Fabrication of Monodisperse Magnetite Hollow Spheres

Monodisperse Fe(3)O(4) hollow spheres with average diameter of 400 nm and shell thickness of 60 nm were prepared through a one-pot solvothermal process with the presence of NH(4)Ac as the structure-directing agent, and a novel gas-bubble-assisted Ostwald ripening process was proposed to explain the formation of hollow structures. According to this mechanism, hollow Fe(3)O(4) and MnFe(2)O(4) ferrite microspheres with controlled particle size were obtained using urea and ammonia as the structure-directing agents, and porous Fe(3)O(4) spheres with particle size of 100 nm and pore size of 10 nm were obtained by the assistance of bicarbonate of ammonia. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy were used to characterize the structure of synthesized products, and the magnetic property investigation shows that the hollow microspheres exhibit a ferromagnetic behavior and possess a higher saturation magnetization (M(s)) than that of the solid microspheres