Portugaliae
Electrochimica Acta

The adsorption capacity of hebba clay and activated carbon towards (Fe3+, Cu2+, Zn2+, Pb2+, Cr3+, Cd2+) metal ions was studied. The adsorption capacity was investigated by batch experiment. The effect of weight of hebba was studied and the results showed that the removal percentages increased as the weight of sorbent increased. The effect of contact time was also studied and the results showed that the removal percentages increased as the contact time increased. The effect of pH of the solution was also studied and the removal percentages for (Cu2+, Zn2+and Cd2+) were affected slightly by changing the pH value, but for (Fe3+, Pb2+ and Cr3+) the effect was higher. Also, the effect of initial concentration of metal ions was studied at four different concentrations (5, 10, 30, 50 mg/L); in case of metal ions (Cu2+, Zn2+ and Cd2+), the removal percentages increased by increasing initial concentration. But for the other metal ions it decreased. The order of increasing removal percentages of metal ions at pH=4.86, concentration of metal ions 30 mg/L, and after four hours of shaking, was (Pb2+ < Cu2+ < Cd2+ < Cr3+ < Zn2+ < Fe3+). But in the case of activated carbon, the order was Cd2+ < Zn2+ < Cu2+ < Pb2+ < Cr6+ < Fe3+.

This work aims to investigate the electro oxidation of methanol, in alkaline solution at a copper electrode modified with electrodeposited natural phosphate and nickel (Ni-NP/Cu), by cyclic voltammetry, impedance measurements and square wave voltammetry. Morphological characterizations were performed by SEM and XRD techniques. It was found that Ni dispersed on natural phosphate (NP) shows a catalytic activity towards methanol oxidation better than massive Ni. Ni and NP were fixed on copper electrode by electro deposition using potentiostatic and galvanostatic techniques.

The electro-bioremediation is a technique that is used for the remediation of hydrocarbon contaminated soils. The aim of this study is to explore the electro-bioremediation of an unsaturated soil, contaminated with hydrocarbon waste generated by the oil industry activity in the area and previously remediated by landfarming, to in order to increase the removal of polyaromatic hydrocarbons. The sample was put in a three-compartment electro-bioremediation glass cell of 58 cm long, the lateral compartments containing the electrolyte; we used bridges of ammonium phosphate to connect the electrolyte with the soil sample in the central compartment. A potential difference of 0.5 V/cm was applied to the electro-bioremediation cells for 60 days. A second cell was used for control and no current was applied to it. The monitoring was carried out by a counting cell and measuring of n-alkanes and polyaromatic hydrocarbons using GC mass. The results showed that this technology has good potential to increase the biodegradation of n-alkane hydrocarbons and polyaromatic hydrocarbons such as phenanthrene, 1-3-metilphenanthrene, chrysene, 3-methylchrysene, 6-methylchrysene, benzo(b)fluoranthrene and benzo(ghi)pyrene which, without the application of direct current, were not biodegraded by microorganisms in the soil. The use of salt bridges maintained the pH between values that are compatible with the degrading bacterial community.

The removal of pollutants from effluents by electrochemical degradation has become an attractive method in recent years. This paper deals with the removal of reactive textile dye Cibacron Navy W-B (CNWB) from an aqueous medium by the electrochemical method using graphite carbon electrodes. Electrochemical behavior of reactive azo dye CNWB was performed with cyclic voltammetry in sulphuric acid medium using glassy carbon as working electrode. The potential range selected for the dye was in the range +700 mV to –450 mV. The voltammetric curve of CNWB shows cathodic peaks at +50 mV, –155 mV and –317 mV and anodic peaks at +382 mV and +547 mV, respectively. The decolourisation efficiency was assessed through UV-Visible studies. The LC-MS of the dye were analyzed before and after electrochemical treatment and confirmed that the azo groups and aromatic rings were destroyed. The effect of pH and nature of supporting electrolytes on the electrochemical degradation of dye was also studied. The maximum Chemical Oxygen Demand (COD) removal efficiency was ~100% for the dye solutions at 5 g/L of NaCl concentration. The results revealed the suitability of the present process for the effective degradation of dye effluents.

Cyclic voltammetric studies were carried out on pure iron in alkaline borate and phosphate buffer solutions at pH 10.8. At higher potentials, on anodic polarization, iron forms FeB4O7 and FeOOH in borate buffer, and FeHPO4 in phosphate buffer which got converted to higher valency phosphates. In phosphate solutions, in presence of halides, the interfacial diffusion layer turned to be cation selective outer sublayer and an anion selective inner sublayer, and in borate solutions a precipitate layer of metal oxyhydroxide was formed, which was anion selective, and anions adsorb on this.

This work attempts to determine the best conditions for applying the Electrochemical Chloride Removal (ECR) in rebars embedded in cement mortar with chloride additions by monitoring the corrosion rates before, during and after the application of an ECR. The ECR was applied at different conditions of current density (1 and 2 A/m2 of steel surface), application times (15, 30 and 60 days) and degree of precorrosion of the rebars. According to the results obtained, if ECR is applied preventively, it is an efficient procedure for delaying the start of corrosion. However, if applied too late, it does not assure the repassivation of corroded reinforced concrete structures and is therefore useless. The efficiency of the ECR depends heavily on the application time and the degree of precorrosion of the rebars.

The influence of a natural extract of fenugreek on the corrosion of steel in 1 M HCl has been studied by weight loss, polarisation and EIS measurements. Results obtained show that the natural substance inhibits the corrosion process. It acts on the cathodic domain without modifying the reduction mechanism. The inhibition efficiency increases with fenugreek concentration to attain 94% at extract of 10 g/L of fenugreek at temperatures between 308 and 353K. It is an efficient inhibitor. The effect of temperature on the corrosion behaviour of steel indicated that inhibition efficiency is temperature-independent. The activation energy of adsorption is determined.

The corrosion behavior of aged and annealed sample of 18 Ni 250 grade maraging steel was investigated in varied conditions of concentration and temperature of sulphuric acid medium, using electrochemical techniques like Tafel polarization and electrochemical impedance spectroscopy (EIS). The results obtained from both the techniques are in good agreement. These results have shown increase in corrosion rate of aged specimen with increase in concentration and temperature of sulphuric acid. With increase in concentration of sulphuric acid from 0.025 M to 0.25 M the corrosion rate of annealed sample was found to increase, but there after in 0.5 M, 0.75 M and 1 M, the rate of corrosion decreases, indicating passivation of alloy surface at higher concentration of sulphuric acid. The corrosion rate of aged specimen was found to be higher than that of the annealed specimen. Similar observations are revealed by SEM images. The thermodynamic parameters like activation energy, enthalpy of activation and entropy of activation were calculated.

Four heterocyclic compounds, namely 4- phenyl-5-acetyl/carbethoxy-3-methyl-6-hydroxyl-6-methyl-4,5,6,7-tetrahydro-2,1-benzoisoxazole and benzopyrazole (BIS1, BP1and BIS2, BP2), were synthesized and their influence on the inhibition of corrosion of mild steel in 1 M H2SO4 was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance (EIS) and scanning electron microscopy (SEM). The values of activation energy and free energy of adsorption of these compounds were also calculated. Adsorption obeys Langmuir adsorption isotherm. The IE of the compounds was found to vary with concentration and temperature. Synergistic effect was also investigated for the four compounds at 0.05 mM concentration by weight loss method in 1 M H2SO4 medium in presence of KI, KBr and KCl. Results obtained revealed that all the four compounds performed excellently as a corrosion inhibitor for mild steel in 1 M H2S04 and their efficiency attains more than 90% at 0.6 mM at 298 K. Polarisation studies showed them to be mixed type inhibitors.

The present study attempted to investigate the best conditions for the use of a mixture of 2-mercaptobenzimidazole and alcohol ethoxylate (C13) as corrosion inhibitor of mild steel in 1 M HCl through the use of the surface response methodology. A matrix of Doelhert to 4 factors was used as the experimental design in this research as it permits the use of the response surface methodology in a spherical field. The response used in the exploitation of the design was the determination of the inhibitor efficiency. It was assessed through gravimetric measurements on samples in the absence and presence of the inhibitor. The results were confirmed using electrochemical impedance spectroscopy (EIS).

Inhibition of the corrosion of zinc in various concentrations of H2SO4 by lincomycin was studied using weight loss and hydrogen evolution methods. The results obtained indicated that lincomycin is a good adsorption inhibitor for the corrosion of zinc in H2SO4 solutions. The inhibition efficiencies of lincomycin for the corrosion of zinc in H2SO4 were found to range from 70.90 to 80.32 %, 69.25 to 77.70 % and from 52.11 to 67.49 % at 303, 313 and 323 K, respectively. The inhibition efficiencies decreased with increase in temperature and with increasing concentration of H2SO4 but increased with increase in the concentration of lincomycin. The adsorption of lincomycin on Zn surface is endothermic, spontaneous and is best described by Langmuir adsorption isotherm. Base on the trend in the variation of inhibition efficiency with temperature and the calculated values of the activation and free energies of adsorption, a physical adsorption mechanism is proposed for the adsorption of lincomycin on the surface of zinc.

The electroreduction of the antidepressant drug Bupropion hydrochloride has been studied in aqueous media at dme. Single well defined wave was obtained in different supporting electrolytes, like, KNO3, ammonium citrate buffer, acetate buffer, B. R. buffer, etc. The effect of pH on this reduction has been studied in B. R. buffer in the pH range 3.13 – 11.0. The Bupropion hydrochloride is best reduced in slightly acidic medium. This behavior was attributed to the reduction of >C=O group present in the drug. The effect of concentration and temperature on half wave potential has also been investigated. The reduction of drug was found to be irreversible and diffusion controlled, hence kinetic parameters (K0fh, αn) are evaluated using Meites Israel and Gaur Bharagav,s method. Further, with increase in temperature the values of K0fh also increase, showing that irreversibility of the system decreases on increasing the temperature.

As a first step towards inhibition of uniform and pitting corrosion processes of Al in SCN- solutions, glycine (Gly) was used. Full immersion tests, using inductively coupled plasma atomic emission spectroscopy (ICP-AES) method of chemical analysis were used to monitor rates of corrosion. The results obtained from the ICP method have been verified by electrochemical assays based on linear and cyclic polarization measurements. Monitoring the open circuit potential (OCP) of the system as a function of immersion time and Gly concentration was also carried out. SEM and EDX examinations of the electrode surface revealed the adsorption of Gly molecule on the surface. Results showed that the presence of Gly in aggressive SCN- solutions decreased the corrosion and passive currents and shifted the pitting potential to more noble values. Thus Gly inhibited uniform and pitting corrosion processes. The inhibition efficiency of Gly enhanced with its concentration. The potential of zero charge (PZC) of the Al electrode has been studied in 0.04 M KSCN solutions without and with Gly and the mechanism of adsorption is discussed. The adsorption of Gly precluded significant adsorption of the aggressive SCN- anions, and hence the corrosion rate was diminished.

To improve the corrosion resistance of mild steel, in this work, bi-layers of BTSE (bis-(triethoxysilyl) ethane) and Ppy coatings have been deposited via adsorption and electrodeposition, respectively. The anticorrosive properties of these bi-layers have been evaluated in an aggressive medium like 3% NaCl, and compared with the layers of BTSE and Ppy in a separate way. In spite of the aggressive solution, it was evaluated a poor behaviour of both Ppy and BTSE coatings using potential measurements, EIS and SEM techniques. A better behaviour was expected because the preparation of the bi-layers Ppy/BTSE and BTSE/Ppy showed a protective behaviour using SEM and salt spray tests. However, EIS results predicted an evolution of these coatings for long immersion times being evident the oxidation of the steel.

The adsorption capacity of Eichhornia Crassipes towards metal ions such as Fe3+, Cu2+, Zn2+, Pb2+, Cr3+ and Cd2+, was studied. The adsorption capacity was investigated by batch experiments. The results showed that the removal percentages increased as the weight of sorbent increased, except for Fe3+ and Zn2+. The effect of contact time was also studied and the results showed that the removal percentages increased as the contact time increased for Cr3+, Zn2+ and Pb2+, but for Fe3+, Cu2+ and Cd2+ the removal decreased. The effect of pH of the solution was also studied and the removal percentages increased as pH increased. Also the effect of the initial concentration of metal ions was studied at four different concentrations (5, 10, 30, 50 mg/L); in case of metal ions (Cu2+, Zn2+ and Cd2+) the removal percentages increased by increasing initial concentration. But, for the other metal ions it decreased by increasing initial concentration over 30 mg/L. The order of increasing removal percentages of metal ions at pH=4.86, initial concentration of metal ions 30 mg/L, and after four hours of shaking was: Cu2+< Cr3+

Ti-15Mo alloy has been evaluated for its electrochemical behavior in phosphate buffer saline solution at the physiological temperature of 37 ºC. A two time constant model of a duplex oxide layer has been used to assess the corrosion behavior of the Ti-15Mo alloy-solution interface using electrochemical impedance spectroscopy (EIS). Interfacial characteristics of the inner barrier layer and the outer porous layer have been studied to understand the role of the alloy as an implant. Ti-15Mo alloy shows a very high barrier layer resistance and a tendency to resist localized corrosion.

The inhibition efficiency of sodium dodecyl sulfate (SDS) in controlling corrosion of carbon steel in aqueous solution containing 120 ppm of Cl− in the presence and absence of Zn2+ has been evaluated by weight loss method. The formulation consisting of 300 ppm of SDS and 75 ppm of Zn2+ gives 93 % inhibition efficiency. A synergistic effect exists between SDS and Zn2+. As the immersion period increases, the inhibition efficiency of SDS-Zn2+ decreases. Polarization study reveals that this formulation controls both the anodic and cathodic reactions. AC impedance spectra reveal that a protective film is formed on the metal surface.

Inhibition of the corrosion of zinc in 0.01 to 0.0 4 M H2SO4 by erythromycin was studied using weight loss and hydrogen evolution methods. The results obtained indicate that erythromycin is a good adsorption inhibitor for the corrosion of zinc in H2SO4 solutions. The inhibition efficiency of erythromycin increases with increasing concentration but decreases with increase in temperature. Thermodynamic and adsorption studies reveal that the adsorption of erythromycin on zinc surface is exothermic, spontaneous and is characterised with increasing degree of orderliness. The adsorption characteristics of the inhibitor are best described by the Langmuir adsorption model. From the variation of inhibition efficiency with temperature and the calculated values of the activation and free energies (which are within the limits expected for physical adsorption), we propose that the adsorption of erythromycin on zinc surface is consistent with the mechanism of physical adsorption.

Myeloperoxidase (MPO) is a neutrophil enzyme that employs hydrogen peroxide (H2O2) to catalyze the oxidation of halides and thiocyanate to their respective hypohalous acids. In this study, the inhibitory effect of nitrite (NO2-) on MPO-catalytic activity was investigated electrochemically. H2O2 consumption during steady-state catalysis was monitored amperometrically by a carbon fiber based H2O2-biosensor at 25 oC. Optimized initial concentrations were 50 nM MPO, 10 μM H2O2, and a selected halide or thiocyanate concentration from physiological range. Under these conditions, reactions were monophasic and rapid (complete H2O2 consumption occurs in < 10 s). As concentration of NO2- increases, reactions change to biphasic (rapid step followed by a slow step) and both steps have been inhibited by NO2-. Our results confirmed the inhibitory effect of NO2- and demonstrated for the first time that NO2- is a strong inhibitor towards MPO-catalyzed oxidation of iodide and bromide; and a weak inhibitor towards MPO-catalyzed oxidation of chloride and thiocyanate.

Surface modification by chitosan (CT) on a glassy carbon electrode (GCE) was employed in the present study to determine metal traces (Cu, Pb, Cd, Co, As and Pt). Previous report about the chitosan film affinity toward positive or negative species demonstrated and allowed the application of these polymeric films for detecting heavy metals in aqueous solutions. The modified surface exhibited an affinity to chelating metal ions in solution, forming complexes. Differential pulse voltammetry combined with a pre-concentrating process and standard addition method were employed for trace analysis, obtaining the detection ranges (Cu (II) from 3.99E-6 to 3.91E-5 mol L-1, Pb(II) from 1.99E-6 to 1.58E-5 mol L-1, Cd(II) from 1.59E-5 to 6.23E-5 mol L-1, As(IV) from 7.99E-6 to 5.04E-5 mol L-1, Pt(IV) from 8.19E-6 to 3.59E-5 mol L-1, Co(II) from 6.11E-4 to 2.78E-3 mol L-1), calibrations plots and relevant equations for each metal. Finally, cyclic voltammetry technique was used to characterize the polymeric surface behavior in presence of different metals and during the differential pulse voltammetric analysis. The results are described and discussed in the light of the existing literature.