【作者】 钟宽；

【导师】 童叶翔；

【作者基本信息】 中山大学 ， 材料物理与化学， 2010， 博士

【摘要】 金属氧化物半导体纳米材料,由于其具有半导体的特性、结构多样性、多种价态的可变性和共存性、可表现出非化学计量学组成和结构的稳定性,在光学、催化和光伏等方面表现出优异的性质。对金属氧化物半导体纳米材料的研究,涉及到晶体生长、纳米科学、结构、催化、电学、光学和表面科学等多门学科,具有很大的挑战意义。因此,制备纳米结构的金属氧化物半导体并研究其相关性质和发掘新性质是非常具有理论和现实意义的。本论文研究的SbxOy,ZnO,CuO及其与Ag修饰纳米结构,在光催化、燃料敏化太阳能电池、CO和碳氢化合物催化氧化和作为燃料电池阳极催化剂方面具有重大的潜在应用。论文主要围绕基于一维的金属氧化物半导体纳米材料的制备、结构表征、生长机理分析和性质表征展开。制备的方法主要基于电化学方法,金属氧化物半导体材料主要为SbxOy,ZnO和CuO,研究的性质主要为光学性质和催化性质。(1)利用化学镀的方法,以Cu片作为基体,实现一般情况下氧化性较强的Cu/Cu2+电对还原相对具有还原性的Sb/Sb3+电对,第一次制备了Sb十四面体疏松三维结构Sb纳米笼,这种三维结构是由Sb纳米线按其菱形晶体晶胞的a、b和c三轴有序延伸编织而得。在氧气氛围下低温加热,可使Sb纳米结构的表面氧化,而其形貌保持不变,但结晶度变差。生长在钝化基体上的Sb纳米笼,由于其与基体上的铜氧化物相互作用,其氧化速率增快。这种疏松的三维结构,可用于催化剂的载体或催化剂。(2)各种ZnO纳米材料可通过电化学腐蚀的方法制备获得。电化学腐蚀分为三种模式:液膜、半浸状态基体上部的气膜和下部的溶液。基于一维的ZnO纳米材料的生长机理为电化学腐蚀和取向连接。ZnO纳米材料的生长受浓度、反应时间、添加剂、基体状态、液膜厚度和溶剂种类等因素影响,通过控制这些条件,观察到了ZnO纳米材料形貌的演化过程,获得的ZnO纳米材料形貌有纳米棒、纳米线、纳米针、纳米颗粒、梳状结构、纳米枝状体和多级结构。采用紫外可见吸收光谱和荧光光谱研究材料的关学性质。各样品的光学带隙随形貌变化而变化。其中,短纳米棒的光学带隙最宽,而粗纳米棒的最窄。除了粗纳米棒,其它样品均表现出带边发射。这种带边发射强度随样品的形貌变化也发生变化,短纳米棒的发光强度最强。(3)以化学镀在Zn基体上沉积的多孔Ag纳米簇作为模板,在热处理下,从Ag纳米簇长出ZnO纳米线。Ag在ZnO纳米线电极上的电化学行为特殊,主要是由于ZnO纳米线电极的特殊性。Ag纳米颗粒修饰的ZnO纳米线超级结构,在紫外区的吸收强度几乎不变,但ZnO的光学带隙变小,且但荧光强度剧烈降低,这是由于在ZnO和Ag之间发生电荷转移。在拉曼实验中,在修饰结构中产生许多有序分布的分裂峰,其产生原因为表面等离子体共振耦合。此外,在修饰结构中会发生不寻常的超级强吸光的特殊现象,我们把之归属于在Ag修饰ZnO纳米线特殊结构上所发生的表面等离子体共振及其耦合、光学非线性特性、电荷转移和等离子体波导的共同作用。(4)采用化学镀和电化学腐蚀的联合方法,制备了ZnO纳米材料修饰Ag亚微米级颗粒的复合材料。控制电化学腐蚀的时间,可以获得较低ZnO覆盖度的镶嵌结构、较高ZnO覆盖度的核壳结构和高ZnO覆盖度的仙人球结构。考察了不同ZnO覆盖度的复合材料的光学性质和光电响应行为。只有镶嵌结构表现出宽范围的紫外可见光吸收,且表现出增强的光电响应效应,主要原因为较大的Ag颗粒,可储存更多的电荷;众多ZnO纳米结构修饰一颗直径较大(亚微米级)的Ag颗粒,使电荷转移效率提高;Ag颗粒的表面等离子体共振且修饰的ZnO不产生影响,可增强Ag与ZnO之间的电荷转移。(5)采用电化学腐蚀的方法,制备了氧化铜纳米颗粒、絮状结构、亚微米级砖形结构和不同特征的纳米棒和纳米片等。这些纳米材料的制备,主要是通过控制晶体生长的条件来获得的。样品生长的条件包括浓度、生长时间、添加剂、生长模式、温度等。探讨了不同形貌、不同表面状态、不同结构和不同分布的氧化铜纳米材料的形成机理。(6)采用XPS和拉曼光谱研究了氧化铜纳米材料的氧吸附能力。考察了不同形貌和结构的氧化铜纳米材料的氧吸附行为。氧吸附能力的大小,主要取决于样品缺陷结构的多少、结晶度的高低、比表面积的大小等。在氧气储存后,样品表现出更强的氧吸附能力。样品在吸附氧的同时,也吸附大量的含碳物,并对其进行原位催化氧化。氧化的程度,在不同的环境下,可发生半氧化、亚深氧化和完全氧化。一般样品的氧吸附能力越高,其对含碳物的催化活性也越高。但样品的催化活性也受其本身结构的影响,即吸附键的强度受样品结构的影响。温度高,有利于催化反应的进行。(7)探讨了氧化铜纳米材料作为直接乙醇燃料电池的阳极催化剂对乙醇电催化氧化的催化作用,提出了一种新的求催化剂载量的方法,研究了氧化铜纳米材料电催化剂催化乙醇的机理及催化行为的特殊性。结果发现,CuO纳米材料对乙醇的电催化氧化表现出高的催化活性,无明显的中毒效应,催化反应动力学快。这主要是由于CuO纳米材料具有高的氧物种吸附能力、良好的碳吸附结构、高价态或其趋势的氧化铜本身具有的催化作用等。CuO纳米材料不用引入第二种物种,通过本身的结构变化,自动可提升催化效率。具有大量缺陷结构的纳米棒,其催化活性更高,这主要是由于其一维的构造,更有利于各物种的吸附与脱附、有利于载流子的传输、有利于其本身的氧化和更大程度地与溶液接触等。更多还原

【Abstract】 Metal oxide semiconductor (MOS) nanostructures have powerful applications in optics, catalysis, and photovoltaics due to their semiconducting properties, structural varieties, ability to change valence, co-existence of mixed valences, nonstoichiometic composition, and stability. The research on MOS nanostructures involve crystal growth, nanoscience, crystal structure, catalysis, electricity, optics, and surface science, which presenting a great challenge. Therefore, synthesizing MOS nanostructures and investigating the related properties or seeking new features are high of significance both in theory and in application. Dissertation is developed centered around the synthesis, structure characterization, formation mechanism discussion, and properties study of MOS nanostructures, including SbxOy, ZnO, CuO, and their composites with Ag. The synthesizing method is mainly based on electrochemical route, the studied properties are mainly related to optics and catalysis.(1) The potential ofφ(Cu/Cu2+) is higher than that ofφ(Sb/Sb3+). However, the successful occurrence of Cu foil to replace Sb3+ to form a Sb coating (a typical chemical plating method) is mainly due to no Cu2+ before reaction and the much lower concentration of Cu2+ during reaction. A regular fourteen-faced polyhedron shape of Sb three-dimensional structure is obtained by this facile method. The structure presents a loose feature which is similar to a cage. The cage is formed by the ordered intertexture of Sb nanowires. Sb cage can be oxidized under moderate hearting in O2 atmosphere with morphology conservation but with poor crystallinity. The cage grown on a passivation substrate can be oxidized much facilely due to the interaction with the copper oxide species in the passivation coating. Such a loose structure may find promising application in catalysis.(2) Various morphologies of ZnO nanostructures can be obtained through a novel method, incorporating electrochemical corrosion with three modes: liquid membrane and above and below the water line in partial immersion. The mechanism of the growth of one-dimensional-based nanostructures is proposed as electrochemical corrosion and oriented attachment, which occur in a liquid membrane or in a vapor membrane or in solution for partial immersion. The evolution of ZnO nanostructures such as nanorods, nanowires, nanopins, nanoparticles, comb-like structures, nanodentrites, and hierarchical structures is observed, and the influence of concentration, reaction time, additives, state of substrate, membrane thickness, and solvent on the morphology of ZnO is investigated. Optical properties of ZnO nanostructures are studied by using UV-visible absorption spectra and photoluminescence (PL). Their optical gaps vary from different morphologies. Among the studied samples, short nanorods show the largest optical gap, while big nanorods present the smallest value of optical gap. PL properties demonstrate that peaks of near-band emission and defect-related luminescence are basically in the same position. However, intensities for different morphologies are of different values, and short nanorods exhibit the best near-band emissions.(3) ZnO nanowires can grow during heat treatment from the micropores of Ag nanoclusters deposited on a Zn substrate. A Ag-modified ZnO nanowires superstucture is obtained by electrodepostion. The elctrochemical behavior of Ag(I) reducing on the surfaces of ZnO nanowires is unusual. The intensity of light absorption in the ultraviolet region almost keeps, but the optical bandgap of ZnO nanowires is red shifted, and the photoluminescence (PL) intensity decreases greatly, which are mainly due to the charge transfer between ZnO and Ag. Moreover, many split Raman peaks appear resulting from surface plasmon resonance (SPR) coupling. Additionally, extraordinary strong light absorption is obtained primarily arising from the interaction of SPR, SPR coupling, nonlinearities, charge transfer, and plasmon waveguides occurring on the superstructure.(4) ZnO nanostructure-modified Ag sub-micron particles composite is prepared by association of chemical plating and electrochemical corrosion. By controlling reaction time, composites with different coverage of ZnO on the surfaces of Ag sub-micron particles such as mosaic structures, core/shell structures, and ball cactus-like structures are obtained. The optical properties and photoelectron response on different composites are also studied. Only mosaic structures present the broad UV-vis absorption and exhibit enhanced photovoltaic effects mainly arising from the relatively large size of Ag particles which can store much more photoinduced electrons, the configuration of many ZnO nanostructres sharing one big Ag particle which promoting the efficiency of charge transfer, and the occurrence of SPR on Ag which enhancing the charge transfer between Ag and ZnO.(5) Copper oxide nanoparticles, floc-like structures, sub-micron brick-like structures, and nanorods and nanofilms with different features in shapes are assembled by an electrochemical corrosion route. The successful obtainment of these nanostructures are mainly based on the control of the growing conditions, including concentration, growing time, additives, growing modes, and temperature. In addition, the formation mechanism of copper oxide nanostructures with different shapes, different surface states, different structures, and different distributions are also investigated.(6) The oxygen adsorption properties of copper oxide nanostructures are studied via X-ray photoelectron spectroscopy (XPS) and Raman spectra (RS). The behavior of oxygen adsorption on different copper oxide nanostructures is investigated. The results show that the oxygen adsorption ability of copper oxide nanostructures depends on the quantities of defect structures, the crystallinity, and the specific surface area. The samples exhibit stronger oxygen adsorption ability after exposure to O2 atmosphere. The adsorbed oxygen can oxidize surface adsorbed carbon species. The degree of the oxidation of the carbon species depends on the reaction condition. Generally, the stronger the ability of oxygen adsorption, the higher the catalytic activities toward the oxidation of the carbon species. Moreover, high temperature enhances catalytic reactions.(7) The catalytic activity toward ethanol electrooxidation on copper oxide nanostructure is studied. The results show that copper oxide nanostruture demonstrates high catalytic activity toward ethanol electrooxidation with high catalytic kinetics and unobvious poisoning effects. The high catalytic activity is mainly derived from the copper oxide nanostructure which presenting the strong oxygen adsorption ability, the catalysis of the high-valence copper species, and the nanoscale of copper oxide catalyst. Without introducing a promoter, copper oxide nanostructure itself can improve its catalytic activity by changing surface structure. Copper oxide nanorods with large quantities of defect structures can exhibit much higher catalytic activity, which is mainly due to its one-dimensional configuration that benefiting the adsorption and desorption of reactants and products, the transportation of carriers, the oxidation of CuO, and the contact of CuO with solution in deep extent. Copper oxide nanostructure can be severed as an electrocatalyst in the anode material in direct ethanol fuel cells.更多还原