超细Pt纳米枝晶材料的可控制备及其多功能性能研究

发布时间：2018-05-03 08:04

本文选题：纳米枝晶 + 催化燃烧　；参考：《上海大学》2015年硕士论文

【摘要】：过渡金属(铂、钯、金、银等)及其合金由于其优异的催化、电学及耐蚀性能,一直吸引着学界广泛的研究兴趣。石油化工、清洁能源、传感分析、环境保护等诸多领域的发展,都有赖于纳米贵金属材料研发领域的进步。业界广泛认为,在纳米尺度对贵金属材料形貌的可控调节,将极大的影响纳米材料的物理化学性能,从而为开发下一代功能材料奠定基础。在贵金属纳米材料中,具有多级分形结构的纳米枝晶材料被广泛运用于催化、光学、传感等领域。然而,形貌可控枝晶形纳米颗粒的制备至今仍是材料合成领域的重大挑战之一。基于此,本文采用一种简便的脉冲电化学沉积方法成功实现了形貌可控超细纳米铂枝晶的制备,并结合材料表征与电化学原理提出了具有择优取向的纳米枝晶生长机理。同时,本文结合实验与理论计算,对纳米铂枝晶的局域电场增强效应和表面等离子体共振(LSPR)进行了系统研究。本文研究的主要内容及结果如下:1.通过调节脉冲电化学沉积方法中的阳极电位,制备得到半球形、花状、枝晶形等不同形貌的铂纳米结构。其中,纳米枝晶形铂颗粒的三次枝晶呈现10-20 nm的超细尺寸。研究发现,铂纳米枝晶各层次的枝晶晶面拥有不同的择优取向:枝干、二次枝晶、三次枝晶分别呈现111,110和311的生长晶向。其生长机理与脉冲电位作用下的表面物种吸脱附及扩散控制具有重要关联。2.甲醇催化燃烧性能表征结果证明,不同形貌铂纳米结构对于该反应的催化活性有:枝晶形花状半球形。特别的,在150 oC反应温度下的Pt纳米枝晶转化频率(TOF)达到了0.33 mmol·min-1·mg-1,其值为相同反应条件下半球形Pt纳米结构催化活性的四倍。3.静电力显微镜研究结果证明,具有高曲率半径的纳米Pt枝晶针尖具有强烈的局域电场增强效应。4.有限元理论计算结果证明,纳米枝晶材料的表面等离子体共振(LSPR)“热点”集中在枝晶“主干-分支”的连接区域,其强度随着横向等离子共振模式比例的增大而增强。同时,在Pt纳米枝晶表面的尖锐形貌区域存在高强的局域电场。通过研究发现,Pt纳米枝晶的LSPR效应对材料的尺寸、构型十分敏感。其中,单根Pt纳米枝晶在波长为672 nm的电场增强系数|Emax|/|Eo|为27,而具有“尾对尾”构型(BB)的纳米枝晶双聚体在波长为920 nm处的电场增强系数|Emax|/|Eo|达到了53。
[Abstract]:Transition metals (platinum, palladium, gold, silver and so on) and their alloys have attracted extensive research interest due to their excellent catalytic, electrical and corrosion resistance. The development of petrochemical, clean energy, sensor analysis, environmental protection and other fields depend on the development of nano-precious metal materials. It is widely believed that the controllable adjustment of the morphology of noble metal materials at nanometer scale will greatly affect the physical and chemical properties of nanomaterials and thus lay a foundation for the development of the next generation of functional materials. Among noble metal nanomaterials, nanocrystalline materials with multilevel fractal structure are widely used in catalysis, optics, sensing and other fields. However, the preparation of controllable dendrite nanoparticles is still one of the major challenges in the field of material synthesis. Based on this, a simple pulsed electrochemical deposition method was used to successfully prepare ultrafine platinum dendrites with controllable morphology, and the growth mechanism of nanocrystalline dendrites with preferred orientation was proposed based on the characterization of materials and electrochemical principle. At the same time, the enhancement effect of local electric field and the surface plasmon resonance (LSPRs) of nanocrystalline platinum dendrites are studied systematically by combining experiments and theoretical calculations. The main contents and results of this paper are as follows: 1. By adjusting the anode potential of pulsed electrochemical deposition, platinum nanostructures with different morphologies, such as hemispherical, flower-like and dendritic shapes, were prepared. Among them, the cubic dendrites of nanocrystalline platinum particles show ultrafine size of 10-20 nm. It is found that the dendrite faces of platinum nanocrystals have different preferred orientations: branch, secondary dendrite, and tertiary dendrite with a growth direction of 111110 and 311, respectively. Its growth mechanism is closely related to the surface species desorption and diffusion control under the action of pulse potential. The results of methanol catalytic combustion showed that the catalytic activity of platinum nanostructures with different morphologies for the reaction was dendrite flower-shaped hemispherical. In particular, the conversion frequency of Pt nanocrystals at 150oC reaction temperature is 0.33 mmol min-1 mg-1, which is four times of the catalytic activity of the hemispherical Pt nanostructures under the same reaction conditions. The results of hydrostatic microscope show that the nanocrystalline Pt dendrite tip with high curvature radius has a strong local electric field enhancement effect. The results of finite element theory show that the "hot spot" of surface plasmon resonance (LSPRs) of nanocrystalline materials is concentrated in the junction region of dendrite "trunk and branch", and its intensity increases with the increase of transverse plasmon resonance mode ratio. At the same time, there is a high local electric field in the sharp surface of Pt nanocrystalline. It is found that the LSPR effect of Pt nanocrystals is very sensitive to the size and configuration of the materials. The electric field enhancement coefficient (Emax / Eo) of single Pt nanocrystalline is 27 at wavelength of 672nm, while the electric field enhancement coefficient (Emax / Eo) of nanocrystalline dimer with "tail to tail" configuration is 53 at 920nm.
【学位授予单位】：上海大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O614.826

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