Synthesis and characterization of hollow mesoporous BaFe12O19 spheres

• Two-step synthesis method for hollow mesoporous BaFe12O19 spheres is proposed.
• Porosity of the product can be regulated by controlling the second step of chemical etching.
• The crystal structure and magnetic properties are examined to be little affected during the chemical etching.
• The mesoporous structure formation mechanism is explained by grain boundary etching.

A facile method is reported to synthesize hollow mesoporous BaFe12O19 spheres using a template-free chemical etching process. Hollow BaFe12O19 spheres were synthesized by conventional spray pyrolysis. The mesoporous structure is achieved by alkaline ethylene glycol etching at 185 °C, with the porosity controlled by the heating time. The hollow porous structure is confirmed by SEM, TEM, and FIB-FESEM characterization. The crystal structure and magnetic properties are not significantly affected after the chemical etching process. The formation mechanism of the porous structure is explained by grain boundary etching.

Hollow spherical BaFe12O19 particles are polycrystalline with both grains and grain boundaries. Grain boundaries have less ordered structure and lower stability. When the particles are exposed to high temperature alkaline ethylene glycol, the grain boundaries are etched, leaving small grooves between grains. These grooves allow ethylene glycol to diffuse inside to further etch the grains. As the grain size decreases, gaps appear on the particle surfaces, and a porous structure is finally formed.Figure optionsDownload as PowerPoint slide