Surface Structure of Organosulfur\nStabilized Silver\nNanoparticles Studied with X‑ray Absorption Spectroscopy

Abstract

With the recent determination of the unexpected surface\nstructure\nfor thiolate-protected gold nanoparticles (−SR–Au–SR–\nstaple-like motif for Au₁₀₂), it is of great interest to\ndetermine whether or not similar systems such as silver exhibit this\nspecial surface structure. A detailed study of the structure and composition\nof a series of organosulfur-stabilized silver nanoparticles (AgNPs)\nwas carried out using X-ray absorption near-edge (XANES) and extended\nX-ray absorption fine structure (EXAFS) from a multielement (Ag, S)\nand multicore (Ag K- and L-edge) perspective. It was determined that\nAgNPs of varied sizes prepared with dodecanethiol did not exhibit\neither a staple-like surface structure or the traditional metal–thiolate\nstructure (e.g., thiolate on 3-fold hollow site of metal surface),\nand instead adopted a layer of silver sulfide on the surface of metallic\nsilver cores. The amount of the sulfide formed was found to be dependent\non the AgNP size. Moreover, a comparison of the surface structure\nof thiolate-AgNPs with those coated with didodecyl sulfide indicated\nthat the formation of a sulfide layer was inhibited when didodecyl\nsulfide was used achieving a surface structure more akin to the traditional\nthiolate bonding. These results show that AgNPs can be tailored to\nhave different surface structure and bonding depending on the silver/sulfur\nmolar ratio of the starting materials and type of organosulfur ligand\nused and, importantly, that the resulting bonding between silver and\nsulfur is very different from that of gold and sulfur.