Charge-transfer reactions of silver stearate-coated nanoparticles in suspensions

Voltammetry of silver stearate-stabilized nanoparticles in the cyclohexane/acetonitrile solution showed a reduction wave at -0.6 V and an oxidation wave at 1.1 V. From TEM, AFM, and UV-vis spectroscopy, the nanoparticles were deduced to be nearly monodispersed spherical particles 5 nm in diameter with the core-shell structure, which was composed of the core by Ag atoms and the shell by silver stearate. The oxidation and the reduction waves were caused by the silver atoms in the core and silver stearate in the shell, respectively. The voltammetric peak currents and the limiting currents at the rotating disk electrode were mostly controlled by diffusion of the nanoparticles in the solution. These currents allowed us to evaluate the ratio of the number of Ag atoms in the core to that in the silver stearate to be ca. 9.6, which agreed with the value obtained from gravimetry by the chemical oxidation. From this value and the diameter of the nanoparticles, we infer that one-third of the silver atoms on the particle surface should be bonded with stearate rather than a monolayer coating to form the shell.