Seeded Growth of Noble-Metal Nanocrystals

技术概述：该项目由美国国家科学基金会的固态和材料化学(SSMC)计划支持，将为合成各种应用的具有可控性能的贵金属纳米晶体奠定科学基础。关键的方法是使用种子介导法分离并独立控制成核和生长步骤。这项研究将分为四个方面：i)由Ag、Au、Pd或Pt组成的单晶立方八面体晶种的合成和表征，其尺寸小于10 nm。还将考察覆盖剂、前驱体和氧化蚀刻对种子结晶度、产量和尺寸分布的影响。Ii)与种子相同的金属生长。这项工作将寻求相关的还原动力学与生长模式，包括现场选择过生长，保形涂层，和树枝状生长。它还将开发一种筛选方法，以快速识别能够促进特定小面形成的封顶剂。3)不同于种子的金属的生长。这项工作将通过引入强还原剂来阻止替换反应，解决当用于种子的金属比要生长的金属更活跃时自发发生的电偶替换等问题。它还将充分探索核壳纳米晶在成分、形状和壳层厚度方面的控制。4)新型纳米晶体的性质和应用。除了系统地研究不同尺寸、形状和组成的纳米晶体的光学性质外，这项工作还将研究不同厚度的壳层如何屏蔽核心的等离子体激发。它还将系统地研究衬底在形成具有不同形状的纳米晶体的热点方面的作用。此外，它还将考察具有明确表面定义和严格控制壳层厚度的核壳纳米晶体的催化和电催化性能非技术摘要：由于纳米晶体的尺寸/形状与化学、物理、电子、光学、磁性和催化性能之间的强烈相关性，人们对尺寸和形状可控的贵金属纳米晶体的兴趣稳步增长。这些纳米晶体在从催化(例如，在燃料电池和催化转换器中)到生物医学研究(例如，作为造影剂和治疗剂)等领域的技术应用也增强了人们的兴趣。然而，系统地和可预测地控制这些特性的尝试取得了有限的成功。一个障碍是缺乏对从原子到原子核、种子再到纳米晶体的进化路径的机械理解和实验控制。这项工作将给该领域带来重大进展，揭示合成贵金属纳米晶体的基本知识和设计规则，这些纳米晶体的尺寸、形状、形貌、组成和结构对各种应用至关重要。这项研究将在以下方面对社会产生深远的影响：i)开发用于传感、生物医学应用和催化的新材料，以解决与国家安全、健康、环境和能源有关的问题；ii)在不同科学领域之间建立联系，包括固体化学、凝聚态物理、表面科学、材料科学、胶体科学、催化和光子学；iii)通过多学科研究和合作加强研究生和本科生教育；iv)通过同行评议的出版物、报告、研讨会、会议报告、本科生和研究生教学、暑期学校讲座和网站，产生和传播新的科学知识；以及v)通过让妇女、少数民族和其他代表性不足的群体参与研究计划来促进高等教育的多样性。

TECHNICAL SUMMARY:This project, supported by the Solid State and Materials Chemistry (SSMC) program at NSF, will build a scientific basis for the synthesis of noble-metal nanocrystals with controlled properties for a variety of applications. The key approach is to separate and then independently control the nucleation and growth steps using a seed-mediated method. The research will be organized into four thrusts: i) Synthesis and characterization of single-crystal, cubooctahedral seeds made of Ag, Au, Pd, or Pt, and with sizes below 10 nm. The effects of capping agent, precursor, and oxidative etching on the crystallinity, yield, and size distribution of the seeds will all be examined. ii) Growth of metals same as the seeds. This work will seek to correlate the reduction kinetics with the growth modes, including site-selected overgrowth, conformal coating, and dendritic growth. It will also develop a screening method for rapid identification of capping agents capable of promoting the formation of specific facets. iii) Growth of metals different from the seeds. This work will address issues such as galvanic replacement that will occur spontaneously when the metal for seeds is more reactive than the metal to be grown by introducing a strong reducing agent to setback the replacement reaction. It will also fully explore the core-shell nanocrystals in terms of control over composition, shape, and shell thickness. iv) Properties and applications of the novel nanocrystals. In addition to a systematic study of the optical properties for nanocrystals with different sizes, shapes, and compositions, this work will investigate how the shells with various thicknesses shield the plasmonic excitation of the cores. It will also systematically investigate the effect of a substrate in forming hot spots with nanocrystals having different shapes. Furthermore, it will examine the catalytic and electrocatalytic properties of core-shell nanocrystals with both well-defined facets on the surface and tightly controlled thicknesses for the shellsNON-TECHNICAL SUMMARY:Interest in noble-metal nanocrystals with controlled sizes and shapes has grown steadily because of strong correlations between the size/shape of nanocrystals and chemical, physical, electronic, optical, magnetic, and catalytic properties. The interest has also been enhanced by the technological applications of these nanocrystals in areas ranging from catalysis (e.g., in fuel cells and catalytic converters) to biomedical research (e.g., as contrast and therapeutic agents). However, attempts to systematically and predictably control these properties have been met with limited success. One barrier is the lack of a mechanistic understanding and experimental control of the evolution pathway from atoms to nuclei, seeds, and finally nanocrystals. This work will bring significant advances to the field by unraveling the essential knowledge and design rules for synthesizing noble-metal nanocrystals with controlled sizes, shapes, morphologies, compositions, and structures crucial to various applications. This research will have profound impacts on the society in the following aspects: i) developing novel materials for sensing, biomedical applications, and catalysis that will address issues related to national security, health, environment, and energy; ii) forging links between different scientific fields that include solid state chemistry, condensed matter physics, surface science, materials science, colloid science, catalysis, and photonics; iii) enhancing both graduate and undergraduate education through multidisciplinary research and collaboration; iv) generating and disseminating new scientific knowledge resulting from the proposed work through peer-reviewed publications, reports, seminars, conference presentations, undergraduate and graduate teaching, summer school lectures, and websites; and v) promoting diversity in higher education by engaging women, minorities, and other underrepresented groups into the research program.