Surfactant-free colloidal syntheses of gold-based nanomaterials in alkaline water and mono-alcohol mixtures

Gold nanoparticles (AuNPs) and gold-based nanomaterials combine unique properties relevant for medicine, biomedical applications, imaging, optics, sensing, catalysis or energy conversion. While the Turkevich-Frens and Brust-Schiffrin methods remain the state-of-the-art colloidal syntheses of AuNPs, there is a need for more sustainable and tractable strategies. Here, a reproducible and scalable surfactant-free synthesis of stable colloidal AuNPs with multiple benefits is achieved by the simple reduction of HAuCl4 at room temperature in alkaline solutions of mono-alcohols and water. A parametric study including more than 350 experiments shows that mixing different alcohols is a simple strategy for achieving size control in the range 6-30 nm in diameter and the order of addition of the chemicals strongly affects the outcome of the synthesis. The synthesis method also applies to surfactant-free palladium (Pd) and bimetallic AuxPdy NPs, nanocomposites and multi-metallic samples, all readily active (electro)catalysts. The simple synthesis bears promising features for fundamental and applied research.