Template-free hydrothermal fabrication of hierarchically organized γ-AlOOH hollow microspheres

Hierarchically organized γ-AlOOH hollow spheres with nanoflake-like porous surface textures were fabricated by chemically induced self-transformation of metastable solid particles of amorphous aluminium oxyhydroxide produced in situ within hydrothermal reaction mixtures containing aluminium sulfate and urea. Thermal treatment of the γ-AlOOH product at 600 °C produced intact hollow spheres of γ-Al2O3. Formation of the hollow γ-AlOOH structures was strongly dependent on the reaction temperature and time, as well as the concentration and molar ratio of the reactants. Hollow γ-AlOOH spheres were not obtained using mixtures of urea and aluminium nitrate or aluminium chloride, as metastable precursor particles were not produced under these conditions. In general, the described method is efficient and environmentally benign, and has significant advantages over traditional template approaches to the large-scale production of hollow inorganic materials. The prepared hierarchically organized γ-AlOOH and γ-Al2O3 hollow spheres should have important applications in areas of catalysis, separation science, biomedical engineering and nanotechnology.