Surfactant-free gold nanoparticles synthesized in alkaline water-ethanol mixtures: leveraging lower grade chemicals for size control of active nanocatalysts

Developing syntheses of nanomaterials compatible with the principles of Green and Sustainable Chemistry is one key step to holistically develop sustainable (nano)technologies. In this respect, water is an ideal green solvent for various syntheses. However, the purity of the chemicals used can strongly influence the synthesis and the properties of the resulting nanoparticles. Here, we leverage on the typically detrimental use of lower grade purity chemicals to achieve a fine size control on surfactant-free gold nanoparticles. As a case study, we focus on the green syntheses of gold nanoparticles obtained at room temperature in alkaline ethanol-water mixtures. The synthesis is shown to be successful using lower grade gold precursor, lower grade ethanol stock solution and lower grade water. A relatively fine size control towards larger NPs in the range 10-30 nm is obtained by controlling the amount of the lower grade water in high purity water. The resulting nanoparticles relevant for various size-effects study at the nanoscale and are active catalysts, as exemplified with the reduction of 4-nitrophenol in presence of NaBH4 as a model reaction for water treatment.