Synthesis and characterization of Bi4Si3O12, Bi2SiO5, and Bi12SiO20 by controlled hydrothermal method and their photocatalytic activity

This is the first report that three compounds, Bi4Si3O12, Bi2SiO5, and Bi12SiO20, can be selectively synthesized by a controlled and template-free hydrothermal method. Crystalline Bi4Si3O12, Bi2SiO5, and Bi12SiO20 are prepared from the reaction of Na2SiO3 and Bi(NO3)3 • 5H2O in an alkaline aqueous solution at 150 °C–250 °C for 24 h, whereas conventional syntheses necessitate operational temperatures above 650 °C. The composition and morphology of bismuth silicates could be controlled by adjusting some growth parameters, including reaction pH and temperature. The products are characterized by X-ray diffraction scanning electron microscope–energy–dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, Diffuse Reflectance UV–visible spectroscopy, Brunauer–Emmett–Teller, and high-resolution X-ray photoelectron spectroscopy. The UV–Vis spectra demonstrate that the three materials are indirect semiconductors with optical bandgaps of 2.65, 3.30, and 3.44 eV for Bi12SiO20, Bi2SiO5, and Bi4Si3O12, respectively. The photocatalytic efficiency of the powder suspension is evaluated by measuring the crystal violet concentration under visible-light irradiation. The order of rate constants shows Bi2SiO5 > Bi4Si3O12 > Bi12SiO20.