Improved BDD anode system in electrochemical degradation of p-nitrophenol by corroding electrode of iron

Abstract

A novel electrochemical system with corroding electrode of iron (Fec) inserted between boron-doped diamond (BDD) anode and carbon felt (CF) cathode, named BDD-Fec-CF system, was initially constructed and investigated in the present study. In this system, p-nitrophenol (p-NP) degradation was significantly enhanced in a wide pH range of 3–11 compared with BDD anode with CF cathode system (BDD-CF) and BDD anode with stainless steel (SS) cathode system (BDD-SS), respectively. Especially under acidic conditions, COD removal efficiency in BDD-Fec-CF system was achieved 89.1%, which was only 35.2% in BDD-SS system under the same conditions. The excellent performance under acidic conditions was mainly attributed to Electro-Fenton reaction. Hydroxyl radicals were formed by reaction between Fe2+ released from Fec electrode and H2O2 generated by dissolved oxygen reduction at CF cathode. Under alkaline conditions, flocs were formed to remove p-NP by coagulation besides anode oxidation, electro-generated oxidants and Fe(VI) oxidation. The fate of Fe was examined whose releasing rate was influenced by strength of electronic field and pH of solution. Under acidic conditions, Fe2+ released from Fec was oxidized into Fe3+ and then was absorbed and reduced at CF cathode. Under alkaline conditions, flocs were formed by reaction between Fe2+ and hydroxyl which came from oxygen reduction.