First-Principle Study Of Mn, Ni, P And B Ion Doped Anatase TiO₂

TiO2 has been attracted extensively attention as an ideal photocatalytic material because of its excellent physical and chemical properties. However, as a wide band gap oxide semiconductor, anatase TiO2 only shows photocatalytic activity under UV-light irradiation. Therefore, to develop highly effective TiO2 photocatalyst, which has high photo quantum yield value and strong redox potential with suitable band structure responsive to visible-light irradiation, is a challenging subject in present photocatalytic research. Ion doping is considered as one of the efficient means. In contrast to experimental investigations, the theoretical analysis by computer simulation could overcome effects of complex experimental factors and clarify the ion doping effects on crystal structure and electronic structure. It is very favorable to analyze the modification mechanism of ion doping. In order to further systematically study the effects of different ion-doped(Mn,Ni,B,P) anatase TiO2 and clarify the role of ion in TiO2 photocatalyst under visible-light irradiation, the First-principles method within the framework of Density Fuctional Theory has been adopted in this thesis to calculate the ion-doped TiO2 supercells. Furthermore, the calculated results will be compared with the experimental results reported in the literatures, and the reasons that ion-doped TiO2 has higher photocatalytic activity in the visible-light region than that of pure TiO2 will be explained. Based on the calculated results, the main conclusions were gained in this thesis as follows:1. The calculated results of pure anatase TiO2 were very agreement with the experimental results. This means that the calculating method and models are reasonable and practicable, and the calculated results should be reliable.2. Ion doping could change the band structure of TiO2. Owing to the formation of the impurity energy levels hybridized with valence electron states of dopants and O 2p states or Ti 3d states, the response region in spectra was extended to visible-light region. The position of impurity energy levels in band gap determined the effects of ion doping on the photocatalytic performance of TiO2.3. There is no impurities level in the forbidden band for the B substituted Ti doped TiO2 and the forbidden band width slightly decreased. Among Mn substituted Ti, Ni substituted Ti, Ni substituted O and B substituted O doping,the impurity levels are in the band gaps, forming the middle levels.