Energy-efficient pulse electrochemical oxidation of Acid Blue 9 using a Ti/SnO2-Sb/α,β-Polytetrafluoroethylene-Fe-PbO2 electrode: Kinetics, mass transfer and mechanism

Abstract This study focused on the electrochemical oxidation of Acid Blue 9 (AB 9) under direct and pulse current modes using a Ti/SnO2-Sb/α,β-Polytetrafluoroethylene-Fe-PbO2 (PTFE-Fe-PbO2) anode. The results showed that 99.0% of AB 9 and 68.9% of COD could be eliminated at initial pH of 5, initial AB 9 concentration of 100 mg L-1, pulse frequency of 4000 Hz, current density of 20 mA cm−2 and pulse duty cycle of 50% after 120 min of electrolysis. The pulse electrochemical oxidation of AB 9 at the investigated conditions followed pseudo-first-order kinetics. Compared with the direct current mode, 76.0% of energy consumption could be saved at pulse current mode. The effect of mass transfer and electrode distance on the pulse electrochemical oxidation of AB 9 was also investigated in terms of mass transfer coefficient and effectiveness factor, the results showed that the reduced electrode distance was beneficial to improve the mass transfer and oxidation efficiency, as well as the energy efficiency. LC-MS analysis revealed that benzenesulfonate group, C-N and C-S bonds in AB 9 molecule were initially cleaved under the attack of ⋅OH, then some carboxylic acids were formed and eventually mineralized to CO2 and H2O. Therefore, pulse electrochemical oxidation with a PTFE-Fe-PbO2 electrode might be a promising alternative to enhance the practicability of electrochemical treatment for dye wastewater.