Direct and indirect electrochemical oxidation of Indigo Carmine using PbO2 and TiRuSnO2

In this paper, the electrocatalytic properties of PbO2 and TiRuSnO2 anodes for direct and indirect electrochemical oxidation of a synthetic solution containing Indigo Carmine (IC) were compared. The electrolysis was performed using an electrolytic flow cell with parallel-plate electrodes and the progresses of oxidation were monitored by UV-vis and COD measurements. The effects of several operating parameters such as electrode material, current intensity, initial dye concentration, and pH on the degradation rate and current efficiency were determined. Some economic considerations were also taken into account. With both electrodes, IC removal was satisfactory described by a pseudo-first-order kinetic and the rate constant increased with applied current, chloride concentration and decreased with initial IC concentration. During direct electrolysis, PbO2 provided a faster oxidation rate, higher current efficiency, and lower energy consumption than TiRuSnO2 anode. On the contrary, in the presence of 825 ppm of NaCl, the TiRuSnO2 anode that has higher electrocatalytic activity for chlorine evolution was more efficient than PbO2.