Abstract
Naked gold nanoparticles synthesized through sonochemical reduction of gold chloride ions remained well dispersed in water even in the absence of any stabilizing agents such as alkylthiols and surfactants. In this work, we examine the mechanism on the colloidal stabilization of naked gold nanoparticles in water. We found that the naked gold nanoparticles dispersed in water were precipitated with the addition of sodium chloride into the naked gold nanoparticle dispersion. This suggests that the naked gold nanoparticles are dispersed in water by electrostatic repulsive interaction. Furthermore, we revealed that the naked gold nanoparticles dispersed in water were precipitated under dark condition. The zeta-potential of naked gold nanoparticles with -40 mV decreased with the elapsed time after the naked gold nanoparticle dispersion moved to dark condition from light condition. This indicates that the precipitation of naked gold nanoparticles under dark condition is caused by the decrease in the electrostatic repulsive interaction among naked gold nanoparticles. Namely, the colloidal stabilization of naked gold nanoparticles in water under light condition is most likely due to the increase in the surface change of naked gold nanoparticles induced by light.
