| Summary: | The objective of this work is to improve the efficiency of TiO<sub>2</sub> photocatalysts by activation treatments and by modification with palladium nanoparticles and doping with SiO<sub>2</sub>. The influence of the additive loading was explored, and two activation treatments were performed: UV exposition and H<sub>2</sub> reduction. TiO<sub>2</sub>/SiO<sub>2</sub>/Pd photocatalysts were synthesized by an original cogelation method: a modified silicon alkoxide, i.e., [3-(2-aminoethyl)aminopropyl]trimethoxysilane (EDAS), was used to complex the palladium ions, thanks to the ethylenediamine group, while the alkoxide groups reacted with TiO<sub>2</sub> precursors. Pure TiO<sub>2</sub> was also synthesized by the sol–gel process for comparison. X-ray diffraction evidenced that the crystallographic structure of TiO<sub>2</sub> was anatase and that Pd was present, either in its oxidized form after calcination, or in its reduced form after reduction. The specific surface area of the samples varied from 5 to 145 m<sup>2</sup> g<sup>-1</sup>. Transmission electron microscopy allowed us to observe the homogeneous dispersion and nanometric size of Pd particles in the reduced samples. The width of the band gap for pure TiO<sub>2</sub> sample, measured by UV/Visible diffuse reflectance spectroscopy at approximately 3.2 eV, corresponded to that of anatase. The band gap for the TiO<sub>2</sub>/SiO<sub>2</sub>/Pd composite samples could not be calculated, due to their high absorption in visible range. The photocatalytic activity of the various catalysts was evaluated by the degradation of a methylene blue solution under UV radiation. The results showed that the photocatalytic activity of the catalysts was inversely proportional to the content of silica present in the matrix. A small amount of silica improved the photocatalytic activity, as compared to the pure TiO<sub>2</sub> sample. By contrast, a high amount of silica delayed the crystallization of TiO<sub>2</sub> in its anatase form. The activation treatment under UV had little influence on photocatalytic efficiency. The introduction of Pd species increased the photocatalytic activity of the samples because it allowed for a decrease in the rate of electron–hole recombinations in TiO<sub>2</sub>. The reduction treatment improved the activity of photocatalysts, whatever the palladium content, thanks to the reduction of Ti<sup>4+</sup> into Ti<sup>3+</sup>, and the formation of defects in the crystallographic structure of anatase.
|
|---|
