With the recent determination of the unexpected surface structure for thiolate-protected gold nanoparticles (−SR–Au–SR– staple-like motif for Au102), it is of great interest to determine whether or ...not similar systems such as silver exhibit this special surface structure. A detailed study of the structure and composition of a series of organosulfur-stabilized silver nanoparticles (AgNPs) was carried out using X-ray absorption near-edge (XANES) and extended X-ray absorption fine structure (EXAFS) from a multielement (Ag, S) and multicore (Ag K- and L-edge) perspective. It was determined that AgNPs of varied sizes prepared with dodecanethiol did not exhibit either a staple-like surface structure or the traditional metal–thiolate structure (e.g., thiolate on 3-fold hollow site of metal surface), and instead adopted a layer of silver sulfide on the surface of metallic silver cores. The amount of the sulfide formed was found to be dependent on the AgNP size. Moreover, a comparison of the surface structure of thiolate-AgNPs with those coated with didodecyl sulfide indicated that the formation of a sulfide layer was inhibited when didodecyl sulfide was used achieving a surface structure more akin to the traditional thiolate bonding. These results show that AgNPs can be tailored to have different surface structure and bonding depending on the silver/sulfur molar ratio of the starting materials and type of organosulfur ligand used and, importantly, that the resulting bonding between silver and sulfur is very different from that of gold and sulfur.
The preparation and characterization of all-thiol-protected noble-metal nanoclusters represent significant advancements in the field of nanomaterials. One of the emerging trends in the study of ...silver nanoclusters in particular, is the generation of sulfide-type silver at their surfaces as a result of surface protection by thiols. Here, X-ray absorption spectroscopy (XAS) was used to identify the structure and composition of 2 nm tiopronin-protected silver nanoclusters arranged in one-dimensional chains. Silver K-edge XAS multipath refinements and wavelet-transformed XAS analysis found that the nanoclusters comprised small metal cores surrounded by thick sulfide-type shells. This further demonstrates that the sulfide-type shell is a prevalent surface structure throughout silver nanoclusters protected by thiols. In addition, the antibacterial activities of the nanoclusters were also examined; they were found to be active against both Gram-positive and Gram-negative bacteria, thereby shedding light on the effects of both the surface structure and the special arrangement of the nanoclusters.
PDF