Synthesis and formation mechanism of hollow carbon spheres encapsulating magnetite nanocrystals

Hollow carbon spheres encapsulating magnetite nanocrystals were obtained in high-pressure argon at 600 °C followed by hydrolysis of Fe(NH₃)₂Cl₂ in the hollow interiors at room temperature and heat treatment in argon at 450 °C for 2 h. The structure, morphology, and properties of the products were characterized by x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and vibrating sample magnetometry. The hollow carbon spheres have diameters of 1-10 μm and wall thicknesses of hundreds of nanometers; the wt% of magnetite nanocrystals in them is ∼13.2%. Equiaxed magnetite nanocrystals range in size from 15 to 90 nm, while acicular magnetite nanocrystals have diameters of ∼20 nm and lengths of 120-450 nm. The saturation magnetization value of the hollow carbon spheres encapsulating magnetite nanocrystals is 4.29 emu/g.