Synthesis and Evaluation of the Photocatalytic Activity of Nanostructured Composites Based on Si[O.sub.2] Recovered by Ti[O.sub.2]

Almost spherical Si[O.sub.2] nanoparticles were recovered by thin films of Ti[O.sub.2] (highly crystalline anatase) produced in situ sol-gel syntheses. Silica coating was proven by scanning electron microscopy and infrared measurements. The outstanding photocatalytic efficiency of this material was proven by the degradation of the dye Ponceau 4R (P4R) in aqueous solution, by monitoring its discoloration as well as by the photocatalytic production of gaseous hydrogen. In the first case, the color of the solutions submitted to the photocatalytic process was reduced to zero in 140 minutes of reaction. Regarding the hydrogen production, 5.5 mmol of [H.sub.2] were obtained in 5 hours of reaction, corresponding to a specific rate of production of 13.6 mmol [g.sup.-1][h.sup.-1], a value much higher than that obtained using Ti[O.sub.2] P25 (2.66 mmol [g.sup.-1][h.sup.-1]) under similar conditions, or even with other photocatalysts reported in the literature. This outstanding photocatalytic activity is coherent with the specific surface area and porosity (respectively 70 [m.sup.2]/g and 15%), estimated for this material. On the other hand, this material presents noticeably superior band gap energy ([E.sub.g]), 3.3 eV, when compared to the typical values found for Ti[O.sub.2]. This small discrepancy, of 3%, may be the result of the mixture of electronic states of both materials. Keywords: titanium dioxide; sol-gel synthesis; TiO2/SiO2 composite; heterogeneous photocatalysis; production of [H.sub.2]