First-principles Study On TiO₂ Codoped With Carbon And Metal Ions

As a method to modified photocatalytic performance of TiO2, doped with other ions can effectively enhance the TiO2 photocatalytic performance and broaden the range of visible light absorption. For the reasons of the experimental condition is complicated, evaluation standard is not unified, it is often inconsistent to explain the mechanism of doping by experiment under the circumstances of high carbon concentration doped TiO2 or carbon and other ions co-doped TiO2.With the development of quantum chemistry and computer science, computational materials has a definite advantage in doping mechanism research. Material calculation can not only reasonably explain the experimental phenomena, and can effectively predict material performance. This thesis adopts the method of First-Principles Theory to study the crystal structure, electronic properties and doping mechanism of carbon and other ions co-doped TiO2.The main calculation results are listed as following:(1) For the reasons of the atomic interaction with the surrounding carbon impurities are different, C atoms doped into the TiO2 in various forms will produce different effects on electronic properties and band structure, But it will produce a impurities state near the Fermi level. Under the condition of high C doping concentration, the C atom tends to exist in TiO2 via forming carbon-carbon bonds.(2) The impurity states of Cr/Mo/W and carbon co-doped TiO2 can effectively narrow band gap of TiO2, reduce the rate of electron-hole recombination and lower the potential of the bottom of the conduction band, this is because charge compensa-tion is exists between the Cr/Mo/W and carbon impurities.(3) Through compared with the different group impurities co-doped with carbon by theoretical calculation, we find that the effect on the band structure, electronic structure and other properties of TiO2 of the same main group element doping is similar. And when the atomic number is smaller, the influence on the energy band structure and electronic properties is more obvious.(4) Summarized the theoretical calculation result of the different impurities co-doped with carbon, it is concluded that the following rules:Co-doping possesses compensation mechanism and synergistic effect. In the case of co-doping, there is a kind of ideal conditions that can affect the photo catalytic properties optimistically. The conditions are the combinations of the elements with same amount of the increase and decrease of the outermost electron number.The innovation of this thesis mainly reflected as:(1) The effect on energy band structure and electronic structure properties of TiO2 of the co doping with C and other elements are systematically discussed.The unique properties of C doped TiO2 system are explored, and so does the excellent Cr/Mo/W and C co doped TiO2 system;(2) A method to study the change of the conduction band potential caused by doping is preliminary discussed, and a doping combination which can cause a great influence on the conduction band potential of TiO2 is identified. Most importantly, the compensation mechanism of co doping is well explained.