Study On Morphological Control Of Mesoporous TiO₂-SiO₂ And Its Photocatalytic Activity

Mesoporous TiO₂-SiO₂ materials have higher photocatalytic activity than mesoporous TiO₂, which have attracted much attention due to their promising applications in the purification of air, the bactericidal action of water, and environmental photocatalytic degradation of organic pollutant compounds and so on. Combination of the two materials will not only increase the thermal stability and mechanical strength, but enhance their optical properties and catalytic performance, which can expand their applications. However, ultrafine powders are easy to agglomerate and hard to separate which affect the actual application in many fields, the morphological control of mesoporous materials can develop the application in adsorption, catalysis, separation and so on. TiO₂-SiO₂ composite films provide a very important way in which to improve the material properties and develop their applications.In the present work, TiO₂-SBA-15 complex materials with a highly ordered mesostructure have been prepared by hydrothermal synthesis method. The prepared materials were characterized by X-ray diffraction patterns (XRD&SAXRD), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FT-IR) and N2 adsorption-desorption experiments. The resulting TiO₂-SBA-15 complex materials showed a highly ordered mesoporous structure with a uniform pore size of 5.95 and 8.24 nm, high specific surface area SBET of 689 m2 g-1 and 347 m2 g-1 at different hydrothermal temperature 100 oC and 130 oC. And all the samples possessed both anatase and rutile phase.The photocatalytic activity of these TiO₂-SBA-15 mesoporous materials have been studied by 4-chlorophenol decomposition and papermaking wasterwater in ultra-violet light in aqueous solution. It can be seen that the TiO₂-SBA-15 with TiO₂: SiO₂ mass ratios of 25: 75, 40: 60, 50: 50 have shown 90.9%, 95.5%, 98.3% of the degradation rates of 4-chlorophenol, respectively, after UV light irradiation 3 h. They showed higher photocatalytic activity than that prepared at the TiO₂: SiO₂ mass ratio of 75: 25. The degradation rates of papermaking wastewater were diverse with different initial pH value. The optimum value was 4, at this point, the chroma removal rate was 86.5% and CODCr removal rate was 48.2% in 3 h.Furthermore, mesoporous TiO₂-SiO₂ with different molar ratios were prepared by a sol-gel process, TiO₂-SiO₂ films were synthesized by spinning-coating simultaneously. The properties of the prepared TiO₂-SiO₂ materials were characterized by XRD, TEM, scanning electronic microscope (SEM), UV-vis diffuse reflectance spectra. The results indicated that these samples had honeycomb-like mesoporous structures with anatase framework. The TiO₂-SiO₂ films had smooth surface.The photocatalytic activities of mesoporous TiO₂-SiO₂ powders prepared here were measured by photodecomposition of methyl orange in UV as well as visible light, which showed excellent photocatalytic activity in both UV and visible light. The influencing factors on the degradation of methyl orange such as initial pH value, catalyst dosage, and the contents of SiO₂ etc. in the photocatalysis system were investigated. When TiO₂-SiO₂ powders with TiO₂: SiO₂ molar ratio of 50: 50 were used as the catalyst, initial pH was 3 and catalyst dosage was 1.5 g L-1, complete photodegradation of the 30 mg L-1 methyl orange was obtained in 1.5 h, and the degradation rate was 88.8% in 10 h under visible light.The photocatalytic activities of mesoporous TiO₂-SiO₂ flims prepared here were measured by photodecomposition of 2 mg L-1 methyl orange in UV light irradiation. When TiO₂-SiO₂ flim with TiO₂: SiO₂ molar ratio of 75: 25 was used as the catalyst, the degradation rate was 88.9% after UV light irradiation 3 h.