Characterization of Palladium Nanoparticles by Using X-ray Reflectivity, EXAFS, and Electron Microscopy

Abstract

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.

Hydrogen-Induced Ostwald Ripening at Room Temperature in a Pd Nanocluster Film

“…The relatively broad reflections can be indexed with the fcc palladium metal structure. The cell parameters of all nonhydrogenated palladium samples are 0.391 nm [16] corresponding to a Pd-Pd first neighbor bond distance of 0.2758 nm, in agreement with the literature range of 0.2751-0.2758 nm [17]. In the last column of Table I the diameter derived from the Debye-Scherrer formula is shown for each diffracting plane.…”

Impact of Protecting Ligands on Surface Structure and Antibacterial Activity of Silver Nanoparticles

“…This type of sulfidation by organosulfur ligands has been previously seen in both dodecanethiol (DDT)-protected Ag NPs 27 and DDT-and octadecanethiol (ODT)-protected Pd NPs prepared in organic solvents. 32 In this context, it is also interesting to note the more recently determined surface structure of thiol-protected Ag 44 28,29 and Ag 62 30 clusters, which exhibit a similar sulfide-like surface around a metallic core. Although the syntheses used to prepare the Ag 44 , Ag 62 , and DDT-Ag NPs were quite different than the synthesis used here, the formation of a similar sulfidized surface in each case may present an interesting trend that may have implications in the synthesis and structural characterization of other thiolprotected Ag nanomaterials.…”

“…Indeed, this technique has been previously used to successfully examine the surface structures of thiolprotected Au, 31 Ag, 27 and Pd NPs. 27,32 As understanding the relationship between the surface and properties of nanomaterials is crucial for both fundamental studies and their applications, we seek to establish that relationship for the type of NPs described herein. We examined the atomic composition and surface structure of Ag NPs prepared with water-soluble, biocompatible cysteine (Cys) and poly(vinylpyrrolidone) (PVP) ligands using XAS, as well as other physical chemistry techniques, in order to first compare the ligand effect on the resulting surface structures.…”

Improved Stability of Pd/Al2O3 Prepared from Palladium Nanoparticles Protected with Carbosilane Dendrons in the Dimethyl Ether Steam Reforming Reaction

“…Pd nanoparticles protected with dodecanethiol were prepared following the procedure described in Ref. [59]. The resulting nanoparticles were solved ring for 30 min, a 1.0 m THF solution of LiBH(C2H5)3 (10 mL; 84 mmol) was added dropwise.…”