Research On Different Methods Modified Bismuth-based Semiconductor Photocatalytic Materials

Bismuth-based semiconductor photocatalytic materials are considered to be the potential novel materials which can replace conventional catalysts due to its Bi 6s electron orbits, the significant absorption capacity of the visible region and the high photocatalytic activity for the degradation of non-preference dyes. However, not all materials containing Bi3+ ions have the high activity; parts of them contain some intrinsic defects, such as lower conduction band position and the easy to light corrosion that can limit its wider application.Using the different methods to modify bismuth-based semiconductor photocatalysts is the emphasis of this dissertation. X-ray diffraction?XRD?, field emission scanning electron microscopy?FE-SEM?, ultra violet-visible?UV-Vis? and diffuse reflectance spectroscopy?DRS? were employed to measure the crystal structure of the catalyst, phase composition, morphology characterization. The specific surface area and pore-size distribution were characterized by brunner emmet teller?BET? measurements. Methyl orange and Methyl blue were selected as the target pollutants to evaluate the activities of photocatalysts in the visible light irradiation??>420 nm?.Finally, explained the relationship of catalyst structure, morphology and optical absorption to photocatalytic activity.Listed below are the methods and results:1) The solid solutions with different concentration ratio of Bi1-x Nix VO4?x=0.05¹.2 mmol? were prepared by the solid state reaction. The experiments showed that the catalysts consist of massive microparticles. With the increasing of Ni O content, the structure of Bi1-x Nix VO4 gradually trend to layer. Bi VO4 and Ni2V2O7 formed a pseudo-binary solid solution with small BET surface at 0.5¹.9 m2/g. Compared with the pure Bi VO4, the light absorption wavelength of Bi1-x Nix VO4 has been red-shifted which brought along with the width of the forbidden bands were about 2.22².29 e V. Bi0.7Ni0.3VO4 exhibited excellent catalytic activity compared to pure Bi VO4 in the photodegradation of Methyl orange, which degradation rate was up to 97.12 % under the irradiation from 300 W xenon lamp after 150 min.2) The samples of BiVO₄-Bi₂O₃ with 3D flower-like nanostructures were synthesized by the two-step hydrothermal method whose reaction time and temperature were variables. Experimental results showed that the crystalline phase of Bi VO4-Bi2O3 contained the miscible crystalline phase of Bi VO4, ?-Bi2O3 and ?-Bi2O3. The samples had the regular 3D flower-like nanostructure, however, with the increased of reaction temperature and time, the flower-like structure turned into a pile of loose sheets, and that greatly influenced the specific surface area and crystallinity of the samples. The prepared Bi VO4-Bi2O3 samples could respond to a wavelength of 495 nm visible light, whose forbidden bands were about 2.4².56 e V. The samples were synthesized with hydrothermal reaction condition at 160 °C for 15 h had the best photocatalytic activity. The degradation rate of Methyl orange was up to 97.07 % in 120 min under continuous illumination from 300 W xenon lamps.3) Using secondary hydrothermal method, the Bi2O3-TiO₂ p-n heterojunction composite was synthesized successfully. Firstly, the dendritic TiO₂ was growth on the FTO, as the substrate to build Bi2O3 as Bi2O3-TiO₂ p-n junction formation. Setting the concentration of seed and growth of liquid were variables to study Bi2O3-TiO₂ photocatalytic activity. The experimental results showed that the samples as Bi2O3-TiO₂ complex dendritic morphology were the surface of TiO₂ substrate covered by the diameter of 1?m Bi2O3 spheres. The maximum absorption range of the sample was 610 nm, and forbidden bands were about 2.04².17 e V. When the amount of Li OH was 2 mmol and the growing concentration upped to 0.2 M, the sample had the highest activity. Under the continuous illumination from 300 W xenon lamps for 75 min, the efficiency of this Bi2O3-TiO₂ sample reached 99.71% in the degradation of Methylene blue. Much better than that of the molar ratio of 1: 1 mechanical polishing of Bi2O3 and TiO₂ powder mixture.