Abstract: This paper reports a method for the preparation of monodispersed gold colloid by seeding growth, with elimination of the nonspherical by-products, which were often observed and difficult to separate in previous works. The formation of nonspherical particles was found to be closely associated with the experimental conditions, such as, molar ratios and addition sequence of the reagents. The larger the [NH2OH]:[HAuCl4] ratio, the less and smaller the nonspherical particles. In addition, the effect of addition sequence can be ascribed to that of [NH2OH]:[HAuCl4] ratio, since different addition sequences make different instantaneous [NH2OH]:[HAuCl4] ratios during the addition and thus lead to different shape distribution of particles. Based on these findings, a method is adopted to rule out the nonspherical particles, by using high ratios of [NH2OH] to [HAuCl4] (the [NH2OH]:[HAuCl4] ratio being kept in the range of 10～30) and favorable addition sequence (NH2OH being added to seeds prior to HAuCl4). No nonspherical nanoparticles can be observed, and the resulted gold colloid shows good monodispersity and excellent size-controllability.

Key words: Seeding growth method, Gold nanoparticles, Nonspherical particles