The Fourth Alloying Mode by Way of Anti‐Galvanic Reaction

Anti‐galvanic reaction (AGR) not only defies classic galvanic theory but is a promising method for tuning the compositions, structures, and properties of noble‐metal nanoparticles. Employing AGR for the preparation of alloy nanoparticles has recently received great interest. Herein, we report an unprecedented alloying mode by way of AGR, in which foreign atoms induce structural transformation of the mother nanoparticles and enter the nanoparticles in a non‐replacement fashion. A novel, active‐metal‐doped, gold nanoparticle was synthesized by this alloying mode, and its structure resolved. A CdSH motif was found in the protecting staples of the bimetal nanoparticle. DFT calculations revealed that the Au₂₀Cd₄(SH)(SR)₁₉ nanoparticle is a 8e superatom cluster. Furthermore, although the Cd‐doping does not essentially alter the absorption spectrum of the mother nanocluster, it distinctly enhances the stability and catalytic selectivity of the mother nanoclusters.     

Au130−xAgx Nanoclusters with Non‐Metallicity: A Drum of Silver‐Rich Sites Enclosed in a Marks‐Decahedral Cage of Gold‐Rich Sites

The synthesis and structure of atomically precise Au_130?xAg_x (average x=98) alloy nanoclusters protected by 55 ligands of 4‐tert‐butylbenzenethiolate are reported. This large alloy structure has a decahedral M₅₄ (M=Au/Ag) core. The Au atoms are localized in the truncated Marks decahedron. In the core, a drum of Ag‐rich sites is found, which is enclosed by a Marks decahedral cage of Au‐rich sites. The surface is exclusively Ag?SR; X‐ray absorption fine structure analysis supports the absence of Au?S bonds. The optical absorption spectrum shows a strong peak at 523 nm, seemingly a plasmon peak, but fs spectroscopic analysis indicates its non‐plasmon nature. The non‐metallicity of the Au_130?xAg_x nanocluster has set up a benchmark to study the transition to metallic state in the size evolution of bimetallic nanoclusters. The localized Au/Ag binary architecture in such a large alloy nanocluster provides atomic‐level insights into the Au?Ag bonds in bimetallic nanoclusters.     

Activation and Deactivation of Gold/Ceria–Zirconia in the Low‐Temperature Water–Gas Shift Reaction

Gold (Au) on ceria–zirconia is one of the most active catalysts for the low‐temperature water–gas shift reaction (LTS), a key stage of upgrading H₂ reformate streams for fuel cells. However, this catalyst rapidly deactivates on‐stream and the deactivation mechanism remains unclear. Using stop–start scanning transmission electron microscopy to follow the exact same area of the sample at different stages of the LTS reaction, as well as complementary X‐ray photoelectron spectroscopy, we observed the activation and deactivation of the catalyst at various stages. During the heating of the catalyst to reaction temperature, we observed the formation of small Au nanoparticles (NPs; 1–2 nm) from subnanometer Au species. These NPs were then seen to agglomerate further over 48 h on‐stream, and most rapidly in the first 5 h when the highest rate of deactivation was observed. These findings suggest that the primary deactivation process consists of the loss of active sites through the agglomeration and possible dewetting of Au NPs.     

Carbon Monoxide Oxidation by Polyoxometalate‐Supported Gold Nanoparticulate Catalysts: Activity,Stability, and Temperature‐ Dependent Activation Properties

Nanoparticulate gold supported on a Keggin‐type polyoxometalate (POM), Cs₄[α‐SiW₁₂O₄₀]⋅n H₂O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was −67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U‐shaped curve. It was revealed by IR measurement that Au^δ+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas‐phase reactions.     

Gold Nanorod/Fe3O4 Nanoparticle “Nano‐Pearl‐Necklaces” for Simultaneous Targeting,Dual‐Mode Imaging,and Photothermal Ablation of Cancer Cells

Perlen auf Gold : Neuartige multifunktionelle Nanopartikel bestehen aus einzelnen Amin‐modifizierten Goldnanostäbchen, an denen Fe₃O₄‐„Perlen“ mit Carboxyendgruppe angebracht sind. Die Partikel eignen sich zur simultanen Erkennung, dualen Bildgebung und photothermischen Ablation von Brustkrebszellen.

     

Polyoxometalate‐Engineered Building Blocks with Gold Cores for the Self‐Assembly of Responsive Water‐Soluble Nanostructures

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle‐like organizations. Using cryo‐TEM imaging and ¹H DOSY NMR spectroscopy, we then provide an unprecedented “solution‐state” picture of how the micelle‐like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water‐soluble assemblies.