Synthesis of Cobalt-Doped Magnetite Nanoparticles

The synthesis of cobalt-doped Fe₃O₄ magnetite NPs was carried out by thermal decomposition (TD), which consists of the precursor reaction at 260 °C to produce NPs. For the TD process, the following chemicals were mixed in 20 mL benzyl ether (Sigma Aldrich, St. Louis, MO, USA, 98%) solution: iron (III) acetyl acetonate (1 mmol, Sigma-Aldrich 97%), cobalt acetyl acetonate (0.5 mmol Sigma Aldrich 97%) and an organic surfactant of 0.1 M Triton X-100. Before heating, the solution was exposed to a nitrogen atmosphere (N₂) to remove oxygen and other gases from the solution. Then, the temperature was increased to 100 °C and the N₂ gas exposure was discontinued. The temperature was then increased to 260 °C and maintained for 60 min. This leads to the formation of monodisperse CoFe₂O₄ nanoparticles, which possess a characteristic dark brown color. The solution was left at room temperature for 24 h and subsequently rinsed and centrifuged for 5 cycles at 8000 RPM. In the first three cycles, 5 mL of 98% methanol was used, while in the last two cycles, 5 mL of double-distilled water was used for washing the magnetic nanoparticle solution. After centrifugation and washing, the precipitate was added into 15 mL of double-distilled water.