Portugaliae
Electrochimica Acta

Using chronoamperometry technique and a ferrous ammonium sulphate bath, an iron film was electroplated on a silver electrode. The characterization of the iron film was carried out using the analytical Electron Probe for Microanalysis (EPMA), X ray Diffraction (DRX) and Spectroscopy Mössbauer Transmission (TMS). The obtained results indicate that the film had an approximated thickness of 20 μm and it was compound mainly of metallic iron with crystalline structure bcc. Analysis EPMA indicated that the iron film presented islands of silver of different sizes in all the area.

The electrical properties of conducting polymers make them useful materials in a large number of technological applications. In the last decade, it has been showed an important effect on the properties of the conducting polymer when iron oxide particles are incorporated into the conductive matrix. In the present study, films of polypyrrole were synthesized in the presence of magnetite particles. The effect of the magnetite particles on the structure of the polymer matrix was determined using Raman spectroscopy and mass variations at different concentrations of Fe3O4 incorporated into the conducting matrix were also calculated by means of quartz crystal microbalance

PtRu/C electrocatalysts were prepared by hydrothermal carbonization process using starch as carbon sources and reducing agents and platinum and ruthenium salts as catalysts of carbonization process and metals source. pH of the reaction medium was adjusted using KOH or TPAOH (tetrapropylammonium hydroxide). The obtained PtRu/C electrocatalysts were characterized by SEM/EDX, TGA, XRD and cyclic voltammetry. The electro-oxidation of methanol was studied by cyclic voltammetry and chronoamperometry. The PtRu/C electrocatalyst prepared using TPAOH was more active for methanol electro-oxidation than the material prepared with KOH.

The goal of this work is the evaluation of the analytical characteristics of the determinations performed using glucose oxidase and acetylcholinesterase based electrochemical sensors, developed applying original or optimized conventional methods of enzyme immobilization. It was found that the sensitivity of glucose determination, for example, varies from 0.048 to 3.36 mA L mol-1 cm-2 and the response time of the glucose oxidase based sensors – from 5 to 30 s, according to the method of the bioreceptor immobilization. The sensitivity of the analysis is affected from the activity of the immobilized biocomponent, from the composition of the solution (concentration of the substrate, of the mediator and of the inhibitor), and from the experimental conditions (pH, temperature, agitation), as well as from the kinetic parameters of the studied process. It was found that the immobilized glucose oxidase conserves its substrate specificity in the presence of a number of glucides (galactose, maltose, fructose, and saccharose) in 100 fold higher concentrations. The selectivity of glucose analysis is ensured applying a suitable potential. Interferences free glucose amperometric determination was performed at 0.00 V/SCE, in the presence of ascorbates and urates. The electrochemical quantification of enzyme inhibitors allows reaching particularly low limits of detection (10-9 - 10-14 mol/L).

Piezoelectric ceramics with perovskite structure based on lead zirconate titanate (PZT) show excellent electrical properties near the morphotropic phase boundary (MPB) and thus are widely used for actuators, sensors as well as microelectronic devices. However, because of the high toxicity of lead oxide and its high vapour pressure during sintering, the use of lead-based ceramics has caused serious lead pollution and environmental problems; for this reason, the development of lead-free piezoelectric ceramics has been demanded to replace lead-based ceramics. Therefore, it is necessary to develop lead-free piezoelectric ceramics with good properties. Among the lead-free piezoelectric materials, the alkaline niobate-based perovskite compounds and Bi-containing materials, have attracted a large amount of attention because of their superior characteristics. The alkaline niobates (K,Na)NbO3 (KNN)-based material exhibits especially good piezoelectric properties and have been studied as substitutes for PZT piezoelectrics. In this work, alkaline niobate-based piezoelectric ceramics were sintetized, system (K0.5Na0.5)xLi(1-x)NbyTa(1-y)O3, and were characterized by X-ray diffraction (DRX) and scanning electron microscopy (SEM). In order to determine their transition temperature, electrochemical impedance spectroscopy (EIS) was used, and it was found the transition temperature was about 420 ºC, which is a desirable value in this kind of materials.

Atrazine is a highly used herbicide and it has been found in both deep and superficial waters. Its solubility in water is reduced and is relatively stable in humid environments, where it has a half-life of one hundred days. Atrazine can be degraded by oxidative photolysis or by microorganisms. It is moderately toxic in humans, animals and plants, because it can be absorbed by inhalation, ingestion or through the skin. In this work, we study the degradation of atrazine in aqueous solution using current controlled electrolysis at a platinum electrode. The effects of pH, current magnitude and direction, and temperature, were evaluated. The atrazine decomposition was monitored during electrolysis by UV-Vis spectrophotometry; quantification of atrazine was done by GC/MS, and quantification of cyanuric acid was done by HPLC. It was found that at 25 ºC in acid media, atrazine is degraded partially to cyanuric acid with formation of persistent intermediate compounds, but at 60 ºC atrazine is completely degraded to cyanuric acid. The TOC results indicate no electrochemical combustion and no mineralization was observed under the experimental conditions studied.

This paper deals with the use of reticulated vitreous carbon (RVC) and graphite felt (GF) as porous electrode for the removal of 20 ppm Cu(II) in 0.5 mol dm-3 Na2SO4 at pH 2 (which resembles a rinsing wastewater generated by a plating industry). The experimental mass transport characterization (kma = buc) showed that for 100 ppi (RVC), the value of the coefficient b, associated with magnitude of porous electrode, is 0.88, while for (GF) is 3.38. On the other hand, c value for 100 ppi (RVC) is 0.06, while for (GF) is 0.62, indicating that the flow pattern is a complex function of the shape of the electrode. The experimental potential drop for 100 ppi (RVC) and (GF) (1.2 cm thick), indicated the absence of hydrogen evolution. Current efficiencies for RVC and GF were function of convection, giving values comprised between 45    68% and 51    73%, respectively, and energy consumption values of 0.3 < Econs < 1.7 and 0.4 < Ec < 1.1 kWh m-3, respectively. Theoretical number of identical cells in the stack (N) necessary to the cupric depletion from 20 to 1 ppm, for 100 ppi (RVC) and (GF) were calculated.

The fuel cells are new alternatives for energy production with low environmental impact. Nowadays, conducting polymers are considered the most promising material to manufacture these type of cells because of their easy application and operation, being polypyrrole (PPy) one of them. The electrochemical synthesis of single-layer polypyrrole and two-layers or multiple-layers polypyrrole/platinum (PPy/Pt) films is reported in this paper. The films were obtained by electropolymerisation of pyrrole and cathodic deposition of platinum from ammonium hexachloroplatinate salt on stainless steel 304. The composition, morphology, conductivity and the electrochemical properties of the films were study by Raman Spectroscopy, SEM, Profilometer, impedance and cyclic voltammetry. The possible use of PPy and PPy/Pt films as electrodes for fuel cells is also discussed.

Paz de Rio, municipality of the North of the department of Boyacá (Colombia), has a coal waste dump for the residues of washing of the coal produced by the preparation of this commodity and locates them without any treatment, action that originates the sterilization of the soil. The big volume produced of the waste causes environmental problems and a health risk for the nearby populations because the toxic metals contained, which flow and polluted the waters of the rivers Soapagua and Chicamocha, and decreases the suitable land for the agricultural uses. In consequence, it is necessary to apply a treatment that decreases the negative effects over the water and soil resources of the region. By this reason, it is required a treatment of the waste, such as the electrokinetic remediation, for applying a voltage gradient for a time (Zhou, 2004). The electric current acts as an agent that moves the contaminants to the anode or the cathode, in agreement with their charges and direction of flux (Acar y Alshawabkeh, 1993). This way, the research found the ability of the electrochemical remediation to handle 6 Kg of the waste, with a humidity of 30 %, applying a voltage of 30-40V.

In this work the physical-chemical properties of six different soils original from Tenerife Island, Spain, are related with the measured electrical current in an electrokinetic experiment. Results show that total electrical charge has relation with properties such as: total metal content, pH, carbon organic content, and cationic exchange capacity. Since all these properties are between those which allow to evaluate the fertility of a soil, an electrokinetic experiment with samples of this soil is proposed like diagnosis tool.

In order to quantifying aluminium by analyzing hemodialysis fluids, two methodologies were developed and validated: square wave adsorptive voltammetry (SWAV) and electrothermic absortion. Performance parameters were established for the two methodologies. They were both applied successfully to the analysis of hemodialysis fluids.

The effect of some analytical organic indicators, e.g. methyl red, methyl orange and methyl violet, on the corrosion of nickel electrode in 0.1 M K2CO3 was studied using galvanostatic and potentiodynamic anodic polarization techniques. The percentage inhibition efficiency was found to increase with increasing concentration of these compounds. The inhibitive action of these compounds is due to their adsorption on the nickel surface, making a barrier to mass and charge transfer, following Freundlich isotherm. The inhibition efficiency decreases in the order: methyl red > methyl orange > methyl violet. It was found that the addition of the chloride, bromide, iodide and thiosulfate ions accelerates the pitting corrosion of nickel in 0.1 M K2CO3 solutions by shifting the pitting potential to more negative direction. The addition of these analytical organic compounds protects the nickel against pitting corrosion in bromide containing solution.

Voltammetric reduction of Zn (II) using L-lysine, L-ornithine, L-threonine, L-serine, L-phenylglycine, L-phenylalanine, L-glutamic acid, L-aspartic acid and vitamin-PP (nicotinamide, niacinamide) at pH = 7.30 ± 0.01, and µ = 1.0 M NaClO4 was reported at 25 and 35 ºC. The nature of current voltage curves was quasireversible and diffusion controlled. Zn (II) formed 1:1:1, 1:1:2 and 1:2:1 complexes with these drugs as confirmed by Schaap and McMaster method. The sequence of stability constant of complexes L-lysine < L-ornithine < L-threonine < L-serine < L-phenylglycine < L-phenylalanine < L-glutamic acid < L-aspartic acid can be explained on the basis of size, basicity and steric hindrance of ligands. The thermodynamic parameters such as enthalpy (∆H), free energy (∆G) and entropy change (∆S) have also been reported. The kinetic parameters viz. transfer coefficient (α), degree of irreversibility (λ), diffusion coefficient (D) and standard rate constant (k) were calculated. The values of ‘α’ confirmed the symmetric nature of ‘activated complex’ between oxidants and reductants response to applied potential between dropping mercury electrode and solution interface.

Fuel cells are receiving growing interest in recent years since they represent one of the most promising energy source to reduce pollutant emission. We propose some new dehydrated salts as an electrolyte in the intermediate temperature fuel cell. The proton conduction in the dehydrated salts was established by the study of DTA/TGA, infrared spectroscopic study, transference number, bulk electrical conductivity measurement and emf study. The electrical conductivity of the dehydrated salts becomes ionic and increases 100-1000 times in the hydrogen ambient with respect to vacuum.

The voltammetric behaviour of quetiapine (QTP) was studied using direct current (DCt), differential pulse (DPP) and alternating current (ACt) polarography. The drug manifests cathodic waves over the pH range of 6 – 11.8. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. At pH 8, the diffusion current-concentration relationship was rectilinear over the range of 8 – 44 μg/mL and 4 – 44 μg/mL using DCt and DPP modes, respectively, with minimum detection limits (LOD) of 0.06 μg/mL and 0.04 μg/mL using the DCt and DPP modes, respectively. The diffusion-current constant (Id) is 1.36 ± 0.04 (n = 10). The proposed method was successfully applied to the determination of the studied compound both in pure form and in formulations. The results obtained were favourably compared with those obtained using a reference method. A pathway for the electrode reaction was postulated.

Electrochemical techniques for on-line monitoring were used to study 70Cu-30Ni alloy corrosion in lithium bromide solution under flow operating conditions in an absorption heat pump. The cause of metallic corrosion on the studied alloy is the localized attack of the passive film surface by bromide ions at lower temperatures, and dissolution of the protective film at higher temperatures and flow conditions. Laboratory experiments were performed using the rotating disk electrode (RDE) under dynamic conditions and different temperatures, similar to the operating pump parameters. This was done to understand the corrosion behavior of the copper alloy prior to on-line monitoring assessment. A corrosion probe consisting in three identical copper alloy ring electrodes embedded in Teflon tube sections to isolate them, with the same diameter as the piping to prevent breaking down pipe flow continuity, was designed and installed. Results under various operating conditions were evaluated. Measurements obtained showed the dynamics of this industrial system and the benefits of real time monitoring in understanding corrosion behavior of 70Cu-30Ni alloy in lithium bromide solution used as working fluid and heat absorbent in heat pumps.

Molecular structure of the azo-dye derived from sulfonamide was synthesized. The elucidation of ligand and complex structures were studied by electronic, infrared and 1H NMR spectroscopies. Proton-ligand constants of sulphonamid azo-derivatives and the stability constant of Mo (III), VO (II), UO2 (II) and Co (II) metal ions with sulfonamide azodye derivatives have been determined potentiometrically in 0.1 M KCl and 30% (v/v) ethanol-water mixture. The data are discussed in terms of the electronic character of the substituents and of the change in temperature. The pK1-H values have been found to increase with increasing electron donating nature of the subsituents. The evaluated dissociation processes are non spontaneous, endothermic and entropically unfavourable. The order of the stability constants of the formed complexes was found to be Mo3+ > VO2+ > UO22+ > Co2+. The influence of substituents on the stability of the complexes was examined on the basis of an electron repelling property of the substituent. The effect of temperature on the stability of the formed complexes was studied and the corresponding thermodynamic parameters (∆G, ∆H and ∆S) were evaluated and discussed. The stoichiometries of these complexes were determined conductometrically and indicated the formation of 1:1 and 1:2 (metal:ligand) complexes.

The inhibition efficiency (IE) of an aqueous extract of Hibiscus rosa-sinensis (white) in controlling corrosion of aluminium at pH 12 has been evaluated by weight loss method in the absence and presence of Zn2+. The formulation consisting of 8 mL flower extract (FE) and 50 ppm of Zn2+ had 98% inhibition efficiency. Polarization study revealed that this formulation functioned as cathodic inhibitor. AC impedance spectra revealed the presence of a protective film formed on the metal surface. FTIR spectra revealed that the protective film consisted of a complex formed between the active principle of the flower extract and Al3+.

Oxygen reduction reaction (ORR) was investigated on a multi-walled carbon nanotubes (MWCNTs)-modified edge plane pyrolytic graphite (EPPG) electrode using cyclic voltammetry (CV) in three kinds of room temperature ionic liquids (RTILs), i.e., 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), 1-n-propyl-3-methylimida-zolium tetrafluoroborate (PMIBF4), and 1-n-butyl-3-methylimidazolium tetrafluoro-borate (BMIBF4). The results demonstrated that, after being modified by MWCNTs on the EPPG electrode, both the reduction peak current of oxygen and the oxidation peak current of superoxide anion were all dramatically increased, and the values of standard rate constant, κs, corresponding to ORR, were greatly enhanced. Under the same condition, in PMIBF4, MWCNTs-modified EPPG electrode exhibited the most satisfied electrocatalysis for ORR, in which standard rate constant, κs, was improved from 2.9 × 10-3 cm s-1 on a EPPG electrode, to 10.4 × 10-3 cm s-1. While in EMIBF4 and BMIBF4, after being modified by MWCNTs, the value of κs was increased from 4.3 × 10-3 to 8.3 × 10-3 and 2.3 × 10-3 to 4.2 × 10-3 cm s-1, respectively. For the catalysis of MWCNTs-modified EPPG electrode towards ORR, the enhanced surface area of electrode and the increased amount of “defect” sites on electrode were thought to be the main reasons for our obtained results.

The inhibition efficiency (IE) of K3[Fe(CN)6] in controlling corrosion of carbon steel in aqueous solution containing 60 ppm of Cl- in the presence and absence of Zn2+ has been evaluated by weight loss method. The formulation consisting of 100 ppm K3[Fe(CN)6] and 50 ppm Zn2+ offers 98% inhibition efficiency to carbon steel immersed in aqueous solution containing 60 ppm Cl-. A synergistic effect exists between K3[Fe(CN)6] and Zn2+. As immersion period increases, the inhibition efficiency of K3[Fe(CN)6]─ Zn2+ system decreases. Polarization study reveals that this formulation controls the cathodic reaction predominantly. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protective film consists of Prussian blue and Zn(OH)2. The film is found to be UV fluorescent.