Controllable Synthesis And Property Research Of Doping Titanium Dioxide Photocatalysts

Nanometer-sized titanium dioxide,used as a photocatalyst,can degrade the trace organic compounds to non-toxic substances,therefore because of high specific surface area, security, stability, non-toxic effects, no secondary pollution, low cost and excellent transport behavior, and large porosity, it is of great value in the practical applications. However,it suffered from the disadvantages that the titanium dioxide nanomaterial cannot show excellent photocatalytic activity without UV light irradiated (because of its band gap is about 3.2 eV) and the utilization of the solar rays is too limited and ineffective,which hinders its widespread applications to great extent. In order to improve the photocatalytic activity, the nano titanium dioxide must be modificated. With those in mind,the main purpose of the paper is to synthesis nano titanium dioxide doped with non-metal elements and rare-earth elements to improve the photocatalytic activity in visible light throught controling the particle size of nano titanium dioxide and the addition of the elements, then the crytal structure change, along with suppressing the recombination of photogenerated electrons and holes.In this paper, by use of salt solution-assisted sol-gel method, the titanium dioxide microspheres were successfully prepared with butyl titanate (TBT) as the main raw material. The F, N and Fe³⁺ were doped completed on the microspheres as the precursor via microwave hydrothermal. Nanoparticles of titanium dioxide with high specific surface area, high crystallinity and morphology rules were obtained, and its photocatalytic activity were studied. The structure of titanium dioxide was systematically analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption, Fourier Transform Infrared Reflectance Spectroscopy (FTIR) and UV-vis diffuse reflectance spectroscopy (UV-vis), and Photoluminescence Spectrospcopy (PL), and then do further discussion on the effects of the degree of crystallinity, surface area, elemental composition and doping on the photocatalytic activity. In addition, titanium dioxide nano-materials doped metal elements to enhance the photocatalytic activity in the infrared light region. The preparation and characterization of the rod-assembly microspheres, hollow microspheres, and the feathery Fe₂O₃/TiO₂ nanoparticles were respectively investigated in this paper, and the growth process was preliminary analyzed from TEM, SEM results.Experimental results are shown as followings. (1) The self-assembled mesoporous microstructures of F-doped TiO₂ microspheres were synthesized via gel-microwave-assisted hydrothermal method. The results showed that the average diameter of microspheres were about 400 nm. Since sodium fluoride doped, nanocrystals (12±0.5 nm) and mesoporous (≈10 nm) formed and roughness clearly enhanced. The PL spectra show F does not result into a new PL phenomenon, but F dopant can enhance the PL intensity of TiO₂ microspheres.And when NaF: TiO₂=2:5, the sample has the better performance in photocatalytic activity. (2) The TiO₂ hollow microspheres were prepared bymicrowave-assisted solvothermal treatment without template. The results show that the particles have hollow structures and the shell was covered by nanocrystals and have higher specific surface area. The possible formation mechanism of hollow TiO₂ spherical structures has simply been proposed. The activity was evaluated by the photocatalytic degradation of methyl orange (MO). The results show that the particles having specific surface area show higher photocatalytic activity. (3) Mesoporous titanium dioxide beads with high surface areas (over 90 m²/g) and tunable pore sizes (from 12.8 to 16.5 nm) were synthesized via a solvothermal process heating by microwave irradiation, with ammonia being used as both a source of nitrogen and a control agent for the mesoporous structure. The doping nitrogen was in the form of NHx or NOx species and was adsorbed on surface of the beads, which caused changes to the surface electronic structure. The results show that the samples which possess higher-order structure, large surface area and well-defined crystallinity have the best performance in photocatalytic activities exhibited as evaluated in the degradation of methylene blue. (4) A series of Fe³⁺-doped TiO₂ nanoparticles (Fe₂O₃/TiO₂) were successfully prepared via hydrothermal treatment. Scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (IR), and UV-visible spectroscopy (UV-Vis) were employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. Results showed that a large number of feather-like nanoparticles existed, indicating that these materials had a large specific surface area. Fe³⁺ ions were possibly well distributed in the lattice structure of TiO₂ and partially replaced Ti⁴⁺ which caused a broadening of the spectral response of TiO₂ and also caused defects in the crystal structure.