Tantalum doped titania photocatalysts: Preparation by dc reactive sputtering and catalytic behavior

TiO2 thin film photocatalysts doped with various Ta amounts were deposited on glass slides by the sputtering method, in Ar/O2 atmosphere. They were characterized by XRD, UV-vis spectroscopy, AFM and EPMA. XRD patterns showed that the films were crystalline and consisted mainly of anatase. The doping with Ta enhanced the crystallinity and determined, for high Ta loadings, the phase transition into rutile. The large blue shift of the bandgap energy absorption in the UV-vis spectra, which is a quantum size effect, shows that the dimensions of the crystallites are smaller than 10 nm. The photocatalytic activity of the sputtered films was tested in the acetone degradation. Depending on the preparation conditions, two optimum Ta loadings were found (0.60 and 1.61 at.%, respectively), which ensure rather high conversions. A direct correlation between the bandgap of the catalysts and the catalytic activity was found. Ta doping was found to improve the ability of the titania photocatalysts to use UV radiations of lower energy, when compared to undoped samples.