Controllable synthesis of α-Bi2O3 and γ-Bi2O3 with high photocatalytic activity by α-Bi2O3→γ-Bi2O3→α-Bi2O3 transformation in a facile precipitation method

Rod-like α-Bi2O3 and tetrahedral γ-Bi2O3 particles have been controlled fabricated by a facile solution crystallization method, which was performed at a mild reaction condition without any surfactants and/or templates. By combining the results of X-ray powder diffraction, high resolution transmission electron microscope, scanning electron microscopy, X–ray photoelectron spectra, and UV-visible absorption spectra, the morphology and crystalline phase evolution of Bi2O3 was studied versus reaction time and reaction temperature. It is interesting to note that the phenomenon of α-Bi2O3 → γ-Bi2O3 → α-Bi2O3 transformation was found. The nanorod α-Bi2O3 phase formed in a short time, while α-Bi2O3 could transform to tetrahedral γ-Bi2O3 crystals upon enough reaction time. However, γ-Bi2O3 may transform into rod-shape α-Bi2O3 with further increasing the reaction time. Moreover, it can be deduced that high reaction temperature promoted the transformation from α-Bi2O3 to γ-Bi2O3, and then from γ-Bi2O3 to α-Bi2O3. The photocatalytic activities of Bi2O3 with different crystalline phases were evaluated by the photocatalytic degradation of rhodamine B as a model pollutant. The γ-Bi2O3, which exhibits lower electrons-holes recombination rate than that of α-Bi2O3, showed excellent photocatalytic activity as compared with the α-Bi2O3.