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

Activation of persulfate is a hot topic in environmentalremediationvia generating reactive species such as SO4 (center dot-) and O-1(2). This study investigated the activationof peroxydisulfate (PDS) by HA with respect to the formation mechanismsof reactive species and their roles in contaminant transformation.SO4 (center dot-), HO center dot,and reactive nitrogen species (RNS, e.g., (NO)-N-center dot, (NO2)-N-center dot, and NH2O center dot) were proved to be predominant reactive species in the HA/PDS systemby electron paramagnetic resonance analysis and radical scavengingtests. The reaction stoichiometric ratio of HA to PDS was about 0.63,involving two major steps: HA initially reacted with PDS to generateSO(4) (center dot-) and NH2O center dot, and NH2O center dot further reactedwith PDS to form SO4 (center dot-) and HNO.Ultimately, N2O was the major product of HA via the dimerizationof HNO. (NO)-N-center dot was formed via the reactions of HNOwith O-2 and HO center dot, and (NO2)-N-center dot could be formed via the reaction of SO4 (center dot-) and NO2 (-). In the HA/PDS system, SO4 (center dot-) and HO center dot primarily contributed to the degradationkinetic of carbamazepine, while RNS also played important roles inthe transformation pathways of carbamazepine, resulting in the formationof nitroso compounds. As pH increased from 2 to 7, the removal rateof carbamazepine was highest at pH 3-4 (66-69% at 60min), which is mainly due to NH2OH showing higher activationefficiency for PDS but faster consumption for SO4 (center dot-) and HO center dot compared to NH3OH+. This study broadens the understanding of peroxide activation byHA and demonstrates the important roles of formed RNS in contaminanttransformation.