Identify The Reactive Intermediates In Fe(?) Active Persulfate Process By Sulfoxides

In previous studies,researchers have demonstrated that Fenton reagents produce hydroxyl radicals under acidic condition while the dominant reactive oxidant convert to ferryl ion?Fe?IV??species at near-neutral p H by using sulfoxides which produce corresponding sulfones with Fe?IV?species,which differ markedly from their hydroxyl radical-induced products,as probe compounds.Recently,persulfate(i.e.,peroxymonosulfate?HSO₅^-?and peroxydisulfate(S₂O₈^2-))has been widely used as an environmental friendly alternative oxidant in advanced oxidation processes?AOP?.It is recognized that a conventional advanced oxidation processes?AOP?by combining peroxymonosulfate?PMS?or peroxydisulfate?PDS?and Fe???based on the generation of sulfate radical or hydroxyl radical,similar to H2O2 / Fe???system.It is puzzling that Fe?IV?species were not taken into account as potential active oxidants when utilize Fe???to active PDS or PMS in any previous studies.The purpose of this study was to explore the possibility of the produce of Fe?IV?species in Fe???/ S₂O₈^2-and Fe???/ HSO₅^-system and the system enhanced by iron reducing agents.In this work,we used liquid chromatography-mass spectrometry identified that,sulfoxides would not be oxidized to sulfones by sulfate radicals,so that sulfoxides can be introduced as probe compounds to distinguish SO₄^·-with Fe?IV?.Represented by methyl phenyl sulfoxide?PMSO?,we investigated the main products of sulfoxides oxidized by SO₄^·-and ·OH respectively and analyzed the possible reaction routes.Meanwhlie,the second-order rate constants of the selected sulfoxides?PMSO?and sulfones?PMSO2?with ·OH and SO₄^·-was determined by a competition kinetic method.Depending on all above studies,we established a method which can be used to distinguish Fe?IV?with free radicals.Utlizing PMSO as probe compounds,the results shown that the prevalence rate of PMSO2?e.g.??PMSO2??in Fe???/ S₂O₈^2-and Fe???/ HSO₅^-system are 100 % under acid conditions,indicating that the reactive oxidant in these two systems is Fe?IV?species rather than free radicals,which stand in sharp contrast with previous studies.In Fe???/ S₂O₈^2-system,the consumption of Fe?IV?by Fe???was the main side reactions and the the consumption of Fe?IV?by S₂O₈^2-was negligible.While in Fe???/ HSO₅^-system,the side reactions induced by Fe???and HSO₅^-were all strong.At near-neutral p H,the degradation amount of PMSO was too small to be calculated exactly for the generation amount of reactive intermediates decreased sharply with the rise of p H.However,the generation of PMSO2 was observed too,suggesting that Fe???/ S₂O₈^2-and Fe???/ HSO₅^-system also produce Fe?IV?under near-neutral conditions.Four species of iron reducing agents were used to accelerate Fe???/ S₂O₈^2-and Fe???/ HSO₅^-system and the generation of reactive oxidants were researched.Compared to Fe???/ S₂O₈^2-system,in which ??PMSO2?reached to 100 %,hydroxylamine led to ??PMSO2?decline to 70 %;polyphenols and benzoquinone have no effects on ??PMSO2?;phenolic acids and amino acids led to the decrease and fluctuation during reaction time of ??PMSO2?.In Fe???/ HSO₅^-system,hydroxylamine sulfate have no effects on ??PMSO2?,while hydroxylamine hydrochloride made ??PMSO2?decreased to 70 % for the interference of Cl-.The ??PMSO2?in the Fe???/ HSO₅^-system enhanced by polyphenols,benzoquinone and phenolic acids compounds were fairly constant and approached to 100 %.The addition of L-Cysteine made the ??PMSO2?of Fe???/ HSO₅^-system decreased to 80 %.The results shown that some iron reducing agents change the rection route of Fe???with HSO₅^-,which led to the generation of free radicals and the decrease of ??PMSO2?.