Department of Chemistry and Biochemistry, ‡Texas Materials Institute, §Institute for Computational and Engineering Sciences, The University of Texas at Austin , 1 University Station, 105 East 24th Street Stop A5300 Austin, Texas 78712, United States.
ACS Nano. 2013 Oct 22;7(10):9345-53. doi: 10.1021/nn4040348. Epub 2013 Oct 2.
Bimetallic PdPt dendrimer-encapsulated nanoparticles (DENs) having sizes of about 2 nm were synthesized by a homogeneous route that involved (1) formation of a Pd core, (2) deposition of a Cu shell onto the Pd core in the presence of H2 gas, and (3) galvanic exchange of Pt for the Cu shell. Under these conditions, a Pd@Pt core@shell DEN is anticipated, but detailed characterization by in-situ extended X-ray absorption fine structure (EXAFS) spectroscopy and other analytical methods indicate that the metals invert to yield a Pt-rich core with primarily Pd in the shell. The experimental findings correlate well with density functional theoretical (DFT) calculations. Theory suggests that the increased disorder associated with <~2 nm diameter nanoparticles, along with the relatively large number of edge and corner sites, drives the structural rearrangement. This type of rearrangement is not observed on larger nanoparticles or in bulk metals.
通过一种均相途径合成了尺寸约为 2nm 的双金属 PdPt 树状大分子包裹的纳米粒子（DENs），该途径包括：（1）形成 Pd 核，（2）在 H2 气体存在下在 Pd 核上沉积 Cu 壳，以及（3）Pt 对 Cu 壳的电置换。在这些条件下，预计会得到 Pd@Pt 核壳 DEN，但通过原位扩展 X 射线吸收精细结构（EXAFS）光谱和其他分析方法的详细表征表明，金属会反转，从而生成富含 Pt 的核，壳中主要为 Pd。实验结果与密度泛函理论（DFT）计算很好地相关。理论表明，与<~2nm 直径的纳米粒子相关的增加的无序以及相对较多的边缘和角位点，促使结构重新排列。这种类型的重新排列在较大的纳米粒子或体金属中观察不到。
