Study On The Preparation And Properties Of Ag@SiO₂Core-shell Nanostructures And Their Composites

Ag@SiO2core-shell nanoparticles have attracted considerable interest because of theirunique properties and wide application. Nano-silvers own unusual optical and electricalcharacteristics. Silica has chemical stability, optical transparency, and monodisperse.Ag@SiO2composite material has both properties of nano-silver and silica, not onlyplaying their respective advantages but also having synergy effect. So Ag@SiO2has broadapplication prospects in the aspects of Surface-enhanced Raman Scattering, antibacterialand catalytic areas. Nano Ag@SiO2sols were synthesized firstly, then Ag@SiO2/TiO2composites were obtained by adding tetra-n-butyl titanate to the sols. Photocatalyticperformance of the composites was investigatived.Nano silver sols were prepared by oil bath method at95oC reacting for one hour, usingsilver nitrate as the source of silver,40vol%glycerin/water as solvent, and sodium citrateas the reducing agent. Then the silver sols were transferred to ethanol solvent, addingtetraethyl orthosilicate (TEOS) and ammonium hydroxide (NH3·H2O) to coat SiO2.NH3·H2O acted as a catalyst to produce spherical silica shell. Ag@SiO2was synthesizedusing one-pot method. The results showed that nano-silver particles are uniformlyspherical, with average particle size of30nm. Ag@SiO2nanoparticles had uniformmorphology with a good monodisperse. The thickness of silica shell could be controlledeasily by tuning the amount of TEOS. We found that trisodium citrate played a critical roleas reducing agent for the reduction of silver ions (Ag+) and protective agent for silvernanoparticles from aggregation, in the coating process of silver nanoparticles with silicashell. UV-vis spectroscopy of Ag and Ag@SiO2sols showed that the plasmon resonancepeaks was shifted to longer wavelengths (known as red-shifting). Besides, the red-shiftedwas more obvious when the shell of silica became thicker.On the basis of the as-prepared Ag@SiO2, precursors of Ag@SiO2/TiO2were in-situ synthesized by sol-gel method, with tetra-n-butyl Titanate acting as titanium source. Aftercentrifuging, washing, drying and calcination, Ag@SiO2/TiO2powders were obtained.The test results demonstrated that the structure of TiO2in Composites were anatase.Fluorescence spectral intensity of Ag@SiO2/TiO2composite was weaker than that of pureTiO2, while diffuse reflection absorption spectra intensity was stronger in ultravioletregion. The degradation of methyl blue (MB) was used as the model reaction toinvestigate the photocatalytic property of Ag@SiO2/TiO2composites. The photocatalyticexperiments results showed that catalytic efficiency of the composite photocatalysts is2.5times that of pure TiO2, indicating that Ag@SiO2nanoparticles played an important role.