Mechanism of the anodic oxidation of 4-chloro-3-methyl phenol in aqueous solution using Ti/SnO 2–Sb/PbO 2 electrodes

Abstract

Electrochemical oxidation of 4-chloro-3-methyl phenol (CMP) was examined using Ti/SnO 2–Sb/PbO 2 anodes. The physicochemical properties of the electrodes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The degradation was studied by monitoring the total organic carbon (TOC) removal of CMP, and variation of the concentration of intermediates by high-performance liquid chromatography (HPLC), ion chromatography (IC) and gas chromatography/mass spectrometry (GC/MS). The mineralization of CMP is confirmed to be controlled by mass transfer or by both chemical reaction and mass transfer. Hydroxyl radicals ( OH) and active chlorine on the electrode surface had a dominant role in the electro-oxidation process. The chloride element in CMP was immediately driven away from parent substance by OH attack, and then accelerated the ring cleavage of methyl- p-benzoquinone, which was formed during the anodic oxidation of CMP. Ultimately, the chlorine of CMP was mainly transformed to hypochlorite and chloride ion in aqueous solution. Additionally, formic acid and acetic acid were relatively stable products that were not electro-oxidized efficiently in our experiments. The degradation pathway of CMP is proposed on the basis of these results.