Preparation Of Hollow Cobalt Ferrite Microspheres And Their Properties

The hollow ferrite microspheres have unique advantages in catalysis,biomedicine and targeted drug delivery fields for their low density,high absorbing ability,large specific surface area,thermal stability and good magnetic properties.It is important to explore and develop a simple and economical method for synthesis of hollow ferrite microspheres and it will contribute to the synthesis of magnetic nanomaterials as well as further practical applications.In this paper,hollow cobalt ferrite microspheres were successfully prepared using a solvothermal method in the presence of ionic liquid.Their magnetic and microwave absorbing properties were discussed.Firstly,solid cobalt ferrite microspheres were prepared by a solvothermal method in the presence of ionic liquid using ammonium acetate as precipitants.Their morphologies,structures and magnetic properties were characterized by field emission scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffractometer?XRD?,thermogravimetry?TG?,vibrating sample magnetometer?VSM?.The influence of the reaction time,reaction temperature,amount of precipitant and concentration of ionic liquid on the structure,morphology and magnetic properties of cobalt ferrites was investigated.The uniform cobalt ferrite microspheres with diameter of about 400 nm were prepared at180?for 32h in the presence of 0.12 mmol/L[C₁₈MIM]Br,0.5mol/L of NH₄Ac and 30ml of ethylende glycol.The saturation magnetization was 60.944 emu/g.Secondly,hollow cobalt ferrite microspheres were successfully prepared by a solvothermal method in the presence of ionic liquid using sodium acetate as precipitants.Their morphologies,structures and magnetic properties were characterized by SEM?TEM and XRD.The effects of the solution loading,reaction time,reaction temperature,amount of precipitant,concentrations of octane and ionic liquid,ionic liquid chain length and cation source on the structure,morphology and magnetic properties of cobalt ferrites were investigated.The microwave absorbing properties of hollow ferrite and solid ferrite were compared.The uniform hollow ferrite microspheres with diameter of 100-200 nm were obtained at 200?for 24h in the presence of 0.2 mmol/L[C₁₈MIM]Br,0.312 mol/L NaAc and 50ml of ethylende glycol.Their saturation magnetization was 76.481 emu/g.The minimum reflection loss of the hollow cobalt ferrite microspheres was-15.23dB and the effective absorption bandwidth was 2.72GHz?15.28-18 GHz?.The minimum reflection loss of the solid sphere is-8.53dB.Compared with the solid cobalt ferrite,the hollow cobalt ferrite microspheres show better absorbing performance.