Fe₂O₃ Nanoparticles within Mesoporous MCM-48 Silica: In Situ Formation and Characterization

Iron(III) oxide nanoparticles were synthesized within mesoporous MCM-48 silica phases. By using multiple cycles of wet impregnation, drying, and calcination procedures, it was possible to form haematite nanoparticles almost exclusively within the pore system. Nitrogen sorption measurements still revealed mesoporosity for the host/guest compound accompanied by a reduction of the BET surface area and the pore radius, both being indications of a decoration/coating of the inner surface of the silica walls. X-ray absorption spectroscopic measurements could prove the existence of small, slightly disordered iron(III) oxide nanoparticles. HRTEM investigations could show that the mesoporous host structure was still intact after the treatment. SAED (selected area electron diffraction) data did not reveal superstructure reflections or any diffuse intensity out of the Bragg reflections, indicating that the noncrystalline Fe 2 O 3 is randomly distributed within the pores.