Maria Luciana Montes

Se desarrollaron nanomateriales híbridos con potencial aplicación en la degradación fotoquímica de contaminantes orgánicos persistentes en agua. Para ello, se sintetizaron nanopartículas de óxidos de hierro recubiertas con sustancias húmicas (HS-FeOx) mediante el método de coprecipitación, obteniéndose un material compuesto por magnetita/maghemita con un recubrimiento del 14 % p/p de HS respecto a la masa total del material, determinado por análisis termogravimétrico, estable en suspensión a pH > 4. La caracterización por métodos espectroscópicos, termogravimétricos, de propiedades magnéticas, entre otros, confirmaron la naturaleza nanométrica y paramagnética-superparamagnética del material, así como la presencia de materia orgánica asociada a las nanopartículas. Posteriormente, se inmovilizaron complejos de renio-ferroceno-fenantrolina (ReFerPhen) sobre HS-FeOx, generando un sistema híbrido (ReFerPhen/HS-FeOx) mediante adsorción en condiciones suaves. Los espectros UV-visible, de fluorescencia y Raman evidenciaron la presencia del complejo en la superficie de las nanopartículas y sugieren interacciones entre ambos componentes. Los resultados muestran que la combinación de óxidos de hierro recubiertos con sustancias húmicas y fotosensibilizadores de renio constituye una estrategia prometedora para potenciar la formación de especies reactivas de oxígeno y mejorar la eficiencia de procesos foto-Fenton. Estos nanomateriales representan una alternativa atractiva para la remoción de contaminantes emergentes en aguas.

Oxytetracycline (OTC) is a broad-spectrum antibiotic widely used in animal husbandry to prevent and treat infections in livestock. A significant fraction of administered OTC can be excreted unmetabolized, raising serious environmental concerns due to the dissemination of antibiotic residues and the potential development of antibiotic-resistant pathogens in surface and livestock drinking water. This study focuses on the synthesis of magnetic activated carbon (MAC), the evaluation of its OTC removal efficiency and the assessment of its magnetically assisted separation from livestock drinking water formulated according to the Food and Agriculture Organization technical guidelines. The results demonstrate that MAC exhibits substantially enhanced performance compared to conventional activated carbon (AC). Specifically, MAC achieved approximately twice the OTC removal efficiency of AC and enabled a dramatic reduction in sedimentation time when assisted by an external magnetic field, decreasing settling from 6 h to approximately 1 min. Under FAO-recommended ranges of pH, ionic strength, and hardness for livestock drinking water, MAC containing 5% magnetic nanoparticles showed, on average, a 24% higher OTC removal capacity than AC. Adsorbent dosage was identified as the dominant factor influencing OTC removal, although water physicochemical conditions also played a significant role. Both MAC5% and AC exhibited maximum adsorption efficiency at neutral to slightly acidic pH and at low concentrations of NaCl and CaCO₃. MAC5% achieved nearly 100% higher OTC removal than AC at moderately saline and hard water conditions (pH = 8, [NaCl] = 60 mg l ⁻¹ , [CaCO ₃ ] = 300 mg l ⁻¹ ). At high salinity and hardness levels ([NaCl] = 6000 mg l ⁻¹ and [CaCO ₃ ] = 500 mg l ⁻¹ ), the adsorption efficiencies of MAC5% and AC became comparable. In terms of solid–liquid separation, the application of an external magnetic field markedly improved MAC5% settling efficiency, independently of pH, salinity, and hardness, confirming its suitability for rapid and efficient water treatment applications.

Organoclays were prepared using Argentinean montmorillonite (Mt), hexadecyltrimethylammonium, or benzalkonium chloride at different concentrations. Surfactant incorporation, a key factor in biocide capacity, was estimated using interlayer space and thermogravimetric analysis (TGA). Subsequently, Fe oxides were grown on the organoclays. Saturation magnetization indicated that all magnetic composites could respond to an external magnetic field. Inhibition experiments showed high antibacterial activity against Enterococcus faecium , Escherichia coli , and Salmonella typhimurium . The synthesized nanocomposites loaded with 150% CEC (cation exchange capacity) of hexadecyltrimethylammonium were the most effective. Those results were more precisely investigated using the viable plate count method. The magnetic materials had a similar antimicrobial effect to those without magnetic properties, indicating that Fe oxides can be nucleated to impart a magnetic response without affecting the biocide properties. The organoclays showed higher antibacterial activity against E. coli than against the other bacteria assayed. In addition, the agar disk-diffusion method revealed that antimicrobial agents were not released from clays, which is a relevant fact in the water treatment process.