Surfactant-free colloidal gold nanoparticles: room temperature synthesis, size control and opportunities for catalysis

Nanomaterials are at the forefront to develop and improve several technologies spanning from catalysis to medicine and sensing. Simple(r) preparation methods of nanomaterials can greatly benefit to fundamental studies and facilitate the development of nanomaterials towards real-life applications. Here, an easily implementable surfactant-free colloidal synthesis, simply achieved in alkaline mixtures of water and mono-alcohol (e.g. ethanol), performed at room temperature in the case of gold nanoparticles, and compatible with the principles of Green Chemistry, is exploited and further developed to easily perform size-effects studies at the nanoscale. Gold nanoparticles in the size range of 5 to 22 nm are easily prepared from a solution of 0.5 mM HAuCl4, 2 mM NaOH and 20 v.% ethanol or methanol, by initiating the synthesis in different simple ways: sonochemistry, stirring, manual shaking, using different grades of precursors, using different solvents. The nanomaterials are shown to be suitable model systems to study size effects at the nanoscale, with the example of alcohol electrocatalytic oxidations performed in alkaline media.