Preparation and characterization of silica-coated iron-oxide bionanoparticles under N2 gas

This paper describes coating of magnetite nanoparticles with silica shells. Controlled co-precipitation technique under N2 gas was used to prevent undesirable critical oxidation of Fe2+. The synthesized Fe3O4 (3 1 1) NPs were first coated with trisodium citrate (T S C) to achieve solution stability and then covered by SiO2 layer using stöber method. For uncoated Fe3O4 NPs, the results showed an octahedral geometry with saturation magnetization range of (82–96) emu/g and coercivity of about (80–120) Oe for particles between (35–96)nm, respectively. The best value of specific surface area (41 m2/g) was obtained at 0.9 M NaOH at 750 rpm. However, it increased to about 81 m2/g for Fe3O4/SiO2 combination with 50 nm as particle size, indicating the presence of about 15 nm SiO2 layer. Finally, the stable magnetic fluid contained well-dispersed magnetite–silica nanoshells which showed fast magnetic response.