Seed-Mediated Continuous Growth of CoFe2O4 Nanoparticles in Triethylene Glycol Media: Role of Temperature and Injection Speed

This study investigates the seed-mediated growth of CoFe2O4 nanoparticles by continuously injecting Co(acac)₂ and Fe(acac)₃ precursors into triethylene glycol under thermal decomposition conditions. We focused on the effects of precursor injection speed and synthesis temperature. The optimal injection rate was ~ 40 mL/h, with higher rates causing excessive secondary nucleation, while lower rates led to nanoparticle aggregation due to faster ligand stripping than monomer adsorption. A novel growth mechanism was proposed, involving secondary nucleation and clusterization, where new seeds adsorb onto growing nanoparticles, aided by the absence of strong stabilizers. Growth kinetics were analyzed using the Arrhenius equation, yielding an activation energy of 40.8 kJ/mol. Temperature also played a critical role in crystallite growth and nucleation. As temperature increased, crystallite size grew from 3.4 ± 0.2 nm at 185 °C to 10.1 ± 0.5 nm at 265 °C, with minimal change in nanoparticle size measured by TEM. Magnetic measurements showed an increase in saturation magnetization, when the reaction temperature was increased. Same impact of temperature on coercive force was also observed. This increase was attributed to crystallite sizes exceeding the 7 nm threshold for CoFe2O4 and low lattice strain. According to hyperthermia measurements the heating ability improved with larger crystallite size and higher Ms, but excessive Hc​ for samples at 265 oC reduced efficiency. The findings enable precise control over nanoparticle growth and nucleation, allowing tailored synthesis of single- or polycrystalline CoFe2O4 with controlled magnetic properties. These advancements hold promise for a wide range of biomedical applications, including magnetic hyperthermia.