Document Type : Original Article
In this research, silica (SiO2) and SiO2@Ag core-shell nanoparticles were synthesized by the co-precipitation method in the presence of ammonia as a reducing agent. First, the effect of different concentrations of tetraethyl orthosilicate (TEOS) as a precursor on the structural and optical properties of silica nanoparticles (SiO2) was investigated. Then, using this optimized concentration of TEOS, silica nanoparticles with silver shell were prepared by two methods: (a) in the absence and (b) in presence of APTES (3-Aminopropyltriethoxysilane). The properties of SiO2@Ag core-shell nanoparticles prepared by two methods were compared and the best method was determined. For the synthesis of Ag nanoparticles, silver nitrate (AgNO3) and sodium borohydride (NaBH4) as reducing agents were used. To functionalize the surface of silica nanoparticles, 3-Aminopropyl-triethoxysilane (APTES) was added to the AgNO3 solution with polyvinyl-pyrrolidone (PVP) as a dispersant. The structural properties of silica and silica-silver core-shell nanoparticles were investigated by XRD and TEM. The average size of a silver single crystal in the core shells prepared by the two methods is about 25 nm and 14 nm, respectively. The optical absorption and bandgap were calculated for silica and SiO2@Ag core-shell nanoparticles. The results indicated that with increasing the concentration of TEOS precursor, the optical absorption of silica nanoparticles increased and their optical band gap reduced from 4.22 eV to 3.55 eV.