One-Step Solvothermal Synthesis of Fe3O4 Acicular Aggregates Induced by Reaction Medium and Urea for Photocatalytic Degradation of Azo Dyes

Based on the magnetic sensitivity of Fe₃O₄ in various fields, we aimed to propose a one-step solvothermal process for the synthesis of single-phase Fe₃O₄ induced by the reaction medium and urea, avoiding high-temperature reduction in H₂ or N₂ atmospheres. Feasibility was tested with purified water (H₂O), methyl alcohol (MA), ethyl alcohol (EA), and ethylene glycol (EG) as reaction media. The findings indicated that the solvothermal reaction system utilizing EA was more effective for the synthesis of cubic magnetic Fe₃O₄. Optimal conditions for synthesizing pure Fe₃O₄ were obtained by optimizing the urea amount and solvothermal reaction parameters. The optimal formulation consisted of 10 mmol of FeCl₃, 80 mmol of urea, and 60 mL of EA subjected to a solvothermal process at 200 °C for 12 h. The resulting Fe₃O₄ (magnetite, cubic) exhibited commendable crystallization with a morphology of acicular aggregates and displayed excellent magnetic sensitivity properties with a magnetization of 92.2 emu/g at 15,000 Oe. The photocatalytic degradation behaviors of the resulting Fe₃O₄ to Methyl Orange, Orange G, and Acid Red 37 azo dyes and the repeated degradation performance of Methyl Orange dye were investigated. Nearly complete degradation of Methyl Orange dye occurred after 2.0 h of photocatalytic reaction, while Orange G and Acid Red 37 dyes achieved similar results after 3.5 and 4.5 h, respectively. The exploration strategy in this work for synthesizing magnetic Fe₃O₄ can be applied to design and fabricate other metal oxides or composites, potentially resulting in novel discoveries in morphology or performance.