Electrochemical decoloration of synthetic wastewater containing Rhodamine 6G: Behaviors and mechanism

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.