The nature of metal atoms incorporated in hematite determines oxygen activation by surface-bound Fe(II) for As(III) oxidation

摘要

The incorporation of secondary metal atoms into iron oxyhydroxides may regulate the surface chemistry of mediating electron transfer (ET) and, therefore, the biogeochemical pollutant processes such as arsenic (As) in the subsurface and soils. The influence of incorporating two typical metals (Cu and Zn) into a specific {001} hematite facet on O-2 activation by surface-bound Fe(II) was addressed. The results showed that Cu-incorporated hematite enhances As(III) oxidation in the presence of Fe(II) under oxic conditions and increases with increasing Cu content. Conversely, Zn incorporation leads to the opposite trend. The As(III) oxidation induced by surface -bound Fe(II) is positively related to the Fe(II) content and is favorable under acidic conditions. Reactive oxygen species (ROS), such as superoxide (center dot O2- ) and H2O2, predominantly contribute to As(III) oxidation as a result of 1-electron transfer from bound Fe(II) to surface O-2 on hematite and radical propagation. Electrochemical analysis demonstrates that Cu incorporation significantly lower the oxidation potential of Fe(II) on hematite, whereas Zn led to a higher reaction potential for Fe(II) oxidation. Subsequently, distinct surface reactivities of hematite for the activation of O-2 to form ROS by surface-bound Fe(II) are evidenced by metal incorporation. Our study provides a new understanding of the changes in the surface chemistry of iron oxyhydroxides because of incor-porating metals (Zn and Cu), and therefore impact the biogeochemical processes of pollutants in soils and subsurface environments.

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