Adsorbate−Induced Diffusion of Ag and Au Atoms Out of the Cores of Ag@Au, Au@Ag, and Ag@AgI Core−Shell Nanoparticles

Abstract

Au@Ag and Ag@Au core−shell nanoparticles were synthesized using sequential laser ablation of metal targets in water. The resulting core−shell particles were then exposed to iodine or 1,6−hexanedithiol. For the Ag@Au + I2 → Au@AgI and Au@Ag + dithiol → Ag@Au−dithiol reactions, inversion of the core−shell structures resulted. These findings demonstrate that adsorbates can influence the core atoms through an intervening shell, and it is possible to use core−shell systems as vehicles for delivering reactivity on demand. Changing the shell material affords an opportunity to vary core susceptibility. Au@AgI nanoparticles, for example, did not react with 1,6−hexanedithiol. These results are most consistent with a charge−transfer-induced diffusion mechanism, analogous to the Cabrera−Mott model used for oxidation reactions of surfaces. The rate of uptake of iodine by Ag nanoparticles, measured with a quartz crystal microbalance, displayed kinetics that could be modeled using the same charge−transfer model.