Formation of Nanoclusters in Gold Nucleation

Abstract

Gold nanoclusters consisting of a specific atom number have gained popularity in research in recent years due to their outstanding properties. Due to their molecule-like behavior, their properties depend strongly on their size. Although they represent the link species between atoms and nanoparticles and are the subject of current research, a high-resolution characterization is still missing. Here, we used the band forming experiment in analytical ultracentrifugation (AUC) to characterize the gold nanoclusters in the moment of their generation using thioglycerol as a stabilizer. The concentration variation of the gold precursor, reducing agent, and stabilizer was investigated. The formation of different cluster species from the smallest Au4 up to Au911 could be observed. Very stable clusters of Au55 appear in every experiment and other cluster sizes more rarely. The extracted UV/Vis spectra could additionally be correlated to every cluster. The variation in the concentration of sodium borohydride and the stabilizer did not lead to a clear trend, but the gold ion concentration directed the size of the formed clusters. A decrease seemed to promote the generation of a higher abundance of smaller clusters accompanied by less big clusters, and vice versa. These results present the characterization of the different nanocluster generations directly in the formation process of nanoparticles and therefore are a contribution to the understanding of their formation.

[μ-1,2-Bis(dipheylphosphino)ethane-κ2P,P’]bis(3-mercapto-1,2-propanediolato-κS-gold(I))

“…H 3 tg is highly water soluble and has low volatility compared to other low-molecular-weight thiols, so it has been utilized as a reducing agent for S-S bonds in biomolecules [1] or a potential drug [2]. H 3 tg is also available as a protecting reagent for the aqueous synthesis of metal or metal chalcogenide nanoclusters, e.g., CdS [3], CdSe [4,5], CdTe [6], ZnO [7], ZnS [8], HgTe [9], TiO 2 [10], Bi 2 O 3 [11], and Au [12][13][14][15]. In coordination chemistry, the reactivity of H 3 tg toward most transition metal ions was investigated based on spectroscopic characterization [16][17][18], but the accurate coordination mode of H 3 tg was uncertain until the late 20th century because of the lack of single-crystal X-ray diffraction analysis.…”

Mechanism of Nucleation of Gold(I) Thiolate Oligomers into Gold–Thiolate Nanoclusters

“…As a new class of nanoscale functional materials, metal clusters have received great theoretical and experimental research attentions. − Nucleation is an important process that controls the morphology and size of metal nanoclusters, which further affect their electrical, optical, structural, magnetic, and catalytic properties. − So far, the nucleation and size growth of nanoparticles are largely understood from the theoretical model based on macroscopic thermodynamics such as the LaMer-Brust nucleation process, , Ostwald ripening theory, Finke-Watzky two-step nucleation mechanism, coalescence and orientated attachment mechanism of nanoparticles, , and so forth. Although these classic theoretical models have been used to understand the thermodynamic process of nucleation and size growth of nanoparticles or nanoclusters, the atomic details of the cluster growth and size transformation are not clarified …”

Analysis of Magic-Size Clusters in Crude Reaction Mixtures Using Multiwavelength Analytical Ultracentrifugation

“…The high resolution in the sedimentation experiment was achieved by layering the analyte over the solvent from a reservoir at the start of the centrifugation process. This technique was also employed to analyze the nucleation and growth of silver and gold particles in situ by initiating the reaction when the content of the reservoir was added to the sample cell. − These experiments were able to separate metal clusters down to a few atoms per particle.…”