Hydroxylamine promoted degradation of sulfamethoxazole by Fe(Ⅲ)-NTA complexes activated peroxydisulfate
To overcome the shortcomings of Fe(Ⅱ)/peroxydisulfate(PDS)advanced oxidation technology such as narrow working pH range and large iron sludge production,Fe(Ⅲ)-nitrilotriacetic acid(NTA)/hydroxylamine(HAm)/PDS system was established in this work to effectively degrade sulfamethoxazole(SMX),an emerging contaminant,under neutral condition.Fe(Ⅲ)-NTA/HAm/PDS system was proved to exhibit a significant advantage over Fe(Ⅱ)/PDS system on the degradation of SMX.Firstly,the introduction of NTA could extend the working pH range of Fe(Ⅱ)/PDS system from acidic to weakly alkaline,which is more beneficial for the practical application of this technology.In addition,the introduction of HAm into this system could effectively drive the cycle of Fe(Ⅱ)/Fe(Ⅲ)and reduce the production of iron sludge,which will reduce the risk of secondary pollution.The result shows that the degradation efficiency of SMX in Fe(Ⅲ)-NTA/HAm/PDS system could reach 91％at pH 7.It was speculated that both·SO4-and·OH were responsible for the degradation of SMX in this system based on the results of the radical scavenging experiment.The effects of solution pH,Fe(Ⅲ)concentration,and PDS dose on the degradation of SMX were also systematically investigated.It is observed that the degradation of SMX in Fe(Ⅲ)-NTA/HAm/PDS system was obviously suppressed with increasing solution pH due to the change in the complexes formed between Fe(Ⅲ)and NTA.In contrast,the degradation of SMX in this system could be promoted by increasing the dosage of Fe(Ⅲ)and PDS.Six degradation products of SMX were detected in Fe(Ⅲ)-NTA/HAm/PDS system and three possible degradation pathways of SMX in this system were accordingly proposed,including bond cleavage,hydroxylation,and amino oxidation.Three different emerging contaminants(i.e.,bisphenol AF,diclofenac,and oxytetracycline)could also be effectively degraded in Fe(Ⅲ)-NTA/HAm/PDS system,suggesting that this system has a huge potential to be applied in the field of emerging contaminants degradation.
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