Mechanism of self-driven naphthol blue black degradation in Fe(III)-activated peracetic acid system: Dominant role of high-valent iron species.

The iron-activated peracetic acid (PAA) system is a novel green advanced oxidation process (AOP), but conventional Fe(III)-activated PAA systems suffer from low efficiency and require co-activator for iron cycling. This study demonstrated efficient degradation of the organic pollutant Naphthol Blue Black (NBB) in a Fe(III)/PAA system without additional co-activator, achieving 95.7 % removal within 7 min, slightly higher than that observed with Fe(II). The degradation efficiency of NBB increased with appropriate elevation of initial concentrations of Fe(III), NBB, and PAA, but was inhibited under high temperature (>25 °C) and elevated pH (>3). High-valent iron species (FeIVO2+) dominated the degradation process, while organic radicals (R-O•) and hydroxyl radical (•OH) played auxiliary roles. Four potential degradation pathways were proposed, and the ecological toxicity of NBB was found to decrease after degradation. The system exhibited strong tolerance to common coexisting ions (NO3-, Cl-, HCO3-, SO42-, NH4+, Ca2+, and Mg2+), but was inhibited by humic acid (HA) and H2PO4- through radical scavenging and iron complexation. Notably, the degradation efficiency of NBB exceeded 92.5 % in various natural water matrices, including groundwater, lake water, and river water. The study revealed that the self-driven degradation efficiency of organic pollutants in the Fe(III)/PAA system correlates with the electronic properties and spatial configuration of coordinating groups in the pollutant molecules. This research introduces a novel strategy for PAA activation and provides a practical approach for removing typical organic pollutants.