锆酸钡光催化还原二氧化碳性能研究

发布时间：2018-04-23 05:14

本文选题：锆酸钡 + 钙钛矿结构　；参考：《南京大学》2015年硕士论文

【摘要】：现如今随着化石能源的不断消耗,大气中的二氧化碳含量越来越高,其所带来的能源污染问题和温室效应的影响越来越明显。因此解决全球能源危机和应对这全球化气候问题是当前科学界的重要任务。众所周知,二氧化碳是大气中最主要的温室气体。面对上述两个问题,最理想的方式就是减少大气层中CO2的含量的同时又能缓解或者解决能源危机。即利用太阳能将二氧化碳转化为碳氢化合物。锆酸钡是理想的钙钛矿结构,其空间群为Pm3m,晶格常数为a=4.19 A,目前已经被广泛研究和使用。具有以下优点：热膨胀系数小,导热性差,良好的机械性,热稳定性和抗腐蚀性。被广泛应用于工程或其他领域中,如航空中超音速发动机的隔热涂层材料,电解质材料和一些复合物工程材料中的界面材料等,是高温超导材料的良好基底。BaZrO3的导带位置在-1.8 eV左右,所以跃迁至导带的光生电子足够还原CH4/CO2, HCOOH/CO2, CO/CO2, HCHO/CO2, CH3OH/CO2。因此从能量的角度来说,BaZrO3中产生的光生电子和空穴有足够的能力来还原CO2和氧化水。本文以探索半导体材料BaZrO3的光催化二氧化碳还原效率为目的,通过Pechini法低温合成BaZrO3。通过X射线衍射(XRD)分析物相,BET测定比表面积,紫外可见分光光度计测定漫反射光谱,并通过Kubelka-Munk方程获得其吸收光谱,从而得知其光学带隙,通过理论计算得知其能带图和态密度,通过扫描电镜(SEM),透射电镜(TEM)获得表面助催化剂的担载情况,获得当光催化效率最高时,最适宜的助催化剂及其担载量。为进一步深入开展理想钙钛矿型化合物的光催化还原CO2性能研究做准备铺垫工作。主要研究内容和结论如下：锆酸钡的带隙高达4.8eV,是间接带隙半导体,价带顶和导带底分别位于3.0eV和-1.8eV (Versus NHE, PH=7.0),其价带主要由02p轨道构成,而导带由过渡金属Zr的4d电子空轨道构成,这在很大程度上限制了其光吸收的范围。在紫外条件之下,沉积在BaZrO3表面的纳米Ag颗粒表现的光催化性能明显要优于担载了其他贵金属后的BaZrO3样品。1273K下制备的BaZrO3样品担载0.3wt%银单质时表现的性能最高。因为Ag的费米能级(EF)比BaZrO3的导带位置要低,所以在银单质担载的BaZrO3样品的表面,受紫外光激发的光生电子,容易穿越界面,从而使电子在Ag处富集,而空穴则留在BaZrO3之中。这将会有效的促进光生电子空穴对的分离效率,有效的降低了其复合的概率。这些研究将有效的为后续的研究打下基础。
[Abstract]:Nowadays, with the consumption of fossil energy, the carbon dioxide in the atmosphere is increasing, and the energy pollution and the effect of Greenhouse Effect are becoming more and more obvious. Therefore, solving the global energy crisis and dealing with the global climate is an important task for the current scientific community. As we all know, carbon dioxide is the most important greenhouse gas in the atmosphere. In the face of these two problems, the ideal way is to reduce the CO2 content in the atmosphere while alleviating or solving the energy crisis. The use of solar energy to convert carbon dioxide into hydrocarbons. Barium zirconate is an ideal perovskite structure with a space group of Pm 3 m and a lattice constant of 4 19 A. Barium zirconate has been widely studied and used. It has the following advantages: small coefficient of thermal expansion, poor thermal conductivity, good mechanical properties, thermal stability and corrosion resistance. It is widely used in engineering and other fields, such as thermal insulation coating materials of supersonic engines in aviation, electrolyte materials and interfacial materials in some composite engineering materials, etc. It is a good substrate for HTS. The conduction band position of BaZrO3 is about -1.8 EV, so the photoelectron transition to the conduction band is sufficient to reduce Ch _ 4 / CO _ 2, HCOO _ H / CO _ 2, CO / CO _ 2, HCHOP / CO _ 2, Ch _ 3OH / CO _ 2. Therefore, the photogenerated electrons and holes produced in BaZrO3 have sufficient capacity to reduce CO2 and oxidized water from the point of view of energy. In order to explore the photocatalytic carbon dioxide reduction efficiency of semiconductor material BaZrO3, BaZrO _ 3 was synthesized by Pechini method at low temperature. The specific surface area was measured by X-ray diffraction (XRD) and the diffuse reflectance spectrum was measured by UV-Vis spectrophotometer. The absorption spectrum was obtained by Kubelka-Munk equation, and the optical band gap was obtained. The energy band diagram and density of states were obtained by theoretical calculation. The surface cocatalyst was supported by scanning electron microscope (SEM) and transmission electron microscope (TEM). The most suitable cocatalyst and its loading capacity were obtained when the photocatalytic efficiency was the highest. Preparation for further research on the photocatalytic reduction of CO2 of ideal perovskite compounds. The main research contents and conclusions are as follows: the band gap of barium zirconate is up to 4.8 EV, which is an indirect band gap semiconductor. The top and the bottom of the valence band are located in 3.0eV and -1.8 EV Versus NHEs, PH7. 0% respectively. The valence band of barium zirconate is mainly composed of 02p orbitals. The conduction band is composed of the transition metal Zr 4d electron empty orbit, which limits the range of light absorption to a great extent. The photocatalytic performance of the Ag nanoparticles deposited on the surface of BaZrO3 was obviously better than that of the BaZrO3 samples loaded with 0.3wt% silver at .1273K. The photocatalytic performance of the Ag nanoparticles deposited on the surface of BaZrO3 was better than that of the BaZrO3 samples loaded with other precious metals. Because the Fermi energy level of Ag is lower than that of BaZrO3, the photogenerated electrons excited by ultraviolet light on the surface of BaZrO3 samples supported by silver are easy to cross the interface, which makes the electrons enrich in Ag and the holes remain in BaZrO3. This will effectively promote the separation efficiency of photogenerated electron hole pairs and effectively reduce the probability of recombination. These studies will effectively lay the foundation for further research.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ132.35;O643.36

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