Rapid Acceleration of Ferrous Iron/Peroxymonosulfate Oxidation of Organic Pollutants by Promoting Fe(III)/Fe(II) Cycle with Hydroxylamine

TLDR

The Fe(II)/PMS system generates reactive oxidants capable of degrading refractory organic contaminants, but the slow Fe(III)→Fe(II) regeneration limits its widespread application. This study adds hydroxylamine to the Fe(II)/PMS process to accelerate the Fe(III)→Fe(II) cycle. Using benzoic acid as a probe, HA addition rapidly degrades BA across pH 2–6 by accelerating the Fe(III)/Fe(II) cycle and producing sulfate and hydroxyl radicals, as shown by ESR and alcohol‑quenching experiments. HA is gradually converted to N₂, N₂O, NO₂⁻, and NO₃⁻, with N₂ as the major environmentally friendly product, demonstrating that the HA/Fe(II)/PMS system offers a promising approach for rapid degradation of refractory organics in water treatment.

Abstract

The reaction between ferrous iron (Fe(II)) with peroxymonosulfate (PMS) generates reactive oxidants capable of degrading refractory organic contaminants. However, the slow transformation from ferric iron (Fe(III)) back to Fe(II) limits its widespread application. Here, we added hydroxylamine (HA), a common reducing agent, into Fe(II)/PMS process to accelerate the transformation from Fe(III) to Fe(II). With benzoic acid (BA) as probe compound, the addition of HA into Fe(II)/PMS process accelerated the degradation of BA rapidly in the pH range of 2.0–6.0 by accelerating the key reactions, including the redox cycle of Fe(III)/Fe(II) and the generation of reactive oxidants. Both sulfate radicals and hydroxyl radicals were considered as the primary reactive oxidants for the degradation of BA in HA/Fe(II)/PMS process with the experiments of electron spin resonance and alcohols quenching. Moreover, HA was gradually degraded to N2, N2O, NO2–, and NO3–, while the environmentally friendly gas of N2 was considered as its major end product in the process. The present study might provide a promising idea based on Fe(II)/PMS process for the rapid degradation of refractory organic contaminants in water treatment.