Formation mechanism and magnetic properties of hollow Fe3O4 nanospheres synthesized without any surfactant

Hollow structured magnetite spheres were fabricated by a simple solvothermal process, with the assistance of various ammonium salts, where ethylene glycol was used as the solvent and reducing agent. The results of X-ray diffraction, scanning electron microscopy and transmission electron microscopy show that the as-synthesized products are pure single-phase Fe3O4 with good crystalline state, and all the samples are hollow structures except for the S-d sample, which was obtained by the assistance of NH4HCO3. The X-ray photoelectron spectrometry manifests that the Fe3+ ions on the surface of the hollow spheres exist in the form of Fe3O4, and Mossbauer measurements reveal that the hollow spheres are similar to the stoichiometric Fe3O4. The possible formation mechanism of hollow magnetite spheres with various sizes was discussed in detail. Meanwhile magnetic properties were determined by using a vibrating sample magnetometer at room temperature. The magnetic properties investigation showed that the Fe3O4 spheres were ferromagnetic with small hysteresis loops. The values of saturation magnetization are 82.989, 78.049 and 87.417 emu g(-1) for the S-a, S-b and S-c samples, which decreases with increasing particle size. This phenomenon may be caused by the content of Fe3+ on A- and B-sites of the spinel ferrite. Based on experimental results, the relationship between their microcomponents also has been studied.