Photoreductive synthesis of monodispersed Au nanoparticles with citric acid as reductant and surface stabilizing reagent

Abstract

Colloidal suspensions of gold nanoparticles (AuNPs) in water can be prepared by heating water containing HAuCl₄ with citric acid as reductant and surface stabilizing reagent. This thermal reduction method, however, promotes aggregation of the formed AuNPs, resulting in bimodal distribution of AuNPs. Here we report that UV (254 nm) irradiation of water containing HAuCl₄ with citric acid at room temperature successfully reduces HAuCl₄ and produces monodispersed AuNPs, while suppressing aggregation of the formed AuNPs. Changing the intensity of UV light or the amount of citric acid added successfully produces AuNPs with tunable sizes and narrow size distributions.