Vapor diffusion synthesis of CoFe₂O₄ hollow sphere/graphene composites as absorbing materials

Novel CoFe₂O₄ hollow sphere/graphene composites were synthesized by a facile vapor diffusion method in combination with calcination at 550 °C. The structure and morphology of as-prepared hybrid materials were characterized by electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Uniform CoFe₂O₄ hollow spheres with a diameter of about 500 nm and a shell thickness of approximately 50 nm were homogeneously distributed on graphene sheets. The electromagnetic parameters were measured using a vector network analyzer. A minimum reflection loss of -18.5 dB was observed at 12.9 GHz for the CoFe₂O₄ hollow sphere/graphene composites with a thickness of 2 mm, and the effective absorption frequency ranged from 11.3 to 15.0 GHz. The CoFe₂O ₄ hollow sphere/graphene composites exhibited better microwave absorbing performance than the CoFe₂O₄ hollow spheres. A possible formation mechanism for CoFe₂O₄ hollow sphere/graphene composites was proposed.