A novel two-step modifying process for preparation of chitosan-coated Fe3O4/SiO2 microspheres

Functionalized Fe3O4 nanoparticles decorated with silica and chitosan have been prepared via two steps in this paper. The first step involved magnetite nanoparticles (Fe3O4) homogeneously incorporated into silica spheres using the modified Stober process. Second, the silica-coated Fe3O4 nanoparticles were covered with the outer shell of cationic polyelectrolyte chitosan by a layer-by-layer assembly process. X-ray diffraction results indicated that the surface-modified Fe3O4 nanoparticles did not lead to phase change compared with the pure Fe3O4. Transmission electron microscopy studies revealed nanoparticles remained monodisperse, and silica shells have trapped more than one magnetic core. Average particle sizes of chitosan-coated Fe3O4/SiO2 microspheres are about 80-100 nm. In addition, super-paramagnetic properties of hybrid microspheres have also been detected by a vibrating-sample magnetometer. It may make the hybrid microspheres of important use in mild separation, enzyme immobilization, etc. (C) 2008 Elsevier B.V. All rights reserved.