| Titanium dioxide is widely applied to photochemical catalysis, bionic medicine, dye sensitized solar cell, and many other fields due to its non-toxic stability, high catalytic efficiency, cheap accessible and a series of excellent properties. Photocatalytic reduction is a method of which could produce photogenerated electrons?e-? and holes?h+? of semiconductors under high-energy UV light. The photogenerated electrons and holes can redox water and oxygen molecules on TiO2 surface to form hydroxide radicals??OH?. The hydroxide radicals and photogenerated holes can react with the contamination adsorbed on TiO2 surface to form carbon dioxide and water, particularly those couldn't removed by traditional physical and biological treatment methods completely. Photocatalytic oxidation technology is a promising application due to its low consumption, green pollution-free. However, pure titanium oxide has wide band gap energy?3.2e V?, which means only under irradiation of UV light wavelength under 387.5nm can TiO2 realize its photocatalytic activity. The rate of absorption and utilization of visible light is greatly low. Furthermore, the photogenerated electrons and holes are extremely unstable and easily recombine. These two aspects is greatly limited the application of titanium dioxide photocatalyst. Therefore, for broad materials scientists, the main research fields are increase the efficiency for solar energy utilization of titanium dioxide and reduce the recombination rate of photogenerated electron-hole pairs.The methods of nanoarchitecture for laminated structure, ion doping and acidification on the surface are used to modify titanium dioxide in this article. This paper mainly research contents as follows:1. Preparation and properties of micro-laminated filmsTiO2, SiO2 and ZnO sols were prepared by the sol-gel method. Tetrabutyl titanate?Ti?OC4H9?4?, tetraethylorthosilicate?TEOS? and zinc acetale dehydrate?Zn?CH3OO?2·2H2O? were as precursors, respectively. Then we used a controllable dip-coating device to prepare SiO2/TiO2 and ZnO/TiO2 micro-laminated films on the surface of a glass substrate in the atmosphere. Through the results of the degradation rate of acid naphthol red?ANR?, we ensured the best order and the optimal layer number of SiO2/TiO2 and ZnO/TiO2 micro-laminated films. The best ion doping concentration of Co, F, H3BO3 modification and the optimum proportion of multi-modification were determined by the performance of modified laminated films in degradation of ANR solution. Then the optimum modified and multi-modified micro-laminated films were used to degrade methyl green?MG?, oxytetracycline?OTC? and formaldehyde?HCHO? solution, respectively. The experimental results showed that, the photocatalytic activities of modified micro-laminated and multi-modified micro-laminated films have enhanced obviously, and the utilization of visible light is also increased. Futhermore, the experiment of degradation of oxytetracycline and formaldehyde have achieved significant results.2. Characterization of micro-laminated filmsThe optical absorption behaviors and the surface structure of the laminated films were characterized by ultraviolet-visible absorption spectroscopy?UV-vis?, photoluminescence?PL?, field emission scanning electron microscopy?FE-SEM?, X-ray diffraction?XRD?, and differential thermal analysis-thermogravimetry?DTA-TG?. The UV-vis and PL results indicated that nanoarchitecture and multi-modification not only increased the range of visible light response but also prohibited the recombination of the photo-generated species. FE-SEM results showed that the micro-laminated film exhibits the layer structure, along with the surface of multi-modified laminated film becomes uniformly and smoothly. XRD and DTA-TG results indicated that multi-modification can improve the crystallinity of anatase and decrease the quantities of rutile and brookite.3. The exploration of photocatalysis mechanismThe photocatalytic activities of films were enhanced, and the range of visible light response is increased obviously through nanoarchitecture for laminated structure. Then enhanced properties mainly due to the effect of electrostatic field, which produced by the interface effect between layer and layer. This electrostatic field promotes the separation of photogenerated electrons and holes. At the same time, SiO2 as a insulator has large specific surface area can suppress the recombination of photogenerated carrier effectively. The function of ZnO is reflected in two aspects: on t he one hand, ZnO blongs to n-type semiconductor which has photocatalytic activity. Under the illumination of high-energy UV light, ZnO can produce photogenerated electrons and holes.On the other hand, the doping energy level is produced by ZnO and TiO2. The presence of doping energy level can increase the photocatalytic performance effectively through reduce the band gap energy of TiO2 to some extent. The effects of ion doping are presented below. Firstly, the ion doping can reduce the band gap energy of TiO2 via form the doping level. As we all know that the narrow band gap energy is of benefit to increase the utilization of visible light of films. Secondly, the doping ions can capture electrons or holes to suppress their recombination. Thirdly, doping ions can access to the TiO2 lattice and create defects, which prevent the transformation of anatase TiO2. Acid treatment not only introduced ions doping but also increased the surface hydroxide radicals which is favourable to the photoreaction. |
PDF Full Text Request