Efficient electrochemical generation of ferrate(VI) by iron coil anode imposed with square alternating current and treatment of antibiotics

Anode passivation is still a main challenge for the electrochemical generation of ferrate(VI, Fe(VI)), leading to the reduction of Fe(VI) production efficiency. In this study, cyclic voltammetry, scanning electronic microscopy, and electrochemical impedance spectroscopy were used to select better anode electrode configurations (iron wire, iron gauze, and iron coil). The results indicate that iron coil had the least degree of passivation. Different imposed current waveforms during the electrochemical generation of Fe(VI) were also investigated, and the iron coil imposed with square alternating current (AC) wave can mitigate the anode passivation, resulting in higher Fe(VI) production efficiency. The optimum conditions for the electrochemical generation of Fe(VI) were evaluated and the optimum temperature (40 ℃), current density (10 mA/cm2), AC cycle period (15 s) and electrolyte concentrations (14 M NaOH) were identified. As a result, 0.12 mol/L Fe(VI) concentration and over 50% of current efficiency can be achieved after 3 h electrolysis. The generated Fe(VI) solution was further applied to oxidize doxycycline(DOX) and sulfadiazine(SDZ) as typical antibiotics. Over 80% of DOX can be removed at a Fe(VI) to DOX molar ratio of 5:1 (pH = 4–9), whilst a higher Fe(VI) to SDZ molar ratio of 20:1 (pH = 7) was needed to obtain 75% SDZ removal.