Synthesis, Characterization And Photocatalysis Of Mesoporous Alizarin-sensitized Titanium-silicates Molecular Sieves

TiO₂ is an excellent photocatalyst with stable chemical property and strong oxidation-reducibility. It is insoluble, innoxious, economic, ect. However, there are several disadvantages of TiO₂ like wide bandgap, narrow excited spectra and ineffectiveness of utilizing the sun light. The bandgap can be reduced by introducing other atoms (metal ions, for example) or by sensitizing using dye molecules, and thus the conversion efficiency of TiO₂ under visible-light irradiation will be improved. The catalytic activity of TiO₂ could be also improved as it was introduced into mesoporous structure or dispersed into mesoporous silicates, which is adjustable and homogeneous in pore size distribution, large in both specific surface area and pore volume, and stable in framework structure. The new mesoporous materials prepared from the methods above will have enormous utilizing potentials in chemistry, optoelectronics, electromagnetics, materials science and environmental science.This thesis focuses on the research subject of mesoporous alizarin-sensitized titanium-silicates molecular sieves with visible-light catalytic activity. Two synthesis methods were adopted: post grafting and one-pot synthesis, to prepare two newly ordered mesoporous alizarin-sensitized titanium-silicates respectively. In the first part, the titanium modified SBA-15 (Ti-SBA-15) was synthesized by using post grafting method, and dye molecules were introduced into the mesopores through the inner -TiOH. In the second part, mesoporous alizarin-sensitized titanium-silicates were synthesized by using one-pot synthesis through sol-gel method. The samples were characterized by FT-IR spectroscopy, powder X-ray diffraction, N₂ adsorption-desorption measurement, UV-Vis spectroscopy and TG-TA analysis.These results showed that the alizarin molecules were introduced into the pore of titanium-silicates in both methods. The XRD analysis showed that both the samples had an ordered structure. TiO₂ nanocrystals exist as anatase form and the nanocrystalline phase made by post grafting method was better than that prepared by the one-pot synthesis. The N₂ adsorption-desorption isothermic measurements showed that both samples had a narrow pore size distribution, higher specific surface area and suitable pore volume, which were suitable for adsorpting and catalysizing organic molecules. Compared with anatase TiO₂, the characteristic peak of UV-Vis spectrum has a red shift, which means the samples have better photocatalytic properties. The FT-IR analysis showed the alizarin combined with TiO₂ by chemical bond and more stable in the samples.The photo-degradation of indigo by using the above samples as the photocatalys was investigated. The results showed that 99% of indigo molecules were degraded under visible light, which indicates the excellent photo-degradation property of alizarin-sensitized titanium-silicates molecular sieves. The sample synthesized by post grafting method has better photo-degrading catalytic activity than that prepared by the one-pot synthesis. 90% of indigo molecules were degraded within 60 min. Alizarin and TiO₂ were combined by stable chemical bond in one-pot synthesisThe synthesis process was studied and the relationship between the structure and the property of these two kinds of alizarin-sensitized titanium-silicates molecular sieves was investigated. We expect to provide basic experimental data for designing and producing high efficiency dye-sensitized photocatalysts.