Portugaliae
Electrochimica Acta

The beneficial effects of the ultrasound (US) like the cleaning of electrode surface and enhancement of mass transport were evaluated in association with potentiostatic electrolyses for the degradation of pentachlorophenol (PCP) at 3.0 V vs. Ag/AgCl, using a boron-doped diamond (BDD) electrode during 270 minutes. Different decay levels of the PCP spectrum bands in 220, 251 and 321 nm, respectively, were observed after application of ultrasound without electrochemical process (18.1, 17.7 and 19.8 %), silent electrolyses (29.3, 71.6 and 70.8 %), pulsed sonoelectrolysis (31.0, 75.1 and 76.3%) and sonoelectrolyses (39.2, 80.0 and 82.6 %). For silent and sonoelectrolyses processes, cleaning/reactivation of the BDD surface by acetonitrile and/or electrochemical treatment was necessary. The pulsed sonolectrolysis were carried out purposely without cleaning/reactivation of the surface. The results showed greater PCP degradation for insonated studies than those obtained for the silent electrolyses, due to the increase of mass transport, minimization of the electrode fouling and the combined generation of hydroxyl radicals by both ultrasound and the polarized BDD surface. These tools (US and BDD), especially the pulsed sonoelectrolysis, can improve the degradation of pesticides and their metabolites in the environment and enable the use of sonoelectrochemistry for wastewater remediation.

The electrochemical oxidation of cibacron red FN-R (CB) has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at a glassy carbon electrode (GCE) in phosphate buffer solutions of pH (2.54–11.79) used as supporting electrolytes. The voltammetric behaviour showed that the electro-oxidation process gave rise to a single peak at 0.692 V vs. Ag-AgCl using DPV in phosphate buffer solution at (pH 3.34). The oxidation process was shown to be irreversible and adsorption-controlled. An analytical method was developed for the determination of cibacron red FN-R in phosphate buffer solution at (pH 3.34) as supporting electrolyte. The anodic peak current varied linearly with cibacron red FN-R concentration in the range 2.0x10−6 mol/L to 1.0x10−5 mol/L of cibacron red FN-R with a limit of detection (LOD) of 4.49x10−7 mol/L and limit of quantification (LOQ) of 1.49x10-6 mol/L. Validation parameters, such as accuracy, precision and recovery were evaluated. The proposed method was successfully applied to the determination of cibacron red FN-R in synthetic industrial effluents and the analytical results compared well with those obtained by the spectrophotometric method.

The aim of this study is to evaluate the potential of benzotriazole (BTAH) for replacement of sodium nitrite (NaNO2) in the zinc phosphate bath (PZn+NaNO2) used for carbon steel (SAE 1010). Surface characterization of phosphated and unphosphated samples was carried out by Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Optical Microscopy and X-ray diffraction. The corrosion resistance of the samples was evaluated by electrochemical techniques such as Open Circuit Potential, Electrochemical Impedance Spectroscopy and Anodic Potentiodynamic Polarization Curves, in a 0.5 M NaCl electrolyte at room temperature. The experimental results showed that not only benzotriazol (PZn+BTAH) presented better corrosion properties than sodium nitrite, but also the amount of the deposited phosphate increased approximately six times comparatively to the bath with sodium nitrite. The results demonstrated that benzotriazole (BTAH) is a potential candidate for replacement of sodium nitrite (NaNO2) in zinc phosphate baths.

Quetiapine (QTF) is a potent serotonin and dopamine receptor antagonist used to treat major depressive disorders and schizophrenia. A simple, precise, accurate and cost-effective titrimetric method for the determination of QTF in bulk drug and in its dosage forms has been developed and validated. The method is based on the potentiometric titration of QTF in glacial acetic acid with acetous perchloric acid using a modified glass-saturated calomel electrode system. The method is applicable over the range of 2.0 – 20.0 mg of QTF. The proposed method was successfully applied to the determination of QTF in its pharmaceutical dosage forms. The results obtained were favorably compared with those obtained using a reference method. The precision results, expressed by intra-day and inter-day relative standard deviation values, were satisfactory (RSD ≤ 1.2%). The accuracy was satisfactory as well (RE ≤ 1.33%). Excipients used as additives in pharmaceutical formulations did not interfere in the proposed procedures, as shown by the recovery study via standard addition technique with percentage recoveries in the range 98.25-101.0 %, with a standard deviation of ≤ 0.62-1.52%.

The corrosion behaviour of Al 6061-TiO2 particulate composites in chloride, nitrate, sulphate and acidic media has been studied in the present investigation. The unreinforced matrix, and the composites containing 2, 4 and 6 weight percent of TiO2 particulates were prepared by liquid metallurgy route using the vortex technique. Their corrosion behaviour was evaluated by weight loss, potentiodynamic polarisation, scanning electron micrograpaph (SEM) and energy dispersive X-ray analysis (EDXA) methods. The studies show that corrosion current density (ICorr) and the corrosion rate were highest in the case of corrodent 0.1 N HCl. The rate of corrosion of both the matrix alloy and the composites decreased with increase in time of exposure in acid medium, possibly due to the formation of a passive oxide layer. Corrosion current (ICorr), corrosion potential (ECorr) and pitting potential (EPit) were obtained from potentiodynamic polarisation studies. In all the media, the ICorr values of unreinforced matrix alloy and composites were found to increase as the TiO2 content increased from 0% to 6%, which could be attributed to the microgalvanic coupling between the reinforcement or conducting interfacial products and the matrix alloy. Insulator TiO2 particulates are perceived to act as inert material and degrade the integrity of the protective oxide layer on the Al matrix alloy. The presence of reinforcement in the matrix increases cathode to anode ratio in the composites, resulting in the formation of pits during localised corrosion. Moreover, the pitting effect was more pronounced in the presence of aggressive Cl- ions compared to mild NO3- and SO42- ions. SEM and EDX analysis of samples in chloride media showed the presence of large pits and completely deteriorated surface, complementing weight loss and polarisation studies.

Three new gemini surfactants referred to as n-2-n (where n= 6, 12, 16) were developed as corrosion inhibitors for mild steel. Their critical micelle concentration (cmc) at equilibrium in water at 30oC was determined. Corrosion inhibition studies of mild steel in formic acid by gemini surfactants were conducted by using weight loss, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements. Scanning electron microscopic study (SEM) was also used to investigate the surface morphology of inhibited and uninhibited metal samples. The results obtained show that the surfactants studied are good mixed type inhibitors. The result was also correlated with several factors, including the chain length of the hydrophobic chains, critical micelle concentration (cmc) and adsorption free energy of these inhibitors. The adsorption of all the gemini surfactants was found to follow Langmuir adsorption isotherm. EIS results indicate that the change in the impedance parameters (Rt and Cdl) with concentration of inhibitors was due to the formation of a protective layer on the surface of mild steel.

Poly(3,4-ethylene dioxythiophene) (PEDOT), poly(aniline) (PANI) and their copolymer (PEDOT-PANI) were electrodeposited onto a glassy carbon electrode. The electrodeposition was performed using cyclic voltammetry from acidic solution containing appropriate monomer concentrations and sodium dodecyl sulphate (SDS) as a wetting agent. The resulting polymer films were characterised using cyclic voltammetry in acidic and neutral phosphate buffer solutions and IR spectroscopy. The specific capacitance of the PEDOT-PANI co-polymer reaches up to 260 F g−1 and had good stability during cycling in mineral acid solution. IR spectroscopy confirms the formation of PEDOT-PANI copolymer. The polymers showed an electrochemical activity towards ascorbic acid oxidation. The oxidation current was linearly dependant up to 20 mM ascorbic acid concentration and the PEDOT activity was much higher than that for PANI and PEDOT-PANI copolymer.

A simple, accurate and sensitive voltammetric method for determination of donepezil (DNZ) using β-cyclodextrin modified carbon paste electrode (CDMCPE) is developed. CDMCPE exhibited significantly increased sensitivity and selectivity for DNZ compared to the bare carbon paste electrode (CPE). Effect of accumulation potential, accumulation time, pH of buffer, etc., on peak currents for the determination of DNZ was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Peak currents showed a linear response in the concentration range 4.2 x 10-8 to 5.6 x10-7 M and 3.2 x 10-9 to 4.2 x 10-8 M at CPE and CDMCPE respectively. Limit of detection (LOD) and limit of quantification (LOQ) were found to be 1.2 x 10-9 and 0.40 x 10-8 M. The proposed method has been successfully applied for the determination of DNZ in spiked urine samples, serum samples and pharmaceutical formulations.

Conductance measurements were employed to determine the critical micellar concentration, CMC, limiting molar conductance at infinite dilution, degree of dissociation and dissociation constant of terbium caprylate and caprate in 60/40 benzene-methanol (v/v). The results have shown that these soaps behave as a weak electrolyte in dilute solutions and Debye-Hückel-Onsager’s equation is not applicable to these soap solutions. The thermodynamic parameters indicate that the micellization process is favoured over the dissociation process.

The adsorption of 4-amino-5-phenyl-4H-1, 2, 4-triazole-3-thiol (APTT) as a corrosion inhibitor on mild steel surface in hydrochloric acid (HCl) solution was studied using the weight loss technique. The surface coverage with the adsorbed APTT was used to calculate the free energy of adsorption, ΔG(0)ads, of APTT using Bockris–Swinkels isotherm. The dependence of free energy of adsorption, ΔG(0)ads, on the surface coverage, θ, is ascribed to the surface heterogeneity of the adsorbent. The effect of APTT was discussed from the adsorption model viewpoint. The adsorption of APTT molecules on the surface occurs without modifying the kinetic of corrosion process.

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).