Ammonia-free preparation of Ag@SiO₂ core/shell nanoparticles

Highlights: • Ammonia catalyzed silica coating of Ag nanoparticles suffered from Ag etching. • An ammonia-free approach was developed for Ag@SiO₂ nanocomposites preparation. • NaOH was used as the base to catalyze the TOES polycondensation. • Control the pH during silica formation was critical to ensure Ag@SiO₂ synthesis. - Abstract: An ammonia-free approach for the preparation of silver@silica core/shell nanocomposites is reported in order to avoid the silver core etching during the preparation in a typical Stöber approach. Silver nanoparticles were used as the core and tetraethoxy orthosilicate (TEOS) was used the silica source. The silica layer formation process was investigated under alkaline conditions. Several bases were selected as the alkaline source and it was found that careful control of the solution pH below 10 during the silica layer formation is critical to ensure stable and aggregation free core–shell nanocomposites preparation as confirmed by UV–Vis spectroscopy and transmission electron microscopy