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, α-Bi₂O₃, (BiO)₂CO₃ or BiOX (X = Cl, Br) in alkaline aqueous solution at 70 °C for 3 h, whereas conventional syntheses from the melt necessitate above 650 °C. All the reactions from different bismuth precursors experienced the same intermediate α-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.