An investigation on synthesis of Fe3O4@nSiO2@mSiO2 hybrid particles and peroxidation

Fe3O4 particles with uniform size, regular shape and good dispersibility are prepared by solvothermal methods. The size of Fe3O4 particles and their magnetic properties can be adjusted during synthesis. Fe3O4@SiO2 composite magnetic particles with layers of mesoporous SiO2 structure are assembled by improved Stöber method. The different shell thickness of SiO2 layer can be adjusted from 35∼150 nm using multi-coating by changing the content of TEOS to form Fe3O4@nSiO2@mSiO2. The Mössbauer spectra show that Fe3O4 particles are almost stoichiometric. However, it is found that the coverage of SiO2 have a significant effect on the occupation of Fe ions in Fe3O4 particles. Peroxidation appears in Fe3O4@SiO2 composite magnetic particles, which might be caused by oxygen in SiO2 layer during wrapping process.