N-doped NaTaO3 synthesized from a hydrothermal method for photocatalytic water splitting under visible light irradiation

Abstract

NaTaO3-xNx catalysts were synthesized by a hydrothermal (H) and a solid-state (S) methods in this study. The H- and S-NaTaO3-xNx samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible (UV–vis) diffuse reflectance spectroscopy, and photoluminescence (PL) spectroscopy. The XRD patterns of the H- and S-samples showed peaks indexed to the pure phase of perovskite NaTaO3 and minor peaks assignable to Ta3N5 at various synthesis temperatures. Substitution of oxygen by nitrogen ions causes the light absorption of the H- and S-NaTaO3-xNx samples to be extended to the 600–650nm region, thus making the samples visible-light active. The NaTaO3-xNx samples exhibited photocatalytic activity for H2 and O2 evolution from aqueous methanol and silver nitrate solutions under visible-light irradiation. The UV–vis and PL spectra of the H- and S-catalysts revealed the presence of cationic vacancies and reduced metallic species, which acted as recombination centers. These results demonstrated that the preparation method plays a critical role in the formation of defect states, thereby governing the photocatalytic activity of the NaTaO3-xNx catalysts.