Na Ta O 3 photocatalysts of different crystalline structures for water splitting into H2 and O2

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.