Reduced graphene oxide loaded with rich defects CoO/Co3O4 for broadband microwave absorption

Graphene-based microwave absorbing (MA) materials have been extensively studied due to their excellent physical properties. However, very few research has successfully achieved broader frequency MA materials while ensuring good wave absorption properties. In this work, we obtained reduced graphene oxide (RGO) modified with magnetic CoxOy nanoparticles by assembling Co nanoparticles onto graphene with a simple hydrothermal method followed by pyrolysis at different temperatures, possessing wideband broad bandwidth microwave absorbing capability. The electromagnetic parameters, attenuation constants, and impedance matching of the CoxOy/RGO composites pyrolyzed at different temperatures were analyzed to determine the optimum pyrolysis temperature for the CoxOy/RGO composites. After heat treatment at 500 °C, a large number of CoO/Co3O4 interfaces appeared. The minimum reflection loss of the sample reaches −67.2 dB and the effective absorbing bandwidth (EAB) (RL < −10 dB) is 9.1 GHz, covering the whole X, Ku, and K bands. It is worth noting that such a good microwave absorption performance is attributed to the fact that the structure of cobalt nanospheres can adjust the effective dielectric constant of the material, and the existence of CoO can promote dipole polarization and interfacial polarization process to improve impedance matching, so as to obtain a wider absorption effect.