The fate of silver ions in the photochemical synthesis of gold nanorods: an Extended X-ray Absorption Fine Structure Analysis

Water-soluble gold nanorods (Au NRs) were synthesized using a silver-ion mediated photochemical route under UV irradiation. Extended X-ray Absorption Fine Structure (EXAFS) measurements on the Ag K-edge were performed on samples obtained at different Ag/Au ratios and at increasing irradiation times in order to investigate the fate of silver ions during the growth of Au NRs. EXAFS measurements allowed to probe the chemical state and the local environment of silver in the final product. Experimental data suggest that Ag atoms are placed on top of the Au particles as metallic Ag(0), while no significant contribution to the EXAFS spectra comes from AgBr or other Ag⁺ based species. The reported results strongly support the deposition of Ag(0) islands on the (110) surfaces of the Au particles, thus driving the anisotropic growth via the (111) surfaces.