Synthesis of nanostructured porous TiO₂ via modified sol-gel and ligand-assisted templating approaches

Mesoporous materials, such as the aluminosilicate-based MCM-41 recently described by Mobil, consist of pores in the 20-100angstrom range, in contrast to zeolites whose pores are less than 15 angstrom. Only recently has this class of materials been extended to include transition metal oxides. These materials have potential application as solid electrolyte devices, as sorbents, and in catalytic processes where high surface area, fast diffusion, and large pore sizes are necessary for high performance. The reported work describes the synthesis of titanium transition metal oxide molecular sieve (Ti-TMS1), the first structurally stable hexagonally-packed mesoporous transition metal oxide material and the first transition metal oxide molecular sieve. The synthesis of this materials was achieved through a novel approach using a modified sol-gel technique in which acetylacetone is required to control the hydrolysis of the titanium alkoxide precursor in such a way as to allow the Ti center to interact with the head group of the surfactant molecule. This contrasts to previous techniques which use charge matching of the inorganic and organic phases to achieve the desired templating interaction. Direct litigation of the titanium alkoxide precursor to the head group of the surfactant prior to hydrolysis followed by treatment with water and subsequent aging also yielded Ti-TMS1. This alternate route does not require acetylacetone to control the hydrolysis in order to allow the surfactant to interact with the inorganic phase, since this interaction is already consolidated prior to the addition of water.