Overlooked Enhancement Of Chloride Ion On The Transformation Of Reactive Species In Peroxymonosulfate/Fe(Ii)/Nh2oh System

Though hydroxylamine (NH2OH) is effective for accelerating pollutants degradation in Fenton and Fenton-like systems, the effect of anions simultaneously introduced by the hydroxylamine salts have always been ignored. Herein, effect of two commonly used hydroxylamine salts, hydroxylamine hydrochloride (NH2OH center dot HCl) and hydroxylamine sulfate [(NH2OH)(2)center dot H2SO4], for the degradation of dimethyl phthalate (DMP) in peroxymonosulfate (PMS)/Fe(II) system was comparatively investigated. Degradation efficiency of DMP with NH2OH center dot HCl was 1.6 times of that with same dosages of (NH2OH)(2)center dot H2SO4 center dot SO4 center dot-, Fe(IV) and center dot OH formed in the PMS/Fe(II)/NH2OH system, but center dot OH was the major species for DMP degradation. Addition of Cl- significantly improved the production of center dot OH and Cl center dot, and the exposure dose of center dot OH (CT center dot OH) was more than 10 times that of CTCl center dot as the concentration of Cl- increased to 1 mM. Calculations based on branching ratios of Cl center dot and center dot OH indicated that the reactions of Cl- with SO4 center dot- and Cl center dot with H2O were not the only production sources of center dot OH in the system. Further experiments with methyl phenyl sulfoxide (PMSO) as the probe indicated that Cl- would facilitate the shift of reactive species from Fe(IV) to radicals (SO4 center dot- or center dot OH) in the system. Both hydroxylation and nitration intermediate products were detected in the oxidation of DMP. Cl- promoted the formation of hydroxylation intermediates and reduced the formation of nitration intermediates. This study revealed for the first time that Cl- could shift reactive species from Fe(IV) to radicals in PMS/Fe(II) system, raising attention to the influence of the coexisting anions (especially Cl-) for pollutants oxidation in iron-related oxidation processes. (C) 2021 Elsevier Ltd. All rights reserved.