Fabrication of Monodisperse Magnetite Hollow Spheres

Abstract

Monodisperse Fe₃O₄ 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 NH₄Ac 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 Fe₃O₄ and MnFe₂O₄ ferrite microspheres with controlled particle size were obtained using urea and ammonia as the structure-directing agents, and porous Fe₃O₄ 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 (<i>M</i>_s) than that of the solid microspheres.