Synthesis of Cu-doped δ-FeOOH nanoparticles by a wet chemical method

Cu-doped maghemite (γ-Fe2O3) and Cu-doped feroxyhyte (δ-FeOOH) nanoparticles were synthesized using a wet chemical method. The synthesis was performed starting from a mixture of iron and copper salts. Cu-doped γ-Fe2O3 and Cu metal nanoparticles were obtained from a solution with a high Cu/Fe ratio, whereas Cu-doped δ-FeOOH nanoparticles were obtained from a solution with a low Cu/Fe ratio. The size of the nanoparticles was below 10 nm. The superparamagnetic behavior of the nanoparticles was determined from their Mossbauer spectra. The hyperfine magnetic field of Cu-doped δ-FeOOH nanoparticles was larger than that of undoped δ-FeOOH nanoparticles. The Cu content of the intermediate species plays an important role in the oxidation process. The intermediate species in the precipitates before rinsing was speculated to be Cu1-xFeIIxFeIII2O4 (x = 0.4–0.7), which was subsequently oxidized in air to form Cu-doped γ-Fe2O3 or Cu-doped δ-FeOOH, depending on the amount of Cu.