Seeded Growth of Noble-Metal Nanocrystals

技术概述：该项目由美国国家科学基金会固态与材料化学（SSMC）项目支持，将为合成具有各种应用控制性能的贵金属纳米晶体奠定科学基础。关键方法是利用种子介导的方法分离并独立控制成核和生长步骤。该研究将分为四个重点：1)由银、金、钯或铂制成的尺寸小于10纳米的单晶、立方面体种子的合成和表征。封盖剂、前驱体和氧化蚀刻对种子结晶度、产量和大小分布的影响都将被检查。ii)与种子相同的金属生长。这项工作将寻求将还原动力学与生长模式联系起来，包括选址过度生长、保形涂层和枝晶生长。它还将开发一种筛选方法，用于快速识别能够促进特定面形成的封盖剂。iii)生长出与种子不同的金属。这项工作将通过引入一种强还原剂来抑制替代反应，解决诸如当用于种子的金属比要生长的金属更具活性时自发发生的电替换等问题。它还将充分探索核壳纳米晶体在组成、形状和壳厚方面的控制。iv)新型纳米晶体的性质及应用。除了系统地研究不同尺寸、形状和组成的纳米晶体的光学特性外，本工作还将研究不同厚度的壳层如何屏蔽核心的等离子激振。它还将系统地研究衬底对形成具有不同形状的纳米晶体的热点的影响。此外，它将研究核壳纳米晶体的催化和电催化性能，这些纳米晶体表面上有明确的面，壳层的厚度也受到严格控制。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存在很强的相关性，因此对具有可控尺寸和形状的贵金属纳米晶体的兴趣稳步增长。这些纳米晶体在催化（如燃料电池和催化转化器）和生物医学研究（如造影剂和治疗剂）等领域的技术应用也增强了人们的兴趣。然而，系统地、可预测地控制这些特性的尝试收效甚微。一个障碍是缺乏从原子到原子核、种子、最后纳米晶体的进化途径的机制理解和实验控制。这项工作将通过揭示合成贵金属纳米晶体的基本知识和设计规则，为该领域带来重大进展，这些纳米晶体具有对各种应用至关重要的控制尺寸，形状，形态，成分和结构。本研究将在以下几个方面对社会产生深远的影响：1)开发用于传感、生物医学和催化的新型材料，解决与国家安全、健康、环境和能源有关的问题；Ii)建立不同科学领域之间的联系，包括固态化学、凝聚态物理、表面科学、材料科学、胶体科学、催化和光子学；Iii)透过多学科研究及合作，加强研究生及本科生教育；Iv)通过同行评审的出版物、报告、研讨会、会议演讲、本科生和研究生教学、暑期学校讲座和网站，产生和传播由拟议工作产生的新科学知识；5)通过让女性、少数族裔和其他未被充分代表的群体参与研究项目，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.