Fe3O4 nanoparticles were prepared by continuously pumping aqueous solutions of FeCl3/FeCl2 and NaOH into a rotating packed bed (RPB), where 0.148 mol/L of FeCl3 center dot 6H(2)O, 0.075 mol/L of FeCl2 center dot 4H(2)O, and 0.888 mol/L of NaOH co-precipitated. A rotational speed of 1800 rpm, liquid flow rates of 500 mL/min, and a temperature of 60 degrees C were adopted. Fe3O4 nanoparticles that were prepared in this manner had an average diameter of 6.4 nm, a maximal saturation magnetization of 50 emu/g, and a BET surface area of 173 m(2)/g. The rate of production of Fe3O4 nanoparticles was 17 kg/day. The H2O2-activating capacity of Fe3O4 nanoparticles that were prepared using the RPB, measured using the decolorization of Rhodamine B (RhB), was related to the Fe3O4 dosage, the H2O2 concentration, and the temperature. At pH 5 and 80 degrees C with an Fe3O4 dosage of 0.30 g/L and an H2O2 concentration of 0.11 mol/L, the Fe3O4 nanoparticles that were prepared using the RPB were observed to activate H2O2 and to have a decolorization efficiency of approximately 100% in 75 min with an observed decolorization rate constant of 0.0592 min(-1). The decolorization of RhB in the Fe3O4-H2O2 process was consistent with the pseudo-first-order kinetic model. (C) 2012 Elsevier B.V. All rights reserved.