Preparation of uniform Au@SiO2 particles by direct silica coating on citrate-capped Au nanoparticles

Preparation of Au@SiO2 particles by direct silica coating on three different sized citrate-capped Au nanoparticles (17, 25 and 33 nm) with Stöber method was investigated in this work. It was found that the uniformity of the resulting Au@SiO2 particles was related to both the sizes of the Au nanoparticles and the concentration of citrate during the particle synthesis. When the citrate concentration during the particle synthesis was low, the 25 and 33 nm Au nanoparticles could be well dispersed in the Stöber system, thus resulting the formation of uniform Au@SiO2 particles containing single core. However, small Au nanoparticles (17 nm) were identified to show poor stability in the Stöber system even under low citrate concentration, the silica coating must be performed in a pre-hydrolyzed Stöber system to get the uniform Au@SiO2 particles. This approach was also applicable to citrate capped Ag nanoparticles. After removal of the excess citrate in the Ag prepared by citrate reduction, uniform Ag/SiO2 particles containing single core colloids could also be prepared by the direct silica coating.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Au@SiO2 particles were prepared by direct silica coating on citrate capped Au particles. ► Uniform Au@SiO2 particles were obtained when the Au particles were stable in Stöber system. ► Silica coating on Au particles with poor stability could be carried out in pre-hydrolyzed Stöber system. ► This approach was also applicable to the preparation of uniform Ag@SiO2 particles.