Efficient Degradation of Metronidazole by In Situ High-Valent Iron-Oxo Species in Nanoclustered Iron–Carbon Particles

High-valent metal species are selective, nonradical species that can enhance advanced oxidation processes (AOPs) for the treatment of difficult-to-degrade pollutants due to their long lifetimes and high steady-state concentrations. As the number of particles in the cluster material increases, high-valent metal sites appear inside the clusters. The special high-valent metal species inside the cluster materials enhance the removal of pollutants, but the mechanism of the role of the cluster materials in the AOPs is not clear. In this paper, nanoclustered iron–carbon particles (BAGAFe) were prepared by carbothermal reduction with gallic acid (GA) as an iron complexing reagent. Low-cost batch preparation of nano zerovalent iron and activated oxidative degradation of metronidazole (MNZ) by peroxydisulfate (PDS) with low dissolved iron (<0.9 mg/L) were achieved. Spectroscopic studies and 18O isotope labeling experiments demonstrated the presence of high-valent iron-oxo species (FeIV═O). Calculation and analysis of steady-state concentrations of various reactive oxygen species (ROSs) demonstrated that FeIV═O contributed 77.8% to the degradation of MNZ. Density functional theory (DFT) and degradation products showed that FeIV═O is the main ROS involved in the degradation of MNZ. This study provides new insight into the preparation of clustered iron–carbon materials and their generation of FeIV═O in activated PDS.