【作者】 张鹏；

【导师】 姚江宏；

【作者基本信息】 南开大学 ， 凝聚态物理， 2013， 博士

【摘要】 本论文针对目前半导体光催化剂可见光光催化效率低的问题,采用掺杂、复合等技术制备出了Si离子掺杂、Sn离子掺杂、N离子和Zr离子双相掺杂以及N-TiO2与N-ZrO2复合纳米结构的催化剂。研究了催化剂制备过程中掺杂离子的掺杂模式、半导体之间的复合模式以及催化剂的能带结构；并讨论了催化剂可见光光催化活性机理。另外,对近几年来被引入光催化领域的量子点结构进行了拓展性研究,通过理论模拟,对量子点阱能带结构进行了计算,分析了影响其能带结构的因素。其主要内容包括以下几个方面：1、采用溶胶-凝胶法制备出纯TiO2和不同浓度Sn4+离子掺杂的TiO2光催化剂(TiO2-Snx%),x%代表Sn4+离子掺杂的TiO2样品中Sn4+离子与Sn4+和Ti4+离子的摩尔百分含量。利用XRD(X射线衍射谱),XPS(X射线光电子能谱)和SPS(表面光电压谱)确定了TiO2-Snx%催化剂的晶相结构和能带结构,结果证明：当Sn4+离子浓度较低时,Sn4+离子进入TiO2晶格,取代并占据Ti4+离子的位置,形成取代式掺杂结构(Ti1-xSnxO2),其掺杂能级在导带下0.38eV处;当Sn4+离子浓度较高时,掺入的Sn4+离子在TiO2表面生成金红石TiO2,形成TiO2和SnO2复合结构(TiO2/SnO2), SnO2的导带位于Ti02导带下0.33eV。利用瞬态光电压谱和荧光光谱研究了TiO2-Snx%催化剂光生载流子的分离和复合的动力学过程,结果表明,Sn4+离子掺杂能级和表面Sn02能带的存在促进了光生载流子的分离,有效地抑制了光生电子与空穴的复合；然而,Sn4+离子掺杂能级能更有效的增加光生载流子的分离寿命,提高了光生载流子的分离效率,从而揭示了TiO2-Snx%催化剂的光催化机理。2、采用溶胶-凝胶法制备出Si4+离子掺杂的TiO2可见光催化剂(TiO2-XSi),该催化剂的可见光催化活性高于纯Ti02和N掺杂的TiO2(Ti02-N)。利用XRD、 XPS、FT-IR和UV-Vis DRS等表征技术,研究了TiO2-XSi催化剂的晶体结构、能带结构和表面性质。研究发现：掺入Si4+离子在Ti02粒子表面主要形成Ti-O-Si物种,并在导带下0.2-0.6eV区域形成表面态能级,该表面态能级存在是催化剂产生可见光响应,实现可见光催化的根本原因。另外,讨论了Si4+离子的掺杂对金红石相和晶粒的生长抑制作用,以及催化剂的比表面积和表面羟基等物种增加对可见光催化的影响。3、采用溶胶-凝胶法制备了一系列的N离子和Zr离子双掺的TiO2催化剂(TiO2-x%Zr)。研究发现,可见光条件下TiO2-x%Zr对对氯苯酚的降解率高于N离子单掺的TiO2催化剂。利用XRD、 Raman、BET、XPS、UV-vis DRS和PL表征技术对催化剂进行了表征。研究发现,在TiO2-N-x%Zr样品中,掺入的N离子以NOx物种的形式存在于TiO2-N-x%Zr催化剂的表面,NOx物种的能级位于TiO2导带上方0.3eV处。掺入的Zr离子有两种存在形式：一种是进入Ti02晶格中并占据了Ti离子的位置；另一种是在TiO2-N-x%Zr催化剂的表面形成ZrTiO4物种。TiO2和其表面的少量ZrTiO4形成了TiO2/ZrTiO4异质结构。电子从NOx物种能级到TiO2导带的跃迁和从ZrTiO4的价带到TiO2导带的跃迁引起了TiO2-N-x%Zr样品对可见光的响应。此外,以取代式掺杂模式存在的Zr离子和NOx物种能级的存在促进了光生电子和光生空穴的分离。因此,TiO2-N-x%Zr样品展现出高于TiO2-N和TiO2-x%Zr的可见光光催化活性。4、利用溶胶-凝胶法,将N离子掺杂的TiO2和N离子掺杂的ZrO2进行复合,制备出了一种新型的复合结构催化齐(?)(TiO2-N/ZrO2-N)。表面NO物种能级的引入、异质结构界面能带结构的形成以及参与光催化反应的光生载流子的数量的增多是TiO2-N/ZrO2-N催化剂表现出高于TiO2-N和纯TiO2的对甲醛的光催化活性的主要原因。此外,ZrO2-N的表面氧空位促进了光生电子和光生空穴在TiO2-N和ZrO2-N界面间的分离,从而有利于TiO2-N/ZrO2-N催化剂光催化活性的提高。我们通过DFT理论的计算模拟,确定了表面NO物种和氧空位能级的位置,且在此基础上对光催化反应的动力学过程进行了讨论。5、利用有效质量近似理论对InAS/InxGa1-xAs量子点阱结构的能带结构和光吸收谱进行了计算。研究表明,通过改变量子点的尺寸或InxGa1-xAs层的厚度能够实现对量子点阱的能带结构的调整。这为量子点阱结构在光催化领域的应用提供了理论依据。更多还原

【Abstract】 Due to the lower utilization of visible light of semiconductor catalysts, we prepared Si-doped TiO2) Sn-doped TiO2, N/Zr-codoped TiO2and TiO2-N/ZrO2-N samples by using the methods of doping and coupling. We inveatigated the doping and coupling mechanism in the preparation of photocatalysts, as well as the photocatalytic of the catalysts under visible light irradiation. Besides, we paid attention to the quantum dots which was introduced to the photocatalysis filed at the recently years. The energy band and absorption spectures of quantum dots were calculated. We analysis the factors which leads the changing of the energyband of quantum dots. Our key words and results are shown as follows:1. Pure TiO2and Sn4+doped TiO2(TiO2-Sn x%) photocatalysts were prepared by a sol-gel method, where x%represents the nominal molar percentage of Sn4+ions in the TiO2structure. The crystal structure and energy band structure of the resultant catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and surface photovoltage spectroscopy. The results show that for a low content of Sn4+ions, the Sn4+ions are doped into the TiO2lattice and replace lattice Ti4+ions in a substitute mode (Ti1-xSnxO2). The energy levels of these Sn4+ions are located0.38eV below the conduction band. Moreover, the rutile SnO2crystal structure evolves with increasing content of Sn4+ions, i.e., a TiO2/SnO2structure is formed. The conduction band of SnO2is located0.33eV lower than that of TiO2. The separation and recombination mechanism of the photo-generated carriers was characterized by photoluminescence and transient photovoltage techniques. The results showed that the formation of the energy levels of Sn4+ions and the conduction band of rutile SnO2can enhance’the separation of the photo-generated carriers, and suppress the recombination of photo-generated carriers. However, the energy levels of Sn4+can lead to a much longer lifetime and higher separation efficiency of the photo-generated carriers. For different content of Sn4+in Sn4+ion doped TiO2(TiO2-Snx%), the abovementioned aspects improve the photocatalytic activity. 2. TiO2photocatalysts (TiO2-XSi) doped by different contents of silicon were prepared by a sol-gel method. The catalysts exhibited a better photocatalytic ability than the pure TiO2and N-doped TiO2(TiO2-N). The samples were characterized by XRD, XPS, FT-IR. and UV-Vis diffuse reflectance absorption spectra. It was revealed that the doped silicon ions formed Si-O-Ti bonds on the surface of TiO2particles. And thus, surface state energy attributed to the silicon dopant was located at0.2-0.6eV below the conduction band of TiO2, which enhanced the response to the visible light and photocatalytic ability. It was discussed the suppression to the formation of rutile phase and the growth of titanium dioxide crystals because of the doped silica in TiO2particles and the effect of catalysts’surface area and surface species such as hydroxyl to the photocatalytic activity.3. A series of nitrogen and zirconium co-doped TiO2(TiO2-N-x%Zr) photocatalysts have been synthesized by a sol-gel method. They show higher activities than both nitrogen doped TiO2(TiO2-N) and zirconium doped TiO2(TiO2-x%Zr) for degradation of4-chlorophenol (4-CP) under visible-light irradiation. The samples were characterized by XRD, Raman, BET, XPS, UV-vis DRS and PL techniques. For TiO2-N-x%Zr samples, the introduced nitrogen is present as surface species (NOx) whose energy levels locate at0.3eV above the valence band of TiO2. Zirconium irons can incorporate into TiO2lattice and substitute the lattice Ti to form substitutional Zr4+irons, whose energy levels located below the conduction band of TiO2. Besides, on the surface of TiO2-x%Zr samples, a small amount of ZrTiO4species was formed, leading to the formation of TiO2/ZrTiO4heterostructures. As a result, the electronic excitations from energy level of NOx species to the conduction band of TiO2together with the electronic excitations from valance band of ZrTiO4to the conduction band of TiO2lead to significant absorption in the visible-light region. In addition, the separation of photogenerated electrons and holes was enhanced by the introduction of surface nitrogen specials and substitutional Zr4+irons. Therefore, TiO2-N-x%Zr samples exhibit higher activity than both TiO2-N and TiO2-x%Zr under visible-light irradiation.4. A new type of photocatalyst was prepared by coupling nitrogen-modified TiO2(TiO2-N) and nitrogen-modified ZrO2(ZrO2-N)[TiO2-N/ZrO2-N] with using a simple sol-gel method. Under visible and UV light irradiation, the TiO2-N/ZrO2-N photocatalyst exhibits a higher photocatalytic activity for HCHO photodegradation than that of TiO2-N as well as pure TiO2, which is due to the introducing of surface nitrogen species (such as N-O species), the formation of energy band structure at heterointerface and the increase of the total number of photogenerated charge carriers (electrons and holes). Besides, the surface oxygen vacancies on the surface of ZrO2-N plays an important role for promoting the separation of photogenerated electrons and holes at the heterointerface in TiO2-N/ZrO2-N and leads to further improvement of the photocatalytic activity of TiO2-N/ZrO2-N photocatalyst. Moreover, for TiO2-N/ZrO2-N, the energy levels of surface nitrogen species and the energy band structure are ascertained by the experiment results and the DFT calculation. The photocatalytic mechanism is discussed by using the energy band structure of TiO2-N/ZrO2-N under visible and UV irradiation.5. Building on the effective-mass envelope function theory, we focuses on the study of the energy band and absorption coefficient in InAs/InxGal-xAs quantum dots in a wells (DWELL) structures. The enegy band structure can be controlled through changing the size of the resultant quantum dots as well as changing the depth of the InxGa1-xAs layer. Hence, the InAs/InxGa1-xAs quantum dot may be can applied in the photocatalysis fileds.更多还原