Controllable Synthesis And Photodegradation Performance Of Bi₂WO₆ Micro/Nanomaterials

Semiconductor photocatalysis has attracted tremendous attention due to its great potential applications in environmental and energyfields. Bismuth tungstate (B12WO6) is a type of multilayered composites which has the simplest structure of Aurivillius oxides.Since the band gap of B12WO6 is 2.7 eV, which has strong photocatalysis performance in the UV and visible region, it has attracted more and more interests of researchers. Therefore, different chemical methods have been developed to prepare different-shaped/sized Bi2WO6 micro/nanomaterials, which could improve the photocatalysis performance to some extent. In this thesis, pure Bi2WO6 and Cu-or Ag-doped Bi2WO6 micro/nanomaterials were synthesized by a hydrothermal method, in which Bi(NO3)3·5H2O and Na2WO4·2H2O was used as Bi and W sources, respectively. The effects of pH values, reaction temperature and on the crystal phase, morphology, optical absorption and photocatalytic properties of the Bi2WO6 were studied systematically.Firstly, the pure Bi2WO6 micro/nanomaterials were synthesized by using Bi(NO3)3·5H2O and Na2WO4-2H2O as raw materials, and the effects of pH vaules, reaction temperature and time on the performance of Bi2WO6 micro/nanomaterials were studied. The results indicated that orthorhombic and rombohedral Bi2WO6 micro/nanomaterials were obtained under acidic and neutral conditions, while Bi3.84Wo.1606.24 phase was obtained under basic conditions. Moreover, the morphology of Bi2WO6 changed from solid floriform to spatial and octahedral shape with the pH values increasing from 2 to 11, in which the solid floriform products were made up of some nanoplates and the spatial structure consisted of irregular flakes. In contrast, the reaction temperature and time has little effects on the crystal structure and morphology, but the specific surface area was affected by the reaction temperature and time. In addition, the optical properties of the as-obtained products were also studied. The photo-degradation of organic pollutants under visible light demonstrated that the products obtained at pH=2, and the reaction temperature of 180℃ and the reaction time of 24h showed the best photocatalytic performance, and the photo-degradation efficiency could reach up to 98% after illustration for 3 hours.Secondly, based on the synthesis of high-quality of pure Bi2WO6, Cu-or Ag-doped Bi2WO6 micro/nanomaterials were synthesized by using Cu(NO3)3·3H2O, AgNO3 as the Cu and Ag sources respectively, in which the pH value was 2, and the reaction temperature was kept at 180℃ as well as the reaction time of 24h. The crystal phase and morphology of the as-obtained products were characterized by using the X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM), and the results indicated the introduction of of metal ions had no significant effects on the crystal phase and morphology of Bi2WO6 The photo-degradation results showed that the doping of Cu ions into the lattice of Bi2WO6 could contribute to the improvement of the photocatalytic performance, and the best photodegradation could be obtained when the weight fraction of Cu was 3%. Moreover, the doping of Ag ions into Bi2WO6 could not improve the photocatalytic activity but were beneficial to the adsorption properties. The results may offer some approaches to improve the photocatalytic performance of Bi2WO6.