Co3Fe7/C core-shell microspheres as a lightweight microwave absorbent

Since electromagnetic pollution is becoming more and more serious, novel composite microwave absorbents are gaining much attention. Here, Co3Fe7/C core-shell microspheres for microwave absorption were synthesized for the first time. At first, hollow CoFe2O4 microspheres were prepared via a solvothermal method at 200 °C for 15 h. Then CoFe2O4-hydrochar microspheres were synthesized by hydrothermal method in an aqueous glucose solution containing hollow CoFe2O4 microspheres. After annealed under Ar atmosphere at 500 °C, the CoFe2O4-hydrochar microspheres were converted into CoFe2O4-Co3Fe7/C microspheres. Co3Fe7/C core-shell microspheres came into being after annealed at 600 °C. Both the CoFe2O4-Co3Fe7 nanoparticles and Co3Fe7 nanoparticles were encapsulated in the carbon shells, and the microsphere morphology could be retained during the carbothermal process. Especially, the core-shell structure caused that the density of the Co3Fe7/C microspheres was below 2 g/cm3. Resulting from the synergistic effect of Co3Fe7 nanoparticles and partially graphitized carbon, the minimum reflection loss (RL) of Co3Fe7/C microspheres was as low as −44.4 dB obtained with 1.6 mm thickness. Owing to the characteristics of low density and good microwave absorption, the Co3Fe7/C core-shell microspheres could be used as a lightweight and highly efficient microwave absorbent.