Transformation of iron oxides in amorphous nanoscale zero-valent iron (A-nZVI) and nZVI: effect on Sb(iii) removal affinity and stability

Abstract

Nanoscale zero-valent iron (nZVI) and modified nZVI have shown great removal capacities towards various heavy metals. However, the aging process of nZVI during the reaction is crucial for the long-term affinity and stability of heavy metals in the environment. In this study, the aging and iron oxide evolution of amorphous nZVI (A-nZVI) and nZVI during the reaction with Sb(III) were investigated and compared. The results indicated that after reacting with Sb(III), iron oxides in A-nZVI were mainly composed of γ-Fe₂O₃ (33.9%) and γ-FeOOH (29.8%), whereas α-Fe₂O₃ (24.9%) and α-FeOOH (31.8%) were dominant in the aged nZVI. The removal capacities for Sb(III) of γ-Fe₂O₃ (69.8 mg g⁻¹) and γ-FeOOH (42.3 mg g⁻¹) were both much higher than those of α-Fe₂O₃ (4.3 mg g⁻¹) and α-FeOOH (8.4 mg g⁻¹). Sb(III) was partially oxidized during the reaction, and DFT calculation showed that the adsorption energies of both Sb(III) and Sb(V) on γ-Fe₂O₃ and γ-FeOOH were higher than those on α-Fe₂O₃ and α-FeOOH. Furthermore, EXAFS analysis revealed that Sb formed an inner-sphere complex with the iron oxides in A-nZVI through the bidentate mononuclear edge-sharing structure (2E). Therefore, A-nZVI showed higher affinity and long-term stability toward Sb(III) remediation.