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 Fe(3)O(4) micron-spheres (NFMSs) by annealing hydrothermally formed FeCO(3) 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 μm and are composed of nanometer-sized porous lamellae. The NFMSs have a large specific surface area (135.9 m(2) g(-1)), reductive Fe(2+) incorporated into their structure, and intense magnetic properties. These properties suggest that NFMSs have potential application in removing toxic Cr(6+) ions from polluted water. At 25°C, each gram of NFMSs product can remove 43.48 mg of Cr(6+) ions, as compared to just 10.2 mg for nanometer-sized Fe(3)O(4) and 1.89 mg for micron-sized Fe(3)O(4). The enhanced removal performance can be ascribed to the structural features. Moreover, the Cr(6+) ion removal capacity of the NFMSs can reach up to 71.2 mg g(-1) at 50°C. The influencing parameters in the removal of Cr(6+) ions, such as contact time, pH, and temperature, have been evaluated. The Cr(6+)-removal mechanism has been investigated. We have found that the NFMSs product not only serves as an effective adsorbent to remove toxic Cr(6+) ions from polluted water, but also as an effective reductant in reducing the adsorbed toxic Cr(6+) ions to much less toxic Cr(3+) through the Fe(2+) incorporated into its structure.