Study on supercritical hydrothermal synthesis of CoFe2O4 nanoparticles

CoFe2O4 nanoparticles with diameter of about 5 nm were prepared at 390 °C by batch supercritical hydrothermal synthesis method. It was found that the characteristic of products depended on pH, temperature, mole ratio (r) of Co2+ to Fe3+ and coexisting cations in reactant solutions. The reaction time and the coexisting cations (Na+ and K+) had little effect on the size and morphology of CoFe2O4 particles. The products were a mixture of CoFe2O4 and Fe2O3 at r < 0.5 and Co1+xFe2−xO4 (0 ≤ x ≤ 1) at r ≥ 0.5. Pure CoFe2O4 nanoparticles with uniform size were synthesized at 390 °C, pH 12 and r = 0.5. The maximum coercivity and saturation magnetization of CoFe2O4 prepared by the present method were 340.6 Oe and 68.9 emu/g, respectively. The mechanism for batch supercritical hydrothermal synthesis of CoFe2O4 nanoparticles is believed to be a homogeneous phase reaction of Co(NO3)2·6H2O and Fe(NO3)3·9H2O aqueous solution.