Unveiling the Inner Structure of PtPd Nanoparticles

Despite all efforts to explore the structural properties of bimetallic nanoparticles, there is still a constraint of proper tools to successfully probe their composition and atomic arrangement. In this work, bimetallic PtPd nanoparticles with approximately 5 nm mean diameter were synthesized to achieve distinct atomic distributions: nanoalloys or core@shell. The samples were probed by medium energy ion scattering (MEIS) and space-resolved elemental analysis via energy-dispersive X-ray (EDX) spectroscopy in scanning transmission electron microscope (STEM) mode. The complementary association of STEM-EDX profiling with MEIS, which simultaneously surveys millions of nanoparticles, becomes a powerful tool for a statistically representative structural analysis. As a result, the measurements provided key details such as core size, shell thickness, and composition and even distinguished core@shell from core@alloy structures. PtPd nanoalloys and Pd-core structures were successfully obtained, while the attempt to produce Pt-core NPs actually resulted in a mixture of nanoalloy and core@alloy structures (core = Pt or Pd). Moreover, MEIS sensitivity to the NPs’ shell enabled us to quantify its most plausible alloy composition

On the Reactivity of Carbon Supported Pd Nanoparticles during NO Reduction: Unraveling a Metal–Support Redox Interaction

Pd nanoparticles (NPs) were successfully obtained by the reduction of PdCl₂ with l-ascorbic acid, whose morphology was revealed by HRTEM to be a worm-like system, formed by linked crystallite clusters with an average short-axis diameter of 5.42 nm. In situ UV–vis absorption measurements were used to monitor their formation, while XPS and XRD characterization confirmed the NPs’ metallic state. A straightforward way to support the obtained Pd NPs on activated carbon (AC) was used to prepare a catalyst for NO decomposition reaction. The Pd/AC catalysts proved to be highly active in the temperature range of 323 to 673 K, and a redox mechanism is proposed, where the catalyst’s active sites are oxidized by NO and reduced by carbon, emitting CO₂ and enhancing their capacity to absorb and dissociate NO

Atomic Structure of Cr₂O₃/Ag(111) and Pd/Cr₂O₃/Ag(111) Surfaces: A Photoelectron Diffraction Investigation

A detailed investigation concerning the atomic structure of Cr₂O₃ and Pd/Cr₂O₃ ultrathin films deposited on a Ag(111) single crystal is presented. The films were prepared by MBE (molecular beam epitaxy) and characterized <i>in situ</i> by LEED (low energy electron diffraction), XPS (X-ray photoelectron spectroscopy), and XPD (X-ray photoelectron diffraction). Evidences of rotated domains and an oxygen-terminated Cr₂O₃/Ag­(111) surface were observed, along with significant contractions of the oxide’s outermost interlayer distances. The deposition of Pd atoms on the Cr₂O₃ surface formed a four-monolayer film, <i>fcc</i> packed and oriented in the [111] direction, which presented changes in monolayer spacing and lateral atomic distance compared to the expected values for bulk Pd. The observed surface structure may shed light on new physical properties such as the induced magnetic ordering in Pd atoms

Surface Composition/Organization of Ionic Liquids with Au Nanoparticles Revealed by High-Sensitivity Low-Energy Ion Scattering

High-sensitivity low-energy ion scattering (HS-LEIS) analysis was used to elucidate the outermost layer of both functionalized and non-functionalized imidazolium ionic liquids (ILs). The IL outermost layer is composed of all atoms of both cations and anions. The HS-LEIS analyses also allow for quantitative measurement of the thickness of IL overlayers on Au nanoparticles prepared by sputter deposition, which was shown to be a monolayer of ions, as predicted by density functional theory calculations

Pd–M/C (M = Pd, Cu, Pt) Electrocatalysts for Oxygen Reduction Reaction in Alkaline Medium: Correlating the Electronic Structure with Activity

The increasing global needs for clean and renewable energy have fostered the design of new and highly efficient materials for fuel cells applications. In this work, Pd–M (M = Pd, Cu, Pt) and Pt nanoparticles were prepared by a green synthesis method. The carbon-supported nanoparticles were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium. A comprehensive electronic and structural characterization of these materials was achieved using X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Their electrochemical properties were investigated by cyclic voltammetry, while their activities for the ORR were characterized using steady-state polarization experiments. The results revealed that the bimetallic nanoparticles consist of highly crystalline nanoalloys with size around 5 nm, in which the charge transfer involving Pd and M atoms affects the activity of the electrocatalysts. Additionally, the samples with higher ORR activity are those whose d-band center is closer to the Fermi level

Influence of the CeO₂ Support on the Reduction Properties of Cu/CeO₂ and Ni/CeO₂ Nanoparticles

Ceria (CeO₂) is being increasingly used as support of metallic nanoparticles in catalysis due to its unique redox properties. Shedding light into the nature of the strong metal support interaction (SMSI) effect in CeO₂-containing catalysts is important since it has a strong influence on the catalytic properties of the system. In this work, Cu/CeO₂ and Ni/CeO₂ nanoparticles are characterized when submitted to a reduction treatment at 500 °C in H₂ atmosphere with a combination of in situ (XAS – X-ray absorption spectroscopy and time-resolved XAS) and ex situ (TEM – transmission electron microscopy and XPS - X-ray photoelectron spectroscopy) techniques. The existence of a capping layer decorating the Ni/CeO₂ nanoparticles after the reduction treatment is shown, representing evidence for the SMSI effect. The kinetics of the SMSI occurrence is elucidated. It is proposed that the electronic factor of the SMSI effect has a strong influence on the reduction properties of the Ni nanoparticles supported on CeO₂, decreasing its reduction temperature if compared to nonsupported Ni nanoparticles. The same phenomenon is not observed for Cu/CeO₂ nanoparticles, where there is no evidence for the SMSI effect, and no changes on the reduction properties between supported and nonsupported Cu nanoparticles are observed

Multitask Imidazolium Salt Additives for Innovative Poly(l‑lactide) Biomaterials: Morphology Control, Candida spp. Biofilm Inhibition, Human Mesenchymal Stem Cell Biocompatibility, and Skin Tolerance

Candida species have great ability to colonize and form biofilms on medical devices, causing infections in human hosts. In this study, poly­(l-lactide) films with different imidazolium salt (1-<i>n</i>-hexadecyl-3-methylimidazolium chloride (<b>C</b>_<b>16</b><b>MImCl</b>) and 1-<i>n</i>-hexadecyl-3-methylimidazolium methanesulfonate (<b>C</b>_<b>16</b><b>MImMeS</b>)) contents were prepared, using the solvent casting process. Poly­(l-lactide)-imidazolium salt films were obtained with different surface morphologies (spherical and directional), and the presence of the imidazolium salt in the surface was confirmed. These films with different concentrations of the imidazolium salts <b>C</b>_<b>16</b><b>MImCl</b> and <b>C</b>_<b>16</b><b>MImMeS</b> presented antibiofilm activity against isolates of Candida tropicalis, Candida parapsilosis, and Candida albicans. The minor antibiofilm concentration assay enabled one to determine that an increasing imidazolium salt content promoted, in general, an increase in the inhibition percentage of biofilm formation. Scanning electron microscopy micrographs confirmed the effective prevention of biofilm formation on the imidazolium salt containing biomaterials. Lower concentrations of the imidazolium salts showed no cytotoxicity, and the poly­(l-lactide)-imidazolium salt films presented good cell adhesion and proliferation percentages with human mesenchymal stem cells. Furthermore, no acute microscopic lesions were identified in the histopathological evaluation after contact between the films and pig ear skin. In combination with the good morphological, physicochemical, and mechanical properties, these poly­(l-lactide)-based materials with imidazolium salt additives can be considered as promising biomaterials for use in the manufacturing of medical devices