Study On Preparation And Visible Light-activated Photocatalytic Performance Of Modified Nano-Titania

With the rapid development of industry, the excessive exploitation of natural resources and deterioration of the environment, the deterioration of mankind living environment has become more and more serious. According to statistics, every year about 15% of the total world production of dyes is lost during the dyeing process and is released in the textile effluents. The release of those colored wastewaters in the ecosystem is a dramatic source of eutrophication and perturbations in the aquatic life. As international environmental standards are becoming more stringent, technological systems for the removal of organic pollutants, such as dyes have been recently developed. As one of the novel treatment method, photocatalysis gains more attentions in the field of environment protection.Ideal photocatalyst should be stable, inexpensive, non-toxic, highly active and can take full advantage of the sunlight. TiO₂ is known as one of the most effective photocatalysts for the degradation of organic pollution, and its photocatalytic behavior has been studied extensively. Due to the size of its band gap （³.2 eV）, TiO₂ is effective only under ultraviolet irradiation （λ<387.5 nm）. Sunlight is comprised of less than 5% ultraviolet light, so it is important to develop new photocatalysts to extend the absorbed wavelength range into the visible region. In addition, TiO₂ has high electrons and hole recombination rate, leading to the low quantum efficiency. To some extent, these two flaws restricted TiO₂ photocatalytic technology to practical application. Therefore, one of the hot photocatalysts is developing new efficient photo catalyst and requesting its obvious response to visible light.In order to further enhance the TiO₂ photocatalyst activeness,this dissertation uses the ion-doped to modify TiO₂ for modification research. The enhanced photocatalytic activity of as-prepared photo catalysts was probed by degradation reaction of methylene blue （MB） solution under visible-light irradiation. Specific work focused on the following aspects:1. This paper describes a method to fabricate S-, C-codoped hierarchically macro/mesoporous nano-TiO₂ （TSC） based on hydrolysis-precipitation synthesis, and the possible formation mechanism of TSC was discussed. The photocatalytic activity was evaluated by degradation of MB solution. Photocatalytic mechanisms of TSC were discussed. The results revealed that the adsorption wave of TSC happened red-shifted. TSC maintained high specific surface area even after calcination at 600℃, which is 144.14 m2/g. TSC showed excellent photocatalysis activity on the decomposition of MB in water under visible-light. Because of synergistic effect of mesoporous and codoping, on the one hand, the band gap of TiO₂ was effectively reduced and the recombination of e-/h+ was inhibited; on the other hand, Titania with mesoporous/macroporous structure improve the adsorption capacity, therefore, increasing its utilization of visible and degradation. The advantages of this method were simple and easy operation, the doping ion uniform distribution, and so on.2. This paper describes an accessible, template-free process to fabricate I2-C-codoped TiO₂ （PIT） with bimodal mesoporous nanocrystallites by using tetrabutylorthotitanate （Ti（OC4H9）4, TBOT） and iodine hydrosol as precursor. The bimodal mesoporous structure of the samples was confirmed by XRD, TEM, BET, UV-vis, XPS and FT-IR. The photo catalytic activity of the as-prepared samples was studied on the degredation of MB. The possible formation mechanism of the I2-C-codoped bimodal mesoporous TiO₂ spheres is discussed.The results showed that PIT had significantly absorption in the visible region. The specific surface area of the bimodal mesoporous PIT thermal treatment in air at 200℃exceeded 226.8 m2/g, and that of the samples thermal treatment in air at 600℃still have 118.2 m2/g, which indicated the samples have relative high thermal stability. These PIT showed higher photocatalytic activity than pure TiO₂ prepared by the same procedure and commercial Degussa P-25 TiO₂ nanoparticles.3. Fe3+ doped nano-TiO₂ were prepared by hydrothermal method using butyl titanate and Fe（NO3）3?9H2O as precursor. XRD, TEM and UV-vis were used to characterize the products. The photocatalytic activity of Fe3+ doped nano-TiO₂ at the different amount of catalyst and pH values on the degradation of MB were studied under visible light. The results showed that the band gap of Fe doped nano-TiO₂ became the absorption red-shifted and the absorption intensities increased. The photocatalytic activity of Fe3+ doped nano-TiO₂ is better at alkaline condition and the best amount of Fe doped nano-TiO₂ is 1.0 g/L.4. The mesoporous AgI/TiO₂ was synthesized by the sol-gel process employing a novel template thioglycollic acid （TGA）. TGA could effectively suppress hydrolysis and condensation rates of Titania in the aqueous solution. The details of mesoporous nanostructures were elucidated by XRD, TEM, BET, XPS and PLS. The effects of calcination temperature and complex level on the structure of the material were systematically investigated. The results revealed that mesoporous AgI/TiO₂ has high heat stability, uniform and very fine network texture. PL spectra revealed that AgI dopant could effectively hinder the recombination of the photogenerated electrons and holes of mesoporous AgI/TiO₂. Titania of AgI doping content of 2% showed best photocatalytic performance on the degradation of MB solution.