Photocatalytic Activity Of TiO₂ Nanopaticles Modified With Metal Ion Under Visible Light Irradiation

New TiO₂ photocatalysts of visible response were prepared by metal ions doping in order to extend its range of photo-response spectrum and increase its photocatalytic activity. The present studies include the following aspects: (1) the preparation of Bi-doped TiO₂ and its photocatalytic performance under visible light illumination; (2) the preparation of Ce doped TiO₂ and its visible light photocatalytic property; (3) the preparation of Pr-doped TiO₂ and its photocatalytic performance under visible light illumination; (4) the preparation of Nd doped TiO₂ and its visible light photocatalytic property.1. The Bi doped TiO₂ is mainly anatase and its grain size is smaller than pure TiO₂, which indicate that doping effectively suppresses the phase transformation and growth of nanocrystals. UV-vis DRS show an extension of light absorption into the visible region. Fluorescence spectra indicate the recombination rate of photo-generated charge decreases. The results of the degradation of Rhodamine B under visible light irradiation show that Bi-doped TiO₂ has a high and stable photocatalytic activity, when the optimal doping concentration is 2.0 % (mol %). In the photocatalytic degradation process, the·OH which adsorbed on the surface of TiO₂ plays the most important role.2. The Ce-doped TiO₂ (Ce-TiO₂) has good durability and enhanced visible light photocatalytic activity. In the photocatalytic degradation process, the adsorbed·OH of Ce-modified TiO₂ plays the crucial role. The results of the degradation of Rhodamine B in the visible experiments show that the optimum doping amount is 3.0 % (mol %). The Ce-TiO₂ consists mainly of anatase and the grain size is smaller than that of pure TiO₂, suggesting that doping Ce effectively inhibits the growth of nanocrystals. UV-visible absorption spectra show that Ce doping lead to the red shift of absorption spectra. Fluorescence spectra show lower recombination rate of the photogenerated charge by Ce doping.3. Pr-doped TiO₂ (Pr-TiO₂) has good durability and the main crystal anatase, and its grain size is smaller than pure TiO₂, indicating that Pr doping effectively inhibits the growth of nanocrystals. The optimal doping amount is 2.0 % (mol %). The increasing of the amount of the adsorbed H2O and hydroxyl groups which showed by FT-IR improves the photocatalytic activity of Pr-TiO₂. Fluorescence spectra show that the surface state of 2.0 % Pr-TiO₂ is lower than that of pure TiO₂, which suggests that photo-charge recombination rate decreases. These results cause the enhanced photocatalytic property of Pr-TiO₂. Furthermore, the·OH which adsorbed on the surface of TiO₂ plays the most important role on the degradation of RhB.4. Nd-doped TiO₂ (Nd-TiO₂) has good durability. When the Nd: Ti = 3.0:100 (mol %), the photocatalyst shows the highest activity among the samples of different contents. The Nd-TiO₂ consists mainly of anatase and the grain size is smaller than that of pure TiO₂, suggesting that doping Nd effectively inhibits the growth of nanocrystals. Compared with pure TiO₂, the results of BET analysis demonstrate by Nd doping the surface area powder and pore volume of Nd-TiO₂ significantly increase. According to FT-IR, the amount of the surface-adsorbed H2O and hydroxyl groups increase, which improves the activity of photocatalyst. In addition, the experiments show that the reactive oxygen species of O2? - and ?OH generated in the photocatalytic process play significant roles. Whereas, the·OH adsorbed on the surface of TiO₂ plays the most important role on the photocatalytic degradation of dye RhB under visible light illumination.