Preparation Of TiO₂-based Nanocomposites And Their Photocatalytic Properties

With the development of the photocatalysis, titanium dioxide has become an effective material of solving the problem of environmental pollution. Titanium dioxide is safe, non-toxic, and possesses stable physicochemical properties and excellent photocatalytic properties, but its relatively wide band gap and high recombination rate of the photogenerated charges still limit its further applications. In recent years, the TiO2-based composite materials have overcome the shortcomings of single titanium dioxide, and its preparation and application have received widespread attention. However, in the process of practical application, the titanium dioxide based composites still get a number of problems to be solved. For example, the adsorption process towards the contaminant molecules is not visible, which degrade the overall photocatalytic performance even if the photocatalysts poseess a high photocatalyst activity; the effective support of immobilizing the TiO2-based composite materials is lack, which result in the loss of the catalyst and the separation and recovery problem. At present, the research on the the adsorption process and the recycling performance of the composite photocatalysts is limited. So studying the charge transfer behavior of the TiO2-based composite materials, coordinating the interaction between adsorption and catalytic process, and preparing the composite materials with excellent recycling properties are important to the industrial applications process.In this paper, we dedicated our efforts to designing and preparing the TiO2-based composite materials which coupled with adsorptive materials or support, and using a variety of analytical techniques to analysize the structural composition, the physicochemical properties, and the spectral absorption characteristics of the composites. Besides, we mainly studied the mechanism of enhanced photocatalytic activity through the aspects of charge transfer and adsorption process, and explored the reason of the degradation and mineralization activity of the TiO2-based semiconductor materials.In the second chapter, we prepared the TiO2/SiO2composite structure by using the TiO2nanoparticles as substrate through a simple "Reflux-stir" process. In this chapter, we prepared the composite structure of SiO2-coated TiO2by adding different amount of SiO2. After the adsorption experiments towards gaesoue benzene and water vapor, it can be found that the samples are effective for the adsorption process of the pollutants and water vapors, and the adsorption process makes the composites exhibit superior photocatalytic activity. It can be found that with the optimal molar ratio of Ti/Si (30:1), the sample exhibits the best photocatalytic activity. The photocatalytic degradation rate for gaseous benzene reached0.0230min-1, which is6.8times of that comparing with original TiO2(0.0034min-1). It is worth noting that after the photocatlysts used for ten times, the mineralization rate of benzene can still get to90.0%.In the third chapter, by using the TiO2-based nanosheets with strong adsorption properties as the substrate, the composite structure of CdS modified TiO2-based nanosheets are synthesized. It is found that the TiO2-based nanosheets possess higher specific surface and pore volume. The higher specific surface area is beneficial for adsorbing the pollutants molecules on the catalyst surface, and the higher pore volume promotes the transfer of photogenerated charges in the photocatalytic process. Moreover, the modification of CdS nanoparticels greatly enhanced the separation efficiency of the photogenerated electrons-holes, and effectively improved the photocatalytic activity. The photocatalytic activities of these composite structures were evaluated by photodegrading of Rhodamine B (RhB) under the visible light irradiation. The results showed that the CdS modified TiO2-based nanosheets composites can effectively enhance the photocatalytic activity, and the reaction rate (0.0113min-1) is5.4times larger than that of the original TiO2-based nanosheets (0.0021min-1).In the fourth chapter, the network structured fiberglass cloth (FGC) is selected as a support, and the CdS sensitized TiO2films are deposited on the surface of the FGC by the processes of sol-gel and chemical bath deposition. Through the characterization results, it is found that the network structure of the fiberglass cloth can serve as an effective support, which is benefit for the adsorption and degradation process. The deposition amounts of the CdS nanoparticles are achieved by changing the initial concentration of the Cd2+or S2-ions solutions, and the deposition amounts of the CdS nanoparticles have a significant influence on the adsorption and photocatalytic activity of TiO2films. When the deposition amount of CdS nanoparticles achieves0.16%, the composite phootocatalysts exhibit the best photocatalytic activities under UV-Visible and visible light irradiation, reach92.8%and32.7%, respectively. The photocatalysts with appropriate CdS amount can not only enhance the charge transfer performance between the two semiconductors and reduce the recombination process, but also can exhibit optimal synergistic effect between the adsorption sites and photocatalytic sites, and then improving the photocatalytic activity.In the fifth chapter, by using the magnetic Fe3O4SiO2as the inside cores, the TiO2/Bi2WO6composites were prepared by hydrothermal method, In the composites, the TiO2nanoparticles and the Bi2WO6nanoplates are linked mutually to each other, and present a grape-like morphology. The composites also possess excellent magnetic recovablity. By the characterization results, it is discovered the TiO2/Bi2WO6composites greatly enhance the adsorption capacity of the RhB moleculars in the solution, and the adsorption rate increased from8.3%(TiO2) to40.7%(TiO2/Bi2WO6). The photocatalytic experiments of RhB degradation under visible light showed the prepared composites possess excellent photocatalytic performance. The degradation rate of RhB reached0.0640min-1, which is49.2times largere than that of the pure TiO2nanoparticles (0.0013min-1) and1.5times greated than that of Bi2WO6(0.0420min-1). In addition, the reason for the improved photocatalyst activity was analysed by the charge transfer process between the two types of semiconductor.