Synthesis of magnetic core–shell iron nanochains for potential applications in Cr(VI) ion pollution treatment

Fe nanochains with diameters of 50–150 nm and average length of about 1 μm were synthesized by titrating NaBH₄ solution into FeCl₂ aqueous solution (i.e., reduction of Fe(II) ions). The microstructures and magnetic properties were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The results reveal that the nanochains have a core–shell structure with α-Fe as the core and amorphous iron oxide as the shell. The Fe core–shell nanochains show the characteristic of soft magnetic materials, achieving the highest magnetization of 200.74 mA·m²·g⁻¹. The influences of the titrating rate of NaBH₄ aqueous solution on the morphology of the Fe nanochains were also studied. It reveals that low titrating rate is beneficial for synthesizing Fe nanochains with uniform morphology. The reduction experiments indicate that these Fe nanochains are of high reducibility. About 90 % Cr(VI) ions are successfully removed after 10 min reaction of 100 mg Fe nanochains in the 100 ml K₂Cr₂O₇ solution (100 mg·L⁻¹) and more than 99 % after 30 min.