Electrodic reduction of core-shell ferrite magnetic nanoparticles

We present square-wave voltammetry ( SWV) and controlled potential coulometry ( bulk electrolysis) experiments performed on maghemite and ferrite nanoparticles of core-shell-type MFe2O4@gamma-Fe2O3 ( where M = Mn2+, Co2+, Cu2+ or Zn2+), dispersed in aqueous media. The potential position of the iron( III) reduction peak identified in SWV measurements does not depend on the core chemical composition. No variations with size and polydispersity are detected. The shift of the reduction peak observed in coordinated configurations is related to the iron oxidizing strength. The electrolysis performed at a controlled potential of NPs indicates that only a fraction of iron( III) is reduced. Using the individual net charge deduced from the controlled potential coulometry measurements, we determine the thickness of the surface shell, which is electrolyzed.