Size-controlled synthesis of monodispersed mesoporous α-Alumina spheres by a template-free forced hydrolysis method

We demonstrated the formation of monodispersed spherical aluminum hydrous oxide precursors with tunable sizes by controlling the variables of a forced hydrolysis method. The particle sizes of aluminum hydrous oxide precursors were strongly dependent on the molar ratio of the Al³⁺ reactants (sulfates and nitrates). In addition, the systematic phase and morphological evolutions from aluminum hydrous oxide to γ-alumina (Al₂O₃) and finally to α-Al₂O₃ through thermal dehydrogenation were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). After annealing the amorphous aluminum hydrous oxide in air at 900°C and 1100 °C for 1 h, we observed complete conversion to phase-pure γ- and α-Al₂O₃, respectively, while maintaining monodispersity (125 nm, 195 nm, 320 nm, and 430 nm diameters were observed). Furthermore, both γ- and α-Al₂O₃ were found to be mesoporous in structure, providing enhanced specific surface areas of 102 and 76 m² g^-1, respectively, based on the Brunauer-Emmett-Teller (BET) measurement.