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

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 gamma-Fe2O3 (33.9%) and gamma-FeOOH (29.8%), whereas alpha-Fe2O3 (24.9%) and alpha-FeOOH (31.8%) were dominant in the aged nZVI. The removal capacities for Sb(iii) of gamma-Fe2O3 (69.8 mg g(-1)) and gamma-FeOOH (42.3 mg g(-1)) were both much higher than those of alpha-Fe2O3 (4.3 mg g(-1)) and alpha-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 gamma-Fe2O3 and gamma-FeOOH were higher than those on alpha-Fe2O3 and alpha-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.