Design, Preparation And Photocatalytic Performs Of Single Or Codoped Nanocomposite

In the 21st century, environment problems caused by the noxious and undegraded organic pollutions such as pesticides, dyes have been deeply affected the survival and development to human being. It is difficult to solve pollution with the traditional environment technology. So to exploit and control the poisonous and undegradated contaminations have become hot research topic in the world. What causes the great interest of the semiconductor photocatalytic technology in the scientific research area is the great potential value to apply in environmental purification and energy issues. In this thesis, we focus on the vital scientific difficult problem to use the UV-light and low quantum efficiency in the photocatalytic technology, and to improve the quantum efficiency and using the visible-light which exist 50% in the sun. Based on the sufficient understand the relationship between the organic pollution and photocatalyst specialty, we research the pollution degradation and mineralization with the single- or codoped- nanocomposite photocatalyst penetrately and systemically. Some new and interesting results are as following:(1) The research of enanced photocatalytic activity of europium oxide/tantalum pentoxide mixed oxides on degradation of rhodamine B and 4-nitrophenol. The Eu₂O₃/Ta₂O₅ mixed oxides with different Eu dopings were prepared by a single-step sol-gel process via hydrolysis of tantalum pentachloride in the presence of europium nitrate. The products were in the amorphous and orthorhombic phase structures, respectively, based on the different calcination temperatures (200 and 500 oC). Composition, morphology, phase structure, Eu₂O₃ doping mode in the Ta₂O₅ matrix, and optical absorption property of the products were characterized by inductively coupled plasma atomic emission spectroscopy, field emission scanning electron microscopy, X-ray diffraction patterns, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The UV-light photocatalytic activity of the products was evaluated by degradation of aqueous rhodamine B and 4-nitrophenol. The results showed that the photocatalytic activity of as-prepared Eu₂O₃/Ta₂O₅ was higher than that of pure Ta₂O₅ regardless of their phase structures. Among the tested samples, 0.49-Eu₂O₃/Ta₂O₅ obtained with 200 oC exhibited the highest activity to degradation of the above two model molecules. The reasons of this enhanced photocatalytic activity were discussed logically.(2) Successfully prepared silver and indium oxide co-doped TiO₂ nanocomposites with enhanced photocatalytic activity, based on the research of In₂O₃-TiO₂ and Ag/TiO₂. The Ag/In₂O₃-TiO₂ nanocomposites were prepared by a one-step sol-gel-solvothermal method in the presence of a triblock copolymer surfactant (P123). The resulting three-component systems mainly exhibited an anatase phase structure, high crystallinity, and extremely small particle sizes with metallic Ag particles well-distributed on the surface. Compared with pure anatase TiO₂, the Ag/In₂O₃-TiO₂ systems showed narrowing of the band gap due to the change in the band position caused by the contribution of the In 5s5p orbits to the conduction band. By tuning loadings of Ag or In₂O₃ and molar ratios of titanium source to the surfactant, size and dispersion of the product particles can be controlled. As-prepared Ag/In₂O₃-TiO₂ nanocomposites were used as the photocatalysts to degrade dye rhodamine B and methyl ter-butyl ether in the liquid phase. At 2.0% Ag and 1.9% In₂O₃ doping, the Ag/In₂O₃-TiO₂ system exhibited the highest UV-light photocatalytic activity. In addition, the UV-light photocatalytic activity of three-component systems exceeded that of the single (TiO₂) and two-component (Ag/TiO₂ or In₂O₃-TiO₂) systems as well as the commercial photocatalyst, Degussa P25. Reasons for this enhanced photocatalytic activity was revealed and the mechanism was speculated.(3) Based on the research of Ag/TiO₂ or VO_x-TiO₂, successfully prepared mixed phase titania nanocomposite codoped with metallic silver and vanadium oxide: new efficient photocatalyst for dye degradation. The Ag/VO_x-TiO₂ was prepared by a one-step sol-gel-solvothermal method in the presence of a triblock copolymer surfactant (P123). The resulting three-component system exhibited an anatase/rutile (weight ratio of 73.8/26.2) mixed phase structure, narrower band gap (2.25 eV), and extremely small particle sizes (ca. 12 nm) with metallic Ag particles well-distributed on the surface of the composite. The Ag/VO_x-TiO₂ nanocomposite was used as the visible- and UV-light-driven photocatalyst to degrade dyes rhodamine B and coomassie brilliant blue G-250 in the aqueous solution. At 1.8% Ag and 4.9% V doping, the Ag/VO_x-TiO₂ system exhibited the highest visible- as well as UV-light photocatalytic activity; additionally, the activity of the three-component system exceeded that of Degussa P25, pure TiO₂, single-doped TiO₂ system (Ag/TiO₂ or VO_x-TiO₂) as well as P123 free-Ag/VO_x-TiO₂ codoped system. The reasons for this enhanced photocatalytic activity were revealed. At the same time, the band gap, schematic representation, and the absorption modle of the Ag/VO_x-TiO₂ composite were discussed.