Study Of Preparation, Characterization And Properties Of TiO₂-based Visible Light Response Nano-photocatalyst

Rear earth (RE) doped TiO₂ nano-photocatalyst attracted the increasing attentions, and many attempts have been made to explore the relationship between the properties of rear earth elements itself and the photocatalytic activities of as-prepared photocatalyst. However, up to now, the effects of the properties of rear earth elements itself on the mechanism of doping process and activity still kept unclear. The RE (La, Ce, Gd, Er, Yb, Y) doped TiO₂ nano-photocatalyst was synthesized using modified sol-gel technique, and the activities were evaluated using oza dye solution and oxalic acid solution as the model reactant under different light source. The as-prepared particles were characterized using XRD, TEM, BET, DRS and XPS. The effects of doping amount and sintering temperature on the crystal morphology, crystal structure and the chemical component were carried out in this study. Further, the process of photodegradation and the mechanism of photocatalyst have been studied well.Nitrogen doped titanium dioxide nanoparticles were prepared by heating titanium hydroxide with urea. The yellow powders obtained after calcination at 450 oC 2 h in air. Photocatalysis the photoconversion KI and oxalic acid solution have been operated under different light source irradiation. X-Ray Diffraction (XRD) and surface area analysis show the presence of anatase/brookite TiO₂ nanoparticles with crystallite size ranging from 7nm to 10 nm and specific surface area ranging from 71.24 to 170.38 m2·g^-1, depending on the amount of urea used. Diffuse Reflectance Spectroscopy (DRS) shows a shift in the range of 400⁵80nm and narrowing of the bandgap up to 2.80 eV, which can be attributed to the creation of visible light absorbing titanium oxynitride centres by the doping process. X-Ray Photoelectron Spectroscopy confirms the presence of Ti-N bond and oxynitride should be main doped nitrogen species due to new coming N-TiO₂ vibration at 550 cm^-1 from Raman spectrum, XPS analysis.Based on the above theorical analysis, cerium and nitrogen co-doped anatase TiO₂ nanoparticles were synthesized using a one-step technique via a modified sol-gel process and characterized by XRD, BET, DRS, Raman and XPS. The photocatalytic mechanism of the degradation of methylene blue (MB) under fluorescent light and visible light irradiation was studied. Co-doping cerium and nitrogen in the crystal lattice of TiO₂ narrowed the band gap from 2.40 eV (Ce-doped TiO₂) to 2.21 eV (Ce/N co-doped TiO₂). Ce⁴⁺/Ce³⁺ pairs, oxynitride species and Ti-O-N and Ti-O-Ce bonds were determined by XPS. The recombination of photogenerated electron-hole pairs was inhibited due to the synergistic effect of doping with Ce⁴⁺/ Ce³⁺ ions and N atoms. The optimal doping ratio was 0.70% Ce and 0.70% N using MB photocatalytic degradation under fluorescent light and visible light irradiation (λ>420 nm). The photocatalytic mechanism and was investigated through methylene blue (MB) photocatalytic degradation using various filtered wavelengths of light (λ>365nm,λ>420nm,λ>500nm,λ>550nm,λ>600nm) for a period. Two experimental parameters were studied systematically, namely the atomic ratio of doped N to Ce and the irradiation wavelength number. The photocatalytic degradation of MB over CNT NPs in aqueous suspension was found to follow approximately first-order kinetics according to the Langmuir-Hinshelwood model. The enhanced photocatalytic degradation was attributed to the increased number of photogenerated·OH radicals.The enhanced photocatalytic degradation under visible light irradiation was attributed to the increasing number of photogenerated·OH radicals. The recombination of photogenerated e--h+ was attributed to be the key factor for the decrease in the photocatalytic degradation efficiency of MB.The targeted dye sensitized solar cells in this study were fabricated using the modified nano-photocatalyst (N doped TiO₂ nanoparticles) as the electrode and N719 as the dye sensitizer. By enforced the connections between the conductivity film and dye, the absorbance of amount, the enhanced efficiency and life time of solar cells have been found. Meanwhile, the properties of photo-generated electrons have been studied in detailed, such as the electron life time, the electron density, the diffusion coefficient. The relationship between the properties of photo-generated electrons, the crystal structure, and the chemical component of N doped TiO₂ nanoparticles was dicussed in this part.