Preparing Bi12SiO20 crystals at low temperature through nontopotactic solid-state transformation and improving its photocatalytic activity by etching

Well-crystalline bismuth silicon oxide (Bi12SiO20; BSO) particles were prepared from the reaction of Na2SiO3 (or SiO2) and a bismuth oxo compound such as Bi(NO3)(3), alpha-Bi2O3, (BiO)(2)CO3 or BiOX (X = Cl, Br) in alkaline aqueous solution at 70 degrees C for 3 h, whereas conventional syntheses from the melt necessitate above 650 degrees C. All the reactions from different bismuth precursors experienced the same intermediate alpha-Bi2O3 to the final product BSO with a cubic or triangular pyramidal shape, depending upon NaOH concentration and Bi/Si molar ratio. Although the photocatalytic efficiency of the obtained BSO microcrystallites was poor due to the large particle size and the associated low specific surface area, we successfully overcame the disadvantage of insufficient active sites on the surface of the BSO microcrystallites through etching. The etched BSO crystals possessed a rough surface and exhibited enhanced photocatalytic activity for RhB degradation under visible light irradiation. Especially, the uniform egg-tart shaped BiOCl hierarchical microstructures assembled by nanosheets were produced by tuning etchant concentration, looking like a man-made solar energy acceptor, which exhibited superior activity for RhB decomposition under visible light in comparison to its precursor BSO.