Shifting the Size-Dependent Redox Potential of Gold Nanoparticles Using CTA⁺ Micelles

Here, we demonstrate an unusual negative shift in the size-dependent reduction potentials of gold nanoparticles (AuNPs) attributed to the presence CTA⁺micelles. Our model reaction follows the chemical equilibrium reaction of CTAB-protected gold nanospheres and the Fe³⁺/Fe²⁺ redox couple which allows us to use the Nernst equation and compute their standard redox potentials. The measured redox potentials decrease with decreasing nanoparticle size, following a size-dependent trend that negatively shifts by ~300 mV under the presence of CTA⁺ at micellar concentration. This shift in the redox potential of AuNPs suggest that controlling the metal-ligand complex interactions with the micelles can serve as a strategy to tune the redox potential of metallic nanoparticles and metal-surfactant complexes. This reaction strategy can also be useful to compute the formation constant of the metal-surfactant complex in relevance to growth and etching of metal nanoparticles.