Comparative photocatalytic behavior of Ta catalysts prepared by d.c.-sputtering, sol–gel and grafting in acetone degradation

Ta-doped photocatalysts were prepared using three different techniques: reactive d.c.-magnetron sputtering, sol–gel and grafting of tantalum on MCM-41 and TiO2. The composition of the catalysts prepared by reactive d.c.-magnetron sputtering consisted in tantalum and titania, while that of sol–gel and grafted catalysts of Ta–titania–silica mixed oxides. The characterization of these catalysts was carried out using the adsorption-desorption isotherms of N2 at 77 K, X-ray diffraction (XRD) patterns, small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), XPS, TEM, and 29Si- and 181Ta-CP/MAS NMR spectra. The behavior of these photocatalysts was checked in acetone degradation. The photocatalytic tests indicate that, depending on the preparation conditions and tantalum content, an enhancement of the activity occurs as compared with pure titania. Sol–gel and Ta-grafted MCM and TiO2 catalysts exhibited a rather poor activity, which was correlated with the lack of crystallinity of titania.