Preparation Of Rare Earth Orthovanadates And Their Luminescent And Catalytic Performances

As rare earth elements have unique electric, chemical and optical properties because of their4f outer shell-electron, they have wide been used in the optics-electricity industries. Rare earth elements can not only be used as host material of photoluminescent materials but also used as activator, co-activator and doping component. The steady state of LaVO4is monoclinic due to bigger ionic radius of La. The monoclinic LaVO4has worse catalytic performance and luminescent performance than the tetragonal one. The performance of tetragonal LaVO4is almost same as that of YVO4and the tetragonal LaVO4:Eu may be a good red phosphor candidate. Therefore, it will be interesting for selective synthesis of tetragonal LaVO4and making the synthesis mechanism clear. In this paper, the selective synthesis of and the synthesis mechanism of LaV04were studied, and several rare earth orthovanadates with nano-size have been prepared and their luminescent performance and catalytic performance have been investigated. The main research results have achieved as follows.1. Selective synthesis of tetragonal LaVO4with Na3VO4as vanadium source by hydrothermal treatmentTetragonal LaVO4has been successfully prepared with Na3VO4as vanadium source and La(NO3)3as lanthanum source, and the effects of pH, hydrothermal temperature and time on textural and structural properties and morphology of LaVO4samples have been investigated. A mechanism of selective producing tetragonal LaVO4has been proposed. The research results show that, pure tetragonal LaVO4can be produced in the matrix solution with pH3.0-10.0at room temperature to180℃for3-48h. The morphology of LaVO4can be influenced by pH in matrix solution, the crystallization temperature and time. Nanorods LaVO4with different sizes and aspect ratios have been prepared in different synthesis conditions.2. Synthesis of tetragonal LaVO4with different vanadium sourcesTetragonal LaVO4has been prepared with V2O5, NaVO3, NH4VO3as vanadium sources respectively, and the proposed synthesis mechanism were also further confirmed. The results show that, when tetragonal LaVO4were prepared with different vanadium sources, adopted hydrothermal condition was different. Tetragonal LaVO4can be prepared in the matrix solution of pH4.5-10.0when V2O5was used as vanadium source; tetragonal LaVO4is still prepared in the matrix solution with pH6.0-9.0when NaVO3and NH4VO3are used as vanadium source. A common process of synthesizing tetragonal LaVO4has been proposed. Preparing tetragonal LaVO4through sonication method was investigated, and tetragonal LaVO4nanorods have been prepared by means of sonication.3. Synthesis of YVO4crystals with different shapes through hydrothermal treatment and sonication methodThe YVO4crystallites with different sizes and shapes have been prepared by hydrothermal treatment and sonication method. Spindle-like, micro-sized bipyramid-capped and micro-sized cuboids YVO4crystallites have been prepared by hydrothermal method. Nanoparticles and nanorods YVO4crystallites have been obtained by sonication method. Effects of pH in the matrix solution and synthesis method on the luminescent performance of YVO4crystallites were investigated. The results show that, pH value of matrix solution can affect the luminescent performance of sample and the sample prepared in the matrix solution with pH2.5has the best luminescent behavior. The sample produced hydrothermally behaves better luminescent property than that produced by sonication method.4. Synthesis of ReVO4(Re=Ce, Eu, Dy, Lu) through hydrothermal treatment and sonication methodMicrorods, nanorods and nanoplates of CeVO4have been prepared hydrothermally, and nanoparticles, nanorods and nanoplates of CeVO4have been prepared by means of sonication. When the CeVO4crystallites were used as a catalyst for the combustion of trichloroethylene, all the CeVO4samples exhibit the catalytic activity; however, the sample produced hydrothermally in the matrix solution with pH13.0exhibits the best catalytic activity, its T90%=275℃. EuVO4, DyVO4and LuVO4crystallites have been produced hydrothermally in the matrix solution with different pHs. and it is found that their morphologies would be changed with different pH values of matrix solution.