Sonoelectrosynthesis of monodisperse metal nanoparticles†
Traditional colloidal syntheses of metal nanoparticles (NPs) are highly sensitive to the selection of and quality of chemical reducing agents and metal precursors. To address these challenges, we demonstrate the complete sonoelectrochemical synthesis of monodisperse metal NPs starting from bulk metal, using Cu as a model system. Electrochemical syntheses of NPs are of great interest as the oxidation and reduction processes that account for product formation can occur directly at the anode and cathode, respectively. This ability has the potential to improve reproducibility by simplifying the chemical pathway to NPs, with electrosyntheses often also providing unique kinetic pathways toward green product formation. Herein, ultrasound is coupled with electrosynthesis to clean the electrode surface, dispersing the NPs produced at the electrode into solution. We were able to shift the size distribution to form monodispersed metal NPs through control of applied potential (Vapplied) and ultrasonic pulses. The synthesis begins with electrooxidation of bulk Cu metal to directly dissolve metal ions into a microemulsion system. This step is followed by sonoelectroreduction of the ions, which facilitates the formation of dispersible, monodisperse Cu NPs with diameters <10 nm. The size distribution can be controlled by adjusting the Vapplied, pulse intensity, and pulse sequence implemented during sonoelectroreduction. We view this technique as a scalable method to synthesize metal NPs from bulk metal without chemical reducing agents.