The Preparation Of Visable-ultraviolet Upconversion Materials And Its Application In Photocatalysis

Environmental problems become serious increasingly now. As a common photocatalyst used in environmental treatment techonlogy, TiO₂ has received much attention.But the large band-gap energy of pure anatase TiO₂ is about 3.2 eV, which requires ultraviolet irradiation for photocatalytic activation (λ< 387 nm, about 4% part of solar light), so it's industrial application has been limited. In order to make use of solar energy more efficiently (mainly visible or infrared light), great efforts have been made to develop TiO₂-based photocatalysts. Many researches have shown that though combination with upconversion luminescence agent, the photocatalytic activity of TiO₂ under sun light can be improved.Therefore, how to choose the doping ion and the matrix material to get high efficient UV upconversion materials, Through what methods to preparation the composite photocatalyst which have good stability and high catalytic efficiency become the focus of our research.In this paper, the preparation of ultraviolet upconversion luminescence agent have been extensive research, the main work are as follows.1. Upconversion luminescence agent Y₂O₃: Er and Y₂O₃: Yb³⁺, Tm³⁺ were obtained by a combustion method. With a 980 nm laser diode excitation, the upconversion emissions were observed. The obvious ultraviolet emission peak has been detected in Y₂O₃: Yb³⁺, Tm³⁺. In addition , the change of upconversion emission intensity depending on the Yb³⁺ concentrations and calcination temperature were discussed. The results showed that Yb³⁺ doping can make the upconversion emission intense owing to the sensitizing effect of Yb³⁺ and the best sample is Y₂O₃:Yb³⁺, Tm³⁺ calcined at 800℃.2. Yb-Tm codoped mesoporous zirconia was prepared by hydrothermal method with cetyltrimethylammonium bromide (CTAB) as templates. The crystalline phase, morphology, specific surface and upconversion emission spectra of the product samples were characterized by XRD, TEM, SEM, BET, FTIR and Fluorescence spectrometry respectively. The results showed that mesoporous TiO₂ with high specific surface are prepared by Low temperature - microwave method to remove template.3. Rare earth ions and transition metal ions codoped Lanthanide silicate were prepared by sol-gel method. Through the XRD and Fluorescence spectrometry, it can be know that the La10(SiO4)6O3: Yb³⁺, Tm³⁺ calcined at 1200℃has the strongest ultraviolet upconversion emission.After the Ultraviolet upconversion luminescence agent can be obtained, we choose the better sample composite with TiO₂.1. The TiO₂/Y₂O₃: Yb³⁺, Tm³⁺ composite photocatalyst have been synthesized by sol-gel method and precipitation method, respectively. Results from scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) measurements demonstrate that TiO₂ shells were formed on the upconversion luminescence agent by precipitation method. By fluorescence spectroscopy and photodegradation experiments, we know that the existence of this structure will not only improve the the upconversion emission, but also enhance the stability and photocatalytic efficiency. The relationship between the cumulate concentration of hydroxyl radical and degradation efficiency can be measured by spectrophotometry and fluorescence method. The results show that the photodegradation efficiency of TiO₂ was affected by·OH concentration.2. The La10(SiO4)6O3: Yb³⁺, Tm³⁺/TiO₂ and ZrO₂: Yb³⁺, Tm³⁺ /TiO₂ composite were prepared by microwave method. By the photodegradation experiments, it can be known that since the presence of the upconversion luminescence agent, the composite can more easily decompose the stable organic pollutants. In addition, through repeated experiments, it can be konwn the sample which prepared by microwave method can also has good stability.