Perovskite-type NaTaO3 derived from a sol-gel synthesis exhibited a larger surface area and a remarkably higher photocatalytic activity in water splitting than the solid-state synthesized NaTaO3. The sol-gel and solid-state NaTaO3 had different crystalline structures of monoclinic P2∕m and orthorhombic Pcmn, respectively. Diffuse reflectance spectra showed that the sol-gel specimen had a slightly larger band gap. The band structure analysis revealed an indirect band gap for the sol-gel NaTaO3, contrary to the direct band gap of the solid-state one. The difference in the electronic structure and surface area explained the higher photocatalytic activity of the sol-gel NaTaO3.

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We report the synthesis of wurtzite-like gallium oxynitride (GaON) photocatalysts by nitridation of Ga(OH) 3 with NH 3 at temperatures between 550 and 900 °C. Ga(OH) 3 is a more suitable precursor for GaON synthesis than Ga 2 O 3 , because its crystal lattice contains unoccupied 12-coordinate sites that facilitate ionic transportation during nitridation. The prepared GaON catalysts had band gap energies from 2.2 to 2.8 eV and showed significant activities in the visible-light promoted evolution of H 2 and O 2 gases from methanol and AgNO 3 solutions, respectively. The maximum H 2 and O 2 evolution rates occurred for catalysts synthesized at 625 and 700 °C, respectively. These active catalysts had an N/O atomic ratio close to unity, suggesting that extensive hybridization of N 2p and O 2p orbitals promotes charge mobility, and thus enhances photocatalytic activity. This study highlights the interesting possibility of synthesizing a large diversity of visible-light active, IIIoxynitride catalysts using this Ga(OH) 3 route.

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Perovskite‐like NaTaO3 powders have potential applications in photoluminescence and photocatalysis. Sol–gel, hydrothermal and solid‐state methods were used to synthesize NaTaO3 powders of different crystalline structures, which were identified by Rietveld refinement simulation of X‐ray diffraction patterns and transmission electron microscopic diffraction. The refinement results show that the sol–gel specimen has a monoclinic phase with a Ta−O−Ta bond angle of 179° while the hydrothermal and solid‐state specimens have an orthorhombic phase with bond angles of 163° and 157°, respectively. By excitation with a 304 nm light source, these NaTaO3 specimens show photoluminescence emission at ca. 450 nm. The photoluminescence intensity of the specimens had an order solid state >hydrothermal >sol–gel, which is opposite to that of the Ta−O−Ta bond angle. On the other hand, the photocatalytic activity of the NaTaO3 specimens in water splitting showed the same order as that of the Ta−O−Ta bond angle. This paper directly evidenced that the Ta−O−Ta bond angle affects the separation rate of the photo‐induced charges, as well as that structure tuning of tantalates is achievable and crucial for applications in photoluminescence and photocatalysis.