Efficient elimination of phenazone by an electro-assisted Fe3+-EDDS/PS process at neutral pH: Kinetics, mechanistic insights and toxicity evaluation.

The feasibility of the degradation of phenazone (PNZ), a common anti-inflammatory drug used for reducing pain and fever, in water at neutral pH by an electrochemically assisted Fe3+-ethylenediamine disuccinate-activated persulfate process (EC/Fe3+-EDDS/PS) was investigated. The efficient removal of PNZ at neutral pH condition was mainly attributed to the continuous activation of PS via electrochemically driven regenerated Fe2+ from a Fe3+-EDDS complex at the cathode. The influence of several critical parameters, including current density, Fe3+ concentration, EDDS to Fe3+ molar ratio, and PS dosage, on PNZ degradation was evaluated and optimized. Both hydroxyl radicals (•OH) and sulfate radicals (SO4●-) were considered major reactive species responsible for PNZ degradation. To understand the mechanistic model of action at the molecular level, the thermodynamic and kinetic behaviors of the reactions between PNZ with •OH and SO4●- were theoretically calculated using a density functional theory (DFT) method. The results revealed that radical adduct formation (RAF) is the most favorable pathway for the •OH-driven oxidation of PNZ, while single electron transfer (SET) appears to be the dominant pathway for the reaction of SO4●- with PNZ. In total, thirteen oxidation intermediates were identified, and hydroxylation, pyrazole ring opening, dephenylization, and demethylation were speculated to be the major degradation pathways. Furthermore, predicted toxicity to aquatic organisms indicated that PNZ degradation resulted in products that were less harmful. However, the developmental toxicity of PNZ and its intermediate products should be further investigated in the environment. The findings of this work demonstrate the viability of effectively removing organic contaminants in water at near-neutral pH by using EDDS chelation combined with electrochemistry in a Fe3+/persulfate system.