Uniform hollow magnetite spheres: Facile synthesis, growth mechanism, and their magnetic properties

• Uniform Fe3O4 hollow spheres with high saturation magnetization were synthesized through a simple solvothermal process.
• Without using any hard templates or external magnetic field.
• The as-prepared magnetite hollow spheres exhibit a ferromagnetic behavior with high Ms of ca. 85.9 emu/g at room temperature.
• The morphology of Fe3O4 with nanoparticles, hollow, and irregular structures could be adjusted by changing the reactive conditions.

Hierarchical porous Fe3O4 hollow spheres with high saturation magnetization were synthesized through a simple solvothermal process in ethylene glycol (EG) in the presence of Tetrabutylammonium chloride (TBAC) and urea. By investigating the effect of reaction temperature, time, the amount of urea, and concentration of iron ion on the formation of hollow spheres, it was proposed that the main formation mechanism of hollow spheres is Ostwald ripening process combined with assembly-then-inside-out evacuation process. Additionally, it is found that the morphology of Fe3O4 with nanoparticles, hollow, and irregular structures could be adjusted by changing the above factors. The resulting products were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometer (VSM). The hierarchical porous Fe3O4 hollow spheres exhibited enhanced saturation magnetization as compared with Fe3O4 nanoparticles.

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