Properties Of Ce Ion And Ce/N Ions Co-doping TiO₂Photocatalyst

With the growing environmental pollution, it is more and more urgent to require a catalyst material with good stability and excellent photocatalytic activity. TiO2have been in deep research in the semiconductor catalysis area for its good chemical stability, inexpensive, non-toxic, photoelectric properties, and other advantages. However, on the one hand, the band gap of anatase TiO2is about3.2eV, which makes it only show photocatalytic activity under UV-light irradiation (λ<387nm), so that its solar energy utilization is very low. On the other hand, the photo-generated electron and hole pairs of TiO2are so easily recombined, which results in a lower photo quantum yield. Therefore, there is an important academic and application value to narrow the band gap of TiO2, broaden its spectrum absorption and improve its photocatalytic activity under visible light irradiation. Recently, many attempts have been made to achieve this goal, such as ion-doping, semiconductor compounding and dye sensitizing. Generally, ion doping is considered to be the most effective among these modification methods for its simple requirement and better modified effect. Furthermore, TiO2co-doped with RE and N ions have excellent photocatalytic activity. In this paper, under the guidance of the theory calculated by our group, the Ce ion doping TiO2(Ce-TiO2) and Ce, N ions co-doping TiO2(Ce/N-TiO2) were prepared by sol-gel and microwave chemical method. The structure and morphology of samples were characterized by XRD, TEM and Nano-series sizer. Meanwhile, the spectroscopic properties were characterized by FT-IR, UV-Vis, PL, and XPS. In addition, the photo-degradation of the methyl blue (MB) and formaldehyde under fluorescent lamp was investigated to test the photocatalytic activity of the samples. The main work and results are as the follows:1. Ce ion doping TiO2(Ce-TiO2) photocatalystThe Ce-TiO2powders were synthesized by sol-gel method, with the distilled water as the solvent and Ce (NO3)3-6H2O as Ce source. The L25(53) orthogonal experiment method was used to investigate the influences of sintered temperature, Ce doping concentration as well as pH value to the photocatalytic activity of Ce-TiO2samples. The result shows the order of the factors from primary to secondary influenced the phtotocatalytic activity of the samples is the follows:sintered temperature> Ce doping concentration> pH value. Meanwhile, the optimal preparation condition is as the following: reaction temperature of60℃, sintered temperature of600℃for4hours, Ce doping concentration of Ce: TiO2=0.33%, and pH value=1.5.The experiment results show that Ce ion doping efficiently inhibit the TiO2phase transition from anatase to rutile and the particle growth of anatase TiO2, broaden its spectrum absorption into the visible light, decrease the recombination of the photo-generated electron-hole pairs. What's more, the absorption edge of Ce-TiO2sample synthesized under the optimal condition expand nearly50nm compared with pure TiO2. The PL spectra intensity of Ce-TiO2is evidently lower than pure TiO2The photo-degradation rate of Ce-TiO2samples to MB within8hours can reach to90.03%under the fluorescent lamp, which is more efficient than that of P25(68.19%).2. Ce/N ions co-doping TiO2(Ce/N-TiO2) photocatalystThe Ce/N-TiO2powders were prepared with sol-gel and microwave chemical reaction method. The research is mainly to investigate the influence of sintered temperature and Ce doping concentration to the photocatalytic activity of the Ce/N-TiO2. The optimal preparation condition is as the following: reaction temperature of60℃, sintered temperature of600℃for4hours, Ce doping concentration of Ce: TiO2=0.25%, N doping concentration10g, microwave reacted pressure=4.827x105Pa, and pH value=1.5.The results show that Ce and N ions co-doping can retard TiO2from anatase to rutile phase, and when the sintered temperature is700℃, few anatase phase appears in the sample. Ce and N ions co-doping inhibits the particle growth of anatase TiO2, broaden its spectrum absorption into the visible light, and decrease the PL spectra intensity. Ce/N-TiO2samples have excellent photocatalytic activity under the fluorescent lamp, and the photo-degradation rate of Ce/N-TiO2to MB in6hours can reach to83.91%, which is more efficient than that of P25(58.72%). Meanwhile, the photo-degradation rate of Ce/N-TiO2to the high concentration formaldehyde in10days can reach to83.91%, while less photo-degradation rate of P25to formaldehyde. Higher photo-degradation rate to formaldehyde can be mainly attributed to that Ce and N ions co-doping is beneficial for anatase TiO2, it can efficiently inhibit the recombination of the photo-generated electrons and holes and broaden its spectrum absorption region.The novelties of the work are mainly focused on the following aspects:(1) The experiment are conducted under the guidance of our group. Such recombination of theory and experiment can effectively overcome the blindness and repeatability of the current research.(2) According to the research, we find that Ce ion and Ce/N ions co-doping can bring in impurity energy levels, which efficiently decrease the recombination rate of photo-generated electron-hole pairs and broaden the absorption region to the visible light.(3) The Ce-TiO2and Ce/N-TiO2samples have excellent photocatalytic activity under the visible light, which is significantly better than that of P25.