Formation of micro/nanostructured AlOOH hollow spheres from aluminum nanoparticles

Micro/nanostructured AlOOH hollow spheres have been obtained via one-step synthesis. Spherical aluminum nanoparticles coated with amorphous oxide film are used as a precursor. Hollow spheres of AlOOH are formed during the oxidation of aluminum nanoparticles with water. In order to study the evolution of hollow spheres, electron microscopy studies of the reaction intermediates at various stages of the process are carried out. Micro/nanostructured AlOOH hollow spheres have a diameter of 500–800 nm, and their shells consist of boehmite nanosheets with a planar size of 200–300 nm and a thickness of 2–10 nm. It is shown that the formation of AlOOH hollow spheres occurs through dissolution of aluminum core, the diffusion of Al³⁺ ions through the surface oxide film, and the formation of islands of amorphous Al(OH)₃ at the particle–water interface. Further, the formation and growth of AlOOH nanosheets and the formation of a porous shell from nanosheets take place. As a result, the oxide film serves as a substrate for growth of boehmite nanosheets and the formation of micro/nanostructured AlOOH hollow sphere. Morphology and physicochemical properties of the hollow spheres are characterized by transmission and scanning electron microscopy, X-ray diffraction, energy-dispersive analysis, and low-temperature nitrogen adsorption.