Generation of Reactive Oxygen Species and Degradation of Pollutants in the Fe/O/Tripolyphosphate System: Regulated by the Concentration Ratio of Fe and Tripolyphosphate.

Tripolyphosphate (TPP) has many advantages as a ligand for the optimization of the Fe/O system in environmental remediation applications. However, the relationship between remediation performance and the Fe/TPP ratio in the system has not been previously described. In this study, we report that the degradation mechanism of p-nitrophenol (PNP) in Fe/O systems is regulated by the Fe/TPP ratio under neutral conditions. The results showed that although PNP was effectively degraded at different Fe/TPP ratios, the results of specific reactive oxygen species (ROS) scavenging experiments and the determination of PNP degradation products showed that the mechanism of PNP degradation varies with the Fe/TPP ratio. When ≥ , the initially formed O is converted to •OH and the •OH degrades PNP by oxidation. However, when < , the O persists long enough to degrade PNP by reduction. Density functional theory (DFT) calculations revealed that the main reactive species of Fe in the system include [Fe(TPP)(HO)] and [Fe(TPP)], whose content in the solution is the key to achieve system regulation. Consequently, by controlling the Fe/TPP ratio in the solution, the degradation pathways of PNP can be selected. Our study proposed a new strategy to regulate the oxidation/reduction removal of pollutants by simply varying the Fe/TPP ratio of the Fe/O system.