Properties Of S Ion And La, Ce Ions Doping TiO₂Photocatalyst

Being of non-toxic, easy to produce and to use, photocatalytically active and chemically inert, TiO2is regarded as an ideal promising candidate among the photocatalysts. While, two drawbacks block up its way to commercial application. One is the wide-band gap (3.2eV); the other is a short lifespan of photogenerated electron-hole carriers. The two weaknesses lead TiO2to limited solar energy utilized and high recombination rate of carriers. Many researcher have studied modification methods to overcome them. Among all the methods, the ion-doped is practical and useful way to the dawn. In this paper, based on the numerical simulation of MS by our group, the La-TiO2, S-TiO2and La/S, Ce/S co-doping TiO2powders were synthesized by sol-gel method and hydrothermal synthesismethod. The samples were characterized by X-ray diffraction (XRD), Nano-series Sizer, ultraviolet-visible diffuse reflection spectrum (UV-Vis), photoluminescence (PL) and so on. The photocatalytic activity of the four systems of single-doped and co-doped TiO2was evaluatedby degradation of methylene blue (MB). The details of work are listed as follows:1. La single doped TiO2system:Catalysts were prepared by sol-gel method with following procedure:Ti(OC4H9)4deionized waterand La(NO3)3·6H2O. The variables of L16(42) orthogonal experiments were designed as La doping content and sintered temperature. The best synthetic conditionsare:In60℃deionized water, the relationship between the doping concentration of La and Ti is La: Ti=1:200(mole ratio), sintered temperature600℃for5h, and pH value is2.5. The absorption spectrums of this powder were extended to430nm, the band gap was decreased to2.8eV, and the improvement of TiO2photocatalytic activity caused by the inhibition of the recombination of photoelectron-hole pairs was increased.2. S single doped TiO2system:Catalysts were prepared by sol-gel method with following procedure:Ti(OC4H9)4deionized waterand Thiourea. The variables of L16(42) orthogonal experiments were designed as S doping content and sintered temperature. The best synthetic conditionsare:In60℃ deionized water, the relationship between the doping concentration of S and Ti is S:Ti=1:40(mole ratio), sintered temperature400℃for5h, and pH value is2.5. The absorption spectrums of this powder were extended to410nm, the band gap was decreased to2.9eV, and the improvement of TiO2photocatalytic activity caused by the inhibition of the recombination of photoelectron-hole pairs was increased.3. La/S, Ce/S co-doped TiO2systems:Catalysts were prepared by sol-gel method with following procedure:Ti(OC4H9)4deionized waterand La(NO3)3·6H2O and Thiourea or Ce(NO3)3-6H2O and Thiourea. The variables of L16(42) orthogonal experiments were designed as La/S or Ce/S doping content and sintered temperature. The best synthetic conditionsare:In60℃deionized water, keeping the relationship between the doping concentration of La and Ti is La:Ti=1:200(mole ratio), and keeping the relationship between the doping concentration of Ce and Ti is Ce’. Ti=1:300(mole ratio), and keeping the relationship between the doping concentration of S and Ti is S: Ti=1:40(mole ratio), sintered temperature500℃for5h, and pH value is2.5. The absorption spectrums of this powder were extended to410nm, the band gap was decreased, and the improvement of TiO2photocatalytic activity caused by the inhibition of the recombination of photoelectron-hole pairs was increased.The innovate points of the work has two aspects:(1) Based on the simulation results of our group, sulfur was chosen as nonmetal dopant that easily reaction with metal ions, and induce La-5d orbital and Ce-4f/5d orbital of rare elements into TiO2, which respectively overlapping with Ti-3d orbital and O-2p orbital, resulting in broadening the conduction band or valence band. Preparing doped TiO2under oxidizing condition, hope to form strong bond between metal and nonmetal elements. The two aspects mentioned above supported one another and narrowed band gap, leading to accelerate the transport of electrons, to reduce the recombination of the photo-generated electron and hole pairs.(2) We found that after the La doping of TiO2has the remarkable photocatalytic activity (96.6%). The result is highter than that of P25, and the efficiency of the other samples are respectively91.02%,84.53%and88.36%.