Effective ultrasound electrochemical degradation of methylene blue wastewater using a nanocoated electrode

•The combination of the ultrasonic and nanocoated electrode was efficient.•The nanocoated electrode could generate more hydroxyl radicals.•Hydroxyl radicals could be easily adsorbed by the nanomaterial.•The ultrasonic can enhance the diffusion of the generated hydroxyl radicals.•Mechanism of the ultrasonic enhanced nanocoated electrodes was discussed.

A novel sonoelectrochemical catalytic oxidation-driven process using a nanocoated electrode to treat methylene blue (MB) wastewater was developed. The nano-scale (nanocoated) electrode generated more hydroxyl radicals than non-nano-scale (non-nanocoated) electrodes did. However, hydroxyl radicals were easily adsorbed by the nanomaterial and thus were not able to enter the solution. Supersonic waves were found to enhance the mass-transfer effect on the nanocoated electrode surface, resulting in rapid diffusion of the generated hydroxyl radicals into the solution. In solution, the hydroxyl radicals then reacted with organic pollutants in the presence of ultrasonic waves. The effect of the nanocoated electrode on the MB wastewater treatment process was enhanced by ultrasound when compared to the non-nanocoated electrode used under the same conditions. The synergy of the nanocoated electrode and ultrasonic waves towards MB degradation was then studied. The optimum operating conditions resulted in a 92% removal efficiency for TOC and consisted of a current of 600 mA, an ultrasound frequency of 45 kHz, and a supersonic power of 250 W. The mechanism of ultrasound enhancement of the nanocoated electrode activity with respect to MB treatment is discussed. The reaction intermediates of the sonoelectrochemical catalytic oxidation process were monitored, and degradation pathways were proposed. The sonoelectrochemical catalytic oxidation-driven process using nanocoated electrodes was found to be a very efficient method for the treatment of non-biodegradable wastewater.