Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130, United States.
J Am Chem Soc. 2012 Sep 26;134(38):15822-31. doi: 10.1021/ja305329g. Epub 2012 Sep 17.
This article describes a systematic study of the nucleation and growth of Ag (and Au) on Pd nanocrystal seeds. By carefully controlling the reaction kinetics, the newly formed Ag atoms could be directed to selectively nucleate and then epitaxially grow on a specific number (ranging from one to six) of the six faces on a cubic Pd seed, leading to the formation of bimetallic nanocrystals with a variety of different structures. In addition to changing the injection rate of precursor, we also systematically investigated other reaction parameters including the capping agent, reductant, and reaction temperature. Our results suggest that the site-selective growth of Ag on cubic Pd seeds could be readily realized by optimizing these reaction parameters. On the basis of the positions of Pd seeds inside the bimetallic nanocrystals as revealed by TEM imaging and elemental mapping, we could identify the exact growth pathways and achieve a clear and thorough understanding of the mechanisms. We have successfully applied the same strategy based on kinetic control to cubic Pd seeds with different sizes and octahedral Pd seeds of one size to generate an array of novel bimetallic nanocrystals with well-controlled structures. With cubic Pd seeds as an example, we have also extended this strategy to the Pd-Au system. We believe this work will provide a promising route to the fabrication of bimetallic nanocrystals with novel structures and properties for applications in plasmonics, catalysis, and other areas.
本文系统研究了 Ag（和 Au）在 Pd 纳米晶种子上的成核和生长。通过仔细控制反应动力学，可以引导新形成的 Ag 原子选择性地在立方 Pd 种子的六个面中的一个特定数量（从一个到六个）上成核，然后外延生长，从而形成具有多种不同结构的双金属纳米晶体。除了改变前体的注入速率外，我们还系统地研究了其他反应参数，包括封端剂、还原剂和反应温度。我们的结果表明，通过优化这些反应参数，可以很容易地实现 Ag 在立方 Pd 种子上的选择性生长。基于 TEM 成像和元素映射揭示的双金属纳米晶体内部 Pd 种子的位置，我们可以确定确切的生长途径，并对机制有清晰和彻底的理解。我们已经成功地将基于动力学控制的相同策略应用于不同尺寸的立方 Pd 种子和一种尺寸的八面体 Pd 种子，生成了一系列具有良好结构控制的新型双金属纳米晶体。以立方 Pd 种子为例，我们还将该策略扩展到了 Pd-Au 体系。我们相信这项工作将为制造具有新颖结构和性能的双金属纳米晶体提供一条有前途的途径，可应用于等离子体学、催化和其他领域。
