Effects Of Molecular Oxygen On The Removal Of Humic Acids And Hexavalent Chromium In Aqueous Solution With Fe@Fe₂O₃Core-shell Nanowires

Nowadays water pollution problem has been growing along with the development of industry, which also threat the human health and social sustainable development. Therefore, it is necessary to develop efficient, environmentally friendly and economic sewage treatment technology to purify the water resource.In view of natural abundance and environmental benignancy of iron, the utilization of nanoscale zero-valent iron (nZVI) to remove pollutants is very attractive. However, the mechanisms of the removal of aqueous pollutants with nZVI are not very clear. Therefore, we comparatively investigate the removal of typical aqueous contaminates like humic acid and Cr(VI) with a special kind of nZVI (Fe@Fe2O3core-shell nanowires) under anoxic and oxic conditions to deeply understand the removal mechanism of aqueous pollutants with nZVI.We first investigated the effects of molecular oxygen on removal of humic acids with Fe@Fe2O3core-shell nanowires and carefully examined the products of humic acids after reacting with Fe@Fe2O3core-shell nanowires under anoxic and oxic conditions with three-dimensional excitation emission matrix fluorescence spectroscopy and gas chromatography mass spectrometry. It was found that humic acids were removed by Fe@Fe2O3core-shell nanowires via adsorption under anoxic condition. In contrast, the oxic removal of humic acids with Fe@Fe2O3core-shell nanowires involved adsorption and subsequent oxidation of humic acids because Fe@Fe2O3core-shell nanowires could activate molecular oxygen to produce reactive oxygen species to oxidize humic acids. This subsequent oxidation of humic acids could improve the oxic removal rate to2.5times that of anoxic removal.We subsequently studied the effects of molecular oxygen on the removal of Cr(VI) with Fe@Fe2O3core-shell nanowires by measuring the production of ferrous ion, total dissolved iron, Cr(VI) and Cr(III) in aqueous solution. X-ray photoelectron spectroscopic analysis (XPS) and X-ray diffraction analysis (XRD) were used to characterize the structure change of Fe@Fe2O3core-shell nanowires during the reaction. It was found that Cr(VI) was removed by Fe@Fe2O3core-shell nanowires via adsorption and reduction under anoxic and oxic conditions. The reduction of Cr(VI) by Fe2+mainly accounted for the removal of Cr(VI). The influence of molecular oxygen on the Cr(VI) removal was different from that of humic acids removal with Fe@Fe2O3core-shell nanowires because the oxic Cr(VI) removal rate was slower than its anoxic removal rate. The inhibitory effect of molecular oxygen on the Cr(VI) removal was attributed to the adverse roles of reactive oxygen species generated during the removal of Cr(VI) with Fe@Fe2O3core-shell nanowires.In summary, this thesis aims to clarify the effects of molecular oxygen on removal of pollutants with nanoscale zero-valent iron by comparing the anoxic and oxic removal of humic acids and Cr(VI) with Fe@Fe2O3core-shell nanowires. This study can shed light on the removal mechanisms of aqueous pollutants with nZVI, and also provide new green methods for the pollutant removal.