Surface Fe(III)/Fe(II) cycle promoted the degradation of atrazine by peroxymonosulfate activation in the presence of hydroxylamine

In this study, we demonstrated that Fe3O4/PMS system in the presence of hydroxylamine (HA) was significantly efficient for atrazine degradation under the near-neutral pH (5.0-6.8) (without buffer). The degradation rate constant of atrazine in Fe3O4/PMS/HA system (0.152 min(-1)) was 38 times of that (0.004 min(-1)) in Fe3O4/PMS system and even 4.75 times of that (0.032 min(-1)) in HA/PMS system. In this Fe3O4/PMS/HA system, the roles of HA were mainly two parts. On one hand, 40% atrazine was decomposed through the activation of peroxymonosulfate (PMS) by HA as a metal-free activator. On the other hand, the addition of HA could highly promote the surface Fe(III)/Fe(II) cycle on the Fe3O4. Meanwhile, the trace dissolved Fe2+ was not the major reason for the atrazine degradation. The reason for different atrazine degradation efficiencies under various aeration conditions was analyzed, which showed that the reduced molecular oxygen was more conducive to accelerate the regeneration of surface Fe(II). Subsequently, the transformation products of HA under different aeration conditions were monitored. What's more, the reactive species were detected by electron paramagnetic resonance (EPR) and quenching experiments, which revealed that both sulfate radical (SO4 center dot-) and hydroxyl radical (HO center dot) were responsible for the atrazine degradation, especially sulfate radical. Finally, the reaction mechanism of Fe3O4/PMS/HA system based on the Fe(III)/Fe(II) cycle and the metal-free activation was proposed according to the comprehensive analysis. This study provides an efficient degradation of atrazine organic pollutant in water by the heterogeneous Fenton-like system.