Shedding light on the aqueous synthesis of silicon nanoparticles by reduction of silanes with citrates

The synthesis of silicon nanoparticles in water has recently attracted a lot of attention. However, many scientists have expressed concerns on the nanomaterials obtained. We decided to explore two different routes to obtain silicon nanoparticles starting from a silane precursor. We report our findings regarding the preparation of nanomaterials under microwave irradiation and hydrothermal conditions starting from aqueous mixtures of (3-aminopropyl) triethoxysilane and sodium citrate. The microwave process, in particular, has been reported to yield silicon quantum dots bearing a surface layer of 3-aminopropyl moieties, allowing for the preparation of luminescent substrates amenable to biological-friendly amide chemistry. However, rigorous experimental design and thorough characterization of the products definitely rules out the formation of silicon nanoparticles. By highlighting the main issues linked to the proper characterization of these materials, we prove that the nanoparticles produced under both microwave and hydrothermal conditions, are a mixture of silica and carbon quantum dots.