Synthesis of Magnetic Cobalt Ferrite Sorbents

Magnetic cobalt ferrite sorbents (CoFe₂O₄) were synthesized following the procedure described by Tavares et al. (2020 (link)) based on the oxidative hydrolysis of iron(II) sulfate followed by co-precipitation of Co(II) and Fe(III) ions in alkaline conditions. Ultra-pure water was first deoxygenated with N₂ under vigorous stirring for 2 h. Then, 1.90 g (34 mmol) of KOH and 1.52 g (15 mmol) of KNO₃ were added to 25 mL of deoxygenated water using a 250-mL round flask. This mixture was heated at 60 °C, under N₂ and mechanically stirred at 500 rpm. After total dissolution, 10 mL of aqueous CoCl₂.6H₂O (6 mmol) and 15 mL of aqueous FeSO₄.7H₂O (11 mmol) were both added dropwise, and mechanical stirring was then set at 700 rpm. The resulting reacting mixture presented a dark-green color after complete addition of the Co(II) and Fe(II) aqueous solutions and the reaction proceeded over 30 min, after which the reaction vessel was placed in an oil bath at 90 °C, under N₂ but without stirring, for 4 h. The resulting black powder was magnetically collected and thoroughly washed with deoxygenated water and ethanol. Finally, the particles were collected and dried in an oven at 40 °C.