| Up-conversion luminescence refers to the process that active materials continuously absorb two or more than two photons, and then emit light with shorter wavelength than excitation light. The upconversion luminescent material is a kind of photoluminescence material that transforms long wavelength radiation to short wavelength radiation. Based on this principle, the visible-ultraviolet upconversion luminescent material could be chosen to composite with titanium dioxide to prepare composite photocatalyst, which also has a good activity under visible light. In this study, sol-gel method was used to prepare visible ultraviolet luminescent material, with yttrium orthosilicate as substrate, and the rare earth ions praseodymium as activator. The impact of the different ions doped to the upconversion luminescent material on the properties of its upconversion fluorescence was discussed, and the degradation of organic pollutants of the composite photocatalyst was also investigated.Firstly, Upconversion luminescence materials were prepared by sol-gel process with Y2SiO5as base material and rare-earth-ion Pr3+as activator, and they were characterized by TGA, XRD, Particle Size, SEM, and fluorescence spectrophotometer. The results showed that samples had the lowest crystallization temperature at950℃, average particle size of the samples were3.42μm and they were spherical and fluffy with a small number of reunion. Upconversion luminescence emission property was tested by fluorescence spectrophotometer. The results showed that samples had upconversion emissions at290-350nm. Contrasting the different concentrations of Pr3+doped, when the Pr3+concentration was1.0%(mol), the intensity of upconversion emission was strongest.Secondly, Pr3+:Y2SiOs was doped with three different metal ions such as Li+, Cu2+, Zn2+, respectively. The luminescence properties of the material changed. We found that Li+doped concentration between7.0%(mol)～8.0%(mol) would cause Y2SiO5transfer from X1phase to X2phase. Doped with appropriate concentration of Li+the crystallization temperature of the material down to about800℃. Doped Li+can improve the luminescent intensity of material. The optimized concentration of doped Li+was10.0%(mol), and the luminescent intensity has increased8ratios. With Li+doped, the optimized concentration of Pr3+has changed from1.0%(mol) to1.2%(mol). While Cu2+doped concentration between3.0%(mol)～4.0%(mol) would cause Y2SiO5transfer from X1phase to X2phase, and the crystallization temperature of the material was down to about820℃; Doped Cu2+could not improve the luminescent intensity of material. The impact of doped Zn2+on the material could be omitted. Finally, Pr3+, Li+:Y2SiOs/TiO2composite catalysts were prepared. They were employed to degrade nitrobenzene. The effects of the mass percentage, catalyst dosage, the initial solution concentration of nitrobenzene, different kinds of materials, the intensity of light, were analyzed in details. The results turned out that when the mass percentage of Pr3+, Li+:Y2SiO5to TiO2was1.0%, catalyst dosage was1.5mg/L, and the initial solution concentration was10mg/L, the highest degradation rate of nitrobenzene was obtained. The degradation rate of nitrobenzene could reach99.13%. Otherwise, three kinds of materials were employed to degrade nitrobenzene, the degradation rate of nitrobenzene rank from high to low:1.2%(mol) Pr3+,10%(mol) Li+:Y2SiO5/TiO2>1.2%(mol) Pr3+,10%(mol) Li+: Y2SiO5>1.0%(mol)Pr3+:Y2SiO5. |
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