Preparation And Photocatalytic Properties Of Bismuth Silicate By Pechini Sol-Gel Method

Bismuth silicate?BSO?is a kind of important inorganic functional materials with excellent acoustooptic,piezoelectric and dielectric properties.Bi₂Si O₅ and Bi₁₂Si O₂₀ are two kinds of compounds in Bi ₂O₃-Si O₂ binary system.And the metastable phase Bi ₂Si O₅ belongs to the Aurivillius phase structure,while the stable phase Bi ₁₂Si O₂₀ belongs to the Sillenite phase structure.The two compounds with unique crystal structure exhibit good photocatalytic properties and can be used for the treatment of organic pollutants.However,the high purity metastable phase Bi₂Si O₅ is difficult to prepare and the utilization efficiency of visible light is also low.The photoc atalytic performance of Bi₁₂Si O₂₀under the visible light is limited by its high recombination rate of photogenerated carriers.At present,the preparation of photocatalytic materials with semiconductor heterojunction is one of the effective methods to restrain the recombination of photogenerated carriers and improve the performance of photocatalytic materials.On the other hand,the preparation of photocatalytic material with photonic crystal structure has become a research focus in improving the photocatalytic performance of semiconductors.The photonic crystal ha s a highly ordered periodic structure,and their special slow photon effect,multiple scattering effect and photon localization effect have significant effec ts on photocatalytic materials by means of improving the utilization of light.In this paper,pure BSO powders were prepared by Pechini sol-gel method using citric acid and polyethylene glycol as the complexing agents,bismuth nitrate and TEOS as the start ing materials,deionized water and ethanol as the solvent.Bi ₁₂Si O₂₀-Bi₂Si O₅ composites were prepared by controlling the molar ratio of Bi/Si in precursors.BSO-Si O₂composite thin films were prepared by spin-coating method using silicon dioxide photonic crystal as the template.BSO powders with inverse opal structure were prepared by template method using polystyrene photonic crystal as the template.The crystal phase,morphology and optical properties of the samples were characterized by X-ray diffraction,scanning electron microscope,Fourier transform infrared spectroscopy,Raman and UV-Vis absorption spectra.The photocatalytic properties of the samples were characterized by the degradation of Rhodamine?Rh B?and Methyl Orange?MO?,and the mechanism wa s also analyzed.The effect of synthesis processes on the preparation of pure BSO powders,the effect of different Si O₂ photonic crystal templates on the photocatalytic properties of BSO-Si O₂ composites and the influence of different filling methods on the preparation of BSO powders with inverse opal structure were mainly studied.The main results show that:?1?pure Bi₂Si O₅ and Bi₁₂Si O₂₀ powders were prepared successfully via Pechini sol-gel method.Bi₂Si O₅ powders have quasi-sphericity morphology and the band gap of Bi₂Si O₅ is 3.5 e V.Bi₂Si O₅ shows a synergistic effect of adsorption and photocatalysis on the degradation of Rh B under UV light and Rh B completely degraded after 110 min.The morphology of Bi₁₂Si O₂₀ powders is block and the band gap is 2.4 e V.The degradation rate of Rh B reaches to 40%under visible light irradiation for 150 min and 99%under UV light irradiation for 40 min.?2?Bi₁₂Si O₂₀-Bi₂Si O₅ composites with excellent visible light photocatalytic activity were prepared when the molar ratio of Bi/Si is 4.The degradation rate of Rh B reaches to 86%under visible light irradiation for 150 min.Enhanced photocatalytic activity of the BSO composites is ascribed to the enhancement in light harvesting ability and the improved charge carrier separation efficiency.?3?Si O₂ colloidal spheres with particle sizes of 180 nm,215 nm and230 nm were prepared by controlling the amount of ammonia.Si O ₂photonic crystal templates with d ifferent thicknesses and different particle sizes of colloidal sphere were prepared via vertical deposition method.The BSO-Si O₂ composite thin films prepared by spin-coating method show better photocatalytic properties than BSO films.The thicker the Si O₂ photonic crystal is,the better photocatalytic performance the composite thin films have.Photonic crystal templates obtained by Si O₂ colloidal spheres with different particle sizes have different photonic band gaps.The photocatalytic property of composite film is the best when the electron band gap of BSO is overlapped with photonic band gap.?4?BSO powders with inverse opal structure were prepared by filtration with block,filtration with gauze and dipping with block.The results show that BSO powders with inverse opal structure are more easily obtained by dipping with block.And BSO powders with inverse opal structure show better photocatalytic property because of the ordered porous structure,slow photon effect and multiple scattering effect of inverse opal structure.