Portugaliae
Electrochimica Acta

Abstract This experimental study investigated electrocatalytic properties of a novel device consisting of a graphite/Tuff composite electrode combined with an aqueous bioelectrolyte (0.1 M NaCl) enriched with electroactive bacteria (EcB). Systematic electrochemical analyses using cyclic voltammetry (CV) and chronoamperometry revealed that this hybrid system has promising energy storage capacities under the applied potential. The involved mechanisms combined electrochemical double-layer phenomena at the porous surface of the carbonaceous material with redox processes catalyzed by the microbial biofilm. The results demonstrate significant catalytic efficiency, resulting in high charge densities and good system stability, opening up interesting prospects for the development of energy storage solutions incorporating biological components. This original approach combines advantages of nanostructured carbon materials with catalytic properties of electroactive microorganisms. Keywords: chronoamperometry; CV; EcB.

Abstract Interaction between Human Serum Albumin (HSA) and Natamycin (NA), a widely used antifungal agent, was herein investigated using a combination of electrochemical, spectroscopic and molecular docking (MD) techniques. UV-Vis spectroscopy revealed that interaction between HSA and NA leads to structural changes in HSA, evidenced by increased absorption peaks. Electrochemical studies demonstrated that NA exhibits irreversible oxidation on a glassy carbon electrode, and its electrochemical activity decreases in presence of HSA, indicating complex formation. Thermodynamic analysis suggested that binding process is spontaneous, driven primarily by Van der Waals forces and hydrogen bonds, with a binding constant (Kb) of 6.86 × 10³, at 298 K. MD further confirmed the interaction, identifying Sudlow site I as primary binding site, with a binding energy of -8.78 kcal/mol. Keywords: human serum albumin; molecular docking; Natamycin; spectroscopy; voltammetry.

Abstract In this study, hydrated iron oxide-modified silicates (Si-Fe(n)) with varying iron concentrations were synthesized via one-step loading. Comprehensive characterization using N₂ adsorption-desorption, Fourier Transform Infrared spectrophotometer, Scanning Electron Microscope, Transmission Electron Microscopy, Energy-dispersive X-ray and X-ray Diffraction revealed that Fe incorporation preserved silica's phase composition and crystal structure (evidenced by consistent XRD peak broadening), achieved uniform iron distribution within silica matrix (EDX/TEM), with 12.5 nm average particle size, and enhanced surface area and Fe-bonded OH groups (FT-IR). These modifications correlated with improved catalytic performance in benzaldehyde oxidation, for which the reaction mechanism was elucidated. Keywords; Benzaldehyde oxidation; catalysis; Density Functional Theory; Hydrated iron oxide modified silicates.

Abstract The development of aluminum metal matrix composites (AMMC) has been advanced in recent years. For advanced engineering materials, various scientists are seeking ways to improve matrix alloys through the utilization of reinforcements. Combining hybrid reinforcements over monolithic reinforcement in matrix alloy composite development has shown to be advantageous, since hybrid reinforcements complement each other in the matrix alloy. Production route of metal matrix composites (MMC) development is germane to improving their properties. This paper reviews the synergetic effects of hybrid reinforcements for AMMC on physical-mechanical properties and microstructure of the alloy. Various production routes were discussed, and the effects of utilizing hybrid reinforcement particulates were examined. Most studies employ stir casting route for MMC production, due to its ease of production and inexpensiveness. The study revealed that the utilization of hybrid reinforcements in MMC improves mechanical properties, with their even dispersion. Improvements in composites’ strength are linked to three mechanisms: Hall-Petch, coefficient of thermal expansion and Orowan’s strengthening mechanisms. Future research perspectives, such as novel processing techniques for MMC production, long-term performance and reliability examination on developed hybrid composites, were suggested to be further studied. Keywords: advanced engineering materials; composite materials; hybrid reinforcement; mechanical engineering; metal matrix composites.

Abstract Understanding how ionizing radiation affects insulating materials is essential for maintaining the reliability and safety of high-voltage systems operating in radiation-prone environments that use mineral insulating oil. In this research, mineral insulating oil was irradiated with gamma rays from a cobalt source of Co60, with a radioactivity of 70 kcl. The irradiation process was carried out at a dose rate of 8.9 kGy/h, and doses up to 250 kGy were used. This study focused on density factor. Other parameters such as moisture content, acidity and breakdown voltage were measured according to internationally recognized standards. Fourier transform infrared spectroscopy (FTIR) was also used to detect changes in oil’s chemical composition. Results indicated that gamma radiation caused a decrease in oil density, with the lowest value of 0.853 mg/cm3. These changes were effectively modeled using polynomial regression, with a high correlation coefficient (R²) of 0.982, demonstrating the model’s reliability in capturing the relationship between radiation dose and density change. Keywords: dielectric; density; gamma irradiation; mineral oil.