Interaction of Persulfate and Hydroxylamine Produces Highly Reactive Species in Aqueous Systems

Activation of persulfate is a hot topic in environmental remediation via generating reactive species such as SO4•– and 1O2. This study investigated the activation of peroxydisulfate (PDS) by HA with respect to the formation mechanisms of reactive species and their roles in contaminant transformation. SO4•–, HO•, and reactive nitrogen species (RNS, e.g., •NO, •NO2, and NH2O•) were proved to be predominant reactive species in the HA/PDS system by electron paramagnetic resonance analysis and radical scavenging tests. The reaction stoichiometric ratio of HA to PDS was about 0.63, involving two major steps: HA initially reacted with PDS to generate SO4•– and NH2O•, and NH2O• further reacted with PDS to form SO4•– and HNO. Ultimately, N2O was the major product of HA via the dimerization of HNO. •NO was formed via the reactions of HNO with O2 and HO•, and •NO2 could be formed via the reaction of SO4•– and NO2–. In the HA/PDS system, SO4•– and HO• primarily contributed to the degradation kinetic of carbamazepine, while RNS also played important roles in the transformation pathways of carbamazepine, resulting in the formation of nitroso compounds. As pH increased from 2 to 7, the removal rate of carbamazepine was highest at pH 3–4 (66–69% at 60 min), which is mainly due to NH2OH showing higher activation efficiency for PDS but faster consumption for SO4•– and HO• compared to NH3OH+. This study broadens the understanding of peroxide activation by HA and demonstrates the important roles of formed RNS in contaminant transformation.