Photocatalysis is an effective advanced oxidation process to mineralize recalcitrant contaminants in aqueous media. TiO₂ is the most used photocatalyst in this type of process. To improve the deficiencies of this material, one of the most used strategies has been to dope TiO₂ with metallic ions. Chemical reagents are often used as dopant precursors. However, due to the depletion of natural resources, in this work it was proposed to substitute chemical reagents and instead use a metallic residue (door key) as a doping precursor. The materials were synthesized using the sol–gel method and calcined at 400 °C to obtain the crystal structure of anatase. The characterization of the materials was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy–energy-dispersive X-ray analysis (SEM-EDX) methods X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The results obtained indicate that Cu⁺/Cu²⁺ and Zn²⁺ ions coexist in the support, which modifies the physicochemical properties of TiO₂ and improves its photocatalytic efficiency. The synergistic effect of the dopants in TiO₂ allowed the mineralization of diclofenac in an aqueous medium when T-DK (1.0) was used as photocatalyst and simulated solar radiation as an activation source.

5-Hydroxymethylfurfural (5-HMF) has been described as one of the 12 key platform molecules derived from biomass by the US Department of Energy, and its hydrogenation reaction produces versatile liquid biofuels such as 2,5-dimethylfuran (2,5-DMF). Catalytic hydrogenation from 5-HMF to 2,5-DMF was thoroughly studied on the metal nickel catalysts supported on Al₂O₃-TiO₂-ZrO₂ (Ni/ATZ) mixed oxides using isopropanol and formic acid (FA) as hydrogen donors to find the best conditions of the reaction and hydrogen donor. The influence of metal content (wt%), Ni particle size (nm), Nickel Ni⁰, Ni⁰/NiO and NiO species, metal active sites and acid-based sites on the catalyst surface, and the effect of the hydrogen donor (isopropanol and formic acid) were systematically studied. The structural characteristics of the materials were studied using different physicochemical methods, including N₂ physisorption, XRD, Raman, DRS UV-Vis, FT-IR, SEM, FT-IR Py_ad, H₂-TPD, CO₂-TPD, H₂-TPR, TEM and XPS. Second-generation 2,5-DMF biofuel and 5-HMF conversion by-products were analyzed and elucidated using ¹H NMR. It was found that the Ni⁰NiO/ATZ3_WI catalyst synthesized by the impregnation method (WI) generated a good synergistic effect between the species, showing the best catalytic hydrogenation of 5-HMF to 2,5-DMF using formic acid as a hydrogen donor for 24 h of reaction and temperature of 210 °C with 20 bar pressure of Argon (Ar).

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.