Decoloration of alizarin red S in aqueous solution by glow discharge electrolysis

The oxidation of alizarin red S by hydroxyl radicals, which were generated from glow discharge electrolysis, was investigated. Various influencing factors such as the applied voltage, the initial pH, the catalytic action of Fe2+ ion and the distance between cathode and anode were examined. Chemical oxygen demand (COD), ultraviolet (UV) absorption spectra, atomic force microscopy (AFM) and gas chromatogram–mass spectrum (GC–MS) were used to monitor the decoloration process. The results show that alizarin red S rapidly underwent decoloration and was eventually mineralized into carbon dioxide, water, and inorganic ions. It was confirmed that phthalic acid and carboxylic acids were produced in the decoloration process. The probable mechanism for the decoloration of alizarin red S induced by hydroxyl radical was also discussed.