Portugaliae
Electrochimica Acta

Abstract The use of pesticides has been increased in recent years, to enhance crops productivity, which may lead to a serious global concern of environmental pesticides monitoring. Isoproturon (IPU: 3-(4-isopropylphenyl)-1,1-dimethylurea) is an herbicide widely used in wheat crops. However, when it enters in the ecosystem, it is heavily toxic to humans. Thus, there is an urgent need to develop sensitive and selective IPU detection methods. In the present work, a novel polymethylmethacrylate/ferrite (PMMA/M(FexOy)) polymer nanocomposite (PNC) modified glassy carbon electrode (GCE) was developed for IPU detection. The PNC/GCE surface morphology was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). PNC electrochemical characterization (EC) was performed by cyclic voltammetry (CV) that showed a quasi-reversible redox behavior. PNC/GCE demonstrated an excellent square wave voltammetric (SWV) response towards IPU, with a limit of quantification (LOQ) of 1.98 × 10-7 M, and a limit of detection (LOD) of 6.5 × 10-8 M, in 1 M HClO4 (perchloric acid), at pH 2.0. EC investigations reflected a peak current that was linearly related to IPU concentrations, with a high detection sensitivity. It also showed much better CV and SWV IPU responses than those of a bare GCE, and further environmental stability, without a high influence of common interfering ions. Keywords: IPU, PPMA/M(FexOy), EC, CV and SWV.

Abstract Pinus oocarpa seed extract corrosion inhibition effect on galvanized steel has been studied in 2 M hydrochloric acid, at 303 K and 333 K, by gravimetric methods. The inhibitor efficiency decreased with higher temperatures, which suggests physisorption. Potassium iodide (KI) synergistic action produced an increase in the extract inhibition efficiency, but its parameter decreased with higher inhibitor concentrations. The galvanized steel optical microscopy shows that the metal surface was coated with P. oocarpa seed extract, and that the cracks observed in the inhibitor absence were filled. This observation suggests that the extract can be used as a coating to prevent galvanized steel corrosion. Keywords: corrosion inhibitor, optical microscopy, gravimetric methods, P. oocarpa and synergistic effect.

Abstract The formation of thick anodic oxide films on antimony in diluted solutions of oxalic acid (CO(OH)2) was studied under galvanostatic and isothermal conditions. The film formation was always accompanied by a dissolution process which strongly depended on the growth conditions. The formation efficiency, as determined by the dissolved metal amount, was affected by the CO(OH)2 concentration, the current density and the anodization time. The dissolved antimony amount increased with higher CO(OH)2 concentrations and anodization time, and with lower current densities. The analysis of the total current density suggests the occurrence of a formed film and a dissolving component. According to the calculations, the anodic oxides composition is close to Sb2O3. The growth of anodic Sb2O3 took place at high electric fields within the oxide film. The thicknesses of the formed films were calculated by taking into account their dissolution. The film formation efficiency was determined at various current densities. Keywords: antimony anodic dissolution, film formation efficiency, galvanostatic anodization and electric field intensity.

Abstract Green corrosion inhibitors find various applications in the field of corrosion engineering and technology. In the present work, powder forms of Pimenta Dioica leaves were added into corrosion media to study their effect. Mild steel coupons corrosion studies showed an increase in the inhibitor efficiency, at higher concentrations, in corrosive media. The coupons electrochemical behavior was studied by OCP measurements. P. Dioica inhibition efficiency, adsorbed layers mechanism and mild steel corrosion rate were analyzed using weight loss measurements. Keywords: Pimenta Dioica, green inhibitor, mild steel, potable water and corrosion study.

Abstract Aniline corrosion inhibitor effect on zinc in a H2SO4 solution has been evaluated by weight loss (WL), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and Scanning Electron Microscope (SEM) techniques. The corrosion rate increased with higher acid concentrations. At constant inhibitor content, with higher acid concentrations, the corrosion rate increased. With higher inhibitor concentrations the corrosion rate decreased, while inhibition efficiency (IE) percentage increased. The maximum IE of 90.18% was obtained at 60 mM of aniline in a 0.5 M H2SO4 solution. Polarization studies revealed that aniline acts as a mixed type inhibitor. EIS spectra are semicircular, which indicates that zinc corrosion was mainly controlled by a charge transfer process. SEM reveals the appearance of a smooth surface on zinc in aniline presence, probably due to the formation of an adsorptive film of electrostatic character. It was found that there is a good agreement between the different tested techniques. Keywords: Zinc, H2SO4, aniline effect, polarization and EIS.

Abstract The adsorption capability of the series of some Macrocyclic Polyether compounds containing 1, 3, 4-thiadiazole entity n-MCTH (n = 1-5), especially 3- MCTH, 4-MCTH and 5 MCTH, and their protonated forms, was studied in the light of DFT quantum modeling and Monte Carlo dynamics calculations. Sensitivity to corrosion has been quantified using the degree of planarity, global and local electronic proprieties, as well as the inhibitor strength of interaction, in neutral and protonated forms, with the (111) iron surface in the metallic complex. The results of both approaches showed the supremacy of the interactions of neutral and proton variants of the 5-MCTH-Fe complexes, compared to their homologues of 3-MCTH-Fe and 4-MCTH-Fe, due to the significant involvement of aryl rings, in addition to the thiadiazole ring, in the process of electron donation and acceptance. Keywords: DFT calculations; Monte Carlo dynamics calculations; global electronic proprieties; local electronic proprieties; and complexation strength.

The inhibition effect of Thymus willdenowii Boiss & Reut essential oil (TW) on the mild steel corrosion in 1 M HCl has been investigated using weight loss measurements, surface analysis (SEM-EDX, three-dimensional profilometry and FT-IR), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The TW oil anticorrosion effect was evaluated using polarization potentiodynamic curves obtained after 30, 60 and 90 min of immersion in a 1 M HCl medium. Gravimetric results have shown that TW oil has a significant inhibition efficiency value of 81.42%, which was attained at 3 g/L. The polarization measurements have shown that TW is a mixed type inhibitor, with a significant reduction in cathodic and anodic current densities. Measurements by electrochemical impedance spectroscopy revealed that resistance to the charge transfer has increased with higher TW oil concentrations. From the use of SEM-EDX and three-dimensional profilometry, it is clear that the metal surface has remarkably improved in the TW oil presence, compared to the one exposed to the acid medium without essential oil. From the TW proprieties and the obtained results, it can be concluded that this oil is a new natural substance that can be used against material corrosion in aggressive solutions.

Stearalkonium chloride (SAC) ultrasonic velocity has been measured in methanol, at 301 K temperature. Jacobson’s model has been used to evaluate adiabatic and molar compressibility, molar sound velocity, solvation number, relative association, relaxation strength and other acoustical constants. The results of ultrasonic measurements of different SAC solutions in methanol indicate that there is a signification interaction between SAC and methanol molecules in diluted solutions. The conductometric study indicates that SAC behaves as a weak electrolyte in methanol. The thermodynamic constants calculated from conductance measurements for SAC solutions in methanol depict that micellization is favored over dissociation processes. The refractive index variation with SAC solutions concentrations shows a marked change in the refractive index value at critical micelle concentrations (CMC). Data treatment of obtained ultrasonic velocity, conductance measurement and refractive index shows that there is significant interaction between SAC and methanol molecules in diluted solutions, and that SAC molecules do not aggregate appreciably below the CMC.

Ethyl 3-hydroxy-2-(p-tolyl)-3,4-dihydro-2H-benzo[b][1,4]thiazine-3-carboxylate (EHBT) inhibition effect and its adsorption onto a mild steel surface in phosphoric acid (2 M H3PO4) was investigated, at temperatures varying between 298 and 328 K, by weight loss, EIS and potentiodynamic polarization techniques. The tested compound showed an inhibition efficiency that was superior to 88 % for a concentration equal to 5 × 10-3 M. Polarization measurements indicated that the examined EHBT acted as a mixed inhibitor. The protection efficiency increased with higher inhibitor concentrations and decreased with an increase in temperature. EHBT adsorption onto the mild steel surface obeyed Langmuir adsorption isotherm. EHBT inhibition action was also evaluated by surface SEM images.

Polypyrrole (PPy) films were electrochemically synthesized on an Au/TiO2 coated quartz crystal electrode in solutions with different heparin (Hep) concentrations. The PPy films morphology was determined by tapping a mode atomic force microscopy (AFM). The influence of the dopant concentration on the coating surface roughness was studied. Electrochemical quartz crystal microbalance (EQCM) results suggest that Hep retained in the PPy films was bound to thrombin. The adsorbed thrombin amount increased with a higher coating surface roughness. PPy films doped with Hep are electroactive and show cation exchange properties under oxidation or reduction conditions in a Ringer solution. The pre-oxidized PPy film adsorbed a greater thrombin amount than the freshly one and even more than the pre-reduced film.

An ionic liquid (IL) based pencil graphite electrode (PGE) sensor was electrochemically fabricated for hydroquinone (HQ), catechol (CC) and resorcinol (RS) simultaneous detection and estimation in aqueous media. PGE surface was modified by 1-hexylpyridinium hexafluorophosphate (HPHP) using cyclic voltammetry (CV). The modified surface was characterized by scanning electron microscope (SEM) and energy dispersive X-ray microanalysis (EDX). The modified electrode showed an excellent electro-analytical activity towards simultaneously HQ, CC and RS, at pH 6.8 in aqueous media. The scan rate effect was diffusion controlled and the concentration effect was linear with current. The limit of detection (LOD) for HQ, CC and RS was found to be 6.38 μmol L¹, 4.56 μmol L¹ and 19.6 μmol L¹, respectively. The sensitivity for HQ, CC and RS was found to be 448.49 μAmM-1cm-2, 627.35 μAmM-1cm-2 and 146.10 μAmM−1cm−2, respectively, in a ternary mixture of dihydroxybenzene isomers (DHBIs). The cost of using PGE was lower than that of the conventional electrodes

Mild steel corrosion behaviour in a 0.5 M hydrochloric acid aqueous medium has been studied using potentiodynamic polarization measurements and Monte Carlo calculations, in the presence and absence of (7-Amino-8-methylphenoxazin-3-ylidene)-diethylazanium dichlorozinc dichloride [known as Brilliant Cresyl Blue (BCB) - dye]. Potentiodynamic measurements indicate that this compound acts as a slightly anodic inhibitor. Monte Carlo simulation was used to understand the studied molecules adsorption ability onto a Fe(1 1 0) surface, at the molecular level. The experimental results and theoretical calculations provided important support for the understanding of the corrosion inhibition mechanism adopted by this molecule.

The technical feasibility of the continuous flow electrocoagulation process for hospital wastewater treatment was evaluated. The wastewater physicochemical characterization was performed according to the chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), naproxen, phenol and phosphates parameters. An experimental Box-Behnken design and statistical response surface methodology (RSM) were used to evaluate the simple and combined effects of the independent parameters (pH, potential, retention time), and to optimize electrocoagulation process conditions, considering the COD response variable. The removal percentage was: COD (75.5%), BOD (59.2%) phenols (80.7%), phosphates (85.3%), TSS (75.6%) and naproxen (55.7%), under optimal electrocoagulation conditions at pH (7.92), potential (40 V) and retention time (15 min). The electrocoagulation process proved to be an efficient and technically viable alternative for hospital wastewater treatment.

Atomic absorption spectroscopy (AAS) of samples taken from the organic phase of a water/1,2-dichloroethane (1,2-DCE) interfacial electrochemical cell, rendered non-polarizable by the tetraphenylarsonium common-ion, revealed significant transfer of heavy metal from the aqueous phase. Heavy metal concentration found within 1,2-DCE cannot be explained via ion pair formation between the metallic species and the common-ion, nor by ion pair formation between the metallic species and the hydrophobic anion of the organic phase. Results suggest that metal may have been anomalously transferred into 1,2-DCE within water-in-oil droplets formed by spontaneous emulsification of the interfacial region.

The presented work was pivoted on iron (II) determination in deep groundwater wells samples by using anodic stripping technique at an iodine-coated platinum electrode. The developed method was based on a preconcentration step for five min., followed by the potential scanning of an iodine-coated platinum electrode between the limit of hydrogen evolution (-0.25 V) and the beginning of iodine desorption from the electrode surface (+0.85 V). The anodic peak of the deposited iron to iron (II) oxidation was clearly centered at ca. 0.74 V. The anodic peak current showed an excellent linear response (R2 = 0.996), within an iron (II) concentration range from 1 to 100 ppm. The obtained limit of detection (LOD) was 0.26 ppm and the limit of quantification (LOQ) was 0.85 ppm. Within the iodine-coated platinum electrode potential window the possible interferences by several ions were evaluated. The developed method was examined by iron (II) concentration determination in deep groundwater wells. The statistical comparisons between the two methods showed the absence of any significant difference between the obtained Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) values and our voltammetric method results, at P = 0.05.

Metallic materials remain an indispensable element in industries. The present study is aimed at the assessment of Parinari polyandra leaves inhibition properties on mild steel in a 1 M HCl solution. This was investigated using gravimetric and electrochemical methods. Physicochemical and spectroscopic analyses of the leaves extract were done using standard methods. A yield of 19.82% was obtained, while the leaves extract FTIR spectra showed bands of 3404 cm-1 and 2926 cm-1, which indicated the presence of a strong band of phenolic O-H and C-H stretch functional groups, respectively. A maximum corrosion inhibition efficiency of 97.22% was obtained. Langmuir adsorption isotherm fitted the inhibitor data well. From electrochemical methods, the corrosion rate value of 17.626 mmpy obtained for the uninhibited mild steel was higher than 0.02044 – 2.2267 mmpy range values recorded for the mild steel surface covered with P. polyandra leaves extract in an acidic medium. SEM images showed the leaves extract inhibition effect against mild steel corrosion in a 1 M HCl solution. Electrochemical analysis using the Tafel plot also showed the leaves extract corrosion inhibition capacity, suggesting a mixed type inhibitor. Thus, P. polyandra leaves extract might act as a green corrosion inhibitor for mild steel utilized in industrial applications.

The corrosion inhibition of newly synthesized Schiff base derivatives, namely (E)-3-(1-((2-aminophenyl)imino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (FMO), (E)-3-(1-((3-aminophenyl)imino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (FMM), and (E)-3-(1-((4-aminophenyl)imino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (FMP) was investigated for mild steel, in a 1.0 M HCl medium, using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization and theoretical calculations. FMO, FMM and FMP inhibition effectiveness increased with higher inhibitors concentrations, and decreased with a rise in temperature. Polarization studies showed that FMO, FMM and FMP were of mixed type nature. The results obtained from AC-impedance technique were analyzed to model the corrosion inhibition process through a suitable equivalent circuit model, where a constant phase element (CPE) has been used. FMO, FMM and FMP were found to obey Langmuir adsorption isotherm and Kinetic-Thermodynamic Model of El-Awady. Quantum chemical calculations were used to provide molecular based explanations for FMO, FMM and FMP inhibitive effects. Monte Carlo simulation studies and experimental results were in good agreement

The electrochemical corrosion behaviour of pipeline steel in a sulphuric acid environment, in the absence and presence of commercial Rutin (CR), was studied using electrochemical techniques. The polarization and impedance curves showed an excellent corrosion inhibition characteristic of Rutin, which was more cathodically controlled. Temperature increase slightly improved CR corrosion inhibition capacity. CR was able to increase the charge transfer resistance up to four days, and showed a smoother corrosion surface morphology in the study environment. Analysis of the corrosion surface film showed that Rutin was chemically adsorbed onto the pipeline steel surface.

Kinetics regularities of hydrogen evolution reaction (HER) on Armco iron and copper anodic ionization, covered with a hydrocarbon film based on I-20A oil with a fixed amount of gun grease of the highest quality (GGHQ), were studied at room temperature. The measurements were carried out in aqueous and methanol solutions with the electrolyte composition of x M HCl + (1 - x) M LiCl and 0.1 М HCl + х М LiCl + (3.9 - х) М LiClO4. The Tafel slope coefficients values, and the orders of reactions, with respect to hydrogen ions (Fe, Cu) and chloride-ions (Cu) were estimated. The effect of oxyethylated amines (OEA), introduced into the solution or hydrocarbon surface coating, on the kinetics of electrode processes, for iron and copper, has been studied. It is shown that HER mechanism on Armco iron and copper anodic ionization does not change in the presence of a hydrocarbon coating on the metal surface. Large OEA molecules freely penetrate from the solution through the hydrocarbon coating to the metal surface, changing partial electrode reactions kinetics. The results are interpreted taking into account the hydrocarbon films surface porous structure.