Hematite nanoparticles as polystyrene microsphere coatings and hollow spheres: Tpreparation and characterization

A novel method of fabricating composite particles with core–shell structures is demonstrated. The particles comprised monodisperse submicrometer-sized copolymer latex spheres as cores and Fe2O3 crystallites as shells. The shell was formed by controlled hydrolysis of aqueous iron solutions, and the growth of hematite on the surface of the copolymer spheres was controlled by slow injection. Hollow spheres were obtained by calcinations of the so-coated copolymer lattices at 500°C in air. The void size of these hollow spheres was determined by the diameter of the copolymer template, and the wall thickness could be easily controlled in the range of 20–60 nm by using this coating process. The structure and the composition of the spheres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). It can be seen that a crystallite change and a crystal phase transformation occurred during coating and calcination of the composite spheres. The formation of the composite particles is simply explained by the nucleation of iron oxide on the surface of the latex followed by growth of the iron compound shell.