Phase Transfer Identification of Core–Shell Structures in Ag–Au Bimetallic Nanoparticles

The difference between the transfer of poly(vinylpyrrolidone)-protected Au and Ag nanoparticles from an aqueous solution to toluene was used to develop a simple experimental procedure that can positively identify the formation of bimetallic Ag–Au nanoparticles with the core–shell structure. The method was validated by UV–visible spectroscopy, EDX, and TEM measurements. Using this technique, we have found that core–shell nanoparticles of Ag–Au were formed by the seed-mediated growth method using Ag nanoparticles as the seeds. The reversed order of using Au nanoparticles as the seeds, on the contrary, could only produce a physical mixture of Ag–Au core–shell nanoparticles and isolated Ag nanoparticles.