Comparative studies between synthetic routes of SiO2@Au composite nanoparticles

We studied two different methods for the deposition of Au nanoparticles (Au NPs) onto the functionalized silica microspheres. One method was to mix the two kinds of particles together and react at room temperature overnight. The other one was to reduce hydrochloroauric acid to Au NPs with sodium citrate in the presence of the functionalized silica microspheres (one for the naked silica microspheres, the other for the Au-attached silica microspheres). We investigated the morphologies of SiO2@Au composite nanoparticles synthesized by these two methods, and found that the latter achieved a denser Au coverage on silica microspheres. Furthermore, we studied the effect of the pH values in a wide range, respectively, for the two methods. A possible mechanism was put forward to interpret the formation of SiO2@Au composite nanoparticles and the effects of the synthetic routes and pH values on the morphologies and optical properties.