Study On The Layerd Tantalotungstate Catalyst

The world is facing serious environmental problem caused by the noxious organic pollution such as dyes in the 21st centry, which have been deeply affected the survival and development to human being. To solve the pollution with traditional environment technology needs high energyconsumption. Therefore, to exploit and control the poisonous contaminations have become hot research topic in the world. What cause the great interest of of the semiconductor photocatalytic technology in the scientific research area is the great potential value to apply in environmental purification and energy issues. In order to take advantage of much more solar energy, visible-light-driven photocatalysts becames very important. The study in this thesis was focused on the using the visible-light which exist 43%in the sun and the preparation of mesoporous assembly layerd tantalotungstate in view of the current problems and difficulties in this area. The as-prepared nanocomposites were characterized by by powder X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, UV-vis and N₂ adsorption-desorption measurements. Some new and interesting results are as following:Firstly, Co-doped (RE = Nd, Pr or Er) layerd tantalotungstate was obtained by solid state reaction with a mixture of Li₂CO₃, Ta₂O₅, WO₃ and Co(CH₃COO)₂·4H₂O. RE- doped (RE = Nd, Pr or Er) was obtained by solid state reaction with a mixture of Li₂CO₃, Ta₂O₅, WO₃ and rare-earth oxide. The resulting compound was characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, N₂ adsorption?desorption measurement and UV-vis spectroscopy. The visible-light or UV-light photocatalytic activity of the products was evaluated by degradation of methylene blue (MB). The results showed that the photocatalytic activity of as prepared Li_1+3xTa_1-xCo_xWO₆ and Li_1+2xTa_1-xRE_xWO₆ was higher than that of pure LiTaWO₆. Among the tested samples, Li_1+3xTa_1-xCo_xWO₆ with x = 0.5% showed the highest visible-light-active to degradation of MB. The reasons of this enhanced photocatalytic activity were discussed logically. Under the under the ultrasonic vibration circumstances, the protonated H_1+3xTa_1-xCo_xWO₆ and H_1+2xTa_1-xRE_xWO₆ by acid treatment can be exfoliated into single molecular layers by TBAOH. The exfoliating rate is about 90%. The The pH dependences of surfaceζpotential for the single molecular layers were determined, illustrating theξpotentials are in the narrow range from -61 to -63 mV when the pH ranges from 5 to 11, meaning it is a relatively stable sol and its isoelectric point is below pH = 1.Secondly, it was revealed that the increasement of interlayer spaceing after intercalated cobalt ion within the TaWO₆^- host galleries is 0.3 nm with a specific surface area of 34 m² g^-1, and average pore size of 4.1 nm. Thermal analyses suggested that the resulting material shows good thermal stability. The analysis results by UV-Vis, XPS revealed that the absorptive response region was extened. Owning to the higher surface area, mesoporosity, effective suppression the rapid combination of photo-generated holes with the photo-induced electrons, and visible-light reponse, the as-prepared intercalated nanocomposites show enhance visible-light photocatalytic activities in the degragation of MB.Thirdly, From the analysis of XRD and BET, it was revealed that the increment of interlayer spacing in REO_y-intercalated HTaWO₆ (RE = Nd,Pr,Er) is 0.45 nm with a specific surface area of 50 60 m² g^-1, and average pore size of 4.1 nm. Thermal analyses suggested that the resulting material shows good thermal stability. The analysis results by UV-Vis, XPS revealed that the absorptive response region was extened and the biding energy of O1s increased. The as-prepared intercalated nanocomposites show enhance UV-light photocatalytic activities in the degragation of MB.Fourthly, cobalt-intercalted RE-doped (RE = Nd or Er) layerd tantalotungstate was prepared with enhanced visible-light photocatalytic activity, based on the research of Li_1+2xTa_1-xRE_xWO₆ and Co-TaWO₆. Compared with pure HTaWO₆, the mesoporous Co-Ta_1-xRE_xWO₆ nanocompoiste showed narrowing of the band gap, biger specific surface area. In addition, at 0.5% RE doping, the visible-light photocatalytic activity of three-component systems exceed that of the single (HTaWO₆) and two-component (Li_1+2xTa_1-xRE_xWO₆ and Co-TaWO₆) systems.Fifthly, Based on the research of Li_1+3xTa_1-xCo_xWO₆ and REO_y-TaWO₆, successfully prepared REO_y-intercalated doped layerd tantalotungstate with enhanced UV-light photocatalytic activity for degradation of MB. Mesoporous REO_y-Ta_1-xCo_xWO₆ was prepared by by exfoliation-restacking process with a little improvement to shorten the preparation time. The activity of the three-component system exceeded that of pure HTaWO₆ and singled-doped layerd tantalotungstate. The reason for this enhance photocatalytic activity were revealed. Additionally, at 0.5% cobalt-doping in REO_y-Ta_1-xCo_xWO₆ nanocomposites shows the best UV-light photocatalytic activity.Sixthly, SnO_2-pillared doped layerd tantalotungstate was successfully fabricated via the exfoliation of layered doped tantalotungstate and restacking of its nanosheets in SnO₂ colloid. It was revealed that the increment of interlayer spacing of in SnO_2-pillared H_1+3xTa_1-xCo_xWO₆ or H_1+2xTa_1-xRE_xWO₆ (RE = Nd or Er) is 2.05 nm with a specific surface area of 90 m² g^-1, and average pore size of 4.0 nm. Thermal analyses suggested that the resulting meterial shows good thermal stability. The analysis results by UV-Vis, IR, XPS suggested there is some strong interaction which made the pillared compounds's absorption wavelengh red-shifted and the biding energy of O1s increased. Owning to the related factors and the electronic coupling between the host and guest, the as-prepared pillered nanocomposites show enhanced photocatalytic activities in the degragation of MB. In particular, the electronic coupling in the semiconductor-semiconductor heterojunction structure effectively suppresses the rapid combination of the photo-generated holes with the photo-induced electrons in the materials.