Spectrophotometric determination of persulfate by oxidative decolorization of azo dyes for wastewater treatment

Abstract

Persulfate can efficiently decolorize azo dyes through oxidizing these compounds, which enabled us to develop a method of rapid spectrophotometric determination of persulfate for monitoring the wastewater treatment on the basis of the oxidation decolorization of azo dyes. Four azo dyes with different molecular structures were investigated as probes, and the influences of operation parameters including reaction time, solution pH, initial dye concentration, and initial concentration of activator Fe²⁺ were checked on the determination of persulfate. Under optimum conditions, the decolorization degree of the dyes responded linearly with persulfate concentration for all the four azo dyes, and the linear range and detection limit were found to be 2.0–150 μmol L⁻¹ and 0.62 μmol L⁻¹ for rhodamine B, 2.0–100 μmol L⁻¹ and 0.42 μmol L⁻¹ for methylene blue, 4.0–150 μmol L⁻¹ and 0.50 μmol L⁻¹ for methyl violet, and 20–150 μmol L⁻¹ and 8.1 μmol L⁻¹ for orange II. A persulfate treatment of a spiked wastewater sample was satisfactorily monitored with the new method.