Switching the primary mechanism from a radical to a nonradical pathway in electrocatalytic ozonation by onsite alternating anode and cathode

Abstract

Concurrently elevating the degradation efficiency of pollutants and realizing the reduction of iron sludge in Fe-based catalytic ozonation is important but still challenging. Herein, we developed an electrocatalytic ozonation (ECO) system with iron plate cathode and graphite felt anode (ECO-Fe-cathode), which was free from added chemical reagents. Unlike the iron plate as a sacrificial anode in the ECO (ECO-Fe-anode) system, this delicately designed system shows a much higher degradation rate of ibuprofen (kobs = 1.490 min−1) than that of the ECO-Fe-anode system (kobs = 0.345 min−1). Simultaneously, the effluent was totally limpid without the corrosion of iron plates and the formation of iron sludge in the ECO-Fe-cathode system. Unexpectedly, the generation of singlet oxygen (1O2) which is indirectly generated by the single-electron transfer derived from superoxide ion (O2•-) is the primary reactive oxygen species (ROS) in the ECO-Fe-cathode system, which is different from the ECO-Fe-anode system with hydroxyl radicals (•OH). Moreover, linear sweep voltammetry (LSV) was applied to reveal the oxygen evolution reaction (OER) performance of the iron plate and graphite felt, and the results showed that graphite felt as anode has better electrocatalytic performance. The electrochemical analysis and density functional theory (DFT) calculation revealed that ozone adsorbed on the iron plate surface is more conducive to facilitating and triggering subsequent reactions. Finally, the different degradation pathways of ibuprofen in both systems were proposed. This work represents a fundamental breakthrough toward the design of an efficient and harmless ECO system for wastewater treatment.