Synergistic effects of photocatalytic and electrocatalytic oxidation based on a three-dimensional electrode reactor toward degradation of dyes in wastewater

Degradation processes and kinetics of methyl orange (MO) by photocatalytic oxidation (PCO), electrocatalytic oxidation (ECO), and photoelectrocatalytic oxidation (PECO) were investigated using a three-dimensional electrode reactor with TiO2/Ti electrode as anode and TiO2 immobilized on columnar activated carbon (TiO2/CAC) as packed bed particle electrodes. The synergistic effects of PCO and ECO under different anode bias voltages were studied. UV irradiation for generating electron-hole pairs and external bias voltage for promoting the separation of photogenerated holes and electrons were conducive to achieving a synergistic effect during the PECO process, thereby significantly improving the efficiency of degradation. Moreover, under an anode bias voltage of 1.0 V, the degradation efficiency of MO in PECO process reached 98.76% at 35 min, which was much higher than that of in PCO (62.43%) and in ECO (33.93%) processes. The degradation rate constant of the PECO was estimated to be 0.1354 min(-1), which was significantly higher than the sum of degradation rate constant of the PCO (0.0260 min(-1)) and ECO process (0.0114 min(-1)). This novel three-dimensional electrode reactor has excellent efficiency of degradation by PECO process and shows a great potential application in wastewater treatment. (C) 2019 Elsevier B.V. All rights reserved.