Physical Stability of Novel Au-Ag@SiO2 Alloy Nanoparticles

The present study deals with nanoparticles synthesis of silver-gold alloys and their electrokinetic-spectroscopic characterization. The synthesis consisted in two steps. The first step: synthesis of silver nanoparticles coated of silica using the novel assisted laser ablation method. The second step: Introduction of a [KAuCl4] in the colloidal solution of silver nanoparticles, previously synthesized, in order to obtain the nanoparticles of silver-gold alloy coated with silica. The colour change and their mean diameter size, caused by the introduction of the gold salt, were found dependent on the [KAuCl4] added in solution. The diameter size diminishes at to increasing [KAuCl4] and the monodispersity is more accented for the samples with high [KAuCl4]. The changes in the interparticle interaction potential, as a function of the [KAuCl4] and time, were analysed using the ζ-potential calculated from their electrophoretic mobilities based on the Derjaguin-Laudau-Verwey-Overbeck (DLVO, ) theory. The introduction of a [KAuCl4] provokes the energy barrier increases, suggesting a higher stability, but as the time elapses, it undergoes a slight decrease and spreads to a plateau for all the samples in the same way. The absorbance measurements (Localized Surface Plasmon Resonance (LSPR)) were studied increasing [KAuCl4] and as a function of the time. With increasing [KAuCl4] the absorption bands diminishes and appear a broadband red-shifted. Upon the time, the two bands becomes fused into one and the λmax starts to diminish in a linear fashion for each [KAuCl4]. Thus, our data suggest that the co-reduced solution at long time consists of alloy nanoparticles and not a mixture of Ag@SiO2 and Au nanoparticles. Keywords Silver-gold Nanoparticles, Coreshell Nanoparticles, Synthesis Nanoparticles, Electrokinetic Nanoparticles, Stability of Nanoparticles, SiO2-Capped Nanoparticles