Fabrication and growth mechanism of hierarchical porous Fe3O4 hollow sub-microspheres and their magnetic properties

Hierarchical porous Fe3O4 hollow sub-microspheres with nanoparticles as the in situ formed building blocks were fabricated via a novel one-pot solvothermal method. The possible formation mechanism of these hierarchical porous Fe3O4 hollow sub-microspheres was explored. In this formation process, solid Fe2O3 sub-microspheres were first obtained, and then gradually reduced to Fe3O4 sub-microspheres with core/shell structure which finally developed into hierarchical Fe3O4 sub-microspheres with hollow interiors through the Ostwald ripening process. Interestingly, solid alpha-Fe2O3 sub-microspheres obtained in the initial stage might act as structure director in the formation of Fe3O4 hollow sub-microspheres. Moreover, preliminary results of magnetic properties of the hierarchical porous Fe3O4 hollow sub-microspheres were also reported. The hierarchical porous Fe3O4 hollow sub-microspheres exhibited enhanced saturation magnetization as compared with Fe3O4 single-crystal hollow sub-microspheres with similar sizes and Fe3O4 hollow nanospheres.