金属和非金属共掺二氧化钛表面的第一性原理研究

发布时间：2018-06-06 18:02

本文选题：TiO_2(101)表面 + 共掺　；参考：《昆明理工大学》2017年硕士论文

【摘要】：锐钛矿相Ti02是一种典型的宽带隙的半导体,只能对紫外光产生响应,而对可见光部分不能吸收,导致对太阳能的利用率较低。Ti02的光生电子和空穴都不稳定,很容易复合,光量子效率低。这两个方面的问题极大地限制了 Ti02在光催化方面的应用。为了解决这些问题,对Ti02进行改性作为一种有效的手段已被广泛研究。大多数的催化反应都是发生在材料的表面,对表面进行掺杂以改善表面电子结构获得与可见光相匹配的TiO2表面更是光催化研究中的一个热点。为了探索锐钛矿相Ti02掺杂改性的机理,进一步改善其在可见光区的光催化活性,本文通过密度泛函计算研究了 C/Fe掺杂锐钛矿相TiO2(101)表面的电子结构和光学性能。同时,还研究了不同掺杂方式和位置对Ti02(101)表面各项性能的影响。常规密度泛函理论是一个很有效的研究工具,但总是低估带隙。采用DFT+U的方法有可能克服这一缺陷,但需要引入参数U,而U值的确定却不容易,因为其与化学环境有关。鉴于此,我们采用高斯09中基于高斯型轨道的HSE06杂化泛函和6-31G基组描述Ti02表面的电子结构和性质,特别是带隙,并且不需要引入任何经验参数。C掺杂后,锐钛矿相Ti02(101)表面结构发生一定程度的畸变,并且间隙掺杂引起的结构畸变程度比替位掺杂产生的畸变程度大。掺杂表面在还原条件下表现出相对较高的稳定性,并且当C替代二配位的桥位02c时,结构最为稳定。C替位掺杂后引入深杂质能级,很容易成为电子-空穴对的复合中心。C间隙掺杂结构中引入浅杂质能级,并能产生可见光响应,从而改善锐钛矿相TiO2(101)表面在可见光区的光催化活性。Fe掺杂锐钛矿相TiO2(101)表面更容易在氧化条件下合成,其中,Fe替位五配位Ti5c的掺杂结构最容易被合成。替位掺杂后,带隙几乎没有变化,并在带隙中间引入深杂质能级,不能有效改善表面的光催化活性。间隙掺杂后,杂质能级出现在价带顶和导带底,并与价带顶和导带底发生耦合,促使带隙减小,使光吸收带边发生一定程度的红移。此外,还有效促进了光生电子-空穴对的分离,故Fe间隙掺杂的结构能够改善锐钛矿相TiO2(101)表面在可见光区的光催化活性。共掺结构在氧化条件下表现出相对较高的稳定性。Fe5cC2c结构的形成能最低,也最容易被合成。由于协同作用,杂质能级同时出现在导带底和价带顶,表现出优于单掺的独特的电子结构。Fe5cC2c和Fe6cC2c两种结构中,杂质能级分别与导带和价带耦合,不仅导致了带隙的减小,使光吸收带边明显红移,而且还能有效地抑制光生电子-空穴对的复合。这样既产生了对可见光的响应,又大大提高了光量子效率,从而有效提高Ti02在可见光区的光催化活性。
[Abstract]:The anatase phase Ti02 is a typical wide band gap semiconductor, which can only respond to ultraviolet light, but can not be absorbed to the visible light, resulting in the low utilization of solar energy. The photogenerated electrons and holes are unstable and can be easily recombined. The quantum efficiency of light is low. These two problems greatly limit the application of Ti02 in photocatalysis. In order to solve these problems, Ti02 modification as an effective means has been widely studied. Most of the catalytic reactions occur on the surface of the material, and doping the surface to improve the electronic structure of the surface to improve the surface of TiO2 surface matching with visible light is a hot spot in the research of photocatalysis. In order to explore the mechanism of doping modification of anatase phase Ti02 and further improve its photocatalytic activity in visible light region, the electronic structure and optical properties of C / Fe doped anatase phase TIO _ 2 / 101) surface have been studied by density functional calculation (DFT). At the same time, the effects of different doping modes and positions on the properties of Ti02C101) surface were studied. Conventional density functional theory (DFT) is an effective tool, but the band gap is always underestimated. It is possible to overcome this defect by using the DFT U method, but it is necessary to introduce the parameter U, but the determination of U value is not easy because it is related to the chemical environment. In view of this, we use HSE06 hybrid functional and 6-31G basis set based on Gao Si type orbital in Gao Si 09 to describe the electronic structure and properties of Ti02 surface, especially the band gap, and we do not need to introduce any empirical parameter. The surface structure of anatase Ti _ (02) O _ (101) is distorted to a certain extent, and the distortion caused by gap doping is greater than that by substitution doping. The doping surface exhibits relatively high stability under the condition of reduction, and when C replaces the bridge 02c with two coordination sites, the structure is most stable and the deep impurity level is introduced after doping. It is easy to introduce shallow impurity energy levels into the composite center. C gap doping structure of electron-hole pair, which can produce visible light response. Therefore, the photocatalytic activity of anatase phase TIO _ 2O _ (10 ~ (1) surface in visible region is improved. Fe doped anatase phase TIO _ (2) O _ (10 _ (101) surface is easier to be synthesized under oxidation conditions, and the doping structure of Fe substituted five-coordination Ti _ (5c) is the most easily synthesized. After the substitution doping, the band gap is almost unchanged, and the deep impurity energy level is introduced in the middle of the band gap, which can not effectively improve the photocatalytic activity of the surface. After gap doping, the impurity energy levels appear at the top of the valence band and the bottom of the conduction band, and coupled with the top of the valence band and the bottom of the conduction band, which makes the band gap decrease and the absorption band edge red shift to a certain extent. In addition, the separation of photogenerated electron-hole pairs is promoted effectively, so the structure of Fe interstitial doping can improve the photocatalytic activity of anatase phase TIO _ 2O _ (101) surface in visible region. The codoped structure shows relatively high stability under oxidation condition. The formation energy of Fe _ 5c C _ 2c structure is the lowest, and it is the easiest to be synthesized. Due to the synergistic effect, the impurity energy levels appear at the bottom of the conduction band and the top of the valence band at the same time, showing that the impurity level is superior to the unique electronic structure. Fe5cC2c and Fe6cC2c, the impurity level is coupled with the conduction band and the valence band, respectively, which not only leads to the decrease of the band gap. The red shift of the light absorption band edge is obvious, and the recombination of photogenerated electron-hole pair can also be effectively inhibited. In this way, the photocatalytic activity of Ti02 in the visible region can be improved effectively by both the response to visible light and the quantum efficiency of light.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ134.11;O643.36

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