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RESEARCH PRODUCT

Synthesis and Physical Stability of Novel Au-Ag@SiO<SUB>2</SUB> Alloy Nanoparticles

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The present study describes the synthesis of nanoparticles of silver-gold alloys and with their electrokinetic and spectroscopic characterisation. The synthesis was made in two steps. In the first step silver nanoparticles coated with silica (Ag@SiO2) were synthesised using a novel method assisted by laser ablation. The second step consisted on the introduction of KAuCl4 in the colloidal solution of Ag@ SiO2 nanoparticles in order to obtain silica-coated silver-gold alloy nanoparticles. The changes of colour and mean diameter of Ag@SiO2 nanoparticles caused by the introduction of the gold salt were found dependent on its concentration. Upon increasing (KAuCl4) the diameter of nanoparticles diminished and the monodispersity increased. The changes in the interparticle interaction potential as a function of (KAuCl4) and time were analysed using ζ-potential values, calculated from their electrophoretic mobilities on the bases of Derjaguin-Laudau-Verwey-Overbeck (DLVO, UT DLVO ) theory. The introduction of KAuCl4 produced a higher stability of the colloid and suggests an increase of the interaction energy barrier. However, as time after synthesis increases the barrier slightly decreases and stabilises at a plateau value. The absorbance measurements (Localised Surface Plasmon Resonance, LSPR) were studied as a function of (KAuCl4) and time. With increasing (KAuCl4) the main absorption band diminishes and red-shifts and a new broad band appears. For each value of (KAuCl4), upon increasing time, the two characteristic bands fuse into one and λmax diminishes in a linear fashion. Altogether, these data suggest that the co-reduced solutions of Ag⁻ and Au³⁻ salts at long time consists of alloy Ag-Au nanoparticles, and not a mixture of Ag and Au nanoparticles.