Electrochemical Decoloration of Synthetic Wastewater Containing Rhodamine 6G: Behaviors and Mechanism

Abstract

Dye wastewater has posed a great threat to our aqueous environment. In this study, the treatment of synthetic wastewater containing Rhodamine 6G by electrochemical technology using RuO 2 -coated Ti mesh as anode was investigated. The effects of solution pH, temperature, and dye auxiliaries on the performance were investigated. Carbon and nitrogen mass balance analyses, UV−vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) were used to elucidate the working mechanism. It was found that lower solution pH and lower temperature facilitated the decoloration of the wastewater. The addition of dye auxiliaries did not significantly affect the decoloration. Under optimal condition, complete decoloration of the synthetic wastewater was obtained within 5 min, and 42.3% of the dye was mineralized. The amine and methyl groups were first detached from the dye molecule, leading to a change in the dye structure from polar into nonpolar to form a water insoluble substance. The insoluble substances were floated by the hydrogen bubbles that were generated from the cathode to produce foam products. On the other hand, the soluble substances that remained in the solution were mineralized via indirect electro-oxidation by active chlorine generated by the anode. A conceptual model for the electrochemical treatment of Rhodamine 6G containing water was proposed to illustrate the mechanism of decoloration.

Indirect electrochemical oxidation of pentachlorophenol in the presence of different halides: behavior and mechanism

“…9. Just like the results in literatures [19] and [35], abnormal impact of temperature on PCP conversion was observed. The PCP conversion dropped at first (from 30 to 45 C) and then increased (from 45 to 60 C).…”

“…The ratio of real/assumed Cl À concentration fluctuated between 0.3 and 0.5. The same as the variation of PCP conversion with different temperatures, the final ratio of real/assumed Cl À concentration under different temperatures in Br À -mediated system also decreased at first (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45) C) and then increased (45-60 C). As the reaction conformed to pseudo-first-order kinetic model which can be depicted by exponential function, the conversion curve was then matched by Eq.…”

“…In general, the EO rate will be increased with the rise of temperature following Arrhenius behavior [33,34]. But strangely in the Cl À -mediated EO process, negative impact of temperature on the incineration rate was reported by Bonfatti et al and Zheng et al [19,35]. So the influence of temperature on the decay of pollutants should be carefully considered when employing halides as mediators in indirect electrolysis process.…”

Toxicity Screening after Electrochemical Degradation of Reactive Textile Dyes

“…According to Zheng [26] the foam originates from the original color molecule. When the amine and methyl groups were detached from the dye molecule, the dye structure changed from polar into nonpolar water insoluble substance.…”

“…When the amine and methyl groups were detached from the dye molecule, the dye structure changed from polar into nonpolar water insoluble substance. Then during electrolysis the amount of hydrogen bubbles generated from the cathode was increased and they contributed to the rise of the foam [26].…”