Preparation of hybrid hollow capsules formed with Fe3O4 and polyelectrolytes via the layer-by-layer assembly and the aqueous solution process

Well-defined magnetic hybrid hollow capsules formed with magnetite (Fe₃O₄) and polyelectrolyte-multilayer films were successfully prepared through colloidal templating with layer-by-layer assembly of polyelectrolytes, followed by aqueous solution deposition of Fe₃O₄. Pd catalyst nanoparticles played an important role in the deposition of Fe₃O₄. Pd nanoparticles favorably adsorbed onto the polyelectrolyte layer with positively charged amino groups. Hollow capsules were obtained by the removal of the melamine–formaldehyde core particles. Although the processes were performed in aqueous solutions at temperatures less than 60 °C, X-ray diffraction patterns revealed that the deposited Fe₃O₄ was highly crystallized. The hollow capsules were stably dispersed in water; however, the capsules rapidly congregated around a locally applied magnet.