Hydrothermal Preparation And Modification Of BiVO₄and Their Photocatalytic Performance Under Visible Light

Environment pollution is the great problem and challenge for the entire world. More andmore scientists are concentrating on how to use solar light to photocatalyze poisonousmaterials, decompose the harmful contaminations, purify the water and eliminate the airpollution and so on, because the photocatalysts with the visible light response can transformsolar energy into chemical energy directly. In recent years, BiVO₄has been recognized as aphotocatalyst for water splitting and pollutant degradation under visible light irradiation.Bi₂WO₆/BiVO₄with heterojunction structure has been synthesized and the compositewere characterized by X-ray diffraction （XRD） and UV-Visible diffuse reflectance spectra.RhB, which is a common pollutant in industry effluent, was chosen as a probe to testphotocatalytic activities of the photocatalysts. In this dissertation, the following several partsof work have been done:（1） Nanometer BiVO₄particles were synthesized by hydrothermal method by usingBi（NO₃）35H₄₂O and NH₄4VO₃as raw materials. The influence of various parameters such asthe hydrothermal temperature, the pH₄of the precursor and the reaction time has been studied,and the obtained optimum fabrication technical conditions were180oC of hydrothermaltemperature, the pH₄=7of the precursor, and the reaction time of hydrothermal is24h. TheXRD patterns revealed that the BiVO₄sample was monoclinic scheelite structure. UV-visiblediffuse reflection spectra indicated that the BiVO₄had a great absorption in the visible lightregion. The band gap of BiVO₄was2.46eV. When the quantity of BiVO₄is3g·L-1and theoriginal concertration of Rhodamine B is10mg·L-1, the RhB degradation rate with the BiVO₄is about92.2%for5h under visible light irradiation.（2） The Bi₂WO₆was coated on the BiVO₄particles and a couple Bi₂WO₆/BiVO₄photocatalyst with heterojunction structure was synthesized. The XRD result indicated thatthe Bi₂WO₆was loaded on the BiVO₄, and there was no obvious difference between the bandgap absorption edges of the BiVO₄and Bi₂WO₆/BiVO₄. It was found that the RhBdegradation rate of the Bi₂WO₆/BiVO₄with the3.0%loading rate was2.7times as great asthat of the BiVO₄by the photocatalytic measurements.The enhanced photocatalytic performance could be attributed to the heterojunction structure of the Bi₂WO₆/BiVO₄. Whenthe composite was illuminated, the photogenerated electrons in the BiVO₄transfer from theconduction band of BiVO₄to the Bi₂WO₆due to the lower conduction band level of Bi₂WO₆.Meanwhile, the photogenerated holes in the Bi₂WO₆transfer from the Bi₂WO₆to BiVO₄because of the higher valence level of BiVO₄. Therefore the recombination of electron-holepairs is restrained and more electrons and holes can transfer to the surface of the compositeand join in the surface reaction. So the photocatalytic activity can be enhanced.Herein, the Bi₂WO₆/BiVO₄photocatalyst with heterojunction structure was preformedhigh photocatalytic activities under visible light irradiation. And it has potential in purificationof the pollutants by its great photocatalytic activities.