Claudia Martínez Gómez

Currently, the search continues for solutions for the treatment of water contaminated by toxic compounds such as chlorophenols that are used in the manufacture of pesticides, insecticides, and the paper industry, among others, and that are considered persistent in the environment, in addition to being extremely toxic, especially 2,4,6-trichlorophenol, which is potentially carcinogenic. In this work, the use of thermally activated Co/Fe hydrotalcites as photocatalysts is presented. The catalysts were characterized by differential thermal and thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N₂ physisorption, diffuse reflectance spectroscopy and photoluminescence. The catalysts were tested in the photo-assisted degradation of 80 mg/L of 2,4,6-trichlorophenol. The catalytic structures present are Co/Fe simple and mixed oxides. The results of the photocatalytic activity show that the materials have good photocatalytic activity with a degradation efficiency of 2,4,6-trichlorophenol, reaching a maximum capacity of 65% for oxides derived from hydrotalcites with a Co/Fe ratio of 2 and calcined at 500 °C, exceeding the activity shown by the reference catalyst, high-performance commercial titanium dioxide. The photocatalytic activity studied for the catalyst with the highest percentage of degradation is attributed to the presence of holes, as well as to the formation of oxidizing species such as superoxide and hydroxyl radicals that are determinants in the degradation mechanism.

The pharmaceutical industry is a major source of pollution in wastewater effluents, characterized by chemical residues that are complex and difficult to degrade. Naproxen, a commonly detected drug in sewage effluents, exceeds safe concentrations for aquifers and is highly persistent, posing significant risks to aquatic life and ecosystems. This drug is known to cause long-term side effects in humans, such as gastrointestinal ulcers and nephrosis, associated with frequent and prolonged use. Additionally, the recent pandemic has led to a marked increase in drug consumption over a short period, exacerbating environmental contamination. Titanium dioxide has been extensively used as a photocatalyst in recent decades, proving effective in reducing these emerging pollutants. In this study, TiO₂ doped with cerium was synthesized using the sol–gel method, with cerium concentrations varied at 1, 3, 5, and 10% by weight. The resulting nanocatalysts were characterized through nitrogen physisorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-Vis diffuse reflectance spectroscopy. Photocatalytic activity was assessed using a UV-Vis spectrophotometer to monitor the degradation of the drugs. XRD analysis confirmed the crystallinity and anatase phase of TiO₂. UV-Vis diffuse reflectance spectra indicated a decrease in bandgap energy of up to 3.00 eV compared to pure TiO₂. The materials demonstrated significant degradation of naproxen (NPX) and acetaminophen (ACTP), both prepared at 30 ppm, over a 6 h reaction period.

In this study, we present the synthesis of TiO₂ nanomaterials doped with different mol% cobalt, prepared by the sol–gel method for CO₂ reduction using UV light. The nanomaterials were calcined at 400 °C for 4 h. Characterization of the nanomaterials was performed using XRD-Rietveld refinement, XPS, Raman spectroscopy, diffuse reflectance spectroscopy (DRS), SEM-EDS, TEM-HRTEM, BET area, photoluminescence, and electrochemical techniques. The results show that the incorporation of cobalt into TiO₂ modifies the structural properties, binding energies, and oxygen vacancy generation, it undergoes a shift towards the visible region, the recombination of charge carriers decreases, and the BET area is slightly modified. The photoreduction of CO₂ with the highest production of methane and ethane is with 1% mol% of cobalt in TiO₂, exhibiting values 3 and 14 times higher with respect to TiO₂, which is attributed to the efficiency in the separation of photogenerated species (e⁻/h⁺) as a consequence of the generation of energetic states that function as an electron trap and thus improve the photocatalytic activity for the photoreduction of CO₂.

CeO₂–ZnO materials were synthesized via a modified sol–gel method, varying the ZnO loading to evaluate its effect on the photocatalytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under UV irradiation. XRD analysis confirmed the cubic fluorite structure of CeO₂ and, at higher loadings, the coexistence with a hexagonal wurtzite phase. At low loadings, Zn²⁺ incorporation into the CeO₂ lattice was evidenced, leading to lattice parameter contraction and the generation of oxygen vacancies. BET and SEM analyses indicated that an intermediate ZnO content (CZ1.5) increased the surface area (~41%) without collapsing the mesoporosity. XPS revealed Ce³⁺ species, defects, and Zn–O–Ce bonds, consistent with the formation of an S-scheme heterojunction. UV–Vis spectra showed similar Eg values (~3.13 eV) across the series, indicating that the photocatalytic enhancement is driven by structural and interfacial effects rather than optical changes. The CZ1.5 catalyst achieved ≈80% degradation and 74% mineralization (TOC), approximately twice that of pure CeO₂, attributed to efficient charge separation and the generation of reactive species O₂•⁻ and •OH. Furthermore, a temperature treatment CZ1.5 calcined to 400°C was the most active above the material treated at 300 and 500 °C.

Understanding how the surface charge environment governs pollutant–catalyst interactions is essential for designing efficient photocatalysts. In this study, ZnO–CeO₂–WO₃ composite materials were synthesized through a simplex-centroid mixture design to evaluate their photocatalytic activity toward the degradation of 4-nitrophenol (4-NPOH) under UV irradiation. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV–Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), nitrogen adsorption–desorption (BET/DFT) and scanning electron microscopy (SEM). Photocatalytic experiments were conducted without pH adjustment to analyze the intrinsic behavior of each oxide and their mixtures. The acid–base equilibrium of 4-NPOH (pK_a = 7.2) allowed evaluating its deprotonation to 4-nitrophenolate (4-NP⁻) and its interaction with the catalyst surface, which depends on the point of zero charge (pH_Pzc) of ZnO, CeO₂, and WO₃. The Zn–W binary system (ZnWO₄ phase) exhibited the highest activity, achieving 81% degradation efficiency and the largest apparent rate constant (k = 5.1 × 10⁻³ min⁻¹). However, a 51% decrease in activity was observed after three reuse cycles, attributed to WO₃ leaching induced by the interaction between 4-NPO⁻ and zinc tungstate hydroxide (Zn[W(OH)₈]). This work establishes a direct correlation between surface charge, pollutant speciation, and photocatalytic performance, providing a mechanistic framework for understanding pH-dependent degradation processes over multicomponent oxide composites.

La aparición de contaminantes emergentes que incluyen diferentes fármacos de uso cotidiano por los seres humanos y una amplia gama de compuestos químicos en los recursos hídricos ha generado una reciente preocupación debido a sus posibles impactos en la salud humana y el equilibrio ambiental. Estos compuestos aún no regulados, no son fácilmente eliminados por los sistemas tradicionales de tratamiento de aguas residuales. A pesar de encontrarse en concentraciones muy bajas, diversos estudios han demostrado que son capaces de convertirse en una amenaza ambiental significativa. Por ello, en el presente trabajo de investigación se plantea el estudio de la fotodegradación catalítica de los fármacos emergentes de naproxeno y diclofenaco utilizando catalizadores de CeO2-ZnO con diferentes concentraciones en peso de ZnO (0.5, 1.5 y 2.5 %) bajo irradiación UV en estándares de laboratorio y aguas de desecho reales. Los materiales de CeO2-ZnO en sinergia demostraron ser más eficaces en la degradación de estos fármacos que el material de CeO2 comercial, mejorando la eficiencia de cargas y mayor absorción de luz UV.

Actualmente, la escasez de agua potable es uno de los principales problemas de los seres vivos debido a la mala disposición de residuos, uso desmedido de este recurso y sobreexplotación demográfica. Debido a esto, existen procesos de oxidación avanzada encargados de estudiar la forma de reciclar el agua, dentro de los más eficaces se encuentra la fotodegradación catalítica, la cual ha demostrado alta eficiencia en la mineralización de una amplia gama de moléculas tóxicas empleando radiación solar o UV y el uso de catalizadores para la producción de radicales hidroxilos en la oxidación de contaminantes. Por ello, en el presente trabajo se plantea el estudio de la fotodegradación catalítica de los contaminantes de ibuprofeno y paracetamol utilizando catalizadores TiO2-ZnO con diferentes contenidos de ZnO (5%, 10%, y 15% en peso) bajo irradiación UV. Los materiales de TiO2 y ZnO en sinergia demostraron ser eficaces en la degradación de estos fármacos, mejorando la eficiencia de cargas y mayor absorción de luz UV

This study aimed to develop Ca²⁺ doped ZnO nanoparticles (NPs) and investigate their antibacterial properties against microorganisms of dental interest. Zn-Ca NPs were synthesized by the sol-gel method with different concentrations of Ca²⁺ (1, 3, and 5 wt. %) and subsequently characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The Kirby–Bauer method was used to measure antibacterial effects. NPs showed the wurzite phase of ZnO and bandgap energies (Eg) from 2.99 to 3.04 eV. SEM analysis showed an average particle size of 80 to 160 nm. The treatments that presented the best antibacterial activity were Zn-Ca 3% and Zn-Ca 5%. ZnO NPs represent an alternative to generate and improve materials with antibacterial capacity for dental applications.

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.

TiO₂, ZnO, and their combination (TiO₂–ZnO) at different molar ratios and pH values (Ti–Zn A and B 3:1, 1:1, and 1:3) via the sol–gel method were characterized by SEM, XRD, UV-Vis, and FT-IR. Moreover, antibacterial tests of the nanoparticles were conducted against Escherichia coli (E. coli), Salmonella paratyphi (S. paratyphi), Staphylococcus aureus (S. aureus), and Listeria monocytogenes (L. monocytogenes). The indirect bandgap of the Ti–Zn binary oxide synthesized in the basic process at molar ratios of 3:1, 1:1, and 1:3 exhibited a higher eV (3.31, 3.30, and 3.19 eV, respectively) compared to pure TiO₂ (3.2 eV) and synthesized in the acid process (3.22, 3.29, and 3.19 eV at same molar ratio, respectively); in addition, the results of the indirect bandgap were interesting due to a difference found by other authors. Moreover, the sol–gel method promoted the formation of a spherical, semi-sphere, and semi-hexagonal shape (TiO₂, Ti–Zn 1:1, and Ti–Zn 1:3) with a size ≤ 150 nm synthesized during the acid process, with a crystallite size of ~71, ~12, ~34, and ~21 nm, respectively, while ZnO NPs developed a hexagonal and large size (200–800 nm) under the same synthesis process (acid). Samples were classified as TiO₂ anatase phase (basic synthesis); however, the presented changes developed in the rutile phase (24% rutile phase) at an acid pH during the synthesis process. Moreover, Ti–Zn maintained the anatase phase even with a molar ratio of 1:3. The most interesting assessment was the antibacterial test; the Ti–Zn A (1:3) demonstrated a bacteriostatic effect compared with all treatments except ZnO, which showed a similar effect in dark conditions, and only Gram-positive bacteria were susceptible (Listeria monocytogenes > Staphylococcus aureus). Therefore, the Ti–Zn characteristic suggests that the results have potential in treating wastewater as well as in pharmaceutical (as drug carriers) and medical applications.