Structural Evolution of Nanoscale Zero-Valent Iron (nZVI) in Anoxic Co2+ Soultion : Interactional Performance and Mechanism

Abstract:

The nanoscale particle and low oxidation reduction potential make nano zero-valent iron (nZVI) an efficient sorbent and reductant for treating many kinds of organic contaminants and heavy metals.The structures of nanoscale zero-valent iron (nZVI) particles are evolving in reactions, and the reactions are influenced by the evolved structures. In order to understand the detail removal process, it is important to investigate the interactions between reactions and structural evolution. In this work, reactions between nZVI and Co²⁺ at different initial concentrations in anoxic aqueous solutions (to eliminate the effects of O₂) were tracked for 10 days using a variety of methods including inductively coupled plasma optical emission spectrometry (ICP-OES), high resolution-transmission electron microscopy (HR-TEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). Continuous removal and reduction of Co²⁺ by nZVI caused by structural evolution were revealed in reaction processes. The system pH (pH measured in mixture), which controls the stability of coprecipitation and the corrosion rate of nZVI, was deemed as the determining factors of structural evolutions. X-ray photoelectron spectroscopy (XPS) results showed that the formation and dissolution of sheet structure impacts on the ratio of Fe (0) on nZVI’s surface and the surface reduction of Co²⁺. The cavity structure provides the possibility of Co migrating from surface to inside of nZVI leading a continuous removal. A subacidity condition could accelerate the evolution to improve the removal of Co²⁺ and the results of structural controlled reactions further indicated that the removal was suspended by sheet structure and enhanced by cavity structure. The results in this study revealed “structural influence” for fully and dynamically understanding nZVI’s reactions.