Synergistic degradation of PNP via coupling H₂O₂ with persulfate catalyzed by nano zero valent iron

H₂O₂ and persulfate (PDS) activated by iron are attracting much attention due to their strong oxidation capacity for the effective degradation of organic pollutants. However, they face problems such as requiring an acidic reaction pH and difficulty of Fe²⁺ regeneration. In this study, the simultaneous activation of H₂O₂ and persulfate by nanoscaled zero valent iron (nZVI) was investigated for the degradation of p-nitrophenol (PNP). The nZVI/H₂O₂/PDS oxidation system exhibited significantly higher reactivity toward PNP degradation than the systems with a single oxidant. A synergistic effect was explored between H₂O₂ and PDS during nZVI-mediated activation, and the molar ratio of H₂O₂/PDS was a key parameter in optimizing the performance of PNP degradation. The nZVI/H₂O₂/PDS system could function well in a wide pH range, and even 95% PNP was removed at an initial pH 10, thus markedly alleviating the pH limitations of Fenton-like processes. Both hydroxyl radicals and sulfate radicals could be identified during H₂O₂/PDS activation, in which H⁺ produced during PDS decomposition promoted H₂O₂ activation. The increase of oxidant concentration could significantly enhance the PNP degradation, while the presence of HCO₃ ^- and HPO₄ ^2- exerted great inhibition. Furthermore, five degradation intermediates of PNP were detected and its degradation pathways in the nZVI/H₂O₂/PDS system were presented. This study reveals that the simultaneous activation of H₂O₂ and PDS by nZVI is a promising advanced oxidation tool as an alternative to typical Fenton processes for recalcitrant pollutant removal.