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

Fe₃O₄ nanoparticles were prepared by continuously pumping aqueous solutions of FeCl₃/FeCl₂ and NaOH into a rotating packed bed (RPB), co-precipitating 0.019mol/L of FeCl₂·4H₂O, 0.037mol/L of FeCl₃·6H₂O, and 0.222mol/L of NaOH. A rotating speed of 1800rpm and liquid flow rates of 0.5L/min were used. The mean size of Fe₃O₄ nanoparticles obtained declined as the temperature was increased. The smallest Fe₃O₄ nanoparticles (5.7nm 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 50emu/g, respectively.