Electrochemical Reduction of Iron Oxide Nanoparticles on Mercury

The electrochemical reduction of well-defined γ-Fe 2 O 3 nanoparticles dispersed and stabilized in aqueous media which are appropriate for electrochemical techniques (analysis and preparation) is studied. A medium, in which metallic iron can be formed and in which iron ions do not precipitate, is examined in detail ([citrate(NH 4 ) 3 ] = 0.01 mol/L, NH 4 ClO 4 /NH 3 pH = 8.6). Our results clearly show that the differences between nanoparticles and ionic species as starting material do not consist in a simple scaling. At intermediate potentials (−0.4 to −1.2 V/ECS) we show that the nanoparticles can be reduced into Fe II, with a fraction of it being free in solution. At more negative potentials (−1.5 to −1.8 V/ECS), nanoparticles are reduced into metallic iron nanoparticles that enter the Hg electrode due to the wetting properties of Hg on iron. There exist strong interactions between the oxide nanoparticles and the electrode, interactions which are shown to be partly of electrostatic nature, that is, depending on the concentration of the supporting electrolyte (NH 4 ClO 4 /NH 3 ).