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Chimica

配体介导成核与钯金属纳米粒子的生长

Published: June 25, 2018
doi:
10.3791/57667
, , , , , , ,
1Department of Chemical Engineering,Virginia Polytechnic Institute and State University, 2Center for Integrated Nanotechnologies,Los Alamos National Laboratory, 3Advanced Photon Source,Argonne National Laboratory, 4X-ray Science Division,Argonne National Laboratory, 5Environmental Molecular Science Laboratory,Pacific Northwest National Laboratory

Summary

本研究的主要目的是通过结合 i.原位小角 x 射线散射 (SAXS) 和配体的动力学建模, 阐明封盖剂在调节钯纳米粒子尺寸中的作用。

Abstract

胶粒的大小、分布和稳定性受到上限配体的存在影响很大。尽管在合成反应过程中, 封盖配体的关键贡献, 但它们在调节胶体纳米粒子的成核和生长速率方面的作用还不清楚。在这项工作中, 我们用原位SAXS 和配体为基础的动力学模型, 证明了 trioctylphosphine (顶部) 在不同溶剂 (甲苯和吡啶) 中的作用。我们在不同合成条件下的结果揭示了钯纳米粒子在反应过程中的成核和生长重叠, 这与拉美型成核和生长模型相矛盾。该模型说明了前驱体和粒子表面的 Pd-顶结合的动力学, 这对于捕获粒径演化和原位粒子浓度是必不可少的。此外, 我们通过设计合成条件以获得所需尺寸的纳米粒子, 说明了我们配体模型的预测力。所提出的方法可以应用于其他合成系统, 因此是预测合成胶体纳米粒子的有效策略。

Introduction

由于纳米材料在催化、光伏、光子学、传感器、药物输送1、2、3等领域的广泛应用, 金属纳米粒子的控制合成具有重要的意义. 4,5。为了合成具有特定尺寸和粒径分布的纳米粒子, 了解颗粒成核和生长的基本机理至关重要。然而, 获得这种标准的纳米粒子对纳米合成群落提出了挑战, 因为在理解合成机制方面进展缓慢, 而文献中缺乏健壮的动力学模型。在二十世纪五十年代, 拉美提出了硫溶胶的成核和生长模型, 在那里有一个核爆发, 随后是6、7核的扩散控制生长。在该模型中, 假设单体浓度增加 (由于前体的还原或分解), 一旦水平高于临界过饱和度, 就可以克服粒子核的能量屏障,产生爆裂成核 (均质成核)。由于所提出的爆破成核, 单体浓度下降, 当它低于临界过饱和水平时, 成核停止。其次, 通过单体向纳米粒子表面扩散, 形成的核被假定生长, 而不会发生额外的成核事件。这就有效地分离出成核和生长的时间, 并控制在生长过程中的大小分布8。该模型用于描述不同纳米粒子的形成, 包括 Ag9、Au10、CdSe11和 Fe3O412。然而, 一些研究表明, 经典的核化理论 (碳纳米管) 不能描述胶体纳米粒子的形成, 特别是金属纳米粒子, 其中的核和生长的重叠观察1, 13,14,15,16,17。在其中一项研究中, Watzky 和 Finke 建立了两个步骤的机制, 形成铱纳米粒子13, 其中一个缓慢的连续核重叠与快速纳米粒子表面生长 (在那里增长是自催化)。对不同类型的金属纳米粒子, 如 Pd14、15、18、Pt19、20和 Rh 21, 也观察到了缓慢的成核和快速的自催化生长. ,22。尽管最近发展成核和生长模型1,23,24,25, 配体的作用在建议的模型经常被忽略。然而, 配体被显示影响纳米粒子的大小 14,15,26和形态学 19,27以及催化活性和选择性28,29. 例如, 杨等。30控制了 Pd 纳米粒子的大小, 范围从9.5 和 15 nm, 通过改变 trioctylphosphine 的浓度 (顶部)。在磁性纳米粒子 (Fe3O4) 的合成中, 当配体 (胺) 与金属前驱体比从1增加到60时, 其大小明显地从11降到 5 nm。有趣的是, 铂纳米粒子的大小被证明对链长度的胺配体 (e., n-己和胺), 在那里可以获得更小的纳米粒度, 可利用较长的链 (i. e.,胺)31。

不同浓度和不同类型的配体所引起的尺寸变化是配体在成核和生长动力学中贡献的明显证据。不幸的是, 很少有研究表明配体的作用, 在这些研究中, 为了简单起见, 通常会做出几个假设, 这反过来又使这些模型仅适用于特定条件32,33。更具体地说, Rempel 和同事们开发了一个动力学模型来描述量子点 (CdSe) 在有盖配体存在时的形成。然而, 在他们的研究中, 假定配体与纳米粒子表面的结合在任何给定时间32的平衡。当配体大量过剩时, 这种假设可能会成立。我们集团最近开发了一种新的配体模型14 , 它占盖配体的结合与前驱 (金属复合体) 和纳米粒子表面作为可逆反应14。此外, 我们的配体模型可能被用于其他金属纳米粒子系统, 其中合成动力学似乎受到配体存在的影响。

在目前的研究中, 我们使用我们新近开发的配体模型来预测钯纳米粒子在不同溶剂中的形成和生长, 包括甲苯和吡啶。对于模型输入, 利用原位 SAXS 在合成过程中获得纳米粒子的浓度和粒度分布。测量粒子的大小和浓度, 辅以动力学建模, 使我们能够提取出关于成核和生长速率的更精确的信息。我们进一步证明, 我们的配体模型, 明确地描述配体-金属结合, 是高度预测性的, 可用于设计合成程序, 以获得所需尺寸的纳米粒子。

Protocol

1. 醋酸钯再结晶 注意: 此协议涉及使用高温玻璃器皿和解决方案的动手操作。使用个人防护设备, 包括护目镜和耐热手套。所有涉及解决方案处理的操作都应在通风罩中进行, 并避免由于无水乙酸的腐蚀性和易燃性质而在附近的其他热源。 将40毫升无水乙酸加入50毫升三颈圆底烧瓶, 0.75 克醋酸钯和搅拌棒。将冷凝器连接到中间颈部, 盖上其他两个开口, 并将烧瓶固定在搅…

Representative Results

为了系统地研究封盖配体是否改变了成核和生长的动力学, 我们采取了以下两种方法: (i) 在与前人研究类似的动力学模型中未考虑配位与金属的结合 (i.、成核和自催化生长) (ii.) 在模型 (i.、以配体为基础的模型中, 考虑了纳米粒子的前体和表面) 对封盖配体的可逆结合。关于甲苯的 Pd 合成, 如图 1所示, 不考虑配体-金属结合, 该模型未能?…

Discussion

在这项研究中, 我们提出了一个强大的方法来检查上限配体对金属纳米粒子的成核和生长的影响。以醋酸钯为金属前驱体和顶部作为配位剂, 合成了不同溶剂 (甲苯和吡啶) 的 pd 纳米颗粒。我们利用原位SAXS 提取还原原子 (成核和生长事件) 的浓度以及纳米粒子 (成核事件) 的浓度, 并将实验观测量用作模型输入。此外, 通过考虑粒子浓度的斜率和原子在早期反应时间的浓度, 我们的方法 (使用…

Divulgazioni

The authors have nothing to disclose.

Acknowledgements

这项工作主要由国家科学基金会 (NSF) 资助, 化学司 (奖项编号 CHE-1507370) 得到承认。在3M 的非终身教师奖中, 他和文汇李承认部分财政支持。这项研究使用了先进的光子源 (光束线 12-C, 用户建议 GUP-45774) 的资源, 美国能源部 (能源部) 在阿贡国家实验室为能源部科学办公室操作的合同号。DE-AC02-06CH11357。作者想感谢弗吉尼亚理工大学化学工程系的博士 Yubing, 他对 SAXS 测量的帮助。所提出的工作部分是在综合纳米技术公司中心执行的, 一个科学用户设施办公室为美国能源部科学办公室操作。洛斯阿拉莫斯国家实验室, 一个平权行动平等机会雇主, 由洛斯阿拉莫斯国家安全有限责任公司管理, 为美国能源部国家核安全管理局根据合同 DE-AC52-06NA25396。

Materials

palladium acetate (Pd(OAc)2) ALDRICH 520764
anhydrous acetic acid SIAL 338826
trioctylphosphine ALDRICH 718165
pyridine MilliporeSigma PX2012-7
toluene SIAL 244511
1-hexanol SIAL 471402
N8 Horizon SAXS Bruker A32-X1
glovebox Vaccum Atmospheres Co. 109035
MR HEI-TEC 115V Hotplate Heidolph 5053000000
hotplate Monoblock insert Heidolph 5058000800
heat-On 25-ml insert Heidolph 5058006200
7 mL vials SUPELCO 27518
micro stir bar PTFE  VWR 58948-353
egg-Shaped Bars  Fisherbrand™  14-512-121
25 mL round bottom flasks ALDRICH Z167495
quartz capillary Hampton Research HR6-148
MATLAB R2016b MathWorks
Bruker SAXS 1.0v Bruker
Diffrac Measurement Center 4.0v Bruker
DOWNLOAD MATERIALS LIST

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Tags

PalladiumNanoparticlesNucleationGrowthSAXSKinetic RatesCapping LigandsColloidalMetal OxidesPalladium AcetateVacuum FiltrationCrystallization
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Mozaffari, S., Li, W., Thompson, C., Ivanov, S., Seifert, S., Lee, B., Kovarik, L., Karim, A. M. Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles. J. Vis. Exp. (136), e57667, doi:10.3791/57667 (2018).
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