Template-free fabrication of α- and β-Bi2O3 hollow spheres and their visible light photocatalytic activity for water purification

For the first time, uniform alpha-and beta-Bi2O3 hollow microspheres were successfully synthesized through a facile template-free solvothermal method followed by calcination of the precursor. A mixture of glycerol (Gly) and ethanol (EtOH) (volume ratio of Gly-EtOH = 1:1) was selected as the solvent, Bi(NO3)(3)center dot 5H(2)O as the bismuth source. The resulting samples were characterized by thermogravimetry (TG), Fourier transform infrared spectra (FT-IR), X-ray powder diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), Brunauer-Emmett-Teller (BET) surface area and UV-Vis diffuse reflectance spectra (DRS). Based on the electron microscope observations, the formation of such hollow spheres structure was proposed as a self-assembly process followed by Ostwald ripening. The sample calcined at 270 degrees C exhibited beta-Bi2O3 phase, whereas the sample calcined at 350 degrees C exhibited alpha phase. The band gaps of the as-prepared materials were estimated by DRS to be 3.50, 2.82, and 2.36 eV for the precursor, alpha- and beta-Bi2O3, respectively. Upon visible light irradiation, the beta-Bi2O3 exhibits much higher photocatalytic activities than the alpha-Bi2O3 and precursor for the degradation of rhodamine B (RhB) in aqueous solution, which could be attributed to its narrower band gap and efficient visible light absorption. (C) 2014 Elsevier B.V. All rights reserved.