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Structural Evolution of Nanoscale Zero-Valent Iron (nZVI) in Anoxic Co(2+) Solution: Interactional Performance and Mechanism

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Structural Evolution of Nanoscale Zero-Valent Iron (nZVI) in Anoxic Co(2+) Solution: Interactional Performance and Mechanism

Yalei Zhang et al. Sci Rep.

Abstract

The structures of nanoscale zero-valent iron (nZVI) particles evolving during reactions, and the reactions are influenced by the evolved structures. To understand the removal process in detail, it is important to investigate the relationships between the reactions and structural evolution. Using high resolution-transmission electron microscopy (HR-TEM), typical evolved structures (sheet coprecipitation and cavity corrosion) of nZVI in anoxic Co(2+) solutions were revealed. The system pH (pH measured in mixture), which controls the stability of coprecipitation and the nZVI corrosion rate, were found to be the determining factors of structural evolutions. X-ray photoelectron spectroscopy (XPS) results indicated that the formation and dissolution of sheet structure impacts on the ratio of Fe(0) on the nZVI surface and the surface Co(2+) reduction. The cavity structure provides the possibility of Co migration from the surface to the bulk of nZVI, leading to continuous removal. Subacidity conditions could accelerate the evolution and improve the removal; the results of structurally controlled reactions further indicated that the removal was suspended by the sheet structure and enhanced by cavity structure. The results and discussion in this paper revealed the "structural influence" crucial for the full and dynamical understanding of nZVI reactions.

Figures

Figure 1
Figure 1. Typical TEM images of structural evolution of 1 g/L nZVI particles reacting with deionized water and with Co2+ at different initial concentrations over 10 days.
Figure 2
Figure 2. TEM images of cavity structures after reaction in 1000 mg/L Co2+ for 10 days.
Figure 3
Figure 3. Variation of system pH and solution pH at different initial Co2+ concentrations ((a) 1000 mg/L; (b) 50 mg/L).
Figure 4
Figure 4. XPS peak area ratios of Co(0) to total Co, Fe(0) to total Fe, total Co to total Fe and metal to (OH + O2−) in 1000 mg/L Co2+.
Figure 5
Figure 5. Conceptual process and mechanism of Co migration on nZVI particles.
Figure 6
Figure 6. Effect of system pH on removal kinetics and Fe2+ release at initial Co2+ concentrations of 1000 mg/L (a,b) and 50 mg/L (c,d).
Figure 7
Figure 7. Effeect of structure pre-control on the removal at initial Co2+ concentration of 1000 mg/L (a) and 50 mg/L (b).

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