【作者】 李强；

【导师】 王青；

【作者基本信息】 兰州理工大学 ， 凝聚态物理， 2011， 硕士

【摘要】 由于无毒、稳定、强氧性以及良好的光催化性能等优点,在近年来TiO₂材料得到了广泛研究。锐钛矿TiO₂光催化材料的禁带宽度为3.2 eV,只有在紫外光的作用下才能显示出明显的活性,而地球表面太阳光谱中,紫外光大约占5%,严重地影响了TiO₂光催化材料、基于TiO₂染料敏化太阳能电池的应用。因此,有效地利用可见光,拓宽TiO₂应用范围,改善其在可见光谱的吸收,使光吸收边向可见光区发生较大的红移,增强TiO₂光催化材料在可见光区的光催化性能,是TiO₂光催化材料的主要研究方向之一。本文针对目前TiO₂光催化材料改性研究中的一些难点,借助计算机模拟了不同的非金属和过渡金属元素掺杂对锐钛矿相Ti0₂电子结构和光学性能的影响,得到最佳的非金属和金属光学性质改性元素,然后对最佳非金属和金属掺杂元素进行组合,共同掺杂进而增强锐钛矿TiO₂在可见光区的吸收。本文工作运用第一性密度泛函理论平面波赝势方法,对非金属元素C、N、F和金属元素Cr、Cu、Zn、V、Sc分别掺杂以及C、Cu共掺杂锐钛矿相Ti0₂的电子结构和光学性质进行了计算和分析。第一章综述了TiO₂的分类、现状以及研究意义,着重介绍了TiO₂光催化材料光学性质的各种改性方式,论述了本论文的选题目的和意义。第二章系统论述了第一性原理密度泛函理论和计算方法。介绍了局域密度近似和广义梯度近似;对密度泛函理论的数值计算方法如线性组合原子轨道法和赝势方法做了说明;对常用的第一性原理软件Gaussian、Material Studio、VASP、WIEN、PWSCF、SIESTA、ADF、ABINIT、CPMD、Octopus做了简要介绍,对CASTEP软件的使用进行了详细说明。第三章采用非金属元素C、N、F分别掺杂锐钛矿相Ti0₂,对其能带结构、态密度、电荷密度和光学性质进行了计算分析。计算结果表明,C/N掺杂锐钛矿相Ti0₂属于受主掺杂,C/N的2p态与O的2p态、Ti 3d态杂化形成杂质能级,光学带隙变窄,光吸收边红移到可见光区;F掺杂锐钛矿相Ti0₂属于施主掺杂,由于F的负电性较强,能级较低,使得价带下移,光学带隙变宽,导致掺杂后光吸收边发生微弱蓝移;三种非金属掺杂元素中以C掺杂锐钛矿TiO₂光学改性效果最佳。第四章采用金属元素Cr、Cu、Zn、V、Sc分别掺杂锐钛矿相Ti0₂,对其能带结构、态密度、电荷差分密度和光学性质进行了计算分析。计算结果表明,Cr掺杂锐钛矿相Ti0₂属于电子掺杂,Cr的3d态电子形成施主杂质能级,导致掺杂后的TiO₂的禁带宽度变窄,光吸收曲线红移到可见光区;Cu掺杂锐钛矿相Ti0₂属于空穴掺杂,这部分空穴态来自于O的2p态,空穴态在带隙中间形成受主杂质能级,光学带隙减小,光吸收边红移到可见光区;Zn掺杂锐钛矿相Ti0₂属于受主掺杂,掺杂Zn后O 2p态和Ti 3d态之间的光学带隙和未掺杂时相比没有大的改变,因此Zn掺杂锐钛矿TiO₂后光吸收边基本保持不变;V掺杂锐钛矿相Ti0₂属于施主掺杂,并在带隙中间引入了杂质能级,光学带隙减小,使得掺杂后锐钛矿Ti0₂光吸收边发生红移; Sc掺杂锐钛矿相Ti0₂属于受主掺杂,掺杂后的TiO₂的禁带宽度没有发生大的变化,光吸收边基本不变。五种金属掺杂锐钛矿TiO₂的元素中以Cu掺杂光学改性效果最佳。第五章运用C、Cu共掺杂锐钛矿相Ti0₂,对其能带结构、态密度、电荷密度和光学性质进行了计算分析。计算结果表明C、Cu共掺杂属于受主掺杂,C的2p态在带隙中间引入了3条杂质能级,Cu由于本身3d态能量较低,所以在其周围O的2p态上留下空穴,在带隙中间引入了一条O 2p态的间隙杂质能级,使得掺杂后的TiO₂光学带隙减小,光吸收边发生红移。因此C、Cu共掺杂锐钛矿TiO₂的光学改性效果要好于其各自单相掺杂。更多还原

【Abstract】 Titanium oxide semiconductors have attracted increasingly attention in recent years due to its many advantages including of non-toxic, stable, strong oxidizing character and excellent photoelectron-chemical effect. However, TiO₂ can only be activated by the ultraviolet irradiation due to its relatively large band gap about 3.2eV for the anatase phase. Ultraviolet in the nature light is about 5%, which is difficult to develop photochemical materials and dye sensitized solar cells of TiO₂. The effective use of visible light to expand TiO₂ scope of application and improve the TiO₂ absorption in the visible spectrum, so that its visible absorption edge occur red shift to enhance the TiO₂ photocatalytic ability in the visible region, which is one of the main research for TiO₂. In this thesis, according to some hot and difficult questions of TiO₂ photocatalytic research, computer simulations have been made to predict the electronic structures and optical properties for doped anatase TiO₂ with the different non-metallic and transition metal elements. The first-principles density functional calculation was chose to investigate the electronic structures and optical properties of non-metallic C/N/F-doped, transition metal Cr/Cu/Zn/V/Sc-doped and C-Cu co-doped anatase TiO₂. In chapter one, the categories, progress in research, research meaning and optical modified methods on photocatalytic performance of TiO₂ were reviewed. The works on this topic and research meaning are introduced.In chapter two, the first-principles density functional theory and calculation methods are descussed. Density functional theory with local density approximation and generalized gradient approximation was explained. Numerical methods for density functional theory such as Linear Combination of Atomic Orbitals and Pseudopotential methods were illustrated. The common packages for the first-principles, such as Gaussian, Material Studio, VASP, WIEN, PWSCF, SIESTA, ADF, ABINIT, CPMD and Octopus, were given a brief introduction. Some operational techniques and features for CASTEP program were described in detail.In chapter three, the energy band structures, density of states, electronic density and optical properties were calculated for non-metallic C/N/F-doped anatase TiO₂, respectively. The results show that, C/N in the anatase TiO₂ is acceptor impurity. It is clear that forbidden band is narrowing due to the formation of impurity energy levels by hybridized with O 2p states, Ti 3d states, and C/N 2p states, which lead to red-shift of the absorption edges toward visible-light region. F atom in the anatase TiO₂ is donor impurity. F doped anatase TiO₂ has lower energy levels because of strong electronegativity, which cause the valence band to shift toward lower energy levels, the optical band gap to narrow and the absorption edges to slightly blue-shift toward ultraviolet region. C doped anatase TiO₂ has better improved effects in the non-metallic C/N/F elements.In chapter four, the energy band structures, density of states, electronic density and optical properties were calculated for the Cr/Cu/Zn/V/Sc-doped anatase TiO₂, respectively. The results show that Cr in the anatase TiO₂ is a donor impurity. It is clear that optical band gap is narrowing due to the formation of impurity energy levels by hybridized with O 2p states, Ti 3d states, and Cr 2p states leading to red-shift of the absorption edges toward visible-light region. Cu in the anatase TiO₂ is an acceptor impurity. The holes originated from O 2p states. The optical band gap is narrowing due to the formation of the impurity energy levels from the O 2p hole states, which result in red-shift of the absorption edges toward visible-light region. Zn atom in the anatase TiO₂ is acceptor impurity. The optical band gap between O 2p states and Ti 3d states is basically the same in the both Zn-doped and pure anatase TiO₂. As a result optical absorption edges are essentially unchanged. V atom in the anatase TiO₂ is donor impurity. It is clear that optical band gap is narrowing due to the formation of the impurity energy levels from the V 3d states leading to red-shift of the absorption edges toward the visible-light region. Sc atom in the anatase TiO₂ is acceptor impurity. The optical band gap is essentially unchanged, which is for that reason absorption edges of Sc-doped TiO₂ don’t red-shift toward the visible-light region. Cu-doped TiO₂ has better improved optical effects in five doping metallic elements.In chapter five, the electronic structures and the optical properties were calculated for metallic C-Cu-codoped anatase TiO₂. The results show that both of C and Cu elements in the anatase TiO₂ are donor impurity. Three impurity levels originating from C 2p states appear in the forbidden band. An impurity level from O 2p states appear in the band gap. The narrowing optical band gap is obviously observed due to the formation of impurity energy levels, which lead to red-shift of the absorption edges toward visible-light region. Therefore, C-Cu-doped anatase TiO₂ has better improved optical effects than theirs single doped.更多还原