Lorena Marín

Hybrid nanocomposites composed of dendritic fibrous nanosilica (DFNS) identified as KCC-1 and resorcinol–formaldehyde (RF) resin were synthesized via the polymer-assisted deposition (PAD) method for the incorporation of Ni and Fe in mono- and bimetallic configurations. The RF resin enabled uniform dispersion Fe-based and Ni-based nanoparticles through coordination with functional groups, while KCC-1 provided a high-surface-area, mesoporous support. A comprehensive structural and chemical characterization confirmed the formation of hematite in the Fe-based system; NiO and metallic Ni in the Ni-based material; and FeO, NiO and metallic Ni in the bimetallic composite, in the form of well-dispersed metal nanoparticles between 3–6 nm. Although a reduction in BET surface area was observed due to resin and metal loading, all nanocomposites retained mesoporous structures with Type IV isotherms and H3-type hysteresis, suitable for catalytic applications. The nanocomposites exhibited structural stability up to 800 °C under N₂, with a total mass loss of 12–14% dominated by moisture desorption below 100 °C (~8–11%) and minor surface group degradation at higher temperatures. These findings demonstrate the potential of the PAD method for fabricating functional hybrid materials with improved metal dispersion.

Magnetic microspheres were fabricated from industrial waste via a single-stage flame spheroidization method using two ferric oxide precursor powders from steel hot rolling industry. The analysis of all samples was carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD), Mössbauer spectroscopy, FTIR and Raman spectroscopy (RS), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). SEM, XRD, Mössbauer spectroscopy, FTIR and RS show the morphology, structure, and phases of the samples studied. The average size for each microsphere was 45 μm (Sample A2) and 60 μm (Sample B2). TGA confirmed the crystallization and phase transition of iron oxides. The VSM study showed high saturation magnetization ( M _s ) for both microsphere samples, with the higher M _s being very close to the reported value for bulk magnetite and exhibiting a very soft magnetic behavior. The flame spheroidization processing route provides a method for producing microspheres with high uniformity and size control. These factors make the method promising for biomedical, environmental remediation, and energy device applications.

Carbon-based nanocomposites coated with iron oxides were synthesized using a wet impregnation method with thermally annealed coal and an iron nitrate precursor. The influence of the thermal treatment atmosphere (air, vacuum, or nitrogen) on the morphology, structure, and magnetic properties of the nanocomposites was examined by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. It was found that the vacuum thermal treatment produced carbon-based nanocomposite containing iron oxide with the highest crystallinity, according to XRD analysis, while also inducing the greatest degree of structural defects in the carbon matrix, as evidenced by Raman analysis. Mössbauer spectroscopy confirmed that all thermal treatment methods promote the formation of the hematite phase, which was found to be the only phase formed in the air-treated nanocomposites, whereas traces of magnetite and the formation of Fe(OH)₃ were detected in the vacuum- and nitrogen-treated nanocomposites, respectively. Magnetic characterization revealed that all nanocomposites exhibit ferromagnetic-like behavior, attributed to the weak ferromagnetic nature of hematite. The best magnetic response (highest saturation magnetization with the widest hysteresis loop) was observed in the vacuum-treated nanocomposites. These findings collectively demonstrate that the synthesis atmosphere plays a crucial role in tailoring the structural and magnetic characteristics of carbon-based iron oxide nanocomposites, offering pathways for their optimization in applications such as catalysis, environmental remediation, or sensing technologies.

The Caribbean faces many environmental issues, and the mitigation and adaptation strategies to address the challenges of global warming are not sufficient in this geographical region. Considering that agriculture is a relevant activity in most countries around this region, our study proposes to enhance Caribbean waste management by transitioning to a sustainable and resilient process in the framework of a green, circular economy. The research has been focused on the thermochemical transformation of the typical residues of Caribbean farm products (plantain rachis, and cassava peel). Biochar samples were synthesized from these biomasses by the slow pyrolysis method at different temperatures (300 °C, 400 °C, and 500 °C). Biochar samples with a smooth surface were synthesized from plantain rachis biomass, while biochar samples with a porous surface were obtained from cassava peel biomass. At the same pyrolysis temperature, all biochar samples derived from plantain rachis exhibited higher production biochar yields than those biochar samples derived from cassava peel. The yield percentages were determined to be 65.7% and 62.0% at a pyrolysis temperature of 300 °C; 45.6% and 37.5% at 400 °C; and 33.7% and 25.4% at 500 °C, respectively. XRD measurements revealed that both biomass-derived biochar samples were found to be enriched with several compounds, such as kalicinite, arcanite, sylvite, CaO₃Si, and MgO₃Si, which vary according to the pyrolysis temperature. FTIR analysis revealed the presence of carbonyl and carboxyl functional groups on the surface of all biochar samples. However, only the aliphatic functional groups were observed on the surface of the biochar samples derived from cassava peel. These characteristics are of particular relevance due to their potential application in soil amendment or water remediation.

Gold nanostructures (AuNSs) were used to fabricate surface-enhanced Raman spectroscopy (SERS) substrates. These AuNSs were produced using the solid-state dewetting method from thin films. The fragmentation process was studied at 300 °C, with durations of thermal treatment of 1, 3, 6, and 12 h. These SERS substrates were then employed to detect Rhodamine B (RhB) as the model analyte, simulating a contaminant in the water at a concentration of 5 ppm. The morphology of the AuNSs was examined using SEM, which revealed a spheroidal shape that began to coalesce at 12 h. The size of the AuNSs was estimated to range from 22 ± 7 to 24 ± 6 nm, depending on the annealing time. The localized surface plasmon resonance of the AuNSs was determined using absorption spectroscopy, showing a shift as the annealing time increased. The SERS signals of RhB adsorbed on the AuNS substrates were validated by performing a 10 × 10 point map scan over each sample surface (1, 3, 6, and 12 h), and a comparative analysis showed no significant differences in the positions of the bands; however, variations in intensity enhancement ranged from 5 to 123 times at 6 and 1 h, respectively.

Gold nanostructures (AuNSs) were used to fabricate surface-enhanced Raman spectroscopy (SERS) substrates. These AuNSs were produced by the solid-state dewetting method from thin films. The fragmentation process was studied at 300 °C, considering the duration of the thermal treatment for 1, 3, 6, and 12 hours. These SERS substrates were then employed to detect Rhodamine B (RhB) as a model analyte, simulating a contaminant in water at a concentration of 5 ppm. The morphology of the AuNSs was examined using SEM, which revealed a spheroidal shape beginning to coalesce after 12 hours. The size of the AuNSs was estimated to range from 22 ± 7 to 24 ± 6 nm, depending on the annealing time. The surface plasmon resonance of the AuNSs was determined using absorption spectroscopy, showing a shift as the annealing time increased. The SERS signals of RhB adsorbed on the AuNS substrates were studied, and a comparative analysis showed no significant differences in the positions of the bands; however, variations in intensity enhancement ranged from 20 to 90 times for 6 and 3 hours, respectively. Three new vibrational modes, observed at 1683, 1720, and 1789 cm–1, have been identified and reported.

The impacts on the morphological, electrical and hardness properties of thermoplastic polyurethane (TPU) plates using multi-walled carbon nanotubes (MWCNTs) as reinforcing fillers have been investigated, using MWCNT loadings between 1 and 7 wt%. Plates of the TPU/MWCNT nanocomposites were fabricated by compression molding from extruded pellets. An X-ray diffraction analysis showed that the incorporation of MWCNTs into the TPU polymer matrix increases the ordered range of the soft and hard segments. SEM images revealed that the fabrication route used here helped to obtain TPU/MWCNT nanocomposites with a uniform dispersion of the nanotubes inside the TPU matrix and promoted the creation of a conductive network that favors the electronic conduction of the composite. The potential of the impedance spectroscopy technique has been used to determine that the TPU/MWCNT plates exhibited two conduction mechanisms, percolation and tunneling conduction of electrons, and their conductivity values increase as the MWCNT loading increases. Finally, although the fabrication route induced a hardness reduction with respect to the pure TPU, the addition of MWCNT increased the Shore A hardness behavior of the TPU plates.

For the past eight decades, understanding the physical mechanisms that occur at the interface between two different materials has been an open question driven by the breaking of crystalline symmetry and the reduction of atomic coordination, which modify the type and orbital occupation of atoms in the interface. Surface science began studying interface phenomena and has advanced significantly thanks to new and sophisticated tools for controlled fabrication and monolayer characterization. This focus has stimulated scientific and technological advancements, especially in the context of electronic devices and a wide range of interdisciplinary applications, such as biointerfaces, next-generation ultrasensitive detectors and actuators, and improved tribological properties. Here we provide a historical context of emerging interfacial phenomena and their influence on properties exhibited in junctions, multilayers, and heterostructures. We discuss advances in magnetic superlattice systems that enhance the information density of hard drives. We also explore electronic and magnetic interface states, as well as new functionalities in interfaces within heterojunctions based on complex oxides. Finally, we highlight advances and perspectives in surface science. En las últimas ocho décadas la comprensión de los mecanismos físicos que ocurren en la superficie límite entre dos materiales diferentes ha estado en constante evolución. Su interés radica en la ruptura de la simetría cristalina y la reducción de la coordinación atómica, las cuales producen modificaciones en el tipo y la ocupación orbital de los átomos en la interfaz. El estudio de los fenómenos interfaciales dio inicio a la ciencia de superficies, cuyo avance ha sido significativo en la medida en que aparecen nuevas y sofisticadas herramientas, tanto para la fabricación controlada de interfaces, como para la caracterización en el rango de la monocapa atómica. El interés se ha centrado no solo en el estímulo científico si no en el tecnológico, sobre todo en el contexto de los dispositivos electrónicos y, más recientemente, en una amplia gama de aplicaciones interdisciplinarias, como las biointerfaces, los detectores y actuadores ultrasensibles de última generación y el mejoramiento de las propiedades tribológicas. En este trabajo presentamos, primero, un contexto histórico de los diferentes fenómenos interfaciales que han ido surgiendo y su influencia en las propiedades que exhiben donde quiera que hay una interfaz, como en el caso de junturas, multicapas y heteroestructuras. Presentamos, asimismo, los avances en los sistemas de superredes magnéticas de importancia en el mejoramiento de la densidad de información de los discos duros, y discutimos sobre los estados interfaciales electrónicos y magnéticos y las nuevas funcionalidades en las interfaces de heterojunturas basadas en óxidos complejos. Por último, resaltamos algunos avances y perspectivas en el campo de la ciencia de superficies.

The rare-earth-free MnAlC alloy is currently considered a very promising candidate for permanent magnet applications due to its high anisotropy field and relatively high saturation magnetization and Curie temperature, besides being a low-cost material. In this work, we presented a simple fabrication route that allows for obtaining a magnetically enhanced bulk τ-MnAlC magnet. In the fabrication process, an electric arc-melting method was carried out to melt ingots of MnAlC alloys. A two-step solution treatment at 1200 °C and 1100 °C allowed us to synthesize a pure room-temperature ε-MnAlC ingot that completely transformed into τ-MnAlC alloy, free of secondary phases, after an annealing treatment at 550 °C for 30 min. The Rietveld refinements and magnetization measurements demonstrated that the quenched process produces a phase-segregated ε-MnAlC alloy that is formed by two types of ε-phases due to local fluctuation of the Mn. Room-temperature hysteresis loops showed that our improved τ-MnAlC alloy exhibited a remanent magnetization of 42 Am²/kg, a coercive field of 0.2 T and a maximum energy product, (BH)_max, of 6.07 kJ/m³, which is higher than those reported in previous works using a similar preparation route. Experimental evidence demonstrated that the synthesis of a pure room-temperature ε-MnAlC played an important role in the suppression of undesirable phases that deteriorate the permanent magnet properties of the τ-MnAlC. Finally, magnetic images recorded by Lorentz microscopy allowed us to observe the microstructure and magnetic domain walls of the optimized τ-MnAlC. The presence of magnetic contrasts in all the observed grains allowed us to confirm the high-quality ferromagnetic behavior of the system.