Synthesis and optical properties of Bi3+ doped NaTaO3 nano-size photocatalysts.

Well-crystallized NaTaO3 nanoparticles doped with and without Bi were synthesized by a hydrothermal method. X-ray diffraction (XRD) patterns showed a systematic shift toward lower angles, which was followed by broadened peaks as the dopant content of Bi3+ increased. The doping of Bi3+ in NaTaO3 was also found to give rise to finer particle sizes. For undoped samples, transmission electron microscopy (TEM) showed the well-crystallized cubic morphology, which however, changed to fairly rough surfaces and somewhat irregular distorted cube-like shaped geometries with the addition of Bi3+. The swelling of the crystallized cell volume was demonstrated by the increased lattice d-spacing from high-resolution transmission electron microscopy (HRTEM) studies. The diffuse reflection spectra showed a red shift in absorbance wavelength with Bi3+ doping, which suggests a decreased band gap energy. Emissions of the TaO6 octahedra unit were observed at 435 nm in the photoluminescence (PL) spectra. The PL intensities increased with the doping content of Bi3+, which was attributed to the increase of oxygen vacancies caused by the substitution of Ta5+ by Bi3+. The photocatalytic degradation of methylenebluechloride was taken as the model reaction to examine the activity of the sample. It was found that the activity decreased with the Bi3+ content.