Preparation of CoFe2O4 hollow spheres with carbon sphere templates and their wave absorption performance

In the synthesis of colloidal carbon spheres (CCSs) from glucose by hydrothermal carbonization, agglomeration and cross-linking often occur, affecting their functions as templates. In this study, the effects of various surfactants on the dispersion and particle size of CCS were investigated. The CCS synthesized with dodecyltrimethylammonium bromide was much larger than those of other groups, and the average diameter exceeded 6.4 μm. CCS with complete spherical shape and good dispersion were obtained using sodium polyacrylate, with a diameter of approximately 450 nm CoFe2O4 hollow spheres were prepared by a simple adsorption–calcination method using CCS as the templates, and the effects of different dispersions and particle sizes on the electromagnetic parameters and microwave absorption properties of hollow spheres were studied. The results show that the absorption bandwidth corresponding to reflection loss less than −7 dB widened from 2.64 GHz to 3.44 GHz with improving dispersion of hollow sphere structure. When the size of the hollow sphere increased to the micron level, the thickness required to reach the maximum bandwidth reduced by 0.5 mm. Compared to the unoptimized hollow spheres, the microwave absorption performance of the as-prepared CCCs improved effectively. The effect of surfactants on the dispersion of CCS and the effect of the dispersion and size of CoFe2O4 hollow spheres on their electromagnetic properties are discussed in detail.