Synthesis and Color Durability of Silver Nanoparticles Immobilized on Silica Particles

This paper presents the syntheses of SiO₂ particles immobilized with Ag nanoparticles and their composite with Au. Ag nanoparticles are present on the surfaces of the SiO₂ particles, and Ag⁺ ions are galvanically replaced with Au³⁺ ions. Finally, a method for maintaining the color durability and dispersibility of the Ag nanoparticles is demonstrated. The particles are primarily synthesized in three steps: In the first step, Sn²⁺ ions are adsorbed on the surfaces of the SiO₂ particles; in the second step, Ag⁺ ions are added, which are reduced and simultaneously adsorbed on the surface while Sn²⁺ is oxidized to Sn⁴⁺; in the third step, Au³⁺ ions are reduced by galvanic replacement and deposited on the Ag surface. Extensive characterization using transmission electron microscopy, scanning transmission electron microscopy, ultraviolet-visible spectroscopy, and X-ray photoelectron spectroscopy reveals that the Ag–Au composite nanoparticles (17.2 ± 4.1 nm) are immobilized on the surface of the SiO₂ particles (<1 µm). The morphology and coloration of the SiO₂ particles with the immobilized Ag–Au composite nanoparticles remain preserved in nitric acid. This preservation is more pronounced than that observed in SiO₂ particles with immobilized Ag nanoparticles. This enhanced durability can be attributed to the formation of stable bonds between Ag and Au.