Abstract in English:

Lignin nanoparticles (LNPs) have emerged as promising bio-based materials for sustainable applications, but conventional synthesis methods often rely on surfactants, chemical modifications, or toxic solvents. In this study, we present a simple and environmentally friendly approach for producing LNPs using ethanol-water mixtures and ultrasonication, without the use of additives or hazardous reagents. Two solvent compositions (70 and 90% ethanol, v/v in water) and varying sonication times (0-2 h) were evaluated to investigate their effects on nanoparticle formation, morphology, and size. Visual assessment and scanning electron microscopy (SEM) revealed that 70% ethanol promotes spontaneous nanoparticle formation with spherical morphology and good dispersion, even without sonication. In contrast, 90% ethanol required prolonged ultrasonication to produce smaller and more uniform particles. Particle size analysis confirmed that ultrasonication enhances particle refinement, especially in the solvent systems with higher ethanol content.. This minimalist, surfactant-free method demonstrates the potential for scalable and green production of lignin nanoparticles, offering a valuable platform for future development of functional bio-based nanomaterials.

Abstract in English:

TiO2 nanotubes have attracted interest since they can be used as photocatalysts in degrading organic pollutants and hydrogen production from water electrolysis. However, there are limitations in the photocatalytic applications of TiO2, since this semiconductor presents a relatively wide band gap (3.0-3.2 eV) and a high recombination rate of electron-hole pairs. Doping TiO2 nanotubes with Fe3+ is suggested to overcome these limitations. The present work aims to produce iron-doped nanotubes (Fe-TiO2) through electrochemical anodization with in situ doping, characterize these nanostructures by scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive spectroscopy (EDS), X-ray diffraction, and UV-Vis (ultraviolet-visible) diffuse reflectance spectroscopy, and evaluate the effect of doping on the photoactivity of TiO2. The synthesis was carried out under a potential of 48 V for 2 h. EDS confirmed the presence of iron in the Fe-TiO2 sample. Microscopy showed that doping caused a reduction in the internal diameter of the nanotubes and the thickness of the anodic film. The average band gaps obtained were 2.962 ± 0.107 eV for Fe-TiO2 and 3.057 ± 0.049 eV for pure TiO2. In the photoelectrochemical tests, the doped samples showed a slightly enhanced photoresponse compared the undoped ones, indicating that doping affects the photocatalytic properties of TiO2.

Abstract in English:

Oil well cementing plays a critical role in ensuring zonal isolation, structural integrity, and long-term well safety. Due to exposure to high pressures, temperatures, and chemically aggressive environments, understanding the microstructural behavior of cement systems is essential. This study presents a microstructural analysis of oil well cement slurries using scanning electron microscopy (SEM) as a central tool for the identification and interpretation of hydration products, morphological changes, and the effects of additives and environmental exposure. A wide range of SEM images was collected and organized into a visual reference catalog, including typical hydrated phases such as calcium silicate hydrate (C-S-H), portlandite, ettringite, tobermorite, and xonotlite, as well as carbonation products like calcite and aragonite. The influence of factors such as curing time, temperature, and the incorporation of additives (e.g., silica, palygorskite, polyurethane) was evaluated in terms of morphology, porosity, and matrix integrity. Additionally, energy dispersive X-ray spectroscopy (EDS) was used to complement the morphological analysis with elemental composition data. The results highlight the relevance of SEM as a powerful and versatile technique for the investigation of cementitious materials, offering valuable insights for both scientific research and practical applications in petroleum well cementing under complex and aggressive conditions.

Abstract in Portuguese:

This paper examines the effectiveness of using open circuit potential measurements as a standalone technique to assess the corrosion resistance of metals. As a case study, we used different brands of aluminum alloys exposed to 0.1 mol L–1 NaCl solution. Five materials were compared: high-purity aluminium (99.999%) and four commercial alloys (1050-T0, 2024-T3, 2198-T851, and 7475-T761). Open circuit potential (OCP) monitoring as a function of time, potentiodynamic polarization tests, surface and cross-sectional microscopy were employed to investigate the electrochemical behaviour and the localized corrosion resistance of these alloys. Despite exhibiting nobler OCP values, 2024-T3 and 2198-T851 showed severe localized attack, including intergranular and crystallographic pitting. In contrast, only high-purity aluminium developed a stable passive film. Depth measurements revealed that 2024-T3 experienced the deepest attack (121 ± 15 μm), followed by high-purity aluminium (91 ± 12 μm), 2198 (36 ± 7 μm), 1050 (31 ± 6 μm), and 7475 (26 ± 5 μm). These findings demonstrate that OCP measurements, being dominated by the matrix-average potential, do not reflect critical microstructural features that influence localized corrosion. Therefore, while OCP may be useful for preliminary assessment and educational applications, it should be supplemented with kinetic and morphological analyses for a reliable evaluation of corrosion in complex alloy systems.

Abstract in Portuguese:

Reduced graphene oxide (rGO) has emerged as a promising material for photothermal applications due to its ability to absorb near-infrared (NIR) light and efficiently convert it into heat. In this study, we investigated the influence of sheet size on the photothermal properties of rGO by employing two exfoliation methods – ultrasonic bath and probe sonication – at varying durations. The resulting materials were characterized by scanning electron microscopy (SEM), infrared and Raman spectroscopy, and X-ray diffraction (XRD). Subsequent chemical reduction with ascorbic acid was confirmed through spectroscopic analyses. SEM images and particle size distribution analyses revealed that longer sonication times, particularly with ultrasonic probes, produced smaller and more uniform flakes. Despite significant differences in lateral dimensions, photothermal experiments under NIR laser irradiation (830 nm) revealed similar temperature increases for all samples, indicating that the size reduction does not play a major role in enhancing the photothermal response under the tested conditions. These findings suggest that the photothermal performance of rGO is primarily governed by the restoration of conjugated sp2 domains during reduction, rather than by the sheet dimensions. The results provide valuable insights into the design of rGO-based photothermal agents, especially for biomedical applications where internalization depends on particle size.

Abstract in English:

Electrospun polymeric nanofibers are a promising approach for photodynamic therapy (PDT) in dermatological treatments by incorporating photosensitizer molecules. In this study, polyamide 6 (PA-6) nanofibers were functionalized with methylene blue (MB) to evaluate their potential as PDT agents. A factorial design was conducted to optimize electrospinning parameters to maximize the generation of reactive oxygen species (ROS). The ability of MB-loaded fibers to generate singlet oxygen was assessed by spectrophotometry based on the degradation of 1,3-diphenylisobenzofuran. In vitro cytotoxicity assays were performed to determine the efficacy of PDT in both tumor (SW480) and non-tumor (HEK293) cell lines, confirming that the fibers induced cell death in both models, with a statistically significant photodynamic effect observed in SW480 tumor cells treated with fibers containing 10 mM MB. These findings suggest that PA-6/MB electrospun fibers represent a promising platform for PDT applications, offering a controlled release of MB and effective ROS-mediated cytotoxicity.

Abstract in English:

The present paper reports the hydrothermal synthesis of nano-TiO2 via microwave-assisted heating. The precursor, titanium(IV) isopropoxide (TIP), and the catalyst, tetramethylammonium hydroxide (TMAH), were subjected to either a single- or a two-step heating process. The resulting TiO2 nanoparticles were designated TDN1 and TDN2, respectively. The particle size, morphology, crystallinity, surface physicochemical properties, and ultraviolet-visible (UV) photocatalytic degradation of rhodamine B (RhB) were determined. The synthesis resulted in the formation of nanoparticles with irregular shapes (TDN1, approximately 6 nm) and cubic/rectangular shapes (TDN2, approximately 9-18 nm), both with anatase structures. The specific surface area was nearly twice that of commercial nano-TiO2. The TDN1 and TDN2 samples photodegraded 90 and 98% of RhB, respectively, after 120 min of UV illumination.

Abstract in English:

Strategies such as extrinsic doping can improve charge separation and enhance the photocurrent response of semiconductor systems. In this work, the effect of alkali metal (K+, Rb+, and Cs+) doping on rutile TiO2 hierarchical thin films synthesized by a hydrothermal method was evaluated. The bottom-up approach yielded nanorods/spherulites of TiO2 on SnO2:F substrate, under acidic conditions, and the influence of alkali ions was evaluated for doping levels of 2.5 and 5.0%. The materials were characterized by several structural and morphological methods, including XRD (X-ray diffraction), SEM (scanning electron microscopy), TEM-SAED (transmission electron microscopy-selected area electron diffraction), and photoelectrochemical measurements. The XRD confirmed the rutile single phase obtained; however, TiO2 morphology was affected by the incorporation of alkali ions with different ionic radii. SEM images revealed that the spherulites observed for undoped TiO2 were suppressed, and the thickness of the nanorods decreased. TEM-SAED analysis indicated preferential nanorod growth. The photoelectrochemical measurements showed changes in the charge carrier density between the pristine TiO2 to the Cs+-doped TiO2. Alkali-doped TiO2 shows potential for use as an electroactive component in the hole transporting layer of photovoltaic solar cells.

Abstract in English:

Titanium is widely used in biomedical implants due to its excellent mechanical properties and biocompatibility, but its bioinert surface hinders osseointegration. Surface modification strategies aim to enhance biological interactions, with scanning electron microscopy (SEM) playing a key role in assessing cellular behavior on modified titanium surfaces. However, SEM sample preparation involving biological material remains challenging. This study compared two preparation protocols using glutaraldehyde fixation: protocol I (critical-point drying) and protocol II (tert-butanol dehydration). Two nanoengineered TiO2 surfaces were evaluated to compare cell adhesion and morphological preservation. Both protocols showed comparable levels of cell adhesion relative to glass controls. However, samples from protocol I appeared overly dry and cracked, impairing visualization of adhesion structures and intercellular connections. In contrast, protocol II better preserved structural integrity, enabling clear observation of adhesion sites, cell networks, and membrane protrusions. Moreover, protocol II dramatically reduced fixation time from 72 h to 60 min, improving both efficiency and biological feature preservation. These findings suggest that tert-butanol-based dehydration (protocol II) is a superior, time-saving alternative to conventional critical-point drying for SEM preparation of biological samples on titanium substrates.

Abstract in English:

This study presents a multi-technique characterization of ceramic fragments excavated from the Bitoca I archaeological site (Marabá, southeastern Brazilian Amazon). Mineralogical and microstructural analyses were carried out by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), portable micro-X-ray fluorescence (µ-XRF), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS). XRD and FTIR revealed matrices dominated by quartz and albite, with residual kaolinite, illite and smectite (montmorillonite) indicating lowto moderate-temperature firing (≤ 850 °C). The amorphous silica phase supported the intentional addition of plant-based temper such as cariapé. µ-XRF showed elevated SiO2/Al2O3 ratios (ca. 5.3), high Fe2O3 (> 7 wt.%), and trace Ti, K, Ca, Mg and P, suggesting heterogeneous raw-material selection and possible tempering with sandy or feldspathic additives. SEM-EDS micrographs confirmed a silico-aluminous groundmass, feldspathic inclusions, organic temper particles, and surface layers enriched in Ca, P and Mg that were consistent with culinary residues. Collectively, the data reconstructs a chaîne opératoire involving: (i) procurement clays from fluvial terraces; (ii) tempering with crushed quartz, feldspar, and organic matter; (iii) open firing or simple kiln use at sub-900 °C; and (iv) vessel employment in cooking or ritual activities. The technological variability recorded - especially the coexistence of quartzand cariapé-tempered wares - corroborates ceramic diversity reported for Amazonian ceramic tradition.

Abstract in English:

This study focuses on developing a dimensional characterization protocol for graphene oxide (GO) intended as a certified reference material (CRM). A comprehensive methodology was established, encompassing sample preparation and advanced techniques for physicochemical and dimensional analysis, including scanning electron microscopy (SEM), atomic force microscopy (AFM) and other physical-chemical characterizations. These techniques enabled evaluation of key parameters such as sheet height, lateral size, number of layers and physicochemical signatures. A computational model based on entropy-driven image segmentation was applied for microscopy image analysis, demonstrating effectiveness in particle delineation and counting but limited capacity to assess the number of layers. To validate this model, a non-automated segmented image database was created as a gold standard. Integration of AFM and SEM data was explored to overcome individual limitations of each technique, reinforcing the value of hybrid metrological approaches. The main outcomes include a validated sample preparation protocol for GO characterization via SEM and AFM, which is being incorporated into the technical groups of the Brazilian Association of Technical Standards (ABNT). Additionally, the C++ image segmentation algorithm, developed in collaboration with National Laboratory for Scientific Computing (LNCC) and Federal University of Bahia (UFBA)), provides a foundation for dimensional analysis of nano-objects in multifunctional hybrid systems, enabling broader industrial applications.