Preparation of multilayered porous alumina hollow spheres by anodization of Al particles

Multilayered porous hollow spheres were obtained by the periodic anodization of small Al particles in different electrolytes and subsequent selective etching. The periodic anodization of small Al particles in concentrated H2SO4 and oxalic acid generated oxide layers on their surface with a periodically modulated solubility in the thickness direction. Hollow spheres composed of multilayered porous alumina shells were prepared by the subsequent etching of residual Al and the oxide layers formed in concentrated H2SO4. The resulting multilayered hollow spheres had a large specific surface area originating from their unique geometrical structure and are expected to find use in various applications such as catalysts, sensors, and drug carriers.