Iron oxide shell mediated environmental remediation properties of nano zero-valent iron

Abstract

Nano zero-valent iron (nZVI) has attracted much more attention for its potential applications in the fields of environmental contaminant remediation and detoxification. Generally, nZVI consists of a zero-valent iron (Fe⁰) core and an iron oxide shell structure. As the underlying Fe⁰ core and the surface oxide shell determine the physical and chemical properties of nZVI, the nature of the oxide shell inevitably affects the organic/inorganic pollutant removal performance of nZVI, which has not been reviewed previously. In this article, we first introduce the synthesis and the oxide shell formation mechanism of core–shell structured nZVI and then discuss various characterization techniques to reveal the structure and chemical composition of the oxide shell. Subsequently, we clarify the roles of the oxide shell in the organic contaminant degradation efficiency and the molecular oxygen activation performance of nZVI and also highlight the effect of the oxide shell on heavy metal removal (including As) with nZVI. In addition, we summarize some oxide shell modification strategies to enhance the capacity and longevity of nZVI. Finally, we discuss the impacts of typical natural groundwater constituents (e.g. cations, anions, organic ligands, and dissolved oxygen) on the reactivity of nZVI and point out some unresolved issues related to the oxide shell dependent contaminant removal properties of nZVI.