Size Effect of Atomic Gold Clusters for Carbon Monoxide Passivation at Ru_core–Pt_shell Nanocatalysts

The surface of Pt_shell–Ru_core nanocatalysts was modified with an atomic-scaled Au cluster of different sizes by a polyol reduction technique using sequence and composition control. Our results, combining the structure, surface chemical analysis, and density functional theory calculation, elucidate that these clusters reduced the oxidation current of carbon monoxide to a maximum extent of ∼53%; consequently, the anti-CO poisoning factor of the NCs was doubled by increasing the Au/Pt ratios from 0 to 15 at%. Such substantial improvement is caused by steric shielding and the electron localization field that reject the sorption of electronegative ligands/molecules at the NC surface by Au clusters. Most importantly, this work clarifies the mechanistic insights of the charge relocation at core–shell nanoparticles by subnanoscaled cluster intercalation and the impacts of cluster size for the chemical durability of catalysts in fuel cell applications

Tracing the Surfactant-Mediated Nucleation, Growth, and Superpacking of Gold Supercrystals Using Time and Spatially Resolved X‑ray Scattering

The nucleation and growth process of gold supercrystals in a surfactant diffusion approach is followed by simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS), supplemented with scanning electron microscopy. The results indicate that supercrystal nucleation can be activated efficiently upon placing a concentrated surfactant solution of a nematic phase on top of a gold nanocrystal solution droplet trapped in the middle of a vertically oriented capillary tube. Supercrystal nuclei comprised of tens of gold nanocubes are observed nearly instantaneously in the broadened liquid–liquid interface zone of a steep gradient of surfactant concentration, revealing a diffusion-kinetics-controlled nucleation process. Once formed, the nuclei can sediment into the naoncrystal zone below, and grow efficiently into cubic or tetragonal supercrystals of ∼1 μm size within ∼100 min. Supercrystals matured during sedimentation in the capillary can accumulate and face-to-face align at the bottom liquid–air interface of the nanocrystal droplet. This is followed by superpacking of the supercrystals into highly oriented hierarchical sheets, with a huge number of gold nanocubes aligned for largely coherent crystallographic orientations

X‑ray Reflectivity Studies on the Mixed Langmuir–Blodgett Monolayers of Thiol-Capped Gold Nanoparticles, Dipalmitoylphosphatidylcholine, and Sodium Dodecyl Sulfate

Langmuir–Blodgett monolayers of thiolated gold nanoparticles mixed with dipalmitoylphosphatidylcholine/sodium dodecyl sulfate (DPPC/SDS) were investigated by combining the X-ray reflectivity, grazing-incident scattering, and TEM analyses to reveal the in-depth and in-plane organization and the 2D morphology of such mixed monolayers. It was found that the addition of a charged single-tail surfactant to the thiolated Au nanoparticle monolayer helps to stabilize the Au nanoparticle monolayer and to strengthen the mechanical property of the mixed monolayer film. For mixing with lipids, it was found that the thiolated gold nanoparticles could be pushed on top of the lipid monolayer when the mixed monolayer is compressed. At a typical comparable total surface area ratio of gold nanoparticle to lipid, the thiolated gold nanoparticles could form a uniform domain on top of the DPPC monolayer. When there are more thiolated gold nanoparticles than that could be supported by the lipid monolayer, domain overlapping could occur to form bilayer gold nanoparticle domains at some regions. At low total surface area ratio of thiolated gold nanoparticle to lipid, the thiolated gold nanoparticles tend to form a connected threadlike aggregation structure. Evidently, the morphology of the thiolated gold nanoparticle monolayer is highly depending on the total surface area ratio of the thiolated gold nanoparticle to lipid. SDS is found to have a dispersion power capable of dispersing the originally uniform Au-8C nanoparticle domain of the mixed Au-8C/DPPC monolayer into a foamlike structure for the mixed Au-8C/SDS/DPPC monolayer. It is evident that not only the concentration ratio but also the size and shape of the template formed by the amphiphilic molecules and their interaction with the thiolated gold nanoparticles can all have great effects on the organizational structure as well as morphology of the thiolated gold nanoparticle monolayer

Fabrication of Bimetallic Au–Pd–Au Nanobricks as an Archetype of Robust Nanoplasmonic Sensors

Conventional gas sensors work upon changes in mechanical or conductive properties of sensing materials during a chemical process, which may limit availabilities of size miniaturization and design simplification. However, fabrication of miniaturized sensors with superior sensitivities in real-time and label-free probing of chemical reactions or catalytic processes remains highly challenging, in particular with regard to integration of materials into a desired smaller volume without losing the recyclability of sensing properties. Here, we demonstrate a unique bimetallic nanostructure, the Au–Pd–Au core–shell–frame nanobrick, as a promising archetype for fabrication of miniaturized sensors at nanoscale. Upon analysis of the aqueous synthesis, both ex situ and in situ, the formation of Au frames is consistent with selective deposition and aggregation of NaBH₄-reduced Au nanoparticles at the corners and edges of cubic Pd shells, where the {100} surfaces, capped by iodide ions, are growth-limited. By virtue of the thin Pd shell (∼3.5 nm) sandwiched in-between the two Au layers of the core and the frame, the Au–Pd–Au nanobrick yields excellent optical sensitivity in hydrogen gas sensing, leading to a large 13 nm spectral shift of light scattering between Pd and PdH_<i>x</i>. The composite nanostructure with a size of ∼60 nm offers an archetype for miniaturized sensors possessing label-free, real-time, and high-resolution probing abilities and hence paves the way for fabrication of highly efficient nanosensors via sustainable methods