A metal-free method of generating sulfate radicals through direct interaction of hydroxylamine and peroxymonosulfate: Mechanisms, kinetics, and implications

The development of efficient, cost-effective, and metal-free activators for the activation of oxidants is important to promote the application of advanced oxidation processes (AOPs) in the wastewater treatment industry. In this study, we propose an innovative AOP that uses a combination of peroxymonosulfate (PMS) and hydroxylamine (HA). The second-order rate constant for this reaction was determined to be 0.34 ± 0.02 M−1 s−1. Target pollutants, including bisphenol A, phenol, and atrazine, were efficiently degraded by this oxidation, and approximately 100% degradation of the phenol was realized after 6 min. The optimal concentration ratio between HA and PMS was approximately 2.0. Electron paramagnetic resonance confirmed the production of radicals; quenching tests using alcohols, phenol, and nitrobenzene further revealed that sulfate radicals were the dominant species. The unprotonated HA was probably responsible for the activation of PMS. However, because of its reaction with sulfate radicals, the optimal pH of HA-PMS was in the range of 4.0–5.0. Common aqueous constituents such as chloride ions (≤10 mM) and bicarbonate (≤5 mM) had no obvious effects on the HA-PMS, which suggests the important implications of this oxidation.