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In this work the preparation and photocatalytic properties of strontium tantalum oxides with perovskite-type structures are presented. The perovskite-type oxides were prepared by the sol-gel method and annealed at 800, 900 and 1,000°C for 36 h. Before and after annealing the solids were characterized by XRD, N 2 adsorption (BET), UV-visible (diffuse reflectance), FTIR, TGA-DTA, and SEM-EDS techniques. The X-ray diffraction patterns of the samples showed the coexistence of three strontium tantalate oxides, Sr 2 Ta 2 O 7 , SrTa 4 O 11 , and Sr 5 Ta 4 O 15 , the relative amounts of which were highly dependent on the annealing temperature. It has been proposed that the photoactivity of the oxides in the decomposition of crystal violet dye could be related to the proportion of the Sr 2 Ta 2 O 7 phase in the annealed samples.

TiO₂anatase powder was prepared by means of the sol-gel method with titanium(IV) butoxide as precursor. The formation of a tetragonal crystal structure of TiO₂anatase at 500 °C was confirmed by X-ray powder diffraction. The characterization of the samples synthesized was complemented by scanning electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, nitrogen adsorption-desorption isotherms (Brunauer-Emmett-Teller) and diffuse reflectance spectroscopy. The photocatalytic activity of the TiO₂anatase powder was evaluated in the degradation of caffeic acid in aqueous solution under ultraviolet radiation. A central composite circumscribed design was used to assess the weight of the experimental variables, pH and amount of catalyst in the percentage of caffeic acid degraded and the optimal conditions. The optimized conditions were found to be pH = 5.2 and a load of TiO₂of 1.1 g L⁻¹. Under these conditions more than 90% of caffeic acid degradation was achieved after 30 min of lamp irradiation. At this time the mineralization reached was almost 60%.