Fe 2 O 3 nanoparticles embedded in a SiO 2 matrix have been synthesized by sol-gel chemistry and high temperature heat treatments. Virtually pure -Fe 2 O 3 (in excess of 93%) is obtained, although a two-phase mixture, -Fe 2 O 3 + R-Fe 2 O 3 , is observed for Fe 2 O 3 /SiO 2 ratios greater than 37 wt %. The -Fe 2 O 3 nanoparticles are stable up to ∼1600 K. Optimized -Fe 2 O 3 nanoparticles are ferrimagnetic, with a Curie temperature T C ≈ 510 K, and remarkably high values of room-temperature coercivity, H C ) 20 kOe.

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Mesoporous silica particles of MCM-41 type were synthesized by sol-gel method from tetraethyl orthosilicate (TEOS) in 2-methoxyethanol and deionized water mixture in base conditions at room temperature. Ammonia or sodium hydroxides were used as catalysts and cetyl-trimethylammonium bromide (CTAB) and n-dodecyl-trimethylammonium bromide (DTAB) as structure directing agents. The porosities and the ordered structure have been analyzed using transmission and scanning electron microscopy, small angle neutron and Xray diffraction, nitrogen adsorption, thermal analysis and FTIR spectroscopy. The samples consist of spherical particles of sub-micrometer size, with radially arranged pores. The comparison of the effect of the different surfactants and catalysts shows that by varying the surfactant type and their proportion, the pore sizes can be controlled. As compared to the commonly used ammonia catalyst, the use of NaOH as catalyst results in a much smaller porosity of the as-prepared materials. These materials are not resisting to the heat treatment at 700 ºC used for the template removal, and the ordered porous structure is completely lost.