This study focused on searching for more effective nanomaterials for environmental remediation and health protection; thus, coliform bacteria, yeast and the organic food dye sunset yellow were selected as target pollutants to be eliminated under solar light by Ag/Cr-TiO₂ and Pd/Cr-TiO₂. Firstly, Cr³⁺ was in situ incorporated into the anatase crystalline lattice by the sol-gel method; then, Ag or Pd nanoparticles were deposited on Cr-TiO₂ by chemical photoreduction. The scientific challenge addressed by the development of these composites was to analyse the recovery of Cr, to be employed in photocatalyst formulation and the enhancement of the TiO₂ photocatalytic activity by addition of other noble metals. By extensive characterization, it was found that after TiO₂ doping with chromium, the parameters of the crystal lattice slightly increased, due to the incorporation of Cr ions into the lattice. The TiO₂ band gap decreased after Cr addition, but an increase in the optical absorptions towards the visible region after noble metals deposition was also observed, which was dependent of the Ag or Pd loading. Generally, it was observed that the noble metals type is a factor that strongly influenced the effectiveness of the photocatalysts concerning each substrate studied. Thus, by using Ag(0.1%)/Cr-TiO₂, the complete elimination of E. coli from samples of water coming from a highly polluted river was achieved. Pd(0.5%)/Cr-TiO₂ showed the highest efficiency in the elimination of S. cerevisiae from a lab prepared strain. On the other hand, the Pd(0.1%)/Cr-TiO₂ sample shows the highest dye degradation rate, achieving 92% of TOC removal after 180 min.

In this work, photocatalytic materials constituted by Cr-doped TiO₂ (Cr-TiO₂) decorated with noble metals show high effectiveness in the mineralization of Acid Orange 7 (AO7) and in the disinfection of real river water. The materials were firstly obtained by sol-gel method to get Cr-TiO₂ that was subsequently modified by photochemical deposition of Ag or Pd nanoparticles (Ag/Cr-TiO₂, Pd/Cr-TiO₂). Chemical-physical characterization results evidenced that the noble metals were homogeneously distributed on the Cr-TiO₂ surface. By using Pd(0.25%)/Cr-TiO₂, the AO7 discoloration efficiency was about 91.4% after only 60 min of visible irradiation, which can be due to the lowest band gap of this material. Moreover, nitrates, chlorides, total hardness, and coliform bacteria content significantly decreased after the treatment of real river water samples (that is contaminated by industrial and domestic effluents) under UV and visible light irradiation in the presence of TiCrOx decorated with noble metals. One hundred percent of elimination rate for E. coli, total coliforms, and other enterobacteriaceae (without regrowth) was achieved by using Ag/Cr-TiO₂ as photocatalyst.

This work describes the application of three different AgBr heterojunctions with TiO₂, SnO₂ and WO₃ in the treatment of two water sources: wastewater from a dairy industry facility (WDI) and water from a polluted river (WPR). All heterojunctions were widely characterised, and it was observed that the physicochemical properties of all the coupled materials were similar; however, the highest elimination of Enterobacteriaceae (>90%) was obtained with the AgBr/WO₃(20%) photocatalyst in WDI. Under the same conditions, with this photocatalyst, the complete removal of bacteria (i.e., E. coli, total coliforms and other Enterobacteriaceae) was achieved in WPR. The chlorides, hardness and colour in the two water samples decreased after photocatalytic treatment with all the coupled materials. However, nitrate levels and chemical oxygen demand increased due to the possible formation of intermediary species from the photodegradation of organic pollutants and the release of metabolic intermediates from bacterial degradation during the photocatalytic process. Overall, heterogeneous photocatalysis based on AgBr-coupled materials shows potential as a tertiary treatment for WDI and for the purification of vegetable irrigation water. However, it is still important to consider the need to optimise the integrity of photocatalytic materials in order to maintain their bactericidal effectiveness through continuous reuse.

As other studies have demonstrated, improving the effectiveness of TiO2 for environmental remediation requires that the properties of this oxide be modified using different synthesis methods. In the current study, labprepared TiO2 was synthesized using the hydrothermal method and two different Ti precursors (titanium butoxide and titanium isopropoxide). After the synthesis, the obtained titania was also modified using photodeposition by platinum nanoparticles. This study aims to evaluate the effectiveness of the photocatalytic materials prepared in photodegrading methyl orange. The Ti precursors used in the TiO2 synthesis had a slight effect on the physicochemical properties of the oxide obtained. When titanium butoxide was used as a precursor, we observed a change in the bandgap value and some material with the largest surface area. Additionally, the addition of Pt increased the absorption of TiO2 in the visible region of the electromagnetic spectrum and slightly decreased the bandgap value of this oxide. The photocatalyst prepared using titanium isopropoxide as a precursor showed the most remarkable effectiveness in the degradation rate of methyl orange. This is the result of the lower band gap value of this material which leads to easier transport of the photogenerated charges during the photocatalytic reaction. We also observed that the addition of Pt has a detrimental effect on the effectiveness of TiO2 in dye degradation, which may be due to possible obstruction of the dye-photocatalyst interaction on the TiO2 surface because of the Pt nanoparticles observed by tem. The effectiveness of commercial TiO2 in methyl orange degradation is slightly higher than that observed in other evaluated solids.

In this work, Titania was modified by sulfation or fluorination and platinum on the surface to improve the Cr (VI) reduction efficiency compared to the bare TiO2 material synthesized by the sol-gel method. The synthesized materials were characterized by XRD, SBET, UV-Vis DRS, XRF, TEM, FTIR, and XPS. The modifications led to higher stability in the Anatase phase and surface area of this semiconductor. The addition of F and Pt in TiO2 led to absorption increases in the visible region of the electromagnetic spectrum. A correlation between the new physicochemical properties obtained after TiO2 modification and the photocatalytic performance of this material was observed. The best result in chromium reduction was obtained using Pt-S-TiO2 as the photocatalyst; this material showed a suitable combination of surface area, high UV-Vis absorption, high hydroxylation, and the existence of Pt nanoparticles on the surface, which favors an increased electron-hole pair half-life. Different reaction parameters were also evaluated, which demonstrated that the best photocatalytic performance was obtained under an N2 atmosphere, a light intensity of 120 W/m2, and 2 hours of total reaction time. Likewise, it was noted that an increase in reaction time from 2 to 5 hours, had a detrimental effect on reducing Cr (VI) efficiency.