利用X射线反射率、扩展X射线吸收精细结构和电子显微镜对钯纳米颗粒进行表征。

Sun Yuan, Frenkel Anatoly I, Isseroff Rebecca, Shonbrun Cheryl, Forman Michelle, Shin Kwanwoo, Koga Tadanori, White Henry, Zhang Lihua, Zhu Yimei, Rafailovich Miriam H, Sokolov Jonathan C

Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York 11794-2275, USA.

Langmuir. 2006 Jan 17;22(2):807-16. doi: 10.1021/la052686k.

We compared the characteristics of dodecanethiolate palladium nanoparticles synthesized by two different techniques, a one-phase method and a two-phase method. From transmission electron microscopy (TEM), we determined that the particle sizes were 46 +/- 10 angstroms and 20 +/- 5 angstroms for the one- and two-phase particles, respectively. Electron diffraction confirmed that their structure was face-centered cubic (fcc). The lattice constant a0 was 3.98 +/- 0.01 angstroms and 3.90 +/- 0.01 angstroms for the one- and two-phase particles, respectively. High-resolution TEM (HRTEM) showed that the one-phase particles had an ordered core surrounded by a disordered shell structure, while the two-phase particles appeared to be crystalline throughout. The particles were also analyzed with extended X-ray absorption fine structure (EXAFS). A cuboctahedral fcc model was used to fit the data, which implied particle sizes of less than 10 angstroms for both the one- and two-phase particles. The discrepancy between the two techniques was attributed to the presence of a disordered phase, which we presumed was composed of Pd-S compounds. Compared with the bulk palladium, lattice expansion was observed in both one- and two-phase particles by electron diffraction, HRTEM, and EXAFS. At the air/water interface, a uniform film that produced surface pressure/area isotherms could only be obtained from the two-phase particles. The one-phase particles did not wet the water surface. X-ray reflectivity data indicated that the Langmuir monolayer of the two-phase particles was only 13 angstroms thick. TEM revealed the diameter of the particles in this layer to be 23 angstroms; hence the particles assumed an oblate structure after spreading. EXAFS examination of a stack of 750 Langmuir monolayers indicated far fewer Pd-S compounds, which may have dissolved in the water. The data were consistent with a model of a monolayer of truncated cuboctahedron Pd particles that were 7 angstroms thick and 19 angstroms in diameter.

我们比较了通过两种不同技术合成的十二硫醇钯纳米颗粒的特性，即单相法和两相法。通过透射电子显微镜（TEM），我们确定单相颗粒和两相颗粒的粒径分别为46±10埃和20±5埃。电子衍射证实它们的结构为面心立方（fcc）。单相颗粒和两相颗粒的晶格常数a0分别为3.98±0.01埃和3.90±0.01埃。高分辨率TEM（HRTEM）显示，单相颗粒具有由无序壳层结构包围的有序核，而两相颗粒似乎整体都是晶体。还使用扩展X射线吸收精细结构（EXAFS）对颗粒进行了分析。使用立方八面体fcc模型拟合数据，这表明单相颗粒和两相颗粒的粒径均小于10埃。两种技术之间的差异归因于无序相的存在，我们推测该无序相由Pd-S化合物组成。通过电子衍射、HRTEM和EXAFS观察到，与块状钯相比，单相颗粒和两相颗粒均出现晶格膨胀。在空气/水界面，只能从两相颗粒获得产生表面压力/面积等温线的均匀薄膜。单相颗粒不会润湿水面。X射线反射率数据表明，两相颗粒的朗缪尔单层仅13埃厚。TEM显示该层中颗粒的直径为23埃；因此，颗粒在铺展后呈现扁球形结构。对750个朗缪尔单层堆叠进行的EXAFS检查表明，Pd-S化合物少得多，这些化合物可能已溶解在水中。数据与厚度为7埃、直径为19埃的截顶立方八面体钯颗粒单层模型一致。