Ca4Bi6O13 powders prepared from a citric acid complex were characterised by X–ray diffraction, UV–vis diffuse reflectance spectra and specific surface area measurements. In a citric acid complex method, the single phase of Ca4Bi6O13 crystal was obtained at 700°C in air. The Ca4Bi6O13 powders calcined at 700°C for 12 h had a crystallite size of 68 nm and a specific surface area of 1.05 m²/g. The optical band gap of Ca4Bi6O13 was estimated to be 2.82 eV. The type of optical transition was direct and this result was consistent with the prediction by a first–principles energy band calculation. The Ca4Bi6O13powders showed a distinct photocatalytic decomposition of methylene blue under visible light irradiation (a wavelength ≥ 420 nm). The visible light response photocatalysis may be ascribed to the small band gap energy, the direct optical transition, and a fairly wide dispersion of the top of the valence band.
Keywords: Ca4Bi6O13, calcium bismuth oxide, photocatalysts, ab initio calculation, energy band, density of states, photocatalytic activity, nanotechnology, citric acid, band gap energy, direct optical transition, valence band