Portugaliae
Electrochimica Acta

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.