LaVO₄-TiO₂ Photocatalyst: Preparation And Photocatalytic Activity

As one of the numerous photocatalyst in the world, titanium dioxide because of its strong oxidizing, chemically stable, non-toxic, widely used in life. However, due to the shortcomings of low quantum yield and low utilization of solar energy, limit the application of titanium dioxide in the degradation of pollutants. Incorporation of metal ions may be introduce lattice defects in the semiconductor crystal or change the crystallinity which affects the electrons and holes combine or change the excitation wavelength of the semiconductor, thereby changing the photocatalytic activity of TiO₂. Semiconductors doped with different metal ions, the diversification causing is not the same. Doped with transition metals can effectively improve the catalytic performance of catalyst, to obtain visible light photocatalytic activity. Doped with rare earth metals can also make the catalyst get visible light photocatalytic activity. After doped with rare earth metal ions (La³⁺, Er³⁺, Ce³⁺, Nd³⁺,Gd³⁺, Sm³⁺ ,Pr⁺),which can greatly improve the adsorption, at the same time effectively inhibit the combination of electrons and holes, and absorption wavelength red shift.Doped with W⁶⁺, V⁺, Fe³⁺, Ag⁺, Ni²⁺, etc.can significantly improve the photocatalytic activity of TiO₂. But not all of the metal ion can improve the photocatalytic activity efficiency of catalyst, Li⁺, Mg²⁺, Al³⁺, Zn²⁺, Ga³⁺, Zr⁴⁺, Nb⁵⁺, Sn4+and Ta⁵⁺,etc.metal ions have little impact of photocatalytic activity. Only the metal ions which the electronic structure and ionic radius,crystal structure of semiconductors,electronic structure matching, can form an effective doping and improve the photocatalytic efficiency.In this paper,use a two-step synthesis method.The frst step,hydrothermal method,use acid dissolced or alkiline solution dissolved as two methods.Method of alkiline solution dissolced,control pH = 4 to obtain monoclinic m-LaVO₄ .Method of acid dissolced,contral pH = 6.5 to obtain zircon-type t-LaVO₄. The second step,three methods were used to synthesize LaVO₄-TiO₂,use TTIP as the source of titanium,control the incorporation rate of LaVO₄ ,and calcination temperature, synthesis photocatalysts with different catalytic activity. By X-ray powder diffraction characterize structure of the catalysts, found TiO₂ in the catalysts were all anatase TiO₂ structure.Used transmission electron microscopy to characterized LaVO₄-TiO₂, proved the TiO₂ in LaVO₄-TiO₂ was anatase titanium dioxide. Photocatalyst prepared by the first method, catalytic properties with the increase in the amount of reduction. Photocatalyst prepared by the second method, LaVO₄-TiO₂-0.25% is the best catalyst. Photocatalyst prepared by the third method,when calcination temperature is 500℃, LaVO₄-TiO₂-0.5% is the best catalyst.