Electrochemical impedance spectroscopy study of a cavitation assisted electro-Fenton process

Abstract

In this work, we report the results of a study to detect and quantify the discoloration of a model dye by an electro-Fenton process, in the presence and in the absence of ultrasound induced cavitation. As expected, a substantial increase in the color removal rate of the solution was observed, reflecting a strong synergetic interaction between the electrochemically induced discoloration kinetics and the ultrasound promoted cavitation. Control experiments to assess the dye degradation kinetics due to pure cavitation, also revealed that the synergetic effect under study takes place at the electrode-solution interphase. In order to gain understanding on the nature of the synergy observed, an electrochemical impedance spectroscopy (EIS) study was carried out. The fitted results of the experimental data suggest that, while the effects of ultrasonic cavitation are significant at the carbon cathode|electrolyte interphase, even in the absence of dissolved O2 gas, the effect is comparatively negligible in the bulk of the solution as well as in the electrolyte located inside the pores of the carbon electrode. EIS results also suggest that the synergy observed during the cavitation assisted electrochemical generation of OH radicals in the absence of dissolved O2, points to the future development of novel wastewater treatment processes that, using air saturated solutions, will overcome the low solubility of O2 that frequently limits traditional electro-Fenton approaches.