Effect and mechanism of Fe2+-activated molecular oxygen advanced oxidation of p-nitrophenol enhanced by aminocarboxylic acid chelating agents
Three advanced oxidation systems,including Fe2+/O2/disodium ethylenediamine tetraacetate(EDTA),Fe2+/O2/trisodium nitrilotriacetate(NTA)and Fe2+/O2/N,N'-Ethylenediamine disuccinic acid(EDDS)systems,were constructed to investigate the effectiveness of the 3 systems focr removing target contaminant p-nitrophenol(PNP).The generation process of reactive free radicals,and their contribution of pollutants degradation as well as the enhancement of aminocarboxylate ligands and its underlying mechanisms were also studied and clarified in the system of Fe2+/O2/EDTA and Fe2+/O2/NTA.The highest PNP degradation efficiency of 50.8％and 81.2％were achieved in the system of Fe2+/O2/EDTA and Fe2+/O2/NTA,respectively,under pH=3 and the molar ratio of Fe2+to ligand of 1∶1.The reactive free radicals generated by Fe2+/O2/EDTA system were HO·and O2,with two generation pathway(one-electron transfer mechanism:O2→O2·-→H2O2→HO·;two-electron transfer mechanism:O2→H2O2→HO·).initial PNP was reduced to p-aminophenol by O2·-;PNP and its reduction products were oxidized by HO to hydroquinone and p-benzoquinone,followed with the ring structure breakage.HO·was the major reactive free radicals generated by Fe2+/O2/NTA system by two-electron transfer mechanism.PNP was directly oxidized by HO·to hydroquinone and p-benzoquinone,followed with the ring structure breakage.The mechanisms of the difference in the activation capacity of the two ligands were studied.
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