Nano-sized Fe3O4 particles that were covered with a porous layer of nano-sized TiO2 (TiO2-masked Fe3O4) were prepared by simply controlling pH of aqueous slurry solution containing the two particles that have different values of iscrelectric point (IEP coating method). The prepared sample showed an effective masking of red-brown color of Fe3O4 Particles into a pale yellow. XPS and TEM measurements confirmed an effective covering of TiO2 particles to the Fe3O4 surface. XANES analyses revealed the transformation of some Fe2+ ions into Fe3+ in the Fe3O4 structure (formation of Fe3O4+delta) due to a close interaction between Fe3O4 and TiO2 during the IEP coating, which was not observed in physical mixture of dry powders of Fe3O4 and TiO2. Compared with pure Fe3O4 or the physical mixture, TiO2-masked Fe3O4 particles exhibited an activity enhancement for both catalytic oxidation of 1,2-dichloro benzene and thermal incineration of catalyst-em bedded polyethylene and polystyrene. Temperature-programmed reduction of CO and temperature-programmed surface reaction of CO with 02 revealed that oxygen vacancy sites on Fe3O4+delta played roles for the adsorption and reaction of CO, and close TiO2 provided oxygen to the Fe3O4.delta sites. Compared with pure Fe3O4 particles, TiO2-masked Fe3O4 particles also provided a good color-masking effect when embedded in polymers and improved the thermal stability of base polymers for high temperature fabrication. (C) 2009 Elsevier B.V. All rights reserved.