2+ and H2O2/Fe

By Sangeeta Dhulashia

Abstract

An advanced oxidation process, which uses Fenton\u27s Reagent (H2O2/Fe2+), is studied in the destruction of three different classes of azo dyes. The optimal pH and stochiometry for H202 and Fe2+ in the oxidation of the azo dyes were investigated; an experimental optimal ratio was also compared to a theoretical optimal ratio of H202 to Fe2+. The optimal oxidation of monoazo and disazo dyes is at pH 3 and pH 4, respectively. The optimal ratio for monoazo and disazo dyes ranged from 1 to 10. The experimentally determined optimal ratios are in excellent agreement with theoretically predicted optimal H202 to Fe2+ ratio of 11. Complexation was observed in oxidation of trisazo dye Direct Blue 71. A lower optimal ratio of H202 to Fe2+ for trisazo dye than ratios required for mono and disazo dyes, is due to a larger amount of Fe2+ associated with Fe complexation of chromophore. Due to a relatively large amount of sludge, which is generated by the common Fenton\u27s Reagent, this study was expanded to characterize the performance of a novel H202 and Fe powder system. This system decolorizes the same dyes from Fenton\u27s treatment. Kinetics and mechanism of the reaction were studied. The kinetics followed pseudo-first order and Fenton\u27s Reagent was the major mechanism. The degradation rate depends upon both numbers of azo bonds and auxiliary groups. The rate of decolorization of the dye decreases as the pH level increases. Hydrogen peroxide and iron powder system resulted in higher color removal, at lower sludge production, for selected dyes at lower pH than the Fenton\u27s Reagent treatment option. Keywords: Azo dyes, Fenton\u27s Reagent, Hydrogen Peroxide, Zero Valent Iron, Hydroxyl Radical, Advanced Oxidation Process, Oxidation, and Optimal Ratio of H20 2/Fe2+

Topics: Electrical and Computer Engineering
Publisher: FIU Digital Commons
Year: 1998
OAI identifier: oai:digitalcommons.fiu.edu:etd-4093

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