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Mysterious Naked Gold Clusters: How to Uncover Their Structural Mysteries in a Vacuum?
In the field of nanotechnology, gold clusters have attracted widespread research interest due to their unique physical and chemical properties. Gold clusters can be found not only as discrete molecules but also as larger colloidal particles, both less than one micron in diameter. The structure and properties of these nanoclusters are largely related to the chemical environment they live in, meaning exploring the structure of bare gold clusters will open new doors for many applications.
Characteristics and structure of bare gold clusters
Bare gold clusters, that is, gold clusters without stabilizer shells, can be synthesized and studied in vacuum using molecular beam technology. The structure of these gold clusters has been studied experimentally by various methods, such as anion photoelectron spectroscopy and far-infrared spectroscopy. These studies show that the structure of bare gold clusters is very different from that of ligand-stabilized gold clusters, highlighting the decisive influence of the chemical environment on the structure of gold clusters.
For example, Au20 forms a perfect tetrahedron, with its gold atoms stacked in a manner very similar to the face-centered cubic (fcc) structure of metallic gold.
Structure of ligand-stabilized gold clusters
Because gold's bulk material exhibits a face-centered cubic (fcc) structure, when the size of the gold particles is reduced, this structure transforms into a central octahedral structure, as shown by Au13. This form of change allows the gold clusters to further extend their structure and form more complex lattice forms. Ligand-stabilized gold cluster structures can be divided into various forms and can be connected and fused to each other through different input clusters.
Au13 in its basic form becomes the basis of large gold nanoclusters, and each additional gold atom forms a new gold cluster.
Discrete gold clusters and colloidal gold clusters
In the study of gold clusters, discrete gold clusters are usually regarded as intrinsic molecular forms, and these forms generally contain organic ligands on the outside. Some special gold clusters such as [Au6C(P(C6H5)3)6]2+ and [Au9(P(C6H5)3)8]3+ are considered to be gold clusters with well-defined interfaces. When bare gold clusters are needed for catalytic applications, these ligands need to be removed, which usually requires high-temperature removal, but can also be accomplished chemically at low temperatures.
A calcination process of up to 200°C or higher can effectively strip off ligands, resulting in bare gold clusters.
Catalytic applications
The catalytic properties of bare gold clusters have attracted widespread attention in the scientific community. Studies have found that when gold clusters are implanted on the surface of FeOOH, they can effectively catalyze the oxidation reaction of CO. Similarly, gold clusters on the TiO2 surface can also perform catalytic reactions at extremely low temperatures. This indicates a close correlation between the structural properties of gold clusters and their catalytic activity.
The catalytic activity of gold nanoclusters is closely related to their structure and size, which prompts us to the necessity of in-depth research on them.
Future prospects of gold nanoclusters
With the development of nanomaterials technology, the application range of gold clusters has become more and more extensive. From optoelectronics to catalysis and even in biomedical applications, gold nanoclusters show great potential. The phenomenon of surface plasmon resonance (SPR) in metal nanoparticles gives these particles special advantages in developing optical devices. Future research may focus on how to further tailor the structure of gold clusters to meet specific application needs.
All this raises a question: In future scientific exploration, can we explore more potential applications of gold clusters to promote the progress and development of science and technology?
