Surfactant-Free Colloidal Syntheses of Gold-Based Nanomaterials in Alkaline Water and Mono-alcohol Mixtures

On the Importance of Fresh Stock Solutions for Surfactant-Free Colloidal Syntheses of Gold Nanoparticles in Alkaline Alcohol and Water Mixtures

A room temperature surfactant-free synthesis of gold nanoparticles in the size range 10–20 nm that only requires HAuCl4 as the precursor, NaOH as the base, water as the solvent and a mono-alcohol such as methanol or ethanol as the reducing agent, has recently been detailed. This approach is promisingly simple to obtain colloids stable for months. Here, it is shown that the use of fresh stock solutions of base is one key to ensure the formation of stable surfactant-free small-sized gold nanoparticles. The need for relatively freshly prepared stock solutions of base does not appear to be as crucial for syntheses using stabilizers and/or viscous solvents such as glycerol. The possibly overlooked importance of the age of the stock solution of base might account for the limited interest to date for the simple room temperature synthesis in low viscosity mono-alcohols highlighted.