Sulfate Radical-Based Advanced Oxidation System Using Iron-Based Catalysts for the Degradation of p-nitrophenol(p-NP) in Aqueous System

The p-nitrophenol (p-NP) is a commonly discharged recalcitrant pollutant in industries such as pharmaceuticals and pesticides, known for its toxicity to the eyes, skin, and respirator system. To effectively eliminate p-NP in water systems, sulfate radicals-based advanced oxidation system (SR-AOP) have been proposed, with zero-valent iron (ZVI) evaluated as the catalyst for peroxymonosulfate (PMS) activation. Under optimal condition, the removal efficiency of p-NP in the PMS+ZVI system reached 98.4% within 6 h, and over 90.0% removal of p-NP was observed across a wide pH range of 3 to 11. The presence of SO₄ ^2- in the aqueous solutions had no impact, while other ions including Cl^-, PO₄ ^3-, CO₃ ^2-, and NO₃ ^- inhibited degradation by forming radicals with low oxidative power. The quenching tests were conducted to identify the radicals contributing to p-NP degradation, confirming superoxide radicals (O₂ ^-·) as the primary reactive oxygen species. Finally, through the characterization of ZVI after degradation, the mechanism of p-NP degradation was elucidated. The observation of the Fe₂O₃ peak through XRD confirmed partial oxidation of ZVI, indicating that ZVI provides electrons to activate PMS.