It is well-known that γ-Al₂O₃ possesses large, specific areas and high thermal, chemical, and mechanical resistance. Due to this, it is the most-used support for catalysts, in this case TiO₂, as it enables it to achieve better dispersion and improves the activity in catalytic photodegradation reactions. In a previous work, it was observed that the optimal content of TiO₂ in γ-Al₂O₃ was around 15% since the degradation of phenol results were maximized and a synergistic effect was generated by the interaction of both oxides. In addition, an increase in acidity crystal size and the generation of localized, oxygen-vacant, electronic states in the forbidden band of γ-Al₂O₃, were observed. This study focuses on the effect of the calcination temperature on a γ-Al₂O₃-TiO₂ catalyst (15% w/w of TiO₂) and its impact on photocatalytic activity. The catalysts prepared here were characterized by X-ray diffraction, N₂ adsorption–desorption, FTIR-pyridine adsorption, MAS-NMR, HRTEM-FFT, UV-vis, and fluorescence spectroscopy.

This study was conducted to identify the correlation between the CO chemisorption (linear interaction and gem dicarbonyl) and the specific size of rhodium particles, and further to determine the influence of this relationship on the catalytic oxidation reaction of methyl tert-butyl ether (MTBE). During the synthesis, first, TiO₂ was developed by the sol-gel method under acidic conditions. Second, Rh was deposited (1 wt %) by the incipient wetness impregnation method. Later, with the aim of controlling the particle size, the Rh/TiO₂ materials were crystallized at different reduction conditions during 3 h heat treatment. The results obtained by TEM micrographs indicated that the average particle size varies between 1.0 and 8.1 nm, depending on the conditions of heat treatment. From the histogram analysis of each TEM micrograph, two correlations were made: (i) the gem-dicarbonyl interaction was typical of Rh particles ≤ 1.5 nm, and (ii) a linear interaction, bridged interaction and dentate interaction were observed in particles ≥ 1.6 nm. The gem-dicarbonyl interaction (particle size ≤ 1.5 nm) was the most active in the oxidation reaction of MTBE.

TiO₂ thin film coatings significantly improve catalyst separation in photocatalytic processes. They can be applied in heterogeneous photocatalysis under sunlight by mixing TiO₂ with other oxides, such as CeO₂, for the removal of pollutants in water. Here, TiO₂-CeO₂ thin films deposited on borosilicate slides were analyzed and applied in solar heterogeneous photocatalysis for the oxidation of pesticides. The films were synthesized by the sol-gel method with spin coating. The waste solutions from the synthesis were used to prepare TiO₂ and TiO₂-CeO₂ powders. These were analyzed by XRD and XPS to explain the behavior of the films. The thin films were characterized by UV-Vis spectroscopy with transmittance, UV-Vis spectroscopy with RDS, profilometry, AFM and SEM. The addition of CeO₂ to TiO₂ caused a decrease in the average crystal size and an increase in the strain index. The addition of a second layer made the TiO₂-CeO₂ thin films thinner. The CeO₂ created surface and electronic defects in the titania films, which enhanced their photocatalytic properties under sunlight in the mineralization of diuron and methyl parathion. The TiO₂-CeO₂-5.0% single-layer thin film samples were the most active in this study and will undoubtedly be applied in larger-scale reaction systems.