Transition metal oxide-doped mesostructured silica films

Abstract

Mixed metal oxide-doped mesostructured silica films have been prepared by a combination of a ligand-assisted templating (LAT) and solvent evaporation-induced self-assembly (EISA) approach using metal alkoxides as precursors. To overcome the problem of the different hydrolysis and condensation rates of the various alkoxide precursors (silicon alkoxides and transition metal alkoxides), the hydrophilic head group of oligo(ethylene oxide) containing surfactants was coordinated to the M(OR) x groups resulting in metal-containing surfactants. These novel surfactants serve different functions in the EISA process: first, they moderate the hydrolysis and condensation rate of the transition metal alkoxide; second, they allow for a positioning of the transition metal alkoxide within the silica matrix; and third, they act as structure-directing agents. The obtained films are characterized by a high loading of the transition metal oxide species within the silica matrix and a homogeneous distribution throughout the whole film as shown by X-ray photoelectron (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Several transition metal oxides have been incorporated into the silica matrix such as titania, zirconia and tantalum oxide.