【作者】 石慧；

【导师】 王琦；

【作者基本信息】 浙江大学 ， 物理化学， 2015， 博士

【摘要】 固体表面的物理和化学组成、原子排列等通常和体相不同,由于表面向外一侧没有临近原子,表面原子有一部分化学键伸向空间形成“悬挂键”,因而表面具有活泼的性质。此外,固体内部三维周期势场在表面中断,表面的电子状态也和体相不同。这些不同使表面具有一些特殊的性质。在催化领域,表面原子有很活泼的化学性质,将气态分子吸附在表面,有时还解离为原子或小分子。对表面化学的研究,使人们对分子的相互作用有了新的认识,提高了对催化剂发生催化作用机制的认识,同时,可以指导制造具有特殊性质的表面层来改善材料和器件的功能。在多相催化中,金属和氧化物表面具有特别重要的作用。诸多金属氧化物中,二氧化钛是具有代表性的催化剂和光催化剂,被广泛应用于能源、环境等领域。实验和理论研究中,二氧化钛经常被当做过渡金属氧化物的模型,希望通过对它的研究从根本层次上认识金属氧化物表面的性质,以此可以帮助改善材料的性质以及设计新型的催化材料。本文采用密度泛函理论(DFT)方法,分别研究了含桥氧空位对的金红石型TiO2(110)表面与甲醇分子的相互作用,含两种不同排列方式的两个桥氧空位的金红石型TiO2(110)表面水分子之间的相互作用。研究了表面上不同位点处的吸附行为,并且从微观层面上探索了分解机理。最后探究了SrTiO3(110)表面与不同pKa值的醇分子之间的相互作用,以水分子、甲醇分子和乙二醇分子为例,揭示了醇分子在SrTiO3纳米晶多面体晶面可控生长过程中所起的作用。第一章,首先介绍了金红石型二氧化钛晶体及(110)表面的几何和电子结构,然后介绍了(110)表面上小分子吸附与分解的研究进展,主要对水分子和醇分子进行了综述。第二章,主要介绍了密度泛函理论的一些基础概念和框架,接下来介绍了常用的计算软件,最后对计算参数的测试进行了说明。第三章,主要研究了含有桥氧空位对(bridging oxygen-vacancy pairs, OVPs)的金红石型二氧化钛(110)表面与甲醇分子的相互作用。研究发现,OVPs本身是所有吸附位点中最稳定的位点。甲醇分子的两种吸附构型—分子形式吸附和分解碎片形式吸附皆为最稳定构型。该位点并不是甲醇分子最理想的分解催化位点。同时,结果表明OVPs的存在对表面上的五配位Ti原子基本没有影响,与OVP不同距离的五配位Ti原子处甲醇分子的吸附与分解行为基本一致。甲醇分子倾向于以分子形式吸附在该位点。第四章,以水分子作为探针分子研究了含有两个桥氧空位的缺陷金红石型TiO2(110)表面。探索了两个桥氧空位的两种不同排列方式,一种排列方式为OVP,另一种排列方式为间隔性桥氧空位(two next nearest neighbored bridging-oxygen vacancies belonging to the same row, NNN-OVs)。结果表明,NNN-OVs是水分子最稳定的吸附位点；水分子的两种吸附形式-—分子和分解碎片形式都占很大的优势,尤其是分解碎片形式的吸附。该位点处水分子的分解能垒与OVP相比也略低。两种缺陷类型下,表面五配位Ti原子处的水分子呈现基本一致的的行为。水分子在该位点处的吸附稳定性最差且优先以分子形式吸附。第五章,主要研究了SrTiO3(110)非计量TiO终结的晶面与水分子、甲醇分子和乙二醇分子的相互作用,揭示了醇分子在SrTiO3纳米晶多面体晶面可控生长过程中所起的作用。研究表明,随着醇分子pKa值的减小,醇分子与SrTiO3(110)晶面的相互作用增强,降低了(110)晶面的表面能,使(110)晶面在生长过程中暴露量增加,相应纳米晶多面体(110)晶面的比例增加。更多还原

【Abstract】 The physical and chemical composition and the order of the atoms of solid surfaces are different from that of the bulk. Due to no atoms on the outer edge of the surface and forming "dangling bonds", the surface has active properties. In addition, the internal three-dimensional periodic potential field interrupts on the surface, so the electronic structures are also different from the bulk. These differences lead to the special properties of the surface. In the field of catalysis, the atoms on the surface are of high chemical reactivity. Molecules could be adsorbed on the surface and dissociate under proper conditions. The studies of surfaces give insight into the interactions between molecules and improve the understanding of catalytic mechanism. It could help researchers to improve the properties of the surface and guide researchers to design surfaces of special function.Metals and metal oxides play important roles in the field of heterogeneous catalysis. Among the metal oxides, the titanium oxide is considered as the promising catalytic and photocatalytic material. It is widely used in many fields, such as the fields of energy and environment. In the experimental and theoretical studies, the titanium oxide is commonly used as the model of transition metal oxides. Researchers hope that these studies could give insight into the metal oxide surface, which would help to improve the properties of materials and design new catalytic materials. In this thesis, density functional theory (DFT) calculations were performed to study the interactions between the defective TiO2(110) surface with bridging oxygen-vacancy pairs and the methanol molecule. In the following, the interactions between the defective TiO2(110) surface with two bridging-oxygen vacancies of two different array and the water molecule were studied. We explore the adsorption behaviors on different sites and the dissociation mechanism. Finally, we focus on the interactions between the TiO-terminated SrTiO3(110) surface and alcohols with different pKa values, to explore the roles of alcohols in the growth of SrTiO3nanocrystals. In chapter1, we introduced the geometric and electronic structures of the bulk and (110) surface of TiO2. Then we summarized the research progress of the adsorbed behaviors of molecules on the TiO2(110) surface, mainly about water and alcohol molecules.In chapter2, we firstly introduced some basic concepts and framework of DFT. Then some softwares often used in DFT were introduced. Thirdly, the testing of calculations was shown.In chapter3, we focused on the interactions between the defective TiO2(110) surface with bridging oxygen-vacancy pairs (OVP) and the methanol molecule. Results show that the OVP site is the most stable site for methanol adsorption, whether in molecular adsorption or dissociated adsorption. But the OVP site is not the most active site for dissociation. In addition, the OVP defect does not have significantly different influence on the adsorption structure and dissociation process of adsorbed methanol on5-fold Ti atoms at diverse positions:close to the vacancy or a little further from the vacancy. Methanol tends to adsorb molecularly on5-fold Ti atoms.In chapter4, we studied the defective rutile TiO2(110) surfaces with OVP and two next nearest neighbored bridging-oxygen vacancies belonging to the same row (NNN-OVs) using one water molecule as the probe. Results show the NNN-OV site is the most favorable site for water adsorption of two modes-molecular and dissociated adsorption, especially for dissociated adsorption. The dissociation energy barrier on NNN-OVs is a little lower than that on OVP. The5-fold Ti sites show similar behaviors despite the existence of different defects. Adsorption on this site is least stable and molecular adsorption is favored.In chapter5, the interactions between the TiO-terminated SrTiO3(110) surface and alcohols with different pKa values were studied. The water molecule, methanol molecule and the ethylene glycol molecule were chosen as three typical molecules. The results indicated that the adsorption energy of alcohol molecules on SrTiO3(110) surface is enhanced with the pKa value of alcohols reduced. It implied that the enhanced relative interaction strength between SrTiO3(110) surface and alcohol molecules would make the surface more stable. As a result, the surface area of SrTiO3(110) suface would expose more. The ratio of SrTiO3(110) surface in the SrTiO3nanocrystal would be added.更多还原