Continuous preparation of Fe3O4 nanoparticles using a rotating packed bed: Dependence of size and magnetic property on temperature

•RPB can prepare superparamagnetic Fe3O4 nanoparticles on a large scale.•The size of Fe3O4 nanoparticles decreased with temperature.•Fe3O4 nanoparticles prepared at 60 °C were spheres with a diameter of 5.7 nm.

Fe3O4 nanoparticles were prepared by continuously pumping aqueous solutions of FeCl3/FeCl2 and NaOH into a rotating packed bed (RPB), co-precipitating 0.019 mol/L of FeCl2·4H2O, 0.037 mol/L of FeCl3·6H2O, and 0.222 mol/L of NaOH. A rotating speed of 1800 rpm and liquid flow rates of 0.5 L/min were used. The mean size of Fe3O4 nanoparticles obtained declined as the temperature was increased. The smallest Fe3O4 nanoparticles (5.7 nm in diameter, as determined by TEM) were obtained at 60 °C. Fe3O4 nanoparticles prepared at all temperatures were superparamagnetic. The saturation magnetizations of Fe3O4 nanoparticles that were prepared at 25 °C, 40 °C, and 60 °C were 45, 50, and 50 emu/g, respectively.

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