| Abstract: | This article describes coating of magnetite nanoparticles (NPs) with amorphous silica shells. Controlled co-precipitation technique under N2 gas was used to prevent undesirable critical oxidation of Fe2+. The synthesised Fe3O4 NPs were first coated with trisodium citrate to achieve solution stability and then covered by SiO2 layer using Stober method. For uncoated Fe3O4 NPs, the results showed an octahedral geometry with saturation magnetisation range of 82–96?emu/g and coercivity of 85–120?Oe for particles between 35 and 96?nm, respectively. The best value of specific surface area (41?m2/g) for Fe3O4 alone was obtained at 0.9?M NaOH at 750?rpm and it increased to about 81?m2/g for Fe3O4/SiO2 combination. The total thickness and the structure of core–shell was measured and studied by transmission electron microscopy. The average particles size was about 50?nm, indicating the presence of about 15?nm SiO2 layer. Finally, the stable magnetic fluid contained well-dispersed magnetite-silica nanocomposites which showed monodispersity and fast magnetic response. |
