Fabrication of monodisperse mesoporous carbon capsules decorated with ferrite nanoparticles

We present here a synthetic method for fabricating hollow magnetic mesoporous nanocomposites (diameter similar to 400 nm) made up of ferrite nanoparticles incorporated to the mesoporous shell (shell thickness similar to 50 nm) of carbon capsules. This methodology has been applied to the insertion of different ferrites such as iron oxide spinel (Fe3O4/gamma-Fe2O3), CoFe2O4, NiFe2O4, and MnFe2O4. The size of these inorganic nanoparticles (similar to 9-17 nm) can be modulated easily by varying the temperature of synthesis, as demonstrated in the case of the iron oxide spinel phase. An important characteristic of these nanocomposites is that, in spite of the large amounts of inorganic nanoparticles deposited (30 or 50 wt %), they retain a large porosity made up of mesopores (similar to 2-4 nm). Moreover, the inner core of these nanocomposites remains completely empty because the ferrite nanoparticles are deposited exclusively on the porous carbon layer. We have demonstrated the usefulness of this kind of nanocomposites for the immobilization of an enzyme (lysozyme). The results obtained suggest that the enzyme is stored mainly in the hollow core of the magnetic capsules. Moreover, we have proved that the nanocomposite loaded with the enzyme can be manipulated easily by means of an external magnetic field.