Electrochemical removal of 4-chlorophenol in water using a porous Magnéli-phase (TiO) electrode.

Electro-oxidation is a promising technology for removal of refractory organic pollutants. While the appeal of this technology lies in its chemical-free nature, commercially scale-up application may be limited by the availability of electrode materials and mass transport. Here we report the development of a flow-through electro-oxidation system for removal of chlorophenols in water using Magnéli-phase (TiO) tubular anode and a 304 stainless steel (SS) tubular cathode. The key to this system was the porous and conductive Magnéli-phase TiO anode, the structure and composition of which was confirmed by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. System efficacy was evaluated by using 4-chlorophenol (4-CP) as a typical refractory contaminant and model chlorophenol. Under optimized conditions, a complete removal of 4-CP could be obtained within 120 min in 0.04 mol L NaSO solution. Electro-produced HO and direct electron transfer were both shown to contribute to the 4-CP electro-oxidation process due to the high selectivity and oxygen evolution potential of the TiO anode. The intermediates of 4-CP degradation were identified and a pathway for its electro-oxidation was proposed. When challenged with industrial wastewater containing 4-CP, chemical oxygen demand (COD) and total organic carbon removal efficiencies of 67.5% and 63.1% respectively could be obtained, accounting for energy consumption of 85.1 kWh·kg COD for degradation of 1 kg of COD in industrial wastewater. This study provides an effective and robust solution for the removal of refractory emerging contaminants from industrial wastewaters using a continuous-flow electro-oxidation system.