For environmental applications, nanosized TiO₂-based materials are known as the most important photocatalyst and are intensively studied for their advantages such as their higher activity, lower price, and chemical and photoresist properties. Zn or Cu doped TiO₂ nanoparticles with anatase crystalline structure were synthesized by sol−gel process. Titanium (IV) butoxide was used as a TiO₂ precursor, with parental alcohol as a solvent, and a hydrolysing agent (ammonia-containing water) was added to obtain a solution with pH 10. The gels were characterized by TG/DTA analysis, SEM, and XPS. Based on TG/DTA results, the temperature of 500 °C was chosen for processing the powders in air. The structure of the samples thermally treated at 500 °C was analysed by XRD and the patterns show crystallization in a single phase of TiO₂ (anatase). The surface of the samples and the oxidation states was investigated by XPS, confirming the presence of Ti, O, Zn and Cu. The antibacterial activity of the nanoparticle powder samples was verified using the gram−positive bacterium Staphylococcus aureus. The photocatalytic efficiency of the doped TiO₂ nanopowders for degradation of methyl orange (MO) is here examined in order to evaluate the potential applications of these materials for environmental remediation.

The tin-doped TiO₂ powders obtained by sol-gel and microwave-assisted sol-gel methods were investigated. The synthesis took place in a basic medium (pH 10, ammonium hydroxide, 25%) starting from tetrabutyl orthotitanate in its parental alcohol. In the case of the dopant, Tin(II) 2-ethylhexanoate as SnO₂ precursor was used in the amount of 1, 2, or 4 mol % SnO₂. Based on thermal analysis data, the powders were thermally treated in air, at 500 °C. The comparative investigation of the structure and morphology of the nanopowders annealed at 500 °C was performed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy with selected area electron diffraction (HRTEM/SAED), scanning transmission electron microscopy (STEM) coupled with EDX mapping, Fourier transmission infrared (FTIR), UV–Vis, Raman and photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), and X-ray florescence spectroscopy (XRF). The obtained materials were tested for the photocatalytic removal of methyl orange dye from aqueous solutions. High degradation efficiencies (around 90%) were obtained by Sn doping after 3 h of UV light irradiation.

Zeolite Y samples with microporous and hierarchical structures containing Ti–Ni and Ti–Co oxides were obtained as active photocatalysts. Different Ti amounts (5, 10% TiO₂) were supported, followed by the loading of Ni or Co oxides (5%). X-ray diffraction evidenced the presence of TiO₂ as an anatase. N₂ adsorption–desorption results showed type IV isotherms for hierarchical zeolite Y samples, and a combination of type IV and I isotherms for zeolite Y samples. UV–Vis diffuse reflectance spectra showed a shift in the absorption band to visible with increasing Ti loading and especially after Co and Ni addition. A significant effect of the support was evidenced for Ti and its interaction with Co/Ni species. The zeolite Y support stabilized Ti in the 4+ oxidation state while hierarchical zeolite Y support favored the formation of Ti³⁺ species, Ni⁰ and Ni²⁺ and the oxidation of Co to 3+ oxidation state. Photocatalytic activity, under UV and visible light irradiation, was evaluated by the degradation of amoxicillin, used as a model test. The photocatalytic mechanism was investigated using ethanol, p-benzoquinone and KI as ·OH and ·O₂⁻ radicals and hole (h⁺) scavengers. The best results were obtained for the immobilized Ni-Ti species on the hierarchical zeolite Y support.

Magnesium oxide (MgO) was synthesized by three different methods: the sol–gel (SG), microwave-assisted sol–gel (MW), and hydrothermal (HT) methods for comparing the influence of the preparation conditions on the properties of the products. The powders were annealed at 450 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM/HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), BET specific surface area and porosity, photoluminescence, and UV–Vis spectroscopy. The samples consisted mainly of periclase as a crystalline phase, and the MW and HT preparation methods generated particles with higher specific surface areas. The powders had less-defined morphologies and high levels of aggregation. The optical band gaps of the samples were determined from UV DRS, and the photocatalytic activities of the magnesium oxides obtained by the three methods towards the degradation of methyl orange (MO) under UV light irradiation was evaluated.

Ag nanoparticles (AgNPs) were biosynthesized using sage (Salvia officinalis L.) extract. The obtained nanoparticles were supported on SBA-15 mesoporous silica (S), before and after immobilization of 10% TiO₂ (Degussa-P25, STp; commercial rutile, STr; and silica synthesized from Ti butoxide, STb). The formation of AgNPs was confirmed by X-ray diffraction. The plasmon resonance effect, evidenced by UV-Vis spectra, was preserved after immobilization only for the sample supported on STb. The immobilization and dispersion properties of AgNPs on supports were evidenced by TEM microscopy, energy-dispersive X-rays, dynamic light scattering, photoluminescence and FT-IR spectroscopy. The antioxidant activity of the supported samples significantly exceeded that of the sage extract or AgNPs. Antimicrobial tests were carried out, in conditions of darkness and white light, on Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans. Higher antimicrobial activity was evident for SAg and STbAg samples. White light increased antibacterial activity in the case of Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa). In the first case, antibacterial activity increased for both supported and unsupported AgNPs, while in the second one, the activity increased only for SAg and STbAg samples. The proposed antibacterial mechanism shows the effect of AgNPs and Ag⁺ ions on bacteria in dark and light conditions.

Using the microwave-assisted sol–gel method, Zn- and Cu-doped TiO₂ nanoparticles with an anatase crystalline structure were prepared. Titanium (IV) butoxide was used as a TiO₂ precursor, with parental alcohol as a solvent and ammonia water as a catalyst. Based on the TG/DTA results, the powders were thermally treated at 500 °C. XRD and XRF revealed the presence of a single-phase anatase and dopants in the thermally treated nanoparticles. The surface of the nanoparticles and the oxidation states of the elements were studied using XPS, which confirmed the presence of Ti, O, Zn, and Cu. The photocatalytic activity of the doped TiO₂ nanopowders was tested for the degradation of methyl-orange (MO) dye. The results indicate that Cu doping increases the photoactivity of TiO₂ in the visible-light range by narrowing the band-gap energy.