Formation mechanism of nonspherical gold nanoparticles during seeding growth: Roles of anion adsorption and reduction rate

A small section of nonspherical particles can be observed in the further growth of spherical gold colloids exposed to a mixture of NH2OH and HAuCl4. The concentration ratio of [NH2OH]:[HAuCl4] is critical for the formation of nonspherical particles as higher ratios produce lower yields and smaller of such particles. These concentrations also affect the reaction kinetics; the reaction rate increases with [NH2OH], while independent of [HAuCl4], which we believe is due to the specific adsorption of AuCl−4 onto gold surface. These nonspherical particles come from the preferential growth of {111} facets as indicated by their TEM images and electron diffraction patterns. We propose this preferential growth is ascribed to the preferential adsorption of AuCl−4 on {111} facets, and some competition which determines the yield of nonspherical particles exists between the AuCl−4 adsorption and the AuCl−4 reduction, faster reduction counteracting the effect of this preferential adsorption and thus suppressing nonspherical particle. This result probably provides some guidance to develop a shape-controlled synthesis of gold particles without any additives.

The competition between the adsorption of AuCl4− and the reduction of AuCl4− at the surface of seed particles determine the shape distribution of resulting gold colloids.Figure optionsDownload as PowerPoint slide