Since the first synthesis of silica M-41S type mesostructured silica by researchers from Mobil in 1992, many attempts are made to generalize the synthesis to other oxidic solids. Thus, the mesostructuration of transition-metal oxides is the subject of much scientific and technological attention, and particularly titanium dioxide due to its numerous applications among those photocatalysis and support for catalytic reactions like gas phase depollution, hydrodesulfurization… While specific surface areas (SSA) of commercial titania samples rarely exceed 200 m².g^-1, some recent synthesis procedures sol-gel based mesostructuration allow to obtain largely higher SSA (up to 700 m².g^-1).¹ Unfortunately, thermal stability of the solids remains low, and calcination generally results in the crystallization of the solid with the collapse of the porosity (and consequently an important decrease in SSA). In this work, we report an original synthesis procedure leading to the preparation of TiO₂ supported mesostructured SiO₂ nanocomposite. The procedure used consists in a sol-gel synthesis of TiO₂ nanocrystals inside the porosity of the SBA-15 type silica host support. A series of TiO₂/SiO₂ (TiO₂ loading from 10 to 55 wt.%) is then prepared from titanium isopropoxide as titania precursor in anhydrous ethanol as solvent. A systematic study of the impregnation steps evidences the difficulty to avoid titania segregation outside the silica porosity. A careful impregnation allows to synthesize 2-3 nm crystallized TiO₂ nanoparticles dispersed inside the silica host support. TEM analysis clearly evidences the preservation of the initial hexagonal structure of the parent support and allows to observe crystallized anatase particles anchored onto the silica walls. As an example, the 55 wt.%TiO₂/SiO₂ sample display a SSA of 480 m².g^-1, a pore volume of 0.47 cm³.g^-1 and a pore diameter of 4.5 nm (sample calcined at 400 °C).

References

1. Yoshitake, H.; Tatsumi, T. Chem. Mater., 2003, 15, 1695.

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