Ultrastable silver nanoparticles

Abstract

Noble-metal nanoparticles have had a substantial impact across a diverse range of fields, including catalysis, sensing, photochemistry, optoelectronics, energy conversion and medicine. Although silver has very desirable physical properties, good relative abundance and low cost, gold nanoparticles have been widely favoured owing to their proved stability and ease of use. Unlike gold, silver is notorious for its susceptibility to oxidation (tarnishing), which has limited the development of important silver-based nanomaterials. Despite two decades of synthetic efforts, silver nanoparticles that are inert or have long-term stability remain unrealized. Here we report a simple synthetic protocol for producing ultrastable silver nanoparticles, yielding a single-sized molecular product in very large quantities with quantitative yield and without the need for size sorting. The stability, purity and yield are substantially better than those for other metal nanoparticles, including gold, owing to an effective stabilization mechanism. The particular size and stoichiometry of the product were found to be insensitive to variations in synthesis parameters. The chemical stability and structural, electronic and optical properties can be understood using first-principles electronic structure theory based on an experimental single-crystal X-ray structure. Although several structures have been determined for protected gold nanoclusters, none has been reported so far for silver nanoparticles. The total structure of a thiolate-protected silver nanocluster reported here uncovers the unique structure of the silver thiolate protecting layer, consisting of Ag2S5 capping structures. The outstanding stability of the nanoparticle is attributed to a closed-shell 18-electron configuration with a large energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, an ultrastable 32-silver-atom excavated-dodecahedral core consisting of a hollow 12-silver-atom icosahedron encapsulated by a 20-silver-atom dodecahedron, and the choice of protective coordinating ligands. The straightforward synthesis of large quantities of pure molecular product promises to make this class of materials widely available for further research and technology development.

[Ag25(SR)18]−: The “Golden” Silver Nanoparticle

“…We found that the [Ag 25 31 , a stability that could not be obtained with other protecting ligands 11,32,12,25 .…”

“…The Ag 25 was also found to exhibit luminescence in the near-infrared region ∼850 nm. Typically, silver clusters are brown to red 11,[26][27][28] and usually are associated with that color, but the color resemblance between Ag 25 cluster and that of large plasmonic Ag nanoparticles may have delayed its discovery. To naked eyes, the purified Ag 25 cluster solution appeared yellow (Figure 1, inset) similar to Au 25 prepared ( Figure S2) using the same thiol.…”

Simple and Efficient Separation of Atomically Precise Noble Metal Clusters

“…[1][2][3] Most of the reports on such clusters are concerned with gold but a few analogues of silver and copper have also appeared in the literature. [4][5][6][7][8][9][10] Molecules such as Au25SR18, [11][12][13] Au38SR24 14 and Au144SR60 15 are some of the most stable species in this family of materials. Catalytic and biological applications of such materials are fast evolving.…”

Perspective: Exchange reactions in thiolate-protected metal clusters

“…[1][2][3][4][5][6][7][8][9][10] The geometric structures of such precise metal clusters can be determined via single-crystal X-ray structural analysis. Therefore, our knowledge of the geometry of metal clusters protected by organic ligands is currently improving rapidly.…”