Donaldo Fabio Mercado

Antimicrobial resistance and waterborne pathogens require efficient and environmentally compliant disinfection strategies. Cu2+-, Zn2+-, and Mn2+-doped ferrite nanoparticles were evaluated for Escherichia coli inactivation under dark and visible-light conditions. As-prepared ferrites exhibited bactericidal activity mainly driven by divalent metal leaching (up to 18.9 ± 0.9 mg L–1 Zn2+, 18.7 ± 0.1 mg L–1 Mn2+, and 6.2 ± 0.7 mg L–1 Cu2+), producing up to ∼3 log10 reductions in colony-forming units per milliliter (CFU mL–1) but exceeding drinking-water guidelines. Hydrothermal treatment transformed the amorphous ferrites into crystalline nanospinels (≈18–21 nm) and markedly suppressed metal release (<3.6 mg L–1). Under dark conditions, hydrothermally treated ferrites exhibited contact-killing behavior with HT-CuFe2O4, achieving complete bacterial inactivation (6 log10) within 2 h. Under visible light, the photocatalytic activity was enhanced, and HT-CuFe2O4 achieved total E. coli elimination within 0.5 h. Electrochemical analysis confirmed p-type semiconducting behavior, favoring hole-driven oxidation and reactive oxygen species generation. Global solar exposure modeling showed that complete disinfection can be achieved at realistic photon doses, with tropical latitudes requiring the shortest exposure times. These results demonstrate that hydrothermal treatment converts doped ferrites into efficient solar-driven photocatalysts for water disinfection.

Commercial TiO₂ P25 was modified with iron species using simple, mild and cost-effective synthesis conditions. The novel TiO₂–Fe material exhibits both high disinfectant activity and long stability under visible light irradiation. The bactericidal activity of the synthesized catalyst was assessed by its capability to inactivate Escherichia coli under both simulated solar and LED-visible light. XRD confirmed the structural integrity of the material, while diffuse reflectance spectroscopy evidenced its absorption in the visible region. Mössbauer and FTIR analysis of the TiO₂–Fe catalyst indicate that iron exists predominantly in the Fe³⁺ state in a Ti–O–Fe bond. Electrochemical studies allowed to correlate the reactivity with the conduction and valence band positions, providing insights into the production of reactive oxygen species (ROS) responsible for bacterial inactivation. A first noteworthy aspect of this study is the identified Ti–O–Fe bond in the TiO₂–Fe material, a feature that has not been previously reported in the literature. Another innovative aspect is the simplicity of the synthesis method, which employs a thermally mild and time-efficient process, thereby providing an efficient and accessible approach for enhancing photocatalytic properties. Our findings suggest that the prepared TiO₂–Fe photocatalyst holds potential for future applications in antimicrobial paint coatings designed for hospital environments, aiming to enhance infection control under indoor lighting conditions.

Bacterial contamination poses serious challenges for public health in several scenarios, such as in developing antimicrobial surfaces for biomedical applications and clean water availability. To face this, in the current work we have incorporated Fe₃O₄ domains onto the graphitic carbon nitride framework (g-C₃N₄). Therefore, a series of iron-doped nanocomposites (g-C₃N₄, g-C₃N₄-25, g-C₃N₄-50, g-C₃N₄-100, and g-C₃N₄-500) were synthesized by controlling the adsorption of Fe on bare g-C₃N₄. These materials were rigorously characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), Z-potential (PZC), fluorescence, electrochemical impedance, and X-ray photoelectron spectroscopy (XPS), confirming the successful formation of Fe₃O₄ nanoparticles and the creation of abundant surface defects. Photocatalytic experiments using ciprofloxacin (1-cyclopropyl-6-fluoro-4-oxo-7-(piperazin-1-yl)-quinoline-3-carboxylic acid) as probe compound, under UV-Vis irradiation, highlighted the g-C₃N₄-25 material as the one having the higher photocatalytic activity. Additional tests using chemical scavengers showed a shift from hydroxyl-radical-driven pathways in bare g-C₃N₄ to the more selective singlet-oxygen in the Fe-modified material. E. coli disinfection under indoor light produced a 6.0 log₁₀ CFU/mL reduction with g-C₃N₄-25, compared to only 2.8 log₁₀ with pristine g-C₃N₄. Comparative experiments with Co- and Cu-doped analogues further showed superior kinetics and ROS yields of the iron material. Finally, the best-performing Fe-g-C₃N₄ catalyst was embedded in an alginate matrix to produce a self-disinfecting surface that maintained a 5.9 ± 0.3 log₁₀ CFU/mL decrease in E. coli after five consecutives 24 h irradiation cycles. These results position Fe-doped g-C₃N₄ as a versatile platform for the sustainable photocatalytic removal of contaminants and durable antimicrobial coatings.

The development of efficient photocatalytic materials for waterborne pathogen inactivation and self-cleaning surfaces in biomedical applications remains a critical challenge due to the rising prevalence of antimicrobial-resistant bacteria. This study systematically investigates the structural, optical, and photocatalytic disinfection properties of graphitic carbon nitride (g-C₃N₄) synthesized at variable temperatures (450–600 °C) and doped with transition metals (Mn, Co, Cu). Through FTIR and UV/Vis spectroscopy, we demonstrate that synthesis temperatures between 450 and 550 °C yield a well-ordered polymeric network with enhanced π-conjugation and charge separation, while 600 °C induces structural degradation. Metal doping with Mn and Co significantly enhances photocatalytic disinfection, achieving complete E. coli inactivation (6-log reduction) within 6 h via optimized reactive oxygen species (ROS) generation. The best material (g-C₃N₄ synthesized at 500 °C and doped with Mn) was integrated into sodium alginate hydrogel surfaces, demonstrating reusable self-cleaning functionality with sustained bactericidal activity (5.9-log CFU/mL reduction after five cycles). This work provides a roadmap for tailoring metal-doped g-C₃N₄ composites for practical antimicrobial applications, emphasizing the interplay between synthesis parameters, ROS dynamics, and real-world performance.

Due to the increasing energy demand and the depletion of light crude oil, the exploitation of heavy crude oil fields is being considered as an alternative. In-situ combustion (ISC) is an enhanced oil recovery thermal technique that involves injecting air or oxygen into the well to promote partial oxidation of the oil. However, the initial ignition of combustion has posed significant challenges. Therefore, special attention must be given to Low Temperature Oxidation (LTO). Furthermore, asphaltenes contribute to coke formation as a fuel. Janus nanomaterials catalysts can be utilized to lower the ignition temperature. In this study, we focused on investigating the catalytic oxidation of asphaltenes primarily in the LTO region. To achieve the research objective, the catalytic oxidation of asphaltenes was studied using janus-functionalized MnO2 nanoparticles that were previously synthesized and characterized using both adipic and hexanoic acid. It was observed that surface functionalization reduces the exothermic nature of the process, and the apparent activation energies for the functionalized materials are lower than those for the virgin asphaltenes and the obtained MnO2, thus demonstrating their catalytic activity. Additionally, the stability of the formed nanofluids is maintained for up to 24 hours.