【作者】 池波；

【导师】 王晓晶；

【作者基本信息】 内蒙古大学 ， 化学， 2011， 硕士

【摘要】 NaTaO3作为一种新型的光催化剂,由于其良好的化学稳定性,耐光腐蚀性,无毒等特性近年来得到了国内外学者的广泛研究。但是由于NaTaO3禁带宽度大,催化活性低,限制了其进一步地应用。经过广泛深入的研究发现,掺杂是提高其催化活性和可见光响应性的有效方法之一。本文基于密度泛函理论,采用第一性原理模拟方法,研究了非金属元素B, C, N, F, S,金属元素Ca, Sr, Ba, Nb, Cr, La,Ir掺杂NaTaO3,分析了掺杂对NaTaO3几何结构,电子结构,和光学吸收谱以及催化剂催化活性的影响。1、本文首先简要介绍了在材料科学领域的计算机模拟技术,对其应用、发展进行了叙述。重点描述了第一性原理方法(First-principles Method)的基本原理、基本方法、取得的成果等。对其中的密度泛函理论(Density Functional Theory DFT)、局域密度近似(Local Density Approximation, LDA)、广义梯度近似(Generalized Gradient Approximation, GGA)等几个重要概念进行了简单说明。2、介绍了在理论模拟中用到的Castep软件包。利用软件包中的建模工具构建了NaTaO3超晶胞模型。基于密度泛函理论,采用广义梯度近似方法描述电子的交换-相关作用并对NaTaO3(?)勺晶胞进行结构优化,得到了最稳定的结构。随后,计算并得到NaTaO3晶胞的几何结构,电子结构和光学吸收谱。3、在优化后得到稳定结构的基础上,对超晶胞进行掺杂。采用广义梯度近似方法描述电子的交换-相关作用并对掺杂后NaTaO3的晶胞进行结构优化,计算并得到掺杂NaTaO3晶胞的几何结构,电子结构,和光学吸收谱。计算发现,非金属元素B, C, N, F, S,过渡金属元素Nb, Cr, Ir掺杂对NaTaO3的几何结构,电子结构和光学吸收谱均有显著地影响。4、结合实验上获得催化反应相关数据,分析了杂质能级位置与形态对NaTaO3光吸收以及光催化效果的影响,认为：(1)当杂质能级位于价带顶与02p轨道杂化或位于导带底与Ta5d轨道杂化时,能有效减小NaTaO3的禁带宽度,从而使NaTaO3的吸收带边向长波长方向移动,形成对可见光的吸收。同时在禁带中间,由于没有杂质能级的存在,因此不会造成淬灭中心,可以有效提高光催化性能。(2)当杂质能级与02s轨道能量相近,对称性匹配时,会在价带以下与02s轨道发生杂化,使得杂质原子与周围的O原子共价键增强,晶胞内应力增大,进而会使得NaTaO3晶体颗粒尺寸减小,并在表面形成台阶状结构。这种催化剂结构上的改变,使得催化剂活性显著增加。更多还原

【Abstract】 As a novel photocatalyst, NaTaO3 have received much research attention due to its excellent chemical stability, light resistance and non-toxic properties. However, the photocatalytic activity of NaTaO3 is limited due to large band gap that incapable to absorb visible light. Basing on previous literatures, it has been found that doping of foreign ions into NaTaO3 host lattice may provide an effective way for enhancement of photocatalytic activity and visible light response. In this work, the doping effects of non-metallic elements (B, C, N, F and S) as well as metal elements (Ca, Sr, Ba, La, Nb, Cr and Ir) on NaTaO3 geometry structure, electronic structure, optical absorption spectra and catalytic activity were systematically investigated by utilizing first principles simulations.1. Firstly, this work provides an image of computer simulation technologies, their applications, and the development in materials science. We focus on the basic principles, the basic approach, the achievements and so on. Density functional theory (Density Functional Theory DFT), local density approximation (Local Density Approximation, LDA), generalized gradient approximation (Generalized Gradient Approximation, GGA), and several other important concepts are simply instructed.2. The software package-Castep was used in theoretical simulation. The modeling tools in the package were adopted to build NaTaO3 supercell model. Based on density functional theory, the structure of NaTaO3 was optimized in the supercell to obtain the most stable structure. Subsequently, we calculated and got geometry structure, electronic structure, and optical absorption spectra of NaTaO3 cell in the four different crystalline forms.3. On the basis of the optimized stable structure, certain non-metal or metal elements were introduced in the supercell. Generalized gradient approximation method was used to describe the exchange correlation effect of electron. We implemented structural optimization to the doped NaTaO3 and obtained geometry structure, electronic structure, and optical absorption spectra of doped NaTaO3 cell. It is found that non-metallic elements (B, C, N, F and S) and transition metals (Nb, Cr and Ir) showed significant impact on the geometry structure, electronic structure, and optical absorption spectra of NaTaO3.4. Combined with photocatalytic data on water, we obtained the impurity level position and shape on the optical absorption and photocatalytic activity of NaTaO3:(1) When the impurity energy level is located in the valence band top and O2p orbital hybridizes Ta5d orbital in the conduction band, it can effectively reduce the band gap of NaTaO3, and the absorption edge of NaTaO3 shifts to longer wavelength. Meanwhile If no impurity level was observed in the middle forbidden band, the photocatalytic performance would improve effectively.2. When the impurity energy level is similar with the O2s orbital energy, the orbital hybridization between impurity energy level and 02s would occur, which makes the covalent bond between the impurity atoms and O atoms more strengthen. This will enhance the stress in the cell and make the crystal grain size of NaTaO3 decrease and form step-like structure at the surface. These changes in the structure of the catalyst will allow the photocatalytic activity increase significantly.更多还原