Portugaliae
Electrochimica Acta

The influence of cathode material on the electrochemical degradation of methyl orange (MO), methylene blue (MB) and malachite green (MG) dyes was investigated. The cathode materials used were platinum (Pt), copper (Cu), zinc (Zn) and aluminum (Al). The electrochemical activity of the selected dyes on the metal cathodes was examined by cyclic voltammetry (CV). The electrochemical treatment was carried out in both divided and undivided cells. The degradation process was monitored by UV-Visible spectroscopy and chemical oxygen demand (COD) measurement. The influence of pH on discoloration and degradation of dyes was studied. The power consumption and current efficiency of the treatment process involving different cathode materials was computed and compared. The role of cathode material in the degradation of dyes has been established.

The degradation of Alizarin Red S by electro-generated species using Pt and BDD electrodes was performed. The results were explained by the generation of OH* radical, S2O82− at BDD electrode and active chlorine species at Pt electrode. The slow degradation is affected by the current density, initial pH, temperature, initial dye concentration and the nature of the supporting electrolyte. However, the ionic strength showed a negligible effect on both electrodes. In the presence of KCl, the intermediates produced during the degradation are similar at both electrodes. In the presence of sulfate (at BDD electrode), the rate and the mechanism of the degradation are different from those in the presence of KCl. TOC analysis showed total mineralization of AR S.

The perovskite BaPb0.9Sb0.1O3 was prepared through the ceramic route and, after being chemical, structural and electrochemically characterized, it was used in the electrochemical oxidation of guaiacol, using Na2SO4 as electrolyte, at current densities of 5 and 10 mA cm-2 and initial guaiacol concentrations of 50, 100 and 200 mg L-1. The guaiacol degradation was followed by UV-Visible absorbance measurements, Chemical Oxygen Demand (COD) tests and Dissolved Organic Carbon (DOC) analysis. The combustion efficiency was also determined. Results have shown COD removals between 40 and 85 % and DOC removals from 34 to 66 % after 120 h assays. The absolute COD and DOC removals increase with guaiacol initial concentration and applied current density. The mineralization tendency, measured as the combustion efficiency, was maximum for the applied current density of 10 mA cm-2 and a guaiacol initial concentration of 200 mg L-1.

The influence of 2,6-bis-(hydroxy)-pyridine (P1), 2,6-bis-(chloro)-pyridine (P2) and diethyl 1,1’-(pyridine-2,6-diyl)bis(5-methyl-1H-pyrazol2-3-carboxylate ( P3) on the corrosion of steel in 1 N HCl solution has been studied by weight loss measurements, potentiodynamic and impedance spectroscopy methods. The inhibiting action increases with the concentration of these compounds to attain 91,5% at 10-3 M for P3. We note good agreement between gravimetric and electrochemical methods. The polarisation measurements show also that the pyridines act essentially as mixed inhibitors and the cathodic curves indicate that the reduction of proton at the steel surface happens with an activating mechanism. The temperature effect on the corrosion behaviour of iron in 1 M HCl without and with these inhibitors at different concentrations was studied in the temperature range from 313 to 353 K, and allows deducing the apparent activation energy, enthalpy and entropy of the dissolution process and the free energy were determined and discussed. The inhibitors were adsorbed on the iron surface according to the Langmuir adsorption isotherm model at different temperatures and some thermodynamic data for the adsorption process are calculated. The experimental study has been finished by quantum theoretical study; the quantum chemical calculations, based on DFT methods at B3LYP/6-31G** level of theory, were performed, by means of the GAUSSIAN 03 set of programs. Structural parameters, such as the frontier molecular orbital energies (EHOMO and ELUMO), gap of energy E, charge distribution, absolute hardness η and softens , fraction of electrons N transferred from pyridine molecules to steel, as well as electronic parameters such as Mulliken atomic populations have been determined. The objective of this quantum theoretical treatment is to attempt to find relationships between their molecular and electronic structures and inhibition efficiency.

The inhibition action of the Pyrazolone Derivative (PYR) on the corrosion of mild steel in 0.5 M sulphuric acid was investigated by weight loss, polarization, impedance and SEM. Results obtained revealed that PYR performed excellently as corrosion inhibitor with efficiency of 91% at 11 ppm at 298 K. Its adsorption on mild steel obeys Langmuir and Temkin isotherm. Polarization curves indicate that PYR behaves as mixed type. The value of ∆G°ads indicates the spontaneous physisorption of PYR. The SEM results confirm the presence of a protective surface layer over the mild steel surface. The reactivity of the compound was analysed through theoretical calculation.

In this study, we investigated the use of ion exchange processes using a chelating resin, Diaion CRB02 for the removal of boron from the bittern solution left after the extraction of sodium sulfate and sodium chloride from the water of Lake Qarun, located in Egypt. The effects of parameters such as the initial boron concentration and the pH value on the breakthrough volume were studied using boric acid as the synthetic simulant of the bittern solution. The breakthrough capacity was shown to be directly proportional to the height of the resin bed and inversely proportional to the initial boron concentration and the feed flow rate. In addition, the optimum pH for boron removal was found to be 10. An electrically assisted process, which had been found to be effective for a strongly acidic cation exchange resin, was also applied to the ion exchange by taking the electric current as a parameter. However, no remarkable effect was observed, which may result from the difference in the function group between an ion exchange resin using electrostatic attractive force and a chelating resin using complex formation.

Electroless Ni–P based composite coatings are more popular due to their excellent hardness, yield strength, wear resistance, frictional resistance, corrosion resistance, and good lubricity. The present study deals with significance of various coating process parameters on the corrosion behavior of the Ni–P–Al2O3 composite coatings on mild steel substrate. Corrosion behavior of the composite coatings after heat treatment at various annealing temperatures (300 °C, 400 °C, and 500 °C) are investigated by potentiodynamic polarization test using 3.5% NaCl solution. For maximization of corrosion resistance, the electrochemical parameters, corrosion potential (Ecorr) and corrosion current density (Icorr), are optimized using Taguchi based grey relational analysis. For optimization four coating process parameters are considered, namely, concentration of nickel source, concentration of reducing agent, concentration of second phase particles (alumina particles), and annealing temperature, as main design factors. The optimum combinations of the said design factors are obtained from the analysis. Analysis of variance (ANOVA) reveals that the concentration of alumina particles and annealing temperature has the significant influence on the corrosion resistance of the composite coatings. The microstructure of the surface is studied by scanning electron microscopy (SEM) and chemical composition is studied by energy dispersive X–ray analysis (EDX). The X–ray diffraction analysis (XRD) is used to identify the phase transformation behavior of the composite coatings.

Cashew nut testa tannin [CASTAN] has been found to inhibit the corrosion of aluminium in hydrochloric acid solutions using gravimetric, thermometric and UV/visible spectrophotometric techniques. CASTAN inhibition was by adsorption on aluminium following Temkin isotherm in 0.1 M HCl and Langmuir isotherm in 0.5 M and 2.0 M HCl at 303 Kelvin. Physical adsorption on aluminium has been proposed in studied HCl solutions; therefore, CASTAN is a cathodic inhibitor. Earlier reports [1] showed CASTAN to contain quercetin, azaleatin, catechin, epicatechin, cyanidin and delphinidin. However, UV/visible spectrophotometric analysis of CASTAN in ethanol reveals quercetin as its major component. This work therefore investigated the correlation between computed molecular parameters and inhibitive properties of CASTAN and adsorption sites on its components. Calculated quantum chemical parameters namely: EHOMO (highest occupied molecular orbital energy), ELUMO (lowest unoccupied molecular orbital energy), energy gap (ΔE) and dipole moment ( ) suggest that CASTAN is a soft inhibitor and it’s components inhibited aluminium corrosion in protonated forms. Calculated Mulliken charges implicated some electron rich sites, namely: the aromatic and conjugated C=C, C=O and O-H as adsorption sites on the inhibitor molecules. Proposed kinetic model reveals complex reaction mechanism, parallel reactions, for aluminium corrosion inhibition by CASTAN.

The effect of the phenolic (OOMW-Ph) and non-phenolic (OOMW-NPh) fractions of the extract of olive oil mill wastewaters was evaluated as corrosion inhibitor of steel in molar hydrochloric using weight loss measurements and electrochemical polarisation. The results obtained reveal that the referred compounds reduce the corrosion rate. The inhibiting action increases with the concentration of the extract compounds to attain 88.9% and 89.1% of OOMW-Ph and OOMW-NPh, respectively. The increase in temperature leads to a decrease in the inhibition efficiency of the compounds in the temperature range 303 at 333 K. The adsorption isotherm of the inhibitors on the steel surface has been determined. The thermodynamic data of activation and adsorption are determined as well. The phenolic compound (bioactive) most abundant in OOMW extracts is hydroxytyrosol (4 - (2-hydroxyethyl) -1, 2-benzenediol), playing an important role in the effect of the anti-corrosion, either alone or in synergy with other two compounds (tyrosol and oleuropein (4 - (2-hydroxyethyl) phenol) which are present with considerable amounts.

Electrochemical metal nucleation is the method for the formation of metal nanoparticles on the electrode surface. Studying the early stage of electronucleation is simpler than other methods as the driving force for nucleation is achieved by changing deposition potentials and concentration of metal ions. In this work, the potential step electrochemical deposition of palladium was studied from its chloride solution at room temperature on glassy carbon electrode surface. The nucleation mechanism was studied by analysis of the resulting current transients. Accordingly, the initial electro-nucleation mechanism of palladium nanoparticles was found to be varying depending on deposition conditions such as deposition potential and palladium concentration. It can be changed from 3D instantaneous (for all deposition potentials studied and in higher electrolytic concentration) to 3D progressive nucleation mechanism (for lower deposition potential and lower electrolytic concentration). In addition, the nucleation rate for each deposition potential as well as the concentration has been determined. The nucleation rate in this research is used to calculate the nuclei density and found to decrease from more negative deposition potential to more positive deposition potential in agreement with the observed shift in electronucleation mechanism.

The inhibition of the corrosion of Mild Steel (MS) in 1 M HCl solution by a new synthesised organic compound, namely 1,1'-(2,2'-(2,2'-oxybis(ethane-2,1-diyl)bis (sulfanediyl))bis(ethane-2,1-diyl))diazepan-2-one, has been studied by weight loss measurements, electrochemical polarisation and electrochemical impedance spectroscopy (EIS). The experimental results have showed that this organic compound revealed a good corrosion inhibition and the inhibition efficiency is increased with the inhibitor concentration to reach 97% at 1 mM. Potentiodynamic polarisation suggested that it is a mixed type of inhibitor. EIS measurements show an increase of the polarisation resistance with the inhibitor concentration and the electrical equivalent circuit is determined. The inhibitor adsorption process on (MS) surfaces obeys the Langmuir adsorption isotherm and the adsorption isotherm parameters (Kads, ΔGads, ΔHads and ΔSads) were determined. The temperature effect on the corrosion behaviour of (MS) in 1 M HCl without and with inhibitor at different concentration was studied in the temperature range from 308 to 353 K and the kinetic parameters activation such as Ea, ΔHa and ΔSa were evaluated.

Adsorptive stripping voltammetry was used to prospect the adsorption property of montelukast sodium (MKST) on the hanging mercury drop electrode (HMDE). Through appointing the adsorptive stripping voltammetric (AdSV) process, a sensitive electroanalytical method for the quantitative analysis of MKST was accomplished. A well-developed voltammetric peak was obtained in pH 10 Britton-Robinson buffer (B-R buffer) at -1.080 V. The cyclic voltammetric studies indicated that the reduction process was irreversible and primarily controlled by adsorption phenomena. The studies of the variation of adsorptive voltammetric peak current with buffer electrolyte, pH, accumulation time (tacc), accumulation potential (Eacc), sweep rate, pulse amplitude, square wave frequency, working electrode area and convection rate have evaluated in the recognition of optimal experimental conditions for MKST analysis. The studied electroanalytical signal showed a linear response for MKST in the concentration range 510-8- 110-6 mol L-1 (r = 0.994). A detection limit of 410-9 mol L-1 with relative standard deviation of 1.1 RSD% and mean recovery of 102%±2.0 were obtained. The possible interferences by several compounds usually present in the pharmaceutical formulation were also evaluated. The analytical quantification of MKST drug in commercially available pharmaceutical formulation and biological samples was electrochemically studied.

Lead present in several industrial wastes has deleterious effects on the quality of water. Cathodic deposition has been considered as one of the suitable means for lead removal. Experiments were carried out using a lab-scale electrochemical cell incorporating flow-by porous graphite electrodes at steady state conditions. The effects of flow rate, current density, lead influent concentration and pH, on lead removal efficiency, current efficiency, lead removal rates, and cell potential, were investigated. It was found that the maximum removal efficiency (97.75%) was obtained at flow rate (100 mL/min), for initial concentration (40 mg/L), with a residual concentration (0.9 mg/L) and maximum current efficiency of (60.7%). In addition, the recovery of lead from wastewater was investigated.

Editorial

Personal opinion of the author on the use of mercury and amalgam electrodes for determination of trace amounts of biologically active organic compounds is expressed. This view is supported by references to numerous reviews and original papers from UNESCO Laboratory of environmental electrochemistry supporting the claim that both mercury and amalgam electrodes can play useful role in modern practically oriented analytical laboratories.

The article deals with preparing of lithiated graphite material. The lithiated graphite material can be used as active electrode material in lithium-ion batteries. Most of the commercially produced lithium-ion batteries have the negative electrode based on graphite. The capacity losses which are caused by irreversible capacity of graphite may reduce the potential capacity of the battery from 15 % up to 45 %. These losses arise on negative electrode interphase (solid graphite electrode and liquid electrolyte), where during the formation process is created the SEI (Solid-Electrolyte Interphase) layer. The layer is composed from lithium atoms and the decomposition products of electrolyte solvents. The SEI layer is indispensable for correct function of lithium-ion battery. In this article are presented experimental methods for synthesis of lithiated graphite material. The article describes the three concepts of preparing lithiated material and its using like a precursor for preparing of negative electrode. The first method is based on using n-butyllithium (C4H9Li) reagent, its behaviour as the donor of lithium atoms, and graphite acts as the acceptor of lithium atoms. The second concept follows the first one only with adding an ionic compound to graphite, in our case FeCl3. The last concept presents the electroless lithiation process, which is based on different electrochemical potential between lithium and graphite.

The organic-inorganic hybrid sol-gel films, the structure of which comprises interconnected inorganic and organic networks have been reported as an environmentally friendly anti-corrosion pre-treatment for several metals, including aluminium alloys. In this paper, an epoxy-silica-zirconia hybrid sol-gel coating was synthesized from glycidoxypropyltrimethoxysilane (GPTMS) and zirconium n-propoxide (TPOZ) precursors and applied to EN AW-6063 alloy by dip-coating. To promote the organic network formation through the epoxy group polymerization at room temperature, two types of amine crosslinkers were added during synthesis: diethylenetriamine (DETA), in different concentrations, and a tri-functional amino-silane. The evolution of the curing process and the corrosion behaviour of the coated aluminium alloy specimens were evaluated by Electrochemical Impedance Spectroscopy (EIS) in 0.5 M NaCl. The morphology and surface chemistry of the hybrid coatings were characterized by Energy Dispersive Spectroscopy (EDS) coupled with Scanning Electron Microscopy (SEM) and by Fourier Transform Infrared Spectroscopy (FTIR). The results obtained revealed that the sol-gel coatings with lower amine ratios required longer curing times, but showed the best anticorrosive performance with time. The increase in amine concentration has led to a more cross linked organic network, resulting in higher initial coatings resistance; however it has turned coatings more hydrophilic, prone to rapid degradation in water.

The article deals with description of rheological and electrical properties of solvents for electrolytes of lithium-ion batteries. Solvents mixture of dimethyl sulfone and sulfolane at different volume ratios and with a lithium salt (LiClO4) appears as a potentially suitable electrolyte. In this work, we investigate the influence of different solvents and their mixtures in order to find a solvent which increases the fire safety of such battery. The aim of this experiment is to investigate the rheological properties, particularly density and dynamic viscosity of solvents with lithium salt in temperature dependence and to find the optimal composition of the electrolyte from the perspective of achieving the lowest dynamic viscosity and better electrical conductivity, because both quantities are closely related with Walden’s rule. The vibration method is used to determine the values of dynamic viscosity.

The aim of this study was to improve the properties of cathodic material for lithium-ion batteries based on LiCoO2. The solid phase reaction method was chosen as a manufacturing method of the doped base material. This method has already been tested for the production of basic material. Materials selected from the group of alkali metals were chosen as the doping elements. The main objective was to use these added elements for stabilizing the structure of the LiCoO2 material and for limiting the process of their degeneration.

This article highlights the fundamental role of mass-transport for interfacial reactions. First, the dissolution of particulate CaCO3 is discussed demonstrating how the dimensions of the dissolving particle can ‘switch’ the reaction mechanism from being diffusion to surface controlled. Second, the influence of mass-transoprt on electrochemical reactions is considered, specifically considering how electrode modification can alter the observed voltammetric response in the absence of changing the electrochemical mechanism or the rate of electron transfer. Finally, these observations on the chemically controlling role of mass-transport are concluded by considering nanoparticle toxicity and how ‘size effects’ may be exhibited even in the absence of altered thermodynamics or interfacial kinetics of the reactions involved.