Preparation and Characterization of Ag Nanoshell on SiO2 Spheres via Electroless Plating Technique in Acidic Conditions

Nanoshells composed of close-packed silver nanocrystals have been fabricated on silica spheres by electroless plating technique. By controlling the solution´s pH in acidic condition during the synthesis of SiO₂-Ag core-shell particles, the homogeneous deposition resulted in thin and uniform silver shells. The deposition process was carried out in two steps: the first step was the modification of silica surface with the adsorption of 3-(2-Aminoethylamino) propyltrimethoxysilane (APTS), and the second step was the deposition of silver by reacting AgNO₃, dextrose and acetic acid. The reaction was performed at high temperature to accelerate the deposition process. The resulting silica-silver core-shell colloids were characterized with XRD, high-resolution TEM and SEM, and UV-visible spectroscopy. It was found that the core-shell structures, such as shell thickness and shell continuity, influenced significantly the absorption spectra. Moreover, the thin shell at about 3nm was very sensitive to the temperature, and the core-shell structure collapsed after 200 C treatment for 30 minutes probably due to the coalescence between adjacent Ag particles. When heating temperature was over than 300 C the Ag particles began to move and leave the SiO₂ surface, causing the corlour of particles to fade gradually