Chen Ching-Hsiang, Sarma Loka Subramanyam, Chen Jium-Ming, Shih Shou-Chu, Wang Guo-Rung, Liu Din-Goa, Tang Mau-Tsu, Lee Jyh-Fu, Hwang Bing-Joe
Nanoelectrochemistry Laboratory, Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan.
ACS Nano. 2007 Sep;1(2):114-25. doi: 10.1021/nn700021x.
In this study, we demonstrate the unique application of X-ray absorption spectroscopy (XAS) as a fundamental characterization tool to help in designing and controlling the architecture of Pd-Au bimetallic nanoparticles within a water-in-oil microemulsion system of water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane. Structural insights obtained from the in situ XAS measurements recorded at each step during the formation process revealed that Pd-Au bimetallic clusters with various Pd-Au atomic stackings are formed by properly performing hydrazine reduction and redox transmetalation reactions sequentially within water-in-oil microemulsions. A structural model is provided to explain reasonably each reaction step and to give detailed insight into the nucleation and growth mechanism of Pd-Au bimetallic clusters. The combination of in situ XAS analysis at both the Pd K-edge and the Au L(III)-edge and UV-vis absorption spectral features confirms that the formation of Pd-Au bimetallic clusters follows a (Pd(nuclei)-Au(stack))-Pd(surf) stacking. This result further implies that the thickness of Au(stack) and Pd(surf) layers may be modulated by varying the dosage of the Au precursor and hydrazine, respectively. In addition, a bimetallic (Pd-Au)(alloy) nanocluster with a (Pd(nuclei)-Au(stack))-(Pd-Au(alloy))(surf) stacking was also designed and synthesized in order to check the feasibility of Pd(surf) layer modification. The result reveals that the Pd(surf) layer of the stacked (Pd(nuclei)-Au)(stack) bimetallic clusters can be successfully modified to form a (Au-Pd alloy)(surf) layer by a co-reduction of Pd and Au ions by hydrazine. Further, we demonstrate the alloying extent or atomic distribution of Pd and Au in Pd-Au bimetallic nanoparticles from the derived XAS structural parameters. The complete XAS-based methodology, demonstrated here on the Pd-Au bimetallic system, can easily be extended to design and control the alloying extent or atomic distribution, atomic stacking, and electronic structure to construct many other types of bimetallic systems for interesting applications.
在本研究中，我们展示了X射线吸收光谱（XAS）作为一种基础表征工具的独特应用，以助力设计和控制水/双（2-乙基己基）磺基琥珀酸钠（AOT）/正庚烷的油包水微乳液体系中钯金双金属纳米颗粒的结构。在形成过程的每个步骤记录的原位XAS测量所获得的结构见解表明，通过在油包水微乳液中依次正确进行肼还原和氧化还原金属转移反应，形成了具有各种钯金原子堆积的钯金双金属簇。提供了一个结构模型来合理地解释每个反应步骤，并深入了解钯金双金属簇的成核和生长机制。在钯K边和金L（III）边进行的原位XAS分析与紫外可见吸收光谱特征相结合，证实了钯金双金属簇的形成遵循（Pd（核）-Au（堆积））-Pd（表面）堆积。这一结果进一步表明，Au（堆积）层和Pd（表面）层的厚度可分别通过改变金前驱体和肼的用量来调节。此外，还设计并合成了具有（Pd（核）-Au（堆积））-（Pd-Au（合金））（表面）堆积的双金属（Pd-Au）（合金）纳米簇，以检验Pd（表面）层改性的可行性。结果表明，通过肼对钯离子和金离子的共还原，堆叠的（Pd（核）-Au）（堆积）双金属簇的Pd（表面）层可以成功改性，形成（Au-Pd合金）（表面）层。此外，我们从推导的XAS结构参数中展示了钯金双金属纳米颗粒中钯和金的合金化程度或原子分布。本文在钯金双金属体系上展示的完整的基于XAS的方法，可以很容易地扩展到设计和控制合金化程度或原子分布、原子堆积和电子结构，以构建许多其他类型的双金属体系用于有趣的应用。
