Synthesis and Characterization of Nanostructured Fe3O4 Micron-Spheres and Their Application in Removing Toxic Cr Ions from Polluted Water

We present a simple and effective method for the synthesis of nanostructured Fe3O4 micron-spheres (NFMSs) by annealing hydrothermally formed FeCO3 spheres in argon. The phase structure, particle size, and magnetic properties of the product have been characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and by means of a superconducting quantum interference device (SQUID). The results have shown that the as-obtained NFMSs have a diameter of about 5 mu m and are composed of nanometer-sized porous lamellae. The NFMSs have a large specific surface area (135.9 m2?g-1), reductive Fe2+ incorporated into their structure, and intense magnetic properties. These properties suggest that NFMSs have potential application in removing toxic Cr6+ ions from polluted water. At 25?degrees C, each gram of NFMSs product can remove 43.48 mg of Cr6+ ions, as compared to just 10.2 mg for nanometer-sized Fe3O4 and 1.89 mg for micron-sized Fe3O4. The enhanced removal performance can be ascribed to the structural features. Moreover, the Cr6+ ion removal capacity of the NFMSs can reach up to 71.2 mg?g-1 at 50?degrees C. The influencing parameters in the removal of Cr6+ ions, such as contact time, pH, and temperature, have been evaluated. The Cr6+-removal mechanism has been investigated. We have found that the NFMSs product not only serves as an effective adsorbent to remove toxic Cr6+ ions from polluted water, but also as an effective reductant in reducing the adsorbed toxic Cr6+ ions to much less toxic Cr3+ through the Fe2+ incorporated into its structure.