Activation Of Peroxymonosulfate By Hydroxylamine For Oxidative Degradation Of Phenolic Compounds And The Production Of Nitrated By-products

Peroxymonosulfate(PMS)-based advanced oxidation technology has been widely applied in environmental remediation and water treatment.PMS has attracted extensive attention for its ability to oxidize and degrade organic contaminants by producing hydroxyl radical(·OH)or sulfate radical(S04·-)through light,heat and transition metals etc.Recently,a kind of SO4·-based organic contaminants degradation method through PMS activation by hydroxylamine(NH2OH)was proposed.However,as a type of nitrogenous substance,when hydroxylamine was introduced into the oxidation of organic contaminants by persulfate,whether nitrogen-containing by-products would be produced is unknown.Therefore,in order to reveal organic degradation effect and potential environmental risk of this activation method,degradation principle of phenolic compounds and generation mechanism of nitrated by-products in PMS activation by hydroxylamine are studied.Phenol was selected as the target compound for its simple chemical structure to investigate the degradation and the production of nitrophenol.Results showed that phenol could be oxidized.Meanwhile,nitrated by-products 2-nitrophenol and 4-nitrophenol were generated and the generation of dinitrophenol and trinitrophenol was not observed.When system pH was 4.0 degradation of phenol reached maximum.When system pH was 5.0 generated nitrophenol reached maximum.When concentration ratio of hydroxylamine and PMS was 2.0,degradation of phenol reached maximum.When concentration ratio of PMS and hydroxylamine was 1.0,generated nitrophenol reached maximum.When the target compound was replaced into other phenolic compounds like triclosan(TCS),acetaminophen(AAP),bisphenolA(BPA),and bisphenolS(BPS),corresponding nitrated by-products were also observed through HPLC-MS(AB SCIEX QTOFR5600).Degradation mechanism of organic in hydroxylamine/PMS system was verified indirectly throughalcohols quenching tests(methanol andtert butyl alcohol)and nitrobenzene degradation experiments.When methanol andtert butyl alcohol were introduced respectively in the degradation of phenol in hydroxylamine/PMS system,inhibited effect of methanol was stronger than tert butyl alcohol obviously.Combined with differences in reaction rate of alcohols with two types of radicals,Sulfate radical(SO4’)was affirmed as the main reactive species preliminary.Furthermore,according to differences in reaction rate of nitrobenzene with.OH and S04*-,it was found that both ·OH and SO4·-were produced yet SO4·-was the dominant reactive species.Production and consumption of reactive oxygen species increased simultaneously with the increase of pH and the steady-state concentration of reactive oxygen species reached maximum at pH 4.Various reactive nitrogen species(·NO,·NO2,N2O3,ONOOH,NO2＋)were responsible for the nitration of phenol(2-NP and 4-NP)directly.However,detailed nitration pathway of various reactive nitrogen species was distinct and each dose was variational with the change of reaction condition.Hence,ratio of two types of mononitrophenol was changeable.Effect of the introduction of Cl-and NO2 on the transformation of phenol was different in hydroxylamine/PMS system in different pH.When pH was 4,introduced anions had almost no effect on the degradation but nitrated by-products would increase.When pH was 6,degradation and nitration of phenol would be inhibited.This phenomenon was caused by the distinction of steady-state concentration of reactive oxygen species.