Tuning Magnetic Nanoparticles: Effect of Temperature on the Formation of Magnetite and Hematite Phases

Magnetic nanoparticles up to 15 nm, such as magnetite (Fe₃O₄), exhibit superparamagnetic properties at room temperature. These nanoparticles are being explored for medical applications, and the coprecipitation method is favored for its cost-effective production and scalability. This study investigates the impact of synthesis temperature on the nanoparticles' physicochemical characteristics. The samples were synthesized at three different temperatures: 60, 70, and 80 °C (T60, T70 and T80). Analysis carried out using X-ray diffraction and Raman spectroscopy techniques revealed that the sample T60 is magnetite. As the temperature increased, the presence of hematite (Fe₂O₃) was detected in samples T70 and T80. In % mass, it was 8.0% for T70 and 8.7% for T80. Raman spectroscopy showed the characteristic bands of the magnetite phase at 341, 500, and 680 cm^-1 and a low percentage of hematite present in the samples T70 and T80. The presence of hematite in the samples offers several advantages, including enhanced catalytic and magnetic properties, improved adsorption of contaminants, and greater thermal and chemical stability. Through various characterization techniques, including XRD, Raman spectroscopy, and transmission electron microscopy (TEM), the average diameter of the magnetic nanoparticles was confirmed to be approximately 5 nm. The coprecipitation route proved efficient for producing magnetite nanoparticles at temperatures below 70 °C. For specific applications, synthesis at temperatures above 70 °C may yield nanoparticles with a small proportion of hematite, introducing new functional properties that broaden their potential applications, such as in catalysis or environmental remediation.