Daina Arenas Buelvas

Goethite (α-FeOOH) is an antiferromagnetic iron oxyhydroxide that frequently exhibits a weak ferromagnetic component, a behavior widely discussed in the literature but still not completely understood at the microscopic level. In Al-substituted goethites, this magnetic response becomes even more complex due to the combined effects of magnetic dilution and local structural perturbations introduced by the substitution of Fe3+ with non-magnetic Al3+ ions. In this study, we investigated the magnetic behavior of synthetic goethites with different Al contents through magnetization measurements as a function of the field and temperature, in combination with compositional and structural characterization using Wavelength Dispersive X-ray Fluorescence (WDXRF) and Raman spectroscopy. The results reveal a progressive reduction in the Néel temperature with increasing Al concentration, accompanied by pronounced magnetic irreversibility at low fields and a decoupling between the temperature evolution of the coercive field and the remanent magnetization. In contrast to pure goethite, where these quantities evolve more coherently, the Al-substituted samples show a faster suppression of remanence, while coercivity remains finite and close to the magnetic transition temperature, indicating distinct mechanisms governing magnetization reversal and magnetic remanence. When considered together with previous spectroscopic results reported for the same samples, these findings support the scenario of intrinsic magnetic inhomogeneity. The magnetic behavior is consistent with the diamagnetic-island model, in which Al incorporation leads to the formation of magnetically weakened regions within the goethite matrix, giving rise to local perturbations of antiferromagnetic order. The present results provide new magnetic evidence supporting the model previously proposed for Al-substituted goethites, while remaining compatible with literature models that attribute weak ferromagnetism in pure goethite to defect- and microstructure-related magnetic disorder.

In this study, we combine computational and experimental methods to investigate urea-derived (CN-U) and thiourea-derived (CN-TU) graphitic carbon nitride (g-C3N4) for surface adsorption, photocatalytic activity, and cell viability using methylene blue (MB) dye degradation. XRD revealed CN-TU is more ordered (d002 = 0.324 nm; crystallite size = 45.4 nm), while CN-U is less crystalline (d002 = 0.326 nm; 18.1 nm). A precursor-dependent shift in absorption edge showed CN-U with wider indirect bandgap (3.07 eV) compared to CN-TU (2.85 eV). Isotherm models and computational analysis reveal monolayer adsorption governed by van der Waals interactions between MB aromatic hydrogens and nitrogen atoms at g-C3N4 inner edges, with experimental data matching computational predictions. A photocatalytic mechanism was proposed based on band-edge analysis, redox potentials, and electron paramagnetic resonance (EPR)-based ROS quantification. Both samples generated • OH, O2•– , and 1O2 under irradiation. Band-edge analysis (ECB /E VB = -1.84/1.24 eV for CN-U; -1.73/1.12 40 eV for CN-TU) supports thermodynamically favorable O2 reduction to O2•– but disfavors direct • OH formation. Spin-trapping EPR confirmed O2•– as predominant ROS (≈53%), 42 with detectable • OH and 1O2. CN-U showed superior performance due to enhanced O2 •– generation. In vitro cytotoxicity by MTT assay in human MRC-5 fibroblasts (20–100 µM, 72 h) indicated significant viability reductions for both materials, with higher cytotoxicity for CN-TU. ADMET analysis showed heptazine polymerization reduces acute toxicity and increases biological adsorption, while increasing bioaccumulation potential. These results demonstrate that precursor selection enables tuning the adsorption–ROS–photocatalysis–cytotoxicity balance in g-C3N4 , advancing rational development of safer, efficient photocatalysts.

This study explores a sustainable approach to developing magnetic nanocomposites by synthesizing a mixed-phase iron oxide (IO) and recycled polyamide (RPA) composite from textile waste. The RPA/IO nanocomposite’s microstructural and magnetic properties were characterized using X-ray diffraction (XRD) with Rietveld refinement, scanning, transmission electron microscopy (SEM, TEM), and vibrating sample magnetometry (VSM). The proportions of the Fe₃O₄ and γ-Fe₂O₃ phases were found to be 23.2 wt% and 76.8 wt%, respectively. SEM and TEM showed a porous, agglomerated IO surface morphology with an average particle size of 14 nm. Magnetic analysis revealed ferrimagnetic and superparamagnetic behavior, with VSM showing saturation magnetization values of 21.81 emu g⁻¹ at 5 K and 18.84 emu g⁻¹ at 300 K. Anisotropy constants were estimated at 4.28 × 10⁵ and 1.53 × 10⁵, respectively, for IO and the composite, with a blocking temperature of approximately 178 K at 300 K. These results contribute to understanding the magnetic behavior of IO and their nanocomposites, which is crucial for their potential applications in emerging technologies.

This study evaluates alternatives using the analytic hierarchy process (AHP) and Fuzzy AHP (FAHP) methodologies across five scenarios (SC1 to SC5), aiming to compare the effectiveness of both approaches in integrating environmental and technical criteria. The results indicate that, in SC1, AHP assigns weights of 14.35% to A1 and 16.22% to A2, while FAHP demonstrates greater dispersion, highlighting A6 with 35.22%. In SC2, AHP prioritizes A1 with 14.16%, whereas FAHP increases the weight of the environmental criterion to 21.18%. In SC3, A1 remains the preferred option in both methodologies, with close weights of 34.00% for AHP and 32.98% for FAHP. In SC4, both methods show similar trends, with A1 standing out at 11.12% and A4 at 34.87%. Finally, in SC5, AHP allocates 8.52% to A1, while FAHP evaluates it at 10.73%. The findings suggest that FAHP allows greater sensitivity to variations in sub‐criteria, enabling a more precise evaluation aligned with sustainability objectives. The significance of environmental and social criteria across the scenarios underscores the necessity of incorporating more sustainable approaches into decision‐making processes. It is concluded that, while AHP delivers consistent results, FAHP may be better suited for contexts characterized by complexity and uncertainty. Furthermore, sensitivity analysis is recommended to examine how variations in criterion weights impact final decisions.

This study explores a sustainable approach to developing magnetic nanocomposites by synthesizing a mixed-phase iron oxide (IO) and recycled polyamide (RPA) composite derived from textile waste. The RPA/IO nanocomposite’s microstructural and magnetic properties were characterized using X-ray diffraction (XRD) with Rietveld refinement, scanning, and transmission electron microscopy (SEM, TEM), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy. XRD confirmed the presence of both magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) phases, with Rietveld refinement indicating 79.4 wt% Fe₃O₄. SEM and TEM showed a porous, agglomerated IO surface morphology with an average particle size of 14 nm. Magnetic analysis re-vealed ferrimagnetic and superparamagnetic behavior, with VSM showing saturation magnetization values of 22.2 emu/g at 5 K and 19.1 emu/g at 300 K. Anisotropy constants were estimated at 2.90×10⁵ and 1.26×10⁵, respectively, for IO and the composite, with a blocking temperature of approximately 149 K. Mössbauer spec-troscopy confirmed both Fe₃O₄ and γ-Fe₂O₃ phases, and the RPA matrix did not significantly impact the IO’s crystal structure. These findings contribute to understanding the magnetic behavior of IO and their nano-composites, which is crucial for their potential applications in emerging technologies.

This study performs a systematic review and analysis of research on the use of multicriteria decision analysis (MCDA) methods for more than 45 years. More than 34,468 documents related to MCDA were identified in more than 130 countries, with an annual increase of 14.15% in scientific production. India, China, and Iran lead in number of publications, covering about 35%. The universities with the most publications include Islamic Azad University and Vilnius Gediminas Technical University. The main journals in this field are Expert Systems With Applications, Sustainability, and Journal of Cleaner Production. The most prolific authors are Zavadskas, E.; Wang, J.; Tzeng, GH; Zavadskas, EK; and Kahraman, C. The most popular methods are TOPSIS, AHP (analytic hierarchy process), VIKOR, PROMETHEE (Preference Ranking Organization Method for Enrichment Evaluation), and ANP. LATAN, which includes countries such as Brazil, Chile, and Mexico, has increased the use of MCDA in recent years. Colombia has also shown a great interest in MCDA, especially in the selection of alternative energy sources and industrial suppliers. This method of literature review provides a comprehensive overview of research at MCDA and offers valuable information for future projects and studies.