All experiments were done at constant temperature of 20 ◦C. In each run, 1500 ml of dye solution was placed into the reactor. The conductivity, pH and current density were adjusted to the desired value before the process. After each run, electrode surfaces were removed by dipping for 1 min in a solution prepared by mixing
100 cm 3 HCl solution (36.5%) and 200 cm3 of hexamethylenete-tramine aqueous solution (2.80%) and washed thoroughly with demineralized water to remove any solid residues on the surfaces, dried and re-weighted