Phosphate Shifted Oxygen Reduction Pathway on Fe@Fe₂O₃ Core–Shell Nanowires for Enhanced Reactive Oxygen Species Generation and Aerobic 4-Chlorophenol Degradation

Abstract

Phosphate ions widely exist in the environment. Previous studies revealed that the adsorption of phosphate ions on nanoscale zerovalent iron would generate a passivating oxide shell to block reactive sites and thus decrease the direct pollutant reduction reactivity of zerovalent iron. Given that molecular oxygen activation process is different from direct pollutant reduction with nanoscale zerovalent iron, it is still unclear how phosphate ions will affect molecular oxygen activation and reactive oxygen species generation with nanoscale zerovalent iron. In this study, we systematically studied the effect of phosphate ions on molecular oxygen activation with Fe@Fe₂O₃ nanowires, a special nanoscale zerovalent iron, taking advantages of rotating ring disk electrochemical analysis. It was interesting to find that the oxygen reduction pathway on Fe@Fe₂O₃ nanowires was gradually shifted from a four-electron reduction pathway to a sequential one-electron reduction one, along with increasing the phosphate ions concentration from 0 to 10 mmol·L^-1. This oxygen reduction pathway change greatly enhanced the molecular oxygen activation and reactive oxygen species generation performances of Fe@Fe₂O₃ nanowires, and thus increased their aerobic 4-chlorophenol degradation rate by 10 times. These findings shed insight into the possible roles of widely existed phosphate ions in molecular oxygen activation and organic pollutants degradation with nanoscale zerovalent iron.