Portugaliae
Electrochimica Acta

Abstract In this study, 2-aminobenzoic acid (ABA) has been used as a complexing ligand for metal ions simultaneous determination by adsorptive cathodic stripping voltammetry (AdCSV). This selective and sensitive method was based on Cu(II), Pb(II) and Cd(II) ions + ABA adsorptive accumulation, by hanging them onto a mercury drop electrode (HMDE), followed by their reduction through differential pulse cathodic stripping voltammetry (DPSCV). Experimental parameters, such as pH, ABA concentration, accumulation time, potential and scan rate, were examined. Under the optimized conditions, linear calibration curves were established for Cu, Pb and Cd concentrations, in the ranges from 5 to 120, 5 to 150 and 5 to 120 ng/mL-1, respectively. Detection limits (LODs) of 2.05, 1.78 and 2.26 ng/mL-1 were obtained for Cu, Pb and Cd, respectively. The proposed method was applied for the determination of these elements in tap and industrial waste water, as real samples. Keywords: copper, lead, cadmium, 2-aminobenzoic acid, AdCSV and water samples.

Abstract In this work, an equi-atomic AlCrFeMnNiV HEA was synthesized by means of arc-melting and casting processes. The casted alloy ingots were heat-treated (annealed) at temperatures of 400, 600 and 800 ºC, for 2 h. The effect of the heat-treatment temperature on the HEA microstructural evolution, compressive strength and corrosion behavior was investigated. Heat-treatment temperatures of 400 and 600 ºC resulted in increased micro-hardness properties that, at 800 ºC, were drastically reduced, although a good combination between strength and ductility was observed. HEA showed an extreme decrease in the current density (J (A/cm2)), after the heat-treatment, with a lower potential (V). The heat-treated HEA demonstrated a good corrosion rate in acidic conditions, as compared to that of nickel (Ni) based, titanium (Ti) alloys and stainless steel (SS) super alloys. Keywords: HEA, AlCrFeMnNiV, arc-melting, casting, heat-treatment (annealing), compression and corrosion.

Abstract A membrane sensor using an ion association complex of hydroxyzine hydrochloride (HDH) with Orange II (ORG-II) dye, in a polyvinyl chloride (PVC) matrix, has been developed and used as a selective electrode for HDH quantification in pharmaceuticals. The sensor is suitable to determine 2.2 × 10-5 - 1.1 × 10-3 mol L-1 HDH, in the pH range from 2.5 to 5.21, with the Nernstian slope of 57.41±1.04 mV/decade, under optimum conditions. The regression coefficient (RC) value of 0.999 shows a good correlation between HDH concentration and the potential measured using the proposed sensor. The sensor limit of detection (LOD) was 4.5 × 10-6 M. A standard-addition procedure was followed to study the effect of various interferents. The results revealed no variations caused by foreign ions or species. The regression equation (RE) and relative standard deviation (RSD) values, from 1.67 to 5, and from 1.86 to 4.81%, respectively, indicated the HDH-ORG sensor acceptable accuracy and precision. The RSD values of ≤5.67 and <5% indicated the sensor acceptable robustness and ruggedness, respectively. It has been successfully used to determine HDH in tablets, and excellent results were obtained. Keywords: HDH, ORG-II, ion-associate, PVC and membrane sensor.

Abstract In this study, gold nanoparticles (AuNPs) were synthesized using sodium borohydride (NaBH4) as reductant. AuNPs size and shape were experimented by using various characterization techniques. The synthesized AuNPs performance capability for atrazine (ATR) detection, at a glassy carbon electrode (GCE), was verified using cyclic voltammetry (CV) as the determining mode. AuNPs impressive electrochemical performance and stability at the GCE led to further studies, without the need to apply nafion. ATR linear concentration plot ranged from 10 to 17 nM, with a lower limit of detection (LOD) of 0.17 nM, and a regression coefficient (R2) of 0.9934, under optimized conditions. The proposed sensor was very reliable, with a relative standard deviation (RSD) of 1.1%, for n = 20, and it was quite sensitive for ATR, with no discernible interference from other ions. Consequently, AuNPs were effectively used to identify ATR in several pesticide industry wastewater samples. Keywords: ATR, AuNPs, GCE, sensor and wastewater.

Abstract Copper (Cu) powder production, in a sulfuric acid (H2SO4) solution with titanium (Ti) ions, was studied by electrolysis, using Cu anodes. It was empirically proven that this process occurs by three different stage-based mechanisms that depend on the electrolyte composition and electrolysis conditions. The first mechanism occurs in a H2SO4 solution with Cu2+ ions and Ti4+ (tetravalent ions). Cu2+ are cathodically reduced, forming Cu powder (CP), since the process occurs at current densities (J) lower than the limiting one. So, part of the current that would be consumed by the hydrogen ions (H+) reduction reaction is spent to reduce Ti4+, which results in Ti3+ (trivalent ions). These, in the cathode space, reduce Cu2+, which, simultaneously, regenerates Ti4+. Then, these diffuse and are again reduced at the cathode, and Ti3+are formed, reducing Cu2+, in a cyclic process that further increases CP production current efficiency (CE) at the near-cathode space, forming more dispersed particles. The second mechanism occurs in a H2SO4 solution with only Ti4+. During the electrochemical circuit current flow, the Cu anode is oxidized to form Cu2+, and Ti4+ are reduced to Ti3+, on the cathode surface. Then, Cu2+ and Ti3+, by diffusing the solution volume and meeting in the inter-electrode space, chemically interact with each other, due to the red-ox (reduction-oxidation) potential difference, forming a dispersed CP and Ti4+. These diffuse one more time, and are again reduced to Ti3+. These processes are cyclically repeated, i.e., Ti4+ work as catalyst. The third mechanism takes place in H2SO4 with Ti3+. When the current flows through the electrolyte, the Cu anode is oxidized, forming Cu2+, which are immediately reduced in the anode by Ti3+, producing CP. Ti4+ are formed due to the red-ox reaction diffusion to the cathode, being reduced to Ti3+on its surface, which again interact with Cu, producing CP on the anode. Since, in all mechanisms (except the first), CP is not directly produced on the cathode surface, but in the inter-electrode space, further growth of Cu particles does not occur. Thus, CP particles of spherical shape, with sizes from 0.01 to 0.1 μm, are formed, with a CE from 95.2 to 99.1%, under optimal conditions. Keywords: ultrafine CP production mechanisms, H2SO4 solution and Ti+ electrolytes.