Abstract
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.
Highlights
INTRODUCTIONFe3+ ions and 16 octahedral sites (site B) are shared by Fe2+ ions and Fe3+ ions
Fe3O4 particles has attracted lasting interests due to its half metallic characteristic of high Curie temperature, large spin polarization, and from its non-toxic and excellent biocompatibility.1–3 the synthesis, assembling and their various properties are extensively exploited for potential applications on biomedicine engineering such as drug delivery, cancer treatment, biosensor, magnetic resonance imaging and so on.4–9 Most of the applications require nanomaterial to be chemically stable, uniform in size and well dispersed in liquid media
Fe3O4@SiO2 composite magnetic particles with layers of mesoporous SiO2 structure are assembled by improved Stöber method
Summary
Fe3+ ions and 16 octahedral sites (site B) are shared by Fe2+ ions and Fe3+ ions. Its magnetization is determined by the difference of magnetic moment between A and B sites. Peroxidation might cause the lack of Fe ions in B site, decrease of the magnetization. We prepare the submicron –micron sized Fe3O4@nSiO2@mSiO2 core-shell structured composite spheres with thicker mesoporous shell by using the improved conventional Stöber poly-condensation method successfully, and examine the magnetic properties and the mechanism behind the magnetism by occupation of Fe ions in Fe3O4@nSiO2@mSiO2 core-shell particles by Mössbauer spectra
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