ABSTRACT
Hydroxylamine (NH2OH) has been verified to efficiently strengthen pollutants oxidation in Fe(II)/peroxydisulfate (PDS) and Fe(II)/H2O2 systems. However, the different effects of hydroxylamine salts types were rarely recognized. Herein, the effects of two commonly used hydroxylamine salts (i.e. NH2OH·HCl and (NH2OH)2·H2SO4) on oxidation kinetics and reactive species composition were compared in Fe(II)/PDS and Fe(II)/H2O2 systems for the first time. Pseudo first order kinetics could only describe benzoic acid (BA) oxidation well in Fe(II)/NH2OH/H2O2 system, which was related to the different concentration changes of Fe(III) determined by [Formula: see text] . Hydroxylamine salts types influenced not kinetic rules, but reaction rates of target compounds. The empirical reaction rate constant of BA in Fe(II)/NH2OH·HCl/PDS system was 141.5% of that in Fe(II)/(NH2OH)2·H2SO4/PDS system under the same concentration of NH2OH (1.4 mM), while the apparent reaction rate constant in Fe(II)/NH2OH·HCl/H2O2 system was 68% of that in Fe(II)/(NH2OH)2·H2SO4/H2O2 system. This opposite effect resulted from the differences in primary reactive species compositions and their interactions with Cl-. Reactive species identification indicated that Cl- would decrease the contribution of ferryl ion (Fe(IV)) and transform sulfate radical (SO4·-) to hydroxyl radical (·OH) in Fe(II)/NH2OH/PDS system, while it competitively consumed the only reactive species ·OH in Fe(II)/NH2OH/H2O2 system. This study highlights the importance of reductants types on strengthening Fenton oxidation and offers a reference for reasonable construction of the relevant systems.
Subject(s)
Ferric Compounds , Hydrogen Peroxide , Ferrous Compounds , Hydroxylamine , Hydroxylamines , Oxidation-Reduction , SaltsABSTRACT
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·HCl) and hydroxylamine sulfate [(NH2OH)2·H2SO4], for the degradation of dimethyl phthalate (DMP) in peroxymonosulfate (PMS)/Fe(II) system was comparatively investigated. Degradation efficiency of DMP with NH2OH·HCl was 1.6 times of that with same dosages of (NH2OH)2·H2SO4. SO4·-, Fe(IV) and ·OH formed in the PMS/Fe(II)/NH2OH system, but ·OH was the major species for DMP degradation. Addition of Cl- significantly improved the production of ·OH and Cl·, and the exposure dose of ·OH (CT·OH) was more than 10 times that of CTCl· as the concentration of Cl- increased to 1 mM. Calculations based on branching ratios of Cl· and ·OH indicated that the reactions of Cl- with SO4·- and Cl· with H2O were not the only production sources of ·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·- or ·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.
