Highly organized nanofiber formation from zero valent iron nanoparticles after cadmium water remediation

Many studies have used nanoscale zero valent iron (nZVI) nanoparticles to remove redox-sensitive metals (e.g., As, Cr, U, Se, Ni, Cu) from aqueous systems by absorption or reduction processes. However, very few investigations present a detailed study of the product formed after the remediation process. In order to quantify the efficiency of nZVI particles as a possible cadmium remediation agent, we prepared nZVI by sodium borohydride reduction of an iron complex, FeCl₃·6H₂O, at room temperature and ambient pressure. Fe⁰ and nanocrystalline structures of iron oxides and oxyhydroxides were obtained with this method. We exposed the nZVI to 6 ppm of Cd²⁺ and characterized the products with X-ray diffraction, X-ray absorption and X-ray photoelectron spectroscopy. Inductively coupled plasma analysis showed that the nZVI remediation efficiency of cadmium ions was between 80% and 90% in aqueous media. All of the physical characterization results confirmed the presence of Fe⁰, α-Fe₂O₃ and FeOOH. High resolution transmission electron microscopy images showed nanofiber formation of a mixture of Fe⁰, oxyhydroxides and oxides iron formed after interacting with cadmium ions, possibly forming CdFe₂O₄. These results suggest that the FeOOH shell and other iron oxides in nZVI could enhance Cd²⁺ removal. This removal is observed to cause a change of the initial structure of nZVI to nanofibers due to possible formation of CdFe₂O₄ as a waste product.