Electrochemical degradation of indigo salt by titanium-based PbO₂ anode

PbO₂ electrode was adopted as the anode for the electro-catalytic oxidative degradation of indigo salt. The main purpose was to study the variations of the UV-vis spectrum and the degradation mechanism of indigo salt on PbO₂ anode. The influences of different factors on the degradation and energy consumption were considered. The results indicated that indigo salt was oxidized by both the direct electron exchange reaction on electrode surface and the hydroxyl radicals produced on the electrode surface through indirect oxidation mechanism. The increase of current density could promote indigo salt degradation and chemical oxygen demand (COD) removal, and also lead to an apparent increase of unit energy consumption. The removal efficiencies of indigo salt and COD could be reduced through the increase of dye concentration but the unit energy consumption was decreased accordingly, indicating that the high concentration of organics is beneficial to the decrease of the unit energy consumption in electro-catalytic reactions. The temperature rise could not enhance the degradation and removal of organics. However, it was beneficial to the decrease of unit energy consumption. In the experiments, the indigo salt degradation efficiency was higher than the COD removal efficiency, and the unit energy consumption of indigo salt degradation was lower than that of COD removal, indicating that the organic removal process is easier than that of COD.