Formation of nitrosated and nitrated aromatic products of concerns in the treatment of phenols by the combination of peroxymonosulfate and hydroxylamine

Recently, the combination of peroxymonosulfate (PMS) and hydroxylamine (HA) has been proposed as a green and efficient sulfate radical (▪)-based advanced oxidation process (AOP) for eliminating organic contaminants. However, we found that toxic nitrosated and nitrated aromatic compounds were generated during the treatment of phenolic compounds by PMS/HA system, indicating the involvement of reactive nitrogen species (RNS) during the interaction of PMS with HA. Specifically, considerable production of p-nitrosophenol (p-NSP) and mononitrophenol were obtained when phenol was oxidized by PMS/HA system under various conditions. At the molar ratio between HA and PMS of 1.0 and pH 5.0, sum of the yields of p-NSP and nitrophenols reached their maxima (around 50%). Moreover, production of p-NSP was inhibited while that of nitrophenols was promoted when applied NH2OH1/2H2SO4 was replaced by NH2OHHCl, which was possibly related to the formation of secondary reactive species induced by the reaction of ▪ with chloride ion. Further, formation of undesirable nitrosated and nitrated aromatic products was obtained in the treatment of other phenolic compounds including acetaminophen, bisphenol A, and bisphenol S by PMS/HA system. Considering the toxicity of nitrosated and nitrated aromatic compounds, practical application of PMS/HA system for environmental decontamination should be scrutinized. [Display omitted] •p-NSP and NPs were generated in the treatment of phenol by PMS/HA system.•Sum of the yields of p-NSP and NPs reached around 50% at certain condition.•Chloride ion exerted an opposite effect on the production of p-NSP and NPs.•Nitro(so) products were formed in the treatment of AAP, BPA and BPS by PMS/HA system.