Properties Of C And Rare-earth Metal （Y,Pr）Doping TiO₂Photocatalyst

TiO2has been attracted many attentions due to its high redox ability, low toxicity, chemical inertness and low cost. However, absorbed a small portion of solar light (<5%of total solar spectrum) in the UV region and the rapid recombination rate of photo-generated carriers. The widespread technological use of the photocatalyst is hindered by these shortcomings. Therefore, it is the most important thing that to find a way to prolong the lifespan of photo-generated carriers and extend the absorbtion to the visible region. Ion doping has been proved to be one of the most effective modification methods.In this thesis, based on the numerical simulation of MS by our group, C-TiO2、Y-TiO2、 C-Y-TiO2and C-Pr-TiO2samples were prepared by sol-gel process with the tetrabutyl titanate, Yttrium nitrate and glucose as precursors and distilled water as the solvent. Among the precursors, the tetrabutyl titanate is source of Ti, Yttrium nitrate is source of Y and glucose provides C to dope into TiO2. All the samples were characterized by XRD, TEM, XPS, Raman, PL and UV-Vis techniques and so on. The photocatalytic activity of samples was evaluated by the degradation rate of methylene-blue (MB) under the irradiation of fluorescent lamp which power is30W. The details of work are listed:1. C single doped TiO2photocatalystsThe molar ratio of C:Ti and sintered temperature of preparation process were studied in this paper. The experiments have been done to evaluate the photocatalytic activity of C-TiO2. The degradation rate of the sample with molar ratio of C:Ti=0.30and sintered at400℃for4hours was the highest. The rate reached85.28%which was significantly higher than that of P25(44.72%) under the same experimental conditions. The results indicated that when carbon ion is incorporated into the lattice of TiO2, not only is the phase transition from anatase to rutile was promoted but also does the recombination of the photo-generated electrons and holes were inhibited. Moreover, the absorption region broaden to visible light region.2. Y single doped TiO2photocatalystsY-TiO2photocatalysts were synthesized and evaluated in the same method. The best degradation condition showed when the sample with molar ratio of Y:Ti=0.6%and sintered at500℃for4hours was tested. The degration rate reaches89.24%within3hours and significantly higher than P25(44.72%) and C-TiO2(85.28%) under the same conditions. The experiments show opposite trendency of the C doping system. Yttrium doping can not only inhibit the phase transition of anatase to rutile but also extend the absorption edge to visible light region and prolong the lifespan of the photo-generated carriers.3. C/Y co-doped TiO2(C-Y-TiO2) photocatalystsThe C/Y co-doped TiO2samples were characterized in the same method. The sample with molar ratio of C:Y:Ti=0.30:0.004:1and sintered at500℃for4hours degraded94.23%MB within3hours, which was higher than P25(44.72%), C-TiO2(85.28%) and Y-TiO2(89.24%) under the visible light. The improved degradation rate of C-Y-TiO2could be caused by the following three aspects:the larger C and Y ions are incorporated into the lattice of TiO2, C, Y co-doping eliminate impurity states in the band gap vis charge compensation between different dopants, which reduce the number of recombination centers and promte the separation of electro-hole pairs. The co-doping also inhibited the growth of crystalline grain. The improvement of photocatalytic activity is ascribed to the synergistic effects of C and Y co-doping.4. C/Pr co-doped TiO2photocatalystsTiO2photocatalysts co-doped with C and Pr were synthesized by sol-gel process. Compared with all the other samples, the one with molar ratio of C:Pr:Ti=0.30:0.004:1and sintered at500℃for4hours is the much better than those samples preparated with same precursor. Its degraded rate was89.97%within3hours and higher than that of P25(44.72%), C-TiO2(85.28%) and Pr-TiO2(75.30%), but lower than C-Y-TiO2(94.23%) under the visible light. The results indicate that C, Pr co-doped inhibited the growth of crystalline grain. It was also found that both C and Pr co-doping can inhibit the recombination of the photo-generated electron and hole pairs and broaden the absorption spectrum to visible light region. The experimental results verify the most part of theoretical result. On the contrary the co-doped part is contradictory. The reasons were ananlized that there must be some neglected problem in the assessment. This is a part need to be studied in-deep in future research work. The highlights of the work are mainly focused on the following aspects:(1) In this paper we can find that Y and Pr respectively co-doped TiO2with C lead to the movement of VB and CB and the narrowing of the energy gap, the light absorption threshold red-shifted to the visible light region. Meanwhile, the recombination of the photo-generated electron and hole pairs was inhibited effectively.(2) Both the C-Y-TiO2and C-Pr-TiO2samples had excellent photocatalytic activity and the co-doped samples better than that of the single doped samples and P25under the same experiment condition.