Room temperature synthesis of surfactant-free gold nanoparticles in alkaline water-alcohols solutions: Benefits of [ethanol+glycerol] mixtures

Gold (Au) nanoparticles (NPs) are relevant for multiple applications such as catalysis, sensing, medicine, and many more. The full exploitation of Au NP properties require their controlled syntheses. Recently, a synthesis method to easily prepare Au NPs at room temperature without the need for any other chemicals than a gold precursor, water, a base and ca. 20 v.% ethanol was reported. This approach using low viscosity solvents is in contrast to previous studies to date preferring the use of polyols such as glycerol. Motivated by our recent reports exploring the pros and cons of using different alcohols for the synthesis, we here explore the opportunities stemming from using mixtures of different alcohols as source of reducing agent. It is shown how using [ethanol+glycerol] mixtures with a low amount of glycerol, e.g. only 2 v.%, can improve the size control over the Au NPs. Time resolved UV-vis study show that this can be attributed to the fastest formation of the Au NPs in presence of even relatively small amount of glycerol. The results provide solid foundation towards the rational development of green syntheses of surfactant-free Au NPs at room temperature.