Portugaliae
Electrochimica Acta

In the present work, a simple and low-cost protocol for determination of gliclazide using modified screen-printed electrodes (SPE) was reported. The immobilization of magnetic core-shell manganese ferrite nanoparticles (MCSNP) onto SPE provides a unique opportunity for charge transfer process. Consequently, the electroanalytical sensing of gliclazide was explored at the modified SPE surface. The response of the modified electrode was linear, in the concentration range from 0.5 to 300.0 μM, and a detection limit of 100 nM was obtained. The proposed method was successfully employed for gliclazide determination in pharmaceutical and human urine samples. The method showed tremendous reproducibility and intra- and inter-day stability, and has proved to be highly reliable for gliclazide analysis in clinical samples.

Recently, there were reported investigations in the field of corrosion prevention, about finding effective environment-friendly alternative inhibitors, to replace toxic and harmful compounds. In the present review, the corrosion inhibition of some materials in various corrosive media, using imidazole derivatives, is summarized. Several organic compounds reported by many researchers are herein presented. This review considers previous studies conducted on various inhibitors, and provides an overview of some experimental techniques performed in order to investigate their corrosion properties.

In this paper, the performance of a composite particle for the deposition of ZnO/Cr2O3 on a zinc electrolyte was examined. Its susceptibility to corrosion in 3.5% NaCl, using linear polarization, was investigated. The developed crystal was characterized by using scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The strengthening properties of the coated samples, i.e. the mechanical response, were studied using a high sensitive diamond microhardness indenter and a MTR-300 rigid wear tester. From the results, the effect of the composite coatings interestingly influenced the performance regarding microhardness, durability, corrosion mitigation and wear damage. In general, the micro-hardness value for the Zn-ZnO material was 125.0 HVN, while it was 130.5 HVN for Zn-8ZnO-16Cr2O3 composite coating. For Zn-8ZnO-20Cr2O3, a better hardness performance was noted with 138.0 HVN. From the wear study, Zn-8ZnO shows 0.018 g/min dissociation against the counter body with the best wear performance obtained at 0.005 g/min. The corrosion properties of the developed composite coating also tend towards a more positive region, with a corrosion rate of 0.850 mm/yr. This shows that the role of composite particulates maximally contributes to improve the strengthening characteristics of the developed coating.

The adsorption capacity of activated carbon and activated carbon with amide group towards Ni(II), Zn(II) and Co(II) from aqueous solutions was studied in varying treatment conditions such as contact time, weight of sorbent, pH and initial concentration of treated metal ions. The adsorption capacity was investigated by batch experiments. The results showed that the removal percentages were enhanced by increasing the weight of the added sorbent, contact time, pH of the solution and the initial concentration of treated metal ions. The optimum order of increasing removal percentages of metal ions by using activated carbon (AC) prepared from sawdust of beech wood at pH=5, with an initial concentration of metal ions of 100 mg/L, and after two hours of shaking, was: Zn(II)

This study reports the evaluation of the anticorrosive performance of polymer epoxy resin, namely, Diglycidyl ether 4, 4’-dihydroxydiphenylsulfone (DGEDDS) and its polymer composite reinforced with Titanium Dioxide (TiO2), for carbon steel (CS) corrosion, in 3% wt. NaCl, using experimental analyses. Thermal, electrochemical and morphological techniques were used to demonstrate the anticorrosive effectiveness of the standard epoxy resin (MP1) and its TiO2 composite (MP2). The effect of UV irradiation (for 2000 h), on the effectiveness of MP1 and its TiO2 composite (MP2), showed that TiO2 presence appreciably enhanced the protection efficiency effect of MP1.

The corrosion inhibition property of Gymneme Sylvestre on aluminum in an acidic medium has been investigated. The experimental techniques include potentiodynamic polarization studies, electrochemical studies, quantum chemical calculation and weight loss method. The results revealed that Gymneme Sylvestre acts as a potential corrosion inhibitor of aluminum in an acidic medium, showing 82% inhibition efficiency at 800 ppm concentration of it. Furthermore, the different thermodynamic parameters, including activation energy, Gibbs free energy and enthalpy have been calculated. The results showed that adsorption of the Gymneme Sylvestre molecule onto the aluminum coupon surface obeys Langmuir adsorption isotherm. The quantum chemical parameters were also calculated for major constituents of Gymneme Sylvestre.

Carbon steel corrosion inhibition in a hydrochloric acid solution by 2-[(5-methyl-isoxazol-3-yl)-methyl]-benzimidazole (MMB) has been studied by electrochemical techniques (PDP and EIS). Results showed that the inhibition efficiency increases with higher MMB concentration, and the maximum value of 86.6% was obtained at 10-3 M concentration. The prepared benzimidazole inhibitor showed higher inhibition efficiency upon raising the solution temperature from 303 to 333 K. Corrosion current density decreased from 660.9 µA cm-2 (blank) to 97.8 µA cm-2 (MMB) and charge transfer resistance increased from 20.2 Ω cm2 (blank) to 150.8 Ω cm2 (MMB). PDP studies showed that MMB is a mixed type inhibitor. The adsorption of this compound onto the carbon steel surface in a 1 M HCl solution followed the Langmuir adsorption isotherm, and the value of the standard free energy of adsorption ( ) is associated to physisorption and chemisorption.

This study investigated one of the chemical compounds taken by diabetic patients as a replacement for natural sugar. Its aim was to identify the electrochemical properties of sodium saccharin in different electrolytes, using a nano-sensor. Sodium saccharine was studied by cyclic voltammetric technique, in different electrolytes, using a modified glassy carbon electrode (GCE) with carbon nanotubes (CNT) as working electrode (CNT/GCE). It was found that the redox current peaks of 0.01 mM sodium saccharine in 1 M Na2SO3 enhanced both redox peaks with the CNT electro-catalyst on the GCE surface. Different concentrations, pH and scan rates of sodium saccharine in Na2SO3 have been studied. Also, the nano sensor showed good reliability and stability towards the chemical compounds in the cyclic voltammetric cell. Other electrochemical parameters were determined, such as the potential peak separation (Epa-Epc≈100 mV), the current ratio (Ipa/Ipc≈1) of the redox peaks and the cathodic-anodic reaction rate. The diffusion coefficient value was determined at different scan rates.

Environmental green compounds have emerged as powerful inhibitors for metals and alloys corrosion. So, this article attempts to show that barbituric (BA) and thiobarbituric acids (TBA) are good green corrosion inhibitors for copper immersed in 0.6 mol/L NaCl. A combination of quantitative and qualitative tools were used in this investigation, such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Polarization measurements indicate that these compounds can function as mixed type inhibitors. It was found that the adsorption of these inhibitors onto the copper surface obeyed Flory-Huggins isotherm. Also, the effect of temperature in the inhibitors absence and presence was studied according to Arrhenius isotherm. Some thermodynamic functions of dissolution and adsorption processes were calculated, such as activation energy (Ea), enthalpy (ΔH*), free energy (ΔGo) and entropy (ΔS*). The barbituric and thiobarbituric acids recorded high inhibition efficiency of copper corrosion at concentrations of 5x10-3 mol/L and 1x10-3 mol/L, respectively.

The corrosion inhibition effect of ethanol extract of Acacia nilotica leaves (ANLE) on mild steel in 0.1 M H2SO4, containing 0.1-0.5 g/L, has been studied using weight loss, Potentiodynamic Polarization (PDP), Fourier Transforms Infra-Red (FTIR) spectroscopy, UV-visible spectroscopy, High-Performance Liquid Chromatography (HPLC) and Scanning Electron Microscopy (SEM) methods. The results from weight loss and PDP show that the inhibition efficiency depends on the concentration of the plant extract, as well as on the time of exposure of the mild steel samples in H2SO4 solutions. The optimum inhibition efficiencies of the extract obtained from weight loss and potentiodynamic measurements were found to be 87.57% and 61.85%, respectively. Thermodynamic parameters, such as Ea, ΔH, ΔG and ΔS, were evaluated at 0.5 g/L, and the results were found to be -78.54 kJ/mol, 74.66 kJ/mol., -17.92 kJ/mol and -90.59 kJ/mol, respectively. From the calculated values of activation energy and free energy of adsorption, and from the trend in the variation of inhibition efficiency with temperature, the inhibitor mechanism of adsorption was found to be physical adsorption, exothermic, spontaneous, being best described by Langmuir adsorption model, because the regression coefficients (R2) values calculated from the plots were closest to unity, confirming a highest degree of linearity. Mild steel surface morphology, in ANLE presence and absence, was studied using SEM. FTIR spectroscopy and UV-visible spectroscopy analyses were used to confirm the adsorption process onto the metal surface. Spectra analysis obtained from FTIR study indicated that ANLE was adsorbed onto the mild steel surface via C-O and N=O functional groups. HPLC was also used to find the main component responsible for inhibition, at 5.990 min, which was Catechin. The obtained results revealed that ANLE acts as a good inhibitor and could serve as an effective mild steel corrosion inhibitor in a 0.1 M H2SO4 solution.

This work is a contribution to the study about the inhibition of mild steel corrosion in a molar hydrochloric acid medium by some benzoxazol derivatives compounds. The study was carried out using gravimetric and electrochemical methods (stationary and transient). We have considered the influence of the inhibitor concentration, the temperature of the medium and the duration of the immersion of the metal sample in the aggressive medium. These studies are complemented with theoretical calculations aimed to correlate the results obtained from experimental measurements using the DFT method. The results obtained in this work through gravimetric and both transient and stationary electrochemical methods showed a satisfied coherence. Theoretical calculations also revealed a good correlation with the experimental results for our compounds.

The inhibition effect of Cefalexin on mild steel corrosion in sodium chloride has been examined with the use of electrochemical potentiodynamic polarization techniques, weight loss measurements and computational studies. Cefalexin showed good protection ability by adsorbing onto the mild steel surface. The mixed inhibition characteristics of Cefalexin were revealed by the potentiodynamic polarization results. The inhibitor efficiency was found to be above 65%, obeying the Langmuir and Freundlich isotherm law, with a correlation regression coefficient of R2= 0.9984 and R2= 0.9488, respectively, establishing the reliability on Cefalexin as an inhibitor.

This work consists in applying and studying the new pentafunctional phosphoric polymeric architecture – pentaglycidyl ether pentaphenoxy phosphorus (PGEPPP) – on the behavior of its coating, in a marine environment. First, we applied the new macromolecular pentafunctional epoxide (PGEPPP) binder, crosslinked by methylene dianiline and formulated by a natural phosphate, to E24 carbon steel, in the presence of two formulations, F1 (PGEPPP/MDA) and F2 (PGEPPP/MDA/PN). Then, we have studied the behavior of the anticorrosive coating on the metal substrate, in 3.5% NaCl. Indeed, the gravimetric, stationary and transient electrochemical studies of the composite (PGEPPP/MDA/PN) are very interesting and reach maximum values which are equal to 94%, 95% and 91%, respectively. We then proceeded to the prediction of the quantum parameters of the new pentafunctional phosphorus epoxy resin; these parameters were calculated according to the method of the Theory of Functional Density (DFT), at the level of 6-311 G (d,p) basis sets. Finally, the results obtained by the Monte Carlo simulation are in very good agreement with the data of the DFT theory and with the experimental data.

The inhibitive effect of different extracts of the Tribulus terrestris plant was estimated on the corrosion of mild steel in 1 M hydrochloric acid (HCl), using weight loss and Tafel polarization curves. The inhibition efficiency was increased with higher extracts concentrations. The effects of temperature on the corrosion behavior of mild steel in 1 M HCl, with the addition of extracts, were also studied. The inhibition efficiency obtained using tafel polarization curves and weight loss measurement gave similar results. Polarization curves showed that different extracts of the Tribulus terrestris plant behave as mixed type inhibitors in hydrochloric acid. The obtained results showed that the different extracts of the Tribulus terrestris plant act as an effective green inhibitor of mild steel corrosion in a hydrochloric acid solution. The corrosion inhibition of mild steel was confirmed by the scanning electron microscopy (SEM) study, which shows a good metal surface, without the presence of corrosion products.

The concentrations of lead and cadmium were determined in markets of hair dyes samples in Morocco. Sixteen synthetic and natural hair dyes were selected. The metals were analyzed after mineralization with nitric acid and hydrogen peroxide. The content was determined using differential pulse polarography and the analytical method was validated. The method was linear with a correlation coefficient value (r) that ranged from 0.992 to 0.999. The limit of detection (LOD) was 0.080 and 0.43 ppm for Pb and Cd, respectively. Finally, the concentrations of the two metals in the different hair dyes samples ranged from LOD to 3617.02 ppm for Pb and from LOD to 459.57 ppm for Cd. The majority of the concentrations were above acceptable levels for cosmetics. It has been demonstrated that heavy metals induce toxicity to human body even at a low level, hence the need to strengthen the control of cosmetic products by the competent authorities in Morocco.

A selective method is presented for the simultaneous determination of Pb and Zn in seawater samples, using Differential Pulse Adsorptive Cathodic Stripping Voltammetry (DPAdCSV). In preliminary studies, it has been proven that Pb and Zn react with calcon, giving rise to the formation of complexes which have adsorptive characteristics with a hanging mercury drop electrode (HMDE) and undergo reduction. The optimum parameters and conditions for determination are investigated. The optimal parameters for DPAdCSV of calcon were found to be 0.3 mol L-1 of acetate buffer, with pH 5, 0.02 mmol L-1 of calcon, adsorptive accumulation potential (Eads) of -0.1 V and adsorptive accumulation duration (tads) of 70 s. Ten replicates were performed, giving RSD values of 1.2% for Pb and 0.4% for Zn. Recovery values were in the range from 98% to 105% for both Pb and Zn. The calibration graphs were linear in the range from 5 to 210 ng mL-1 and 5 to 200 ng mL-1 for Pb and Zn, respectively. The limit of detection (LOD) was 0.01 ng mL-1 for Pb and 0.05 ng mL-1 for Zn. The interference of some common ions was studied and it was concluded that the method could be successfully used to determine the concentration of Pb and Zn in seawater samples.

Sodium dodecyl sulfate modified carbon paste electrode (SDSMCPE) was prepared as a sensor for Tartrazine (TR) detection, at 0.2 M PBS, with pH 6.5. TR Electrocatalytic activity was found to be significantly improved compared to those obtained using a conventional paste electrode. TR electrochemical oxidation was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). SDSMCPE showed TR electrocatalytic oxidation in the linear range from 2×10-5 to 5×10-5 M and from 6×10-5 to 1.1×10-4 M, with the detection limit of 52×10-7 M. The proposed SDSMCPE-sensor exhibited enhanced electrochemical sensing, selectivity and stability for TRdetection. Finally, the use of a SDSMCPE-sensor was demonstrated for TRdetection in a lemon yellow powder sample.

Three different films modified with silver species were considered to enhance the corrosion resistance of AZ91D Mg alloy and to impart its surface with antibacterial activity. First, coatings were electrodeposited under potentiostatic conditions in electrolyte solutions containing Na2MoO4 and/or Ce(NO3)3 as main compounds, and H2O2, ascorbic acid or citric acid as additives. Incorporation of silver species was done by immersion of the samples in AgNO3 solutions. The obtained modified films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion protection properties of the films were examined in a simulated physiological solution by open circuit measurements, linear polarization and electrochemical impedance spectroscopy (EIS). The antibacterial effect of the coatings was evaluated using Escherichia coli bacteria. Cerium and molybdenum-based coating modified with silver provides superior antibacterial and anticorrosive properties compared to the other films studied.

The present work is focused on the influence of the metal salts on the photocatalytic efficiency of TiO2 for the elimination of E 131 VF food colorant. Two series of TiO2 photocatalysts loaded with Fe(II) and Cu(II) were prepared by using the wet impregnation method. The samples were characterized by XRD, IR, Raman and scanning electron microscopy. The degradation of the food colorant was followed by the measurement of the absorbance. The kinetics of degradation fitted well to the zero pseudo order with Cu-TiO2, but it followed the 1st order with Fe-TiO2. In general, the photoactivity of TiO2 was reduced by the presence of the transition metal ions, even at low molar ratio %. The recalcination of the doped samples at higher temperatures reduced more the degradation activity. Several reasons were suggested to explain the dramatic decrease in the activity of the prepared samples.

Molecular modelling approach has been used for the prediction of anticorrosion properties of 1, 2, 4-triazole derivatives on steel in acidic medium by the quantum chemical calculation and molecular dynamics (MD) simulation methods. Quantum chemical parameters such as the highest occupied molecular orbital (E-HOMO), the energy of the lowest unoccupied molecular orbital (E-LUMO), energy band gap (ΔE), dipole moment, global electronic chemical potential (μ), chemical softness (σ), chemical hardness (η) and electrophilicity (𝜔) have been calculated and discussed. The reactive sites of the inhibitor molecules were found to be on the nitrogen-atom of the Triazolic ring and on the π-electron centers. Furthermore, molecular dynamics simulation was applied to search for the best inhibitor adsorption configuration over Fe (110) surface. The best adsorption energy was found to be -430.27 kcal/mol (inhibitor 3). The adsorptions occurred via chemisorption.