General Synthesis of Homogeneous Hollow Core−Shell Ferrite Microspheres

A general method has been developed for the synthesis of homogeneous hollow core−shell microspheres of spinel ferrites (MFe2O4, M = Zn, Co, Ni, Cd) by using carbonaceous saccharide microspheres as template. The products were characterized by X-ray powder diffraction, inductively coupled plasma-atomic emission spectroscopy, scanning electronic microscopy, transmission electron microscopy, and nitrogen sorption measurement. The effects of the concentration of metal salts have been studied using ZnFe2O4 as an example. Increasing the concentration of metal salts could avoid the generation of impurity phase. The core size and shell thickness of hollow spheres obtained can be manipulated by changing the concentration of metal salts. Gas-sensor investigations revealed the ZnFe2O4 hollow spheres used as gas-sensor materials possess high sensitivity and quick responses to organic gases such as ethanol.