Theoretical Study On Anatase Titanium Dioxide Surfaces And Their Interaction With Water

As an important and versatile material, titanium dioxide (TiO2) can be widely applied in many fields, for example, as white pigment in paints and cosmetic products, as gas sensor, as a corrosion-protective coating, as an optical coating, plays a role in the biocompatibility of bone implants, and so on. In particularly, for the energy crisis and environment pollution that we have to be confronting with two urgent issuses nowadays, TiO2 can also play an important role, because under UV-light irradiation, it can split water to produce hydrogen as a photo-electrode, transfer electron in DSSCs to convert solar energy to power, produce electron-hole pairs to decompose the organic pollutions, and has super-hydrophilic effect that can be applied in self-cleaning and anti-fogging. Owing to these excellent properties, TiO2 acts as a typeical prototype of metal oxide, and has been in-depth investigated in the past decades. The topic of this dissertation was proposed based on the aforementioned background, in order to provide theoretical explaination for the future development of TiO2.Most applications of TiO2 are involed into its surface structure and properties, because most of physical, chemical phenomena occur at the surface. Namely, the surface properties are the important factors to determine the reaction speed of related chemical reactions. And on the other hand, most applications of TiO2 are also involed into the interaction with water. For example, many its reactions are always carried out in the water solutions or humid environment, or need water to participate (water-splitting to produce hydrogen, oxygen, or surface hydroxyl group, etc.). Thus, in-depth investigations of the surface properties and its interaction with water can promote its wider applications in the future. However, the experimental technology are still difficult to provide further surface information at the atomic level, resulting in that one only used hypothesis or surmise to explain some experimental phenomena. In order to solve this problem, in this dissertation, we adopted the method of the density functional theory calculations to systematically study the surface properties of anatase TiO2, and their interaction with water. Based on the calculated results, we provide reasonable explainations and underlying mechanism for some experiemtnal phenomena. For this purpose, we had carried out the following aspects research work.In the first chapter, we reviewed the research background, the research progress in the related filed. Here, we Then, we emphasized its applications for the energy crisis and environmental pollution. Finally, we summarized the research motivation and contents of this dissertation.In the second chapter, we studied the surface structure and properties of six low-index surfaces of anatase TiO2, including (101), (100), (001), (103)f, (103)s, and (110). We paid our emphases on the surface properties and the surface electronic structure. According to the comparisons of surface energy, surface band structure, surface density of states, and surface work function, we analyzed the structure-performacce relationship of anatase TiO2. Based on these calculation results, we could better understand the selectivity of photocatalysis and some phenonmena at nano scale.In the third and forth chapter, we focused on the interaction of water with anatase TiO2 (101) surface. Firstly, we compared the molecular adsorption and dissociation adsorption of water, via the interaction forms and bonding ways, in order to clarify the stable adsorption configuration of water on this surface. Then, we calculated the surface diffcusion of water on anatase TiO2 (101) surface. Finally, we continuously added the water coverage, and at last constructed water-TiO2 interface. In this section, we obtained the overall evolutionary process of the interface, and the interfacial structure and properties, including static properties and dynamic properties. We paid our attention onto the structure and origin of the interracial electric field, and the electric field in the electric double layer.In the fifth chapter, we calculated the adsorption behavior and decomposing pathway of water on six low-index anatase TiO2 sufaces. According to the analysis of electronic transfer, electronic structure, and the composing of activity energy, we found some factors that determine the water-splitting process on anatase TiO2 surfaces, and the relationship between surface properties and surface activity.In the sixth and seventh chapter, we focused on the doping effects of N/V monodoping and N-V codoping on the anatase TiO2 (101) surface. Firstly, we calculated their doping position and configurations, and obtained the electronic structures of doping systems. Then, we studied the synergistic effect of N-V codoping, and their enhancement for the photocatalytic performance of TiO2. According to the impurity formation energy, we proposed a feasible synthesize route for NOVTi-doped TiO2. Finally, we used water as a detectting molecule to analyze the doping effect of N/V on surface, in which we calculated the adsorption behavior and decomposing pathway of water on the modified surface.At the end of this dissertation, in the eighth chapter, we summarized the main conclusions of this dissertation, and proposed some possible subjects for the futher research in the related fields.