| Titanium dioxide is a kind of important semiconductor material. Due to its high stability and unique electronic structure, titanium dioxide is well-known for its wide applications in photocatalysis of water splitting and environment protection. As a key step of water splitting, adsorption of water and its dissociation on TiO2 surface plays an important role in the relevant interfacial applications. At the same time, the surface stress of TiO2 will vary during the interfacial process. Accordingly we expect that applying external strain is a possible way to tune the properties of adsorption and dissociation of water on TiO2(110) surfcae, and thus to affect the photocatalysis properties of TiO2.In this thesis, by using the first principles calculation methods, we have studied the energetics of the adsorption and dissociation of water on rutile TiO2(110) surface. Furthermore, changes of the surface stress after water adsorption and dissociation have been calculated for models with different slab thickness. The influences of external strain on the relative stability of the thin film and the water adsorption and dissociation are predicted according to the properties of the surface stress. The main contents and conclusions are as follows.1. We have studied the surface energy, surface stress and the electronic structure properties of rutile TiO2(110) surface. The influences of external strain on the surface energy of clean slab with different film thickness are analyzed. We found that tensile strain(> 8%) leads to reversal of odd-even oscillation of surface energy for slabs of more than 5 layers.The surface energy of the sball with even layers is greater than that of odd layers. Therefore, the external strain is able to change the relative stability of the celan film.2. The adsorption energy of water and changes of surface stress after adsorption has been calculated. In consistent with previous results, we found that the adsorption of water is exothermic in all coverage smaller than one monolayer, no matter whether the water molecule dissociates or not. Moreover, the molecular water is stable against dissociation. Again, the odd-even oscillation appears for the adsorption energies of water. According to the changes of surface stress, we predict that the adsorption of water becomes energetically more or less favorable under tensile or compressive biaxial strain, respectively, when film thickness is larger than 5 atomic trilayer.3. We have studied the dissociation barrier and the corresponding variation of surface stress during the water dissociation on TiO2(110) surface, discuss Based on the properties of the surface stress, the dissociation barriers under different external strain is predicted. The dissociation barrier is slightly reduced by increasing tensile strain except for one monolayer coverage. The change of dissociation barrier with strain is more dramatic for lower coverage. Therefore, we can expect that tensile strain is an effective way to facilitate the water dissociation on TiO2(110) surface.According to our results, we have demonstrated that tensile strain may become an effective way to facilitate the water dissociation on TiO2(110) surface, not only thermodynamically but also kinetically.The thesis is arranged as follows. In the first chapter, I will give a brief introduction about the background of strain engineering of the surface properties, as well as the experimental and theoretical background of water adsorption on rutile TiO2(110) surface. In the second chapter, I will introduce the research methods, especially on the first principles calculation methods. In the third chapter, we will show the influence of external strain on clean TiO2(110) surface properties. In the fourth chapter, the influence of external strain on the adsorption of water on TiO2(110) surface is discussed. In the fifth chapter, we will demonstratethe influence of external strain on dynamics of water dissociation on TiO2(110) surface... |
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