Synthesis of Fe3O4@SiO2@ZnO core-shell structured microspheres and microwave absorption properties

Multifuncational Fe3O4@SiO2@ZnO core-shell structured microspheres have been synthesized by combining the hydrothermal method and sol-gel process. The composition, morphology, microstructure and magnetic properties were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometer. The results reveal that the as-synthesized microspheres have a good monodispersity, uniform core-shell structure with distinct two-layer coatings and high magnetization. Dielectric constants and microwave absorption properties of the synthesized composites were studied by a vector network analyzer between 2 and 18 GHz at room temperature. The results indicate that the Fe3O4@SiO2@ZnO microspheres exhibit better absorption performance than the Fe3O4 and Fe3O4@SiO2 microspheres. The excellent microwave absorption properties of the composites are attributed to the special multilayer structures of Fe3O4@SiO2@ZnO microspheres and the effective complementarity between dielectric loss and magnetic loss. Moreover, a possible formation mechanism based on the hydrothermal method and sol-gel process was also proposed. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.