Preparation And Properties Of Bismuth Silicate Composite Photocatalyst

Water pollution is one of the important problems of global environmental pollution,which has seriously threatened human health and social development.Photocatalysis can degrade dye wastewater into inorganic small molecules using solar energy and is expected to be an effective way to solve energy shortage and water pollution.Bismuth silicate（Bi₂Si O₅）is a new kind of semiconductor photocatalyst with good dielectric,piezoelectric,non-toxic and stable chemical properties.However,Bi₂Si O₅has some disadvantages,such as wide band gap,absorption of ultraviolet light and fast electron-hole recombination rate.Therefore,the modification of Bi₂Si O₅is studied in this paper.The specific research contents and experimental results are as follows:1.Ag₃PO₄/Bi₂Si O₅composite photocatalyst was prepared by ultrasonic assisted precipitation method.X-ray diffraction（XRD）,Scanning electron microscopy（SEM）,energy dispersive spectroscopy（EDS）,High resolution trans mission electron microscopy（HRTEM）,X-ray photo-electron spectroscopy（XPS）,specific surface area and aperture analysis（BET）,Photoluminescence spectra（PL）,UV-visible diffuse reflectance（UV-Vis DRS）and chemical oxygen demand（COD）were used to analyze the composition,morphology,optical properties and photocatalytic reaction mechanism of the samples.XRD results showed that the photocatalyst was composed of Ag₃PO₄and Bi₂Si O₅.HRTEM,EDS,and XPS validated XRD conclusions.SEM and TEM images showed that the morphology of the photocatalyst was granular and nano-flake.BET experiments showed that proper specific surface area was beneficial to improve the performance of photocatalyst.PL spectra suggest that the improved performance of photocatalyst may be due to the effective separation of photogenerated electron-hole pair.COD test results showed that about 73.92%of the dye molecules were degraded into inorganic small molecules.UV-Vis DRS analysis showed that the absorption edge of the composite photocatalyst was redshifted compared with that of Bi₂Si O₅.The combination of Ag₃PO₄and Bi₂Si O₅enlarged the visible light absorption range of the sample.2.Using bismuth nitrate pentahydrate（Bi（NO₃）₃·5H₂O）,sodium silicate nine hydrates（Na₂Si O₃·9H₂O）,sodium hydrogen phosphate（Na₂HPO₄）and silver nitrate（Ag NO₃）as experimental materials,Ag/Ag₃PO₄/Bi₂Si O₅photocatalysts were synthesized by ultrasonic assisted precipitation method.The photocatalytic activity of photocatalyst was evaluated by changing pollutant type,Rh B concentration and irradiation light source.The results showed that the photocatalyst could completely degrade 10 mg/L methylene blue（MB）under the irradiation of 70 W-halogen lamp for 60 min,and the degradation efficiency was 100%.After illumination for 60 min,the degradation efficiencies of 10 mg/L rhodamine B（Rh B）and 10mg/L methyl orange（MO）were 95.07%and 57.06%,respectively.The degradation efficiency of 10 mg/L Rh B was 96.18%when sunlight irradiated for 60 min.3.Bi₂Si O₅material was synthesized from Bi（NO₃）₃·5H₂O and Na₂Si O₃·9H₂O,and Bi PO₄/Ag₃PO₄/Bi₂Si O₅photocatalyst was synthesized by ultrasonic assisted precipitation method with Bi₂Si O₅as substrate.The effects of ultrasonic time,solvent and Bi/Ag mole ratio on the photocatalytic performance of the samples were investigated.The results showed that when the ultrasonic time was 50 min,the reaction solvent was distilled water,and the Bi/Ag molar ratio was 1:9,the photocatalyst has excellent photocatalytic performance.The degradation efficiency of 10 mg/L Rh B can reach 99.84%after irradiation for 40 min with 70W-halogen lamp.The degradation efficiency of 20 mg/L MB can reach 74.06%.The degradation efficiency of MO at 10 mg/L can reach 82.93%.Free radical capture experiments confirmed that hole（h⁺）and superoxide radical（·O₂^-）were the main active species in the degradation of Rh B,and hydroxyl radical（·OH）almost did not play a role.