Document Type : Original Article
In this research, silica (SiO2) and SiO2@Ag core-shell nanoparticles were synthesized by co-precipitation method in the presence of ammonia as reducing agent. At first, effect of various concentrations of tetraethyl-orthosilicate (TEOS) as precursor on the structural and optical properties of silica (SiO2) nanoparticles was studied. Then, using this optimized concentration of TEOS, silica nanoparticles with silver shell were prepared by two methods: (a) in 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 synthesis of Ag nanoparticles, silver nitrate (AgNO3) and sodium borohydride (NaBH4) as reducing agent were used. For functionalizing the surface of the silica nanoparticles, 3-Aminopropyltriethoxysilane (APTES) with polyvinylpyrrolidone (PVP) as dispersant were added to the AgNO3 solution. The structural properties of silica and silica-silver core-shell nanoparticles were studied by XRD and TEM. The average sizes of silver single crystal in the prepared core-shells by two methods is about 25 nm and 14 nm, respectively. The optical absorption and band gap were calculated for silica and SiO2@Ag core-shell nanoparticles. The results showed that with increasing the concentration of TEOS precursor, the optical absorbance of silica nanoparticles is increased and their optical band gap was decreased from 4.22 eV to 3.55 eV.