Synthesis and characterization of poly(divinylbenzene)-coated magnetic iron oxide nanoparticles as precursor for the formation of air-stable carbon-coated iron crystalline nanoparticles

Maghemite (γ-Fe₂O₃) nanoparticles of 15 ± 3 nm diameter were prepared by nucleation of gelatin/iron oxide followed by growth of γ-Fe₂O₃ films onto these nuclei. The γ-Fe₂O₃ nanoparticles were coated with polydivinylbenzene (PDVB) by emulsion polymerization of divinylbenzene (DVB) in an aqueous continuous phase containing the γ-Fe₂O₃ nanoparticles. The PDVB-coated γ-Fe₂O₃ nanoparticles, dispersed in water, were separated from homo-PDVB nanoparticles using the high gradient magnetic field (HGMF) technique. The influence of DVB concentration on the amount of PDVB coating, on the size and size distribution of the coated γ-Fe₂O₃ nanoparticles and on their magnetic properties, has been investigated. Air-stable carbon-coated iron (α-Fe/C) crystalline nanoparticles of 41 ± 12 nm diameter have been prepared by annealing the PDVB-coated γ-Fe₂O₃ nanoparticles at 1050 °C in an inert atmosphere. These nanoparticles exhibit high saturation magnetization value (83 emu g^-1) and excellent resistance to oxidation. Characterization of the PDVB-coated γ-Fe₂O₃ and of the α-Fe/C nanoparticles has been accomplished by TEM, HRTEM, DLS, FTIR, XRD, thermal analysis, ζ-potential, and magnetic measurements.