第六周期过渡元素掺杂锐钛矿二氧化钛的电子结构及光学性能的第一性原理计算

发布时间：2018-06-28 17:09

本文选题：第一性原理 + 锐钛矿TiO_2　；参考：《伊犁师范学院》2017年硕士论文

【摘要】：TiO_2半导体性能稳定、光催化能力强、没有毒性、制备容易、高效低成本,是很好的光催化剂,在治理环境上有广泛应用,其中锐钛矿相优势更加突出,因而受到了人们的重视。然而,纯TiO_2带隙宽度大,只响应小于384nm波长的紫外光,因此,扩大TiO_2对可见光的响应范围有助于TiO_2光催化能力的提升。本文以锐钛矿TiO_2作为本征体,第六周期过渡元素(Hf、Ta、W)以不同比例单掺,通过计算分析找到了Hf、Ta、W对锐钛矿TiO_2适合的掺杂浓度,再以适宜的浓度与S共掺杂,计算体系的晶胞体积、态密度等性质并进行前后对比分析。分析结果如下:(1)过渡元素X(X=Hf、Ta、W)掺入TiO_2后,晶格参数改变,受X原子的影响,掺杂后TiO_2晶格畸变,使得体系的体积变大,并随X原子掺入浓度的加深而变大。S掺入TiO_2后,Ti-S键的离子性强于之前Ti-O键,晶格出现畸变。过渡元素X(X=Hf、Ta、W)与S共掺TiO_2,晶格参数改变,晶格进一步形变,体积增加。(2)随着Hf、Ta、W掺杂浓度的加深,相对于本征TiO_2,导带在不断下移,价带顶位置除了Ta掺杂体系相对于纯锐钛矿TiO_2没有多大变化,另两掺杂体系价带顶逐渐下移,Hf、W单掺体系随掺杂浓度的增加导带下移程度大,导致共掺体系的带隙宽随之变窄,TiO_2的光催化能力增强。当Hf、Ta、W掺杂浓度为0.125时,较为理想,适合作为共掺基底。过渡元素X(X=Hf、Ta、W)单掺体系与本征TiO_2相比,反射系数在可见光区域有所下降。相同的浓度Hf、Ta、W过渡元素掺入后,静态折射率依次增大。S掺杂锐钛矿TiO_2后,引起体系的导带底下降,价带顶没有多大变化,因而带隙变窄,相对于纯锐钛矿TiO_2,电子态向低能区移动,同时S掺杂体系的吸收光谱呈红移现象,光催化能力得到较大提升。(3)随着Hf、Ta、W与S的共掺杂,导带在不断下移,价带顶位置除了Ti_(0.875)Hf_(0.125)O_(1.875)S_(0.125)体系相对本征TiO_2没有多大变化,另两共掺体系价带顶逐渐下移,还产生了杂质能级,而导带下移趋势大令带隙宽进一步变窄,TiO_2的光催化能力提升。过渡金属X(X=Hf、Ta、W)与S共掺后,导带底由Ti-3d态、X-5d态和O-2p态共同影响,其O-2p轨道、Ti-3d轨道、X-5d轨道和S-2p轨道相互作用,影响着价带,与本征TiO_2及单掺对比,电子态向低能区移动,其中Ta、W与S共掺后,TiO_2的导电性能增强。过渡元素与S元素共掺杂后,体系吸收光谱显著红移,进而拓展了其对可见光的响应范围,同时共掺体系的反射系数在可见光区段有所下降。Hf、Ta、W与S共掺体系的静介电常数和静态折射率都依次增大(其中Ti_(0.875)Hf_(0.125)O_(1.875)S_(0.125)体系静介电常数和静态折射率都小于纯锐钛矿TiO_2)。研究得出,过渡元素与S元素单掺及共掺可以改变TiO_2的电子结构,缩小带隙宽,使其吸收更多低能区段的光,出现吸收峰。说明过渡元素单掺杂及与S元素共掺能有效扩大TiO_2对可见光的响应范围,本论文也从电子跃迁的机理上解释了红移现象的原因,为研究者利用掺杂的方式增大TiO_2光催化效率指明了方向。
[Abstract]:TiO_2 semiconductor has stable performance, strong photocatalytic ability, no toxicity, easy preparation and high efficiency and low cost. It is a good photocatalyst. It is widely used in the environment of treatment. The advantages of anatase phase are more prominent, so people pay more attention to it. However, pure TiO_2 band gap is wide and only responds to ultraviolet light less than 384nm wavelength, so T is expanded. The response range of iO_2 to the visible light is helpful to the enhancement of TiO_2 photocatalytic ability. In this paper, the anatase TiO_2 is used as the intrinsic body, and the sixth periodic transition elements (Hf, Ta, W) are mixed in different proportions. Through the calculation and analysis, the doping concentration of the anatase TiO_2 suitable for Hf, Ta and W is found, and the crystal cell volume of the system is calculated with the suitable concentration and S co doping. The results are as follows: (1) when the transition element X (X=Hf, Ta, W) is mixed with TiO_2, the lattice parameters change, the X atom is influenced by the X atom, and the lattice distortion of the TiO_2 lattice, which makes the volume of the system larger, and increases with the concentration of the X atoms, increases the.S content of TiO_2, and the ionic property of the Ti-S bond is stronger than the prior Ti-O. The transition element X (X=Hf, Ta, W) Co doped TiO_2, the lattice parameter changes, the lattice parameters change, the lattice further deformation, the volume increase. (2) with the Hf, Ta, W doping concentration deepening, relative to the intrinsic TiO_2, the conduction band is constantly moving down, the valence band top position is not much change except that Ta impurity system is relative to the pure anatase, and the other two doping system price. The band top gradually moves down, Hf, W single doped system increases with the increase of doping concentration, resulting in the band gap width of the co doping system narrowing and the enhanced photocatalytic ability of TiO_2. When Hf, Ta, W doping concentration is 0.125, it is ideal and suitable as the co doping base. The reflection coefficient of the transition element X (X=Hf, Ta, W) is compared with the intrinsic TiO_2. The visible light region decreased. After the same concentration of Hf, Ta, and W transition elements, the static refractive index increased after.S doping anatase TiO_2, resulting in the decrease of the conduction band bottom and no much change in the valence band top, thus the band gap narrowed and the electronic state moved to the low energy region relative to the pure anatase TiO_2, while the absorption spectrum of the S doping system was red. (3) with the co doping of Hf, Ta, W and S, the conduction band is constantly moving down, the top position of the valence band is not much changed in addition to the intrinsic TiO_2 in the Ti_ (0.875) Hf_ (0.125) O_ (1.875) S_ (0.125) system, and the valence band top of the two co doping system gradually moves down, and the impurity energy level is produced, and the direction of the guide band moves down the band gap. When the width is further narrowed, the photocatalytic ability of TiO_2 is enhanced. After the transition metal X (X=Hf, Ta, W) is Co doped with S, the conduction band is influenced by the Ti-3d state, the X-5d state and the O-2p state. The O-2p orbits, Ti-3d orbit, the X-5d orbits and the orbit interact to influence the valence band. The conductivity of iO_2 is enhanced. After the co doping of the transition element and the S element, the absorption spectrum of the system is significantly red shift, and then the response range of the visible light is expanded. Meanwhile, the reflection coefficient of the Co doped system decreases.Hf, Ta, W and S Co doped systems increase in turn (including Ti_ (0.875) Hf_ (0.) (0.) Hf_ (0.875) Hf_ (0.). 125) the static permittivity and the static refractive index of O_ (1.875) S_ (0.125) system are less than pure anatase TiO_2. The study shows that the single doping and co doping of the transition elements and S elements can change the electronic structure of TiO_2 and narrow the band gap, so that it absorbs more light in the low energy zone and appears the absorption peak. It is indicated that the single doping of the transition elements and the co doping with the S elements can be effectively expanded. In this paper, the reason for the red shift is explained from the mechanism of the electron transition, which indicates the direction for the researchers to increase the photocatalytic efficiency of TiO_2 by doping in the mechanism of the large TiO_2's response to the visible light.
【学位授予单位】：伊犁师范学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O469

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