Gold Nanoparticle Assemblies on Surfaces: Reactivity Tuning through Capping-Layer and Cross-Linker Design

Covalently Conjugated Gold-Porphyrin Nanostructures

Gold nanoparticles show important electronic and optical properties, owing to their size, shape, and electronic structures. Indeed, gold nanoparticles containing no more than 30–40 atoms are only luminescent, while nanometer-sized gold nanoparticles only show surface plasmon resonance. Therefore, it appears that gold nanoparticles can alternatively be luminescent or plasmonic and this represents a severe restriction for their use as optical material. The aim of our study was the fabrication of nanoscale assembly of Au nanoparticles with bi-functional porphyrin molecules that work as bridges between different gold nanoparticles. This functional architecture not only exhibits a strong surface plasmon, due to the Au nanoparticles, but also a strong luminescence signal due to porphyrin molecules, thus, behaving as an artificial organized plasmonic and fluorescent network. Mutual Au nanoparticles–porphyrin interactions tune the Au network size whose dimension can easily be read out, being the position of the surface plasmon resonance strongly indicative of this size. The present system can be used for all the applications requiring plasmonic and luminescent emitters.

Metallic Nanocrystal Ripening on Inorganic Surfaces

In this paper, we demonstrate the formation of hybrid nanostructures consisting of two distinctive components mainly in a one-to-one ratio. Thermolysis of inorganic nanotubes (INT) and closed-cage, inorganic fullerene-like (IF) nanoparticles decorated with a dense coating of metallic nanoparticles (M = Au, Ag, Pd) results in migration of relatively small NPs or surface-enhanced diffusion of atoms or clusters, generating larger particles (ripening). AuNP growth on the surface of INTs has been captured in real time using in situ electron microscopy measurements. Reaction of the AuNP-decorated INTs with an alkylthiol results in a chemically induced NP fusion process at room temperature. The NPs do not dissociate from the surfaces of the INTs and IFs, but for proximate IFs we observed fusion between AuNPs originating from different IFs.

Enhanced Electrocatalytic Activity of Ethanol Oxidation Reaction on Palladium-Silver Nanoparticles via Removable Surface Ligands

This work developed a facile colloidal route to synthesize BH₄^--capped Pd_xAg_y nanoparticles (NPs) in water using the reducing ionic liquids of [C_nmim]BH₄, and the resulting NPs were prone to form the nanocomposites with [amim]⁺-modified reduced graphene (RG). The removal of the metal-free inorganic ions of BH₄^- can create the profoundly exposed interfaces on the Pd_xAg_y NPs during the electrooxidation, and favor the ethanol oxidation reaction (EOR) in lowering energy barrier. The counterions of [C_nmim]⁺ can gather ethanol, OH^- ions, and the reaction intermediates on catalysts, and synergistically interact with RG to facilitate the charge transfer in nanocomposites. The interface-modified RG nanosheets can effectively segregate the Pd_xAg_y NPs from aggregation during the EOR. Along with the small size of 4.7 nm, the high alloying degree of 60.2%, the large electrochemical active surface area of 64.1 m² g^-1, and the great peak current density of 1501 mA cm^-2 mg^-1, Pd₁Ag₂@[C₂mim]BH₄-amimRG nanocomposite exhibits the low oxidation potentials, strong poison resistance, and stable catalytic activity for EOR in alkaline media, and hence can be employed as a promising anodic catalyst in ethanol fuel cells.

Nanocrystallinity and direct cross-linkage as key-factors for the assembly of gold nanoparticle-superlattices

We report here how the crystallinity of AuNPs and the choice of binding sites of molecular cross-linkers control their aggregation. The combination of different binding moieties (N-oxides, ArF-I) and the reactivity of the particles' facets allow control over the organization and crystallinity of the AuNP assemblies.