Study of the Optical, Structural and Electrophoretic Properties (Zeta Potential and Hydrodynamic Diameter) of SiO2-Coated Ag Nanoparticles

Colloidal solutions containing silica-coated silver nanoparticles (Ag@SiO₂) were synthesized through a two-step process integrating physical and chemical mechanisms. In the first step, laser ablation of a silicon target submerged in deionized water generated an H₂O-SiO₂ colloid, termed the as-cast colloid. This contained nanometric SiO₂ particles alongside micrometer-sized or larger silicon fragments produced by laser shockwave-induced target surface fragmentation. To refine particle size distribution and elevate nanometric SiO₂ concentration, the as-cast colloid underwent secondary laser irradiation, effectively fragmenting larger particles. The second step involved adding ionic silver to both as-cast and irradiated colloids, yielding Ag@SiO₂ nanoparticles. Structural properties were probed via XRD and TEM; optical characteristics via UV-Vis spectroscopy; and electrophoretic mobility via zeta potential measurements, both pre- and post-silver incorporation, to elucidate irradiation's influence on synthesis. For controlled agglomeration, AlCl₃ was used to modify surface charge, neutralizing silanol groups on the silica shell and minimizing electrostatic repulsion through aluminum ion interactions. These findings demonstrate tunable Ag@SiO₂ colloids with precise surface properties for future development of advanced nanomaterials suitable for microbicidal applications.