Room Temperature Surfactant-Free Synthesis of Gold Nanoparticles in Alkaline Ethylene Glycol

Abstract

Gold nanoparticles are easily obtained by a range of room temperature processes. In particular, polyols-based syntheses performed in alkaline conditions without the need for surfactants lead to small size nanoparticles around 10 nm in diameter. While highly viscous polyols, such as glycerol, have been the most studied polyols with which to perform the reaction, the use of alternative alcohols with lower viscosity could benefit the processing of the nanoparticles. Here, we show that ethylene glycol is a suitable alternative to glycerol. Via a study comprising more than 70 experiments overall, we identified that the key parameters by which to control nanoparticle size and colloidal stability are the amount of base used and the amount of ethylene glycol. Too-high or too-low values of base and/or ethylene glycol do not lead to stable colloidal nanoparticles. An optimal Base/Gold molar ratio is around 4 and an optimal amount of ethylene glycol is around 30 v.% to obtain stable ca. 10 nm Au NPs and to develop a green room temperature surfactant-free colloidal synthesis of gold nanoparticles.