Replacement-Free Growth of Au on Ag Nanocrystal Seeds

金在银纳米晶体种子上的无置换生长

• 批准号: 1412006
• 负责人: Dong Qin
• 金额: $ 37万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1412006&HistoricalAwards=false
• 关键词: Replacement; Free; Growth; Au; Ag

Dong Qin from the Georgia Institute of Technology is supported by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry to grow metal nanocrystals on other ("seed") metal nanocrystals with metal combinations that have not previously been possible. A nanocrystal is a crystal whose size is limited to several billionths of a meter, and such small crystals often have unusual properties. Noble-metal nanocrystals have received steadily growing interest in recent years owing to their fascinating properties and widespread use in applications ranging from catalysis to sensing, imaging, and biomedicine. Today, growing them on seed particles has emerged as a prevalent route to the syntheses of nanocrystals from a number of noble metals, such as silver (Ag), gold (Au), palladium (Pd), and platinum (Pt), as well as some of their bimetallic combinations. Despite the remarkable successes, the seed usually has to be the less reactive molecule or it gets eaten away ("galvanic replacement") during the growth process of the second metal. The project is aimed at finding a way to avoid galvanic replacement even when the seed particle is made of the more reactive metal. The new classes of bimetallic nanocrystals being made can be used in a broad range of applications since they may enhance spectroscopy of nearby molecules and catalysis of chemical reactions. The proposed research encompasses disciplines across materials science, chemistry, colloidal science, solid-state physics, optics, and surface chemistry. The project builds an interdisciplinary education program in nanoscale science and engineering for graduate and undergraduate students, with a major focus on the following components: i) learning that exposes students to a multifaceted, integrated approach to understanding the fundamentals of nanomaterials and their unique properties due to nanoscale sizes; ii) training that offers students hands-on experience in the laboratory and the school user facilities in exploring research tools and discoveries and frontiers of nanotechnology; and iii) engaging that connects the students with community and society to impart and promote a conceptual understanding of nanoscale science and technology in high school students and teachers. This project is to develop a scientific basis for achieving seeded growth with two metals that have been plagued by galvanic replacement reactions. Specifically, the team aims to achieve replacement-free growth of Au on Ag nanocubes using a faster, parallel reduction to kinetically compete with and thus inhibit a galvanic reactions. The proposed research includes the following major thrusts: i) synthesis of Ag nanocubes with edge lengths at 30, 60, and 90 nm as uniform samples, together with different degrees of corner truncation; ii) determination of the kinetic parameters (rate law and activation energy) for the reduction of HAuCl4 by a strong reducing agent, such as ascorbic acid, NH2OH, and NaBH4; iii) measurement of the kinetic parameters for the galvanic reaction between HAuCl4 and Ag nanocubes of different sizes and with different degrees of corner truncation; iv) understanding the role of surface diffusion in controlling the final structure (core-frame vs. core-shell) of the bimetallic nanocrystals; and v) evaluation of the optical properties and chemical stability of the bimetallic nanocrystals. Collectively, a solid understanding of the system involving Ag and Au serves as the foundation for achieving replacement-free growth of a less reactive metal on the seeds made of a more reactive metal. These new classes of Ag-Au nanostructures can find widespread use in optical applications with greatly improved performance in terms of chemical stability and activity, together with their potentials for emerging applications such as sensing, imaging, biomedicine, and photonics, as well as in the conversion of solar light into energy through the field enhancement effect. The principle for the galvanic replacement-free growth of Au on Ag can also be extended to other pairs of noble metals, including Ag-Pd, Ag-Pt, Ag-Rh, and Ag-Ir. The resultant bimetallic nanocrystals with a core-frame or core-shell structure may find immediate use in catalysis and environmental protection.

乔治亚理工学院的董勤（音译）在化学系大分子、超分子和纳米化学项目的支持下，在其他（“种子”）金属纳米晶体上生长金属纳米晶体，这是以前不可能实现的。纳米晶体是一种尺寸只有几十亿分之一米的晶体，这种小晶体通常具有不同寻常的特性。近年来，贵金属纳米晶体因其迷人的特性和在催化、传感、成像和生物医学等领域的广泛应用而受到越来越多的关注。今天，在种子颗粒上种植纳米晶体已经成为一种普遍的方法，可以从许多贵金属合成纳米晶体，如银（Ag）、金（Au）、钯（Pd）和铂（Pt），以及它们的一些双金属组合。尽管取得了显著的成功，但种子通常必须是活性较低的分子，否则它会在第二种金属的生长过程中被吃掉（“电替代”）。该项目旨在找到一种方法，即使种子颗粒是由活性更强的金属制成的，也可以避免电替换。正在制造的新型双金属纳米晶体可以用于广泛的应用，因为它们可以增强附近分子的光谱和化学反应的催化作用。拟议的研究涵盖了材料科学、化学、胶体科学、固态物理、光学和表面化学等学科。该项目为研究生和本科生建立了一个纳米尺度科学与工程的跨学科教育计划，主要侧重于以下组成部分：1)学习，使学生接触到多方面，综合的方法来理解纳米材料的基本原理及其由于纳米尺度而产生的独特性质；Ii)为学生提供在实验室和学校使用设施中探索研究工具、发现和纳米技术前沿的实践经验；iii)将学生与社区和社会联系起来，在高中学生和教师中传授和促进对纳米尺度科学和技术的概念理解。这个项目是为实现两种金属的种子生长发展科学基础，这两种金属一直受到电替代反应的困扰。具体来说，该团队的目标是通过更快的平行还原来实现Au在银纳米立方上的无替代生长，从而与电反应竞争，从而抑制电反应。拟开展的研究主要包括以下几个方面：1)合成边缘长度为30、60和90 nm的银纳米立方体作为均匀样品，并进行不同程度的角截断；ii)测定抗坏血酸、NH2OH和NaBH4等强还原剂还原HAuCl4的动力学参数（速率规律和活化能）；iii)测定不同尺寸、不同角截断度的HAuCl4与银纳米立方体电反应的动力学参数；Iv)了解表面扩散在控制双金属纳米晶体最终结构（核-框架与核-壳）中的作用；(5)评价双金属纳米晶体的光学性质和化学稳定性。总的来说，对涉及Ag和Au的体系的深刻理解是实现活性较低的金属在活性较高的金属制成的种子上无替代生长的基础。这些新型Ag-Au纳米结构可以在光学应用中得到广泛的应用，在化学稳定性和活性方面大大提高了性能，同时它们在传感、成像、生物医学和光子学等新兴应用中具有潜力，以及在通过场增强效应将太阳光转化为能量方面具有潜力。Au在Ag上无电替代生长的原理也可以推广到其他贵金属对，包括Ag- pd、Ag- pt、Ag- rh和Ag- ir。合成的具有核-框架或核-壳结构的双金属纳米晶体在催化和环境保护方面有直接的应用前景。