Ionic liquid-assisted solvothermal synthesis of hollow CoFe2O4 microspheres and their absorbing performances

Hollow CoFe2O4 microspheres were successfully synthesized in high yield using a solvothermal method in the presence of long-chain ionic liquid [C18MIM][Br]. Uniform CoFe2O4 hollow spheres with a diameter of 100-200 nm and a shell thickness of approximately 10-50 nm are assembled by nanoparticles of 5-10 nm and have cubic spinel structures. A minimum reflection loss of −15.23 dB was observed at 16.98 GHz for hollow CoFe2O4 microspheres with a thickness of 5.5 mm, and the effective absorption frequency ranged from 15.28 to 18 GHz. Hollow CoFe2O4 microspheres exhibited better microwave absorbing performance than solid microspheres. A possible formation mechanism of hollow CoFe2O4 microspheres was discussed.