| Eu3+, Ce3+doped nano-TiO2 and Ce-Eu co-doped TiO2 were synthesized by sol-gel method. The effects of internal and external factors on photocatalystic activity of the Ce-Eu co-doped TiO2 were discussed by designing the orthogonal experiments. The red mud ceramic filter materials were coated with the optimal formula of TiO2, which was used for water treatment. The samples were characterized by the testing techniques such as TG-DTA, XRD, FE-SEM, TEM, SEM, UV-Vis absorption spectra and so on. The photocatalystic mechanism of Eu3+, Ce3+doped TiO2 and Ce-Eu co-doped TiO2 was discussed.The photocatalystic properties of samples had some relation with the doping amount of rare earth Eu3+and Ce3+. The photocatalystic degradation on methyl blue of samples can reach 85.36% and 85.15% respectively, when the addition amount is 0.15g/50mL, the initial concentration of MB solution is 10mg/L, the pH value is 6.5, the heating temperature is 550℃and doping amount (molar ratio) was n(Eu3+): n(TiO2)=0.5% or n(Ce3+):n(TiO2)=0.05%. They showed better photocatalystic properties than the undoped TiO2, the degradation rate was increased by 22.08% and 21.78% accordingly. The temperature when the Rutil appeared was decreased to 650℃because of the addition of Ce3+. The Rutil was beneficial to the photocatalystic properties of the sample. The degradation rate of the sample whose doping amount was n(Ce3+):n(TiO2)=0.05% increased to 85.52%.The results of the orthogonal experiments showed that the important order of the internal factors that affect the photocatalystic properties of doped TiO2 were heating temperature, the amount of Ce3+, the amount of Eu3+in turn. The optimal formula of the sample is that the amount of Ce3+ and Eu3+ is 0.02mol% and 0.02mol% respectively, heating temperature is 550℃. The important order of the external factors that affect the photocatalystic properties were the initial concentration of MB, the addition amount of samples, the pH value in turn. The photocatalystic activity was the best when the addition amount is 0.15g/50mL, the initial concentration is 10mg/L and the pH value is 6.5.The study on the photocatalystic properties of the rare earth doped TiO2 showed that the photocatalytic activity were Co-doped TiO2> Eu3+doped> Ce3+doped> undoped samples. When the doping amount (molar ratio) was n(Eu3+):n(Ce3+): n(TiO2)=0.2:0.02:100, the photocatalystic degradation can reach 86.23%, which increased by 22.95% compared to the un-doped TiO2 samples.The grain size was 19.7nm, lattice distortion was 0.5259, unit cell volume was 136.26×10-3nm3, the kinetic constant of the photocatalytic reaction was 7.766×10-3. The absorption threshold was 445nm, and the band gap was 2.87 eV, which had 53nm red shifted than that of pure TiO2. The sample with the doping amount (molar percent) n(Ce3+): n(TiO2)=0.2%, had the maximum red shift, and the absorption threshold reached 446nm.The photocatalystic mechanism of Eu3+, Ce3+doped TiO2 and Ce-Eu co-doped TiO2 was as follows:A charge imbalance was caused because of the electron structure ([Xe]4f6)and radius of Eu3+, which had an effect on the recombination of e- and h+, the additional energy band of h+ broaden the absorption spectra. Ce3+ doped TiO2 brought out a series of poor results, like Ce3+, Ce4+co-exist, lattice distortion, the charge imbalance, low recombination of e-and h+; It made up of photosensitive structure formation, leading to excited electrons entered into the conduction band and enlarged the spectral response range of TiO2. When Ce-Eu co-doped nano-TiO2, Ce3+as a sensitizer ion transfer the energy to Eu3+, it captured and passed electrons to the O2 be absorbed on the surface, which resulted in the increase of effective electron and hole, also made the sample be excited by wavelength with lower energy.The photocatalystic properties of the filter coated with TiO2 for 10min twice was 73.40%, when the amount of filter is 0.15g/50mL, the concentration of MB is 15mg/L and the pH value is 6.5, and this value was higher than that of uncoated filter, which was 70.28%.There was a 2μm TiO2 film on the surface of the red mud ceramic filter which was heated at 550℃. The removal rate of As(v) by TiO2 modified filter was 95.96%, when 2g TiO2 modified filter absorbing in a solution of 2mg/L As (v)at pH=2 for 240min. |
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