本文選題：第一性原理 + 銳鈦礦TiO_2��； 參考：《伊犁師范學院》2017年碩士論文

【摘要】：TiO_2半導體性能穩(wěn)定、光催化能力強、沒有毒性、制備容易、高效低成本,是很好的光催化劑,在治理環(huán)境上有廣泛應用,其中銳鈦礦相優(yōu)勢更加突出,因而受到了人們的重視。然而,純TiO_2帶隙寬度大,只響應小于384nm波長的紫外光,因此,擴大TiO_2對可見光的響應范圍有助于TiO_2光催化能力的提升。本文以銳鈦礦TiO_2作為本征體,第六周期過渡元素(Hf、Ta、W)以不同比例單摻,通過計算分析找到了Hf、Ta、W對銳鈦礦TiO_2適合的摻雜濃度,再以適宜的濃度與S共摻雜,計算體系的晶胞體積、態(tài)密度等性質并進行前后對比分析。分析結果如下:(1)過渡元素X(X=Hf、Ta、W)摻入TiO_2后,晶格參數(shù)改變,受X原子的影響,摻雜后TiO_2晶格畸變,使得體系的體積變大,并隨X原子摻入濃度的加深而變大。S摻入TiO_2后,Ti-S鍵的離子性強于之前Ti-O鍵,晶格出現(xiàn)畸變。過渡元素X(X=Hf、Ta、W)與S共摻TiO_2,晶格參數(shù)改變,晶格進一步形變,體積增加。(2)隨著Hf、Ta、W摻雜濃度的加深,相對于本征TiO_2,導帶在不斷下移,價帶頂位置除了Ta摻雜體系相對于純銳鈦礦TiO_2沒有多大變化,另兩摻雜體系價帶頂逐漸下移,Hf、W單摻體系隨摻雜濃度的增加導帶下移程度大,導致共摻體系的帶隙寬隨之變窄,TiO_2的光催化能力增強。當Hf、Ta、W摻雜濃度為0.125時,較為理想,適合作為共摻基底。過渡元素X(X=Hf、Ta、W)單摻體系與本征TiO_2相比,反射系數(shù)在可見光區(qū)域有所下降。相同的濃度Hf、Ta、W過渡元素摻入后,靜態(tài)折射率依次增大。S摻雜銳鈦礦TiO_2后,引起體系的導帶底下降,價帶頂沒有多大變化,因而帶隙變窄,相對于純銳鈦礦TiO_2,電子態(tài)向低能區(qū)移動,同時S摻雜體系的吸收光譜呈紅移現(xiàn)象,光催化能力得到較大提升。(3)隨著Hf、Ta、W與S的共摻雜,導帶在不斷下移,價帶頂位置除了Ti_(0.875)Hf_(0.125)O_(1.875)S_(0.125)體系相對本征TiO_2沒有多大變化,另兩共摻體系價帶頂逐漸下移,還產(chǎn)生了雜質能級,而導帶下移趨勢大令帶隙寬進一步變窄,TiO_2的光催化能力提升。過渡金屬X(X=Hf、Ta、W)與S共摻后,導帶底由Ti-3d態(tài)、X-5d態(tài)和O-2p態(tài)共同影響,其O-2p軌道、Ti-3d軌道、X-5d軌道和S-2p軌道相互作用,影響著價帶,與本征TiO_2及單摻對比,電子態(tài)向低能區(qū)移動,其中Ta、W與S共摻后,TiO_2的導電性能增強。過渡元素與S元素共摻雜后,體系吸收光譜顯著紅移,進而拓展了其對可見光的響應范圍,同時共摻體系的反射系數(shù)在可見光區(qū)段有所下降。Hf、Ta、W與S共摻體系的靜介電常數(shù)和靜態(tài)折射率都依次增大(其中Ti_(0.875)Hf_(0.125)O_(1.875)S_(0.125)體系靜介電常數(shù)和靜態(tài)折射率都小于純銳鈦礦TiO_2)。研究得出,過渡元素與S元素單摻及共摻可以改變TiO_2的電子結構,縮小帶隙寬,使其吸收更多低能區(qū)段的光,出現(xiàn)吸收峰。說明過渡元素單摻雜及與S元素共摻能有效擴大TiO_2對可見光的響應范圍,本論文也從電子躍遷的機理上解釋了紅移現(xiàn)象的原因,為研究者利用摻雜的方式增大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.
【學位授予單位】：伊犁師范學院
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O469

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