A novel method was used to synthesize orthorhombic FeNbO 4 nanoparticles by a hydrothermal process followed by calcination at 600 °C, and their optical, photoelectrochemical, and photocatalytic properties were investigated. The microstructural and local structural properties were characterized using X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy (TEM), and Raman spectroscopy. The FeNbO 4 particles obtained were composed of much smaller nanocrystallines, with an average size of 10-20 nm, compared to particles prepared at 1000 °C through a conventional solid-state reaction method. Moreover, the optical band gap energy of the nanoparticles was estimated to be 1.93 eV from the UV-vis diffuse reflectance, and their flat-band potential in 1 M NaOH was -0.4 V (SCE). The X-ray photoelectron spectroscopy analysis revealed that the nanoparticles had fewer surface defects, such as oxygen vacancies, than the particles prepared by the solid-state reaction method. The FeNbO 4 nanoparticles also exhibited a much higher photocatalytic activity for the degradation of rhodamine B dye solution under visible light irradiation (>420 nm). This higher photocatalytic activity of the FeNbO 4 nanoparticles was attributed to their higher optical absorption ability and smaller particle size, as well as fewer surface defects.

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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 Al(3+) reactants (sulfates and nitrates). In addition, the systematic phase and morphological evolutions from aluminum hydrous oxide to γ-alumina (Al(2)O(3)) and finally to α-Al(2)O(3) 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-Al(2)O(3), respectively, while maintaining monodispersity (125 nm, 195 nm, 320 nm, and 430 nm diameters were observed). Furthermore, both γ- and α-Al(2)O(3) were found to be mesoporous in structure, providing enhanced specific surface areas of 102 and 76 m(2) g(-1), respectively, based on the Brunauer-Emmett-Teller (BET) measurement.