Metastable β-Bi2O3 Nanoparticles with Potential for Photocatalytic Water Purification Using Visible Light Irradiation

Photocatalytic studies under visible light irradiation using nanosized beta-Bi2O3 are reported. beta-Bi2O3 nanoparticles are prepared starting from the well-defined bismuth oxido cluster [Bi38O45(OMc)(24)(DMSO)(9)]center dot 2DMSO center dot 7H(2)O (OMc = O2CC3H5) using a straightforward hydrolysis and annealing protocol. Powder X-ray diffraction studies, transmission electron microscopy, diffuse reflectance UV/Vis spectroscopy and nitrogen adsorption measurements (using the Brunauer-Emmett-Teller (BET) theory) are used for the characterization of the as-prepared beta-Bi2O3. By time-dependent annealing, the crystallite size can be controlled between (17 +/- 2) nm and (45 +/- 5) nm with BET surface areas of 7 to 29 m(2)g(-1). The indirect band gap of the as-prepared beta-Bi2O3 amounts to (2.15 +/- 0.05) eV. The decomposition rates for rhodamine B (RhB) solutions are in the range of 2.46 x 10(-5) to 4.01 x 10(-4) s(-1) and depend on the crystallite size, amount of catalyst and concentration of RhB. Photocorrosion experiments have shown the formation of Bi2O2CO3 after several catalytic cycles. However, the catalyst can be recycled to phase-pure beta-Bi2O3 nanoparticles by annealing for one hour under argon atmosphere at 380 degrees C. Furthermore, the photocatalytic activity of as-prepared beta-Bi2O3 nanoparticles for the decomposition of phenol, 4-chlorophenol, 2,4-dichlorphenol, 4-nitrophenol, triclosan and ethinyl estradiol is demonstrated.