Portugaliae
Electrochimica Acta

Bio refineries are gaining popularity as population increase drives up energy and resource demands. This approach aimed to employ biomass to generate energy and recover valuable chemicals. Nitrogen (N) and Phosphorous (P) are essential nutrients for manufacturing fertilizer, which contributes significantly to global food production. Hydrothermal carbonization (HTC) is an effective energy recovery process that can also be used before treatment to improve nutrient recovery. During HTC management, some P and N dissolve in water, while the remainder stays in hydrochars (HC). HCs are commonly utilized as soil additions due to their high fertilizer and phosphate content. However, water retains significant levels of these chemicals, making it a viable source of recovery. HTC may improve the removal of nutrients by extraction (water process) or concentration (HC) of biomass, especially when combined with other processes. This paper provides a summary of both N and P pathways throughout the HTC process in terms of nutrient recovery, including current methods and future trends. Keywords: biomass; hydrothermal carbonization; Nitrogen; nutrients; phosphorus.

Abstract This study focused on the development of insulating refractory bricks using quartzite, with a comprehensive analysis of their mechanical and thermal properties. The bricks were made from quartzite with 10% bentonite binder and water, added for mixing. Various tests were done (X-ray Fluorescence, Thermogravimetric and Differential Thermal Analyses, apparent porosity, shrinkage, Loss on Ignition (LOI), compressive yield stress, and water absorption (WA)), following American Society for Testing and Materials’ procedures. Microstructural analysis of the sample was observed using Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). These results provided valuable insights into the stability of the developed refractory bricks at high temperatures. Analysis of chemical composition from quartz bricks revealed significant SiO2 content (94.303%), emphasizing the material’s superior refractory properties. LOI (0.5%) and shrinkage (0.2%) results indicated enhanced performance with good thermal stability and strength. Compressive stress yield indicated that the material exhibits good strength relative to the amount of binder used. WA results confirmed that the brick sample is suitable for high-temperature applications. SEM/EDS analysis unveiled intricate microstructural features, affirming the bonding agent’s influence on the material’s composition. Keywords: Differential Thermal Analysis; refractory material; Scanning Electron Microscopy-Energy/Dispersive X-ray Spectroscopy; silica quartzite bricks; Thermogravimetric Analysis.

This work sought to establish whether starting particle size (SPS) is an important parameter on the properties of hydroxyapatite (HAP) extracted from cattle bone (CB) waste material by heat treatment, for biomedical applications, such as temperature and holding time. CB was processed to obtain micron-sized particles of 50, 150, 250 and 350 m. The powders were heated to a constant temperature and holding time of 900 °C and 3 h, respectively, to enable their transformation into HAP. Evolved HAP was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR). Results indicated that physico-chemical properties were very sensitive to SPS of CB. XRD results revealed that crystallite size and degree of crystallinity of evolved HAP increased with greater SPS. Based on EDX results, concentration of essential elements of Ca, P, O and C in HAP also varied according to SPS increasing from 36.0 to 50.5 wt. % for Ca, decreasing from 13.7 to 9.9 wt. % for P, 36.2 to 29.6 wt. % for O and 12.6 to 9.3 wt. % for C. FTIR spectra indicated that concentration of functional groups is sensitive to SPS, with amounts of OH- and PO43- increasing, while CO32- decreased with an increase in SPS. Thus, SPS is an important parameter in evolution of HAP from CB waste via calcination process. Keywords: biomedical; CB waste; evolution; HAP; SPS.

Residual stresses formed during quenching can significantly impact the integrity of engineering components. This study examined how varying immersion speeds in water affected both mechanical behavior and residual stress distribution in SAE 1025 steel. To achieve this, a hybrid approach combining finite element simulations (using ANSYS 2020 R1 and JMatPro) with controlled laboratory experiments was employed. The immersion speed control mechanism was developed and calibrated. Steel samples were quenched at five immersion speeds, ranging from 0.05 to 0.8 m/s. Metallographic analysis, Vickers microhardness testing and tensile testing were assessed and then compared to simulation predictions. A significant finding was the 83% reduction in maximum residual stress as immersion speed increased from 0.2 to 0.8 m/s. Furthermore, residual stress was significantly lower at the leading (first-contact) end of each sample and higher at the trailing end. Simulation results showed strong agreement with experimental findings, achieving an average error of 7.5% across the temperature range and a correlation coefficient (R²) of 0.97. Ultimately, the prediction of residual stress distributions achieved in this study will enable the production of safer and more durable components, critical for demanding engineering applications where performance and integrity are non-negotiable. Keywords: cooling rate; deformation; heat treatment; homogenization; immersion speed; residual stress.

In this work, the electrochemical performance of various Membrane Electrode Assemblies (MEAs) using Nafion® membranes (NR211, XL, NR212 and N115) incorporating low platinum-loading electrodes (0.05 and 0.1 mgPt cm-2), developed with two different commercial catalyst 60% Pt/C and 40% Pt/C, have been evaluated. The electrodes were manufactured depositing the catalytic ink, prepared with catalyst HiSPEC4000 and HiSPEC9100, onto the gas diffusion layers, by wet powder spraying. In order to carrying out this study, a robust testing protocol for Proton Exchange Membrane Fuel Cells (PEMFCs) was designed, consisting of three steps: activation, polarization curve measurements (current-voltage), and Electrochemical Impedance Spectroscopy (EIS). Tests were repeated to assess the effects of oxidant (air or oxygen) and operating pressure, with parameters adjusted sequentially: air atmospheric → air + 1 bar → air + 2 bar → O2 atmospheric → O2 + 1 bar → O2 + 2 bar. Results point out that, by the increasing of the back pressure consistently, the maximum power density across all four MEAs is improved, regardless of oxidant. Switching from air to oxygen led to significant power increases of 57.3, 56.6, 54.3, and 37.2% for MEAs with Nafion® NR211, XL, NR212, and N115, respectively. This suggests that thicker membranes result in higher PEMFCs performance due to lower internal resistance. The MEA with Nafion® NR211 (25 μm thickness) achieved the highest performance, emphasizing that reducing membrane thickness enhances functionality. This insight will inform future research on optimizing membrane thickness. Additionally, reducing platinum content in the catalyst from 60 to 40% Pt/C in NR211 and NR212 membranes showed stable performance, confirming their suitability with lower Pt concentrations. The new catalyst formulation performed better than the previous one under H2/O2 and higher back pressures, where lower Pt loading limitations become more apparent. Keywords: low Pt load; PEM fuel cell; Nafion® membranes; test protocol.

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.

Concerns about environmental pollution and depletion of petroleum and coal supplies in the twenty-first century have prompted a shift towards more sustainable and environmentally friendly alternatives. Lignocellulosic biomass (LCB), which contains hemicellulose, lignin (Ln), and cellulose, is a widely available natural bioresource. Ln, a natural biopolymer, has become more recognized as a valuable material with economic uses. The current research provides in-depth information on the evolution of phenol, from an impediment to a bridge connecting many industries with diverse applications. Successful valorization of Ln for the production of bio-based platforms, fuels, and chemical products has been the subject of extensive investigation. Understanding Ln properties and factors that influence its conversion into useful products might help optimize biomass utilization. Improved bioprocessing processes can convert LCB components into value-added products, including Ln. This study summarises and compares current improvements in Ln extraction, along with depolymerization technologies that might improve bioprocessing cost-effectiveness. Commercial importance of Ln-derived goods, such as aromatics, biological polymers, and biofuels, including agrochemicals, is also addressed. Most recent trends in Ln conversion into value-added compounds, and current technical and commercial applications of Ln that have economic significance are herein discussed. Keywords: agricultural waste; Bf; Bm; LCB; Ln extraction.

The following work presents a new method that aims to study the quality of toothpastes, in particular, excessive presence of fluoride, which is a corrosive agent for dental alloys. Results showed that the proposed method allowed analysis of electrochemical properties from compounds that exist in these oral hygiene products, generally based on the concentration effect of fluoride present in toothpastes. Excess doses of fluoride can cause serious effects, such as corrosion of dental alloys. Cyclic voltammetry (CV), linear voltammetry (LV) and electrochemical impedance spectroscopy (EIS) curves were herein recorded to identify characteristic electrochemical signals of different ingredients, in particular, fluoride concentration Keywords: CV; EIS, fluor; LV; toothpastes.

Agricultural residues are being explored as sustainable energy sources to mitigate global warming and reduce greenhouse gas emissions. This study investigates biofuel production from a free-fall reactor using sugarcane bagasse (SCB) and cassava rhizome (CR) as feedstocks, employing both experimental and modelling approaches. Pyrolysis was conducted with varying SCB-CR blend ratios, from 400 to 650 °C, with a 30 min residence time, to analyse yields of biochar, bio-oil and biogas. Ultimate and proximate analyses were performed on feedstocks and biofuels, to determine their properties. Mathematical models for biofuel yields were developed using multi-expression programming (MEP), and validated against multilinear regression (MLR). Optimal 50:50 SCB-CR composition produced the highest bio-oil yield of 36.2%, with a heating value of 23.6 MJ/kg, at 550 °C, alongside with 16.2% biochar and 47.6% biogas. MEP models demonstrated superior accuracy, with R² values of 0.974, 0.917 and 0.774, for biochar, bio-oil and biogas, respectively, outperforming MLR models. Results indicate that co-pyrolysis of SCB and CR enhanced biofuel yield and quality, due to synergistic effects. Integration of experimental data with modelling provides a pathway in optimizing process parameters for large-scale biofuel production. Keywords: biofuel; CR; modelling; MEP; pyrolysis; SCB.

Nanocomposites (NC) derived from electrically conductive polymers have emerged as promising materials for advanced applications in sensors, semiconductors and supercapacitors. The performance of these materials is critically influenced by environmental factors, with humidity exposure (HE) playing a pivotal role in determining their thermal and electrical behaviours. PIN, recognized for its high redox activity, tunable conductivity and thermal stability, has been integrated with WC, a material known for its exceptional hardness, wear resistance, high electrical conductivity (σDC) and thermal resilience. In this study, a novel series of NC electro polymers with WC were synthesized via FeCl₃-initiated chemical oxidative polymerization of indole in CTAB presence. WC was incorporated at varying wt% (5, 10 and 15), to assess its impact on the composites’ properties. Influence of relative humidity (40%) on thermal stability and σDC of NC was systematically evaluated. Structural and morphological analyses were performed to elucidate composites’ conductivity, stability and reliability under fluctuating humidity conditions. Results revealed that inclusion of WC significantly enhanced thermal and electrical properties of PIN, while providing superior resistance to humidity-induced degradation. Notably, NC with 15 wt% WC exhibited highest σDC, achieving 36.4mS/cm after 6h of HE. These findings highlight NC’s potential as robust materials for diverse applications in industrial, environmental, medical and agricultural domains, where stability under variable humidity conditions is paramount. Keywords:band gap; conductivity; HE; nanocomposite; PIN; WC.

This work focused on the electrochemical behaviour of a silver (Ag) deposit, from a mirror factory effluent, on the surface of an aluminium electrode. To carry out this study, two samples were taken from the same location of the mirror factory, before and after copper plating. Different applied potentials were selected based on results obtained from linear sweep voltammetry (LSV) analysis (potential window). Based on chronoamperometry (CA) measurements and electrochemical impedance spectroscopy (EIS) results, it can be seen that applied potentials affected the Ag deposit’s electrochemical behaviour, proving that it tended to be favoured by cathodic potential. Keywords: Ag recovery; CA; electrochemical behaviour; electrodeposition; EIS; LSV; SEM; EDS; XRD; XRF.

Clobazam (CLB) is a benzodiazepine and a central nervous system depressant. This first ever reported paper introduced a novel potentiometric sensor designed for the simple cost-effective assay of CLB in pharmaceuticals and spiked human urine (SHU). The sensor leveraged an ion association complex between CLB and bromophenol blue (BPB), which is a sulfonephthalein dye, integrated into a poly vinyl chloride matrix, with dibutyl phthalate as plasticizer, and prepared in tetrahydrofuran. IR spectral data were obtained to confirm the formation of CLB-BPB ion-association complex. For CLB, potentiometric measurements of the sensor yielded a linear calibration curve in the range of 9.3 × 10-5 to 4.8×10⁻4 M, with a regression coefficient of 0.9712. The slope of 30.35 indicated Nernstian behaviour of the sensor, corroborating two N atoms in CLB. The sensor demonstrated excellent performance, with a mean accuracy of about 98%, recovery from tablet formulations of 96.83%, and recovery over 96% from SHU samples. The interference study revealed the inactive role of common cations and anions, while measuring CLB potential. Additionally, the sensor showed excellent accuracy, precision, robustness and ruggedness, which makes it highly suitable for routine assays in pharmaceutical and physiotherapeutic laboratories. This method provides a reliable tool for monitoring CLB levels, addressing the need for effective therapeutic drug monitoring. Keywords: BPB; CLB; ion-association complex; pharmaceutical and potentiometric sensor; spiked human urine sample.

Fish oil is one of the most valuable dietary complements for healthy bodily functions. The effects of this product vary from fast and healthy development of cognitive abilities to prevention of cardiac diseases. One of most important components of fish oil is Omega-3, made from a variety of fatty acids (FA), such as Eicosatetraenoic Acid (EPA) and Docosahexaenoic acid (DHA), on which the present study has focused. As the human body can hardly synthesize these elements on its own, it is crucial to include them as part of a daily diet. However, fish oil capsules on the market are highly priced, and might contain chemical additives. This work’s main goal was to propose a valorization method for the waste of Sardina pilchardus, of which choice was based on its oily properties, and on the fact that it is the most present and consumed species in Morocco. Fish oil extraction was completely organic, and performed without any additives or chemicals. This oil can be used as animal feed additive and supplement. Additionally, the presence of multiple FA, specially EPA and DHA, was herein proved by using Gas Chromatography-Mass Spectrometry analysis. Obtained quantities of pure oil exceeded 50 mL/kg fish waste. Keywords: fish oil; fish waste; GS-MC; Middle-atlas; Morocco; Omega-3; Sardina pilchardus; valorization.

Agriculture, food and food-processing sectors produce 1.3 billion tonnes of lignocellulosic-based biomass (LCB) globally each year. LCB is a viable alternative energy source, due to its economical nature and minimal waste production. LCB may be efficiently transformed into fuels like bioethanol, biodiesel and biogas, along with higher-value products, such as organic acids, enzymes, biopolymers and charcoal. Nonetheless, owing to its structural intricacy and resistance, LCB presents difficulties for large-scale application. Consequently, its preparation is essential for effective delignification. The approach isolates hemicellulose and cellulose (CL) from lignin within a complex polymer matrix. This diminishes matrix size, while augmenting surface area of CL molecules, hence enhancing their accessibility to microorganisms and enzymes for hydrolysis and fermentation, respectively. Pretreatment procedures may be classified as chemical, physical, chemical/physical or biological. Physical methods include mechanical grinding, ultrasound and electromagnetic radiation. Chemical methodologies comprise acid/alkaline hydrolysis, organosol processes, ionic liquids and ozonolysis. Physical-chemical processes encompass ammonia fibre explosion, CO2 detonation, moisture explosion and liquid hot water filtering. The use of particular yeasts, fungi and bacteria in biological pretreatment processes is not yet extensively implemented. Keywords: biofuels; biomass; hydrolysis; pretreatment procedures; value-added goods.

Non-muscle-invasive bladder cancer (NMIBC) presents a significant challenge in terms of diagnosis, follow-up and recurrence monitoring. Current methods for follow-up, such as cystoscopy and cytology, are invasive, time-consuming, and often associated with discomfort for patients. Hence, there is a pressing need for the development of non-invasive, cost effective and efficient techniques for NMIBC monitoring. In this study, an electrochemical simplified method for the follow-up of NMIBC is proposed, offering a promising alternative to conventional approaches. The method is based on the detection of cancerous cells using a carbon paste electrode (CPE). This electrode showed considerable activity for the detection and characterization of cancerous cells which are manifested by the appearance of two redox peaks, and also a remarkable increase in specific capacitance. The effect of the presence of iron ions in the electrolytic medium showed a very considerable difference in voltammograms. Fenton reaction was manifested by two redox peaks characteristic of the presence of cancer cells. Keywords: BC; CPE; CB; EIS; non-invasive follow up; SWV.

Nanoscale zero-valent iron (nZVI) is considered the most effective remediation material for contaminated soils, especially by heavy metals. In this case, nZVI were extracted from two different iron salt precursors, FeCl3 (FC) and Fe(NO3)3 (FN), and then coated onto SiO2, at 650 and 800 ºC. Synthesis of nZVI was carried out in a C₂H₆O medium, under N atmospheric conditions, using Fe3+ with Fe(NO3)3 and FeCl3, as counter ions, and NaBH4 as reducing agent. XRD and SEM were used to characterize structures of nZVI. Furthermore, electrical properties of nZVI produced in an aqueous medium were examined. Keywords: electrical conductivity; FC; FN; nZVI; SiO2.