Photoactive β-Bi2O3 architectures prepared by a simple solution crystallization method

Metastable tetragonal bismuth oxide (β-Bi2O3) architectures of pumpkin shape were successfully prepared by a solution crystallization technique, which was performed at 70 °C without further calcination or other complex treatment. The elementary units of β-Bi2O3 architectures are microrods of ~1 μm in width. The metastable crystalline structure was determined by X-ray powder diffraction (XRD), and the crystal evolution process from irregular particles to pumpkin aggregates was investigated on a field emission scanning electron microscope (FESEM). The tetragonal β-Bi2O3 crystalline powders exhibited orange in color, which could transform to yellow monocline α-Bi2O3 crystals upon enough reaction time as 60 min, the corresponding morphology changes from pumpkin structure of β-Bi2O3 crystals to big diamond structure of α-Bi2O3 crystals. The stabilization of metastable β-Bi2O3 crystals in the solution system is a size controlled process. By tuning experimental parameters, such as NaOH concentration, reaction temperature, stirring rate etc., metastable β-Bi2O3 crystals can preserve stably in the reaction system for different time. The pumpkin β-Bi2O3 architectures showed excellent photocatalytic activity to Rhodamine B (RhB) degradation under visible light irradiation, which is due to an indirect dye photosensitization degradation process.