Portugaliae
Electrochimica Acta

Abstract Molecularly imprinted polymers (MIPs) are an important class of compounds with wider sensing applications for the determination of substances ranging from small molecular masses to macro size. The hyphenation of MIP principle with other likewise conducting polymers yields the devices for sensing purposes. MIPs are robust against environmental conditions, more economical than natural receptors, and their preparation is also adequate for substances without natural receptors. Organic mediated MIPs compounds are of current interest, due to their applicability as quantification tools to determine electroactive substances in a variety of real samples. MIPs are highly selective for target molecules, mechanically strong, resistant to temperature and pressure, inert towards acids, bases, metal ions and organic solvents, highly stable for longer periods, and operative at room-temperature. Therefore, during past years, MIPs have been used as electrochemical and optical sensors, sorbents, solid phase media, and so on. Herein, there is a focus on the use of Pyrrole (Py) as a monomeric molecule to fabricate MIPs. Py or poly-Py (p-Py) based MIPs are synthesized and used in various capacities as chemo electrochemical sensors. A detailed discussion on the application of Py-mediated MIPs for the electrochemical determination of some organic compounds of therapeutic and environmental interest is herein presented as a review. Keywords: fabrication, Py, MIPs, electrochemical sensors and determination.

Abstract The purpose of this study was to fabricate lead ion selective electrode (Pb-ISE) sensors based on a 2:8 ratio of methyl-methacrylate-co-butyl acrylate thin film copolymers (MB28). These sensors were prepared by using a photo-polymerization technique on a pencil graphite electrode (PGE), with a poly-pyrrole-Cl (p-Py-Cl) thin film as a sensor transducer. During the Pb-ISE sensor fabrication process, the membrane composition optimization process has been carried out. The best sensor composition contained 1 mg potassium tetrakis (4-chlorophenyl) borate (KTpClPB) and 4.3 mg Pb ionophore IV. The fabricated Pb-ISE had a Nernstian number of 28.2 ± 0.5 mV/dec, a broad linear range from 10-3 to 10-10 M and a limit of detection (LOD) of (6.6 ± 1.6) x 10-11 M, providing an excellent performance. In addition, the sensor showed a fairly good coefficient of effectiveness (CE) (Log Kpota,b) against K+ (potassium), Na+ (sodium), NH4+ (ammonium), Mg2+ (magnesium), Cu2+ (copper) and Cd2+ (cadmium) cations, which were -6.6 ± 0.2, -6.1 ± 0.2, -6.7 ± 0.2, -12.4 ± 0.3, -4.4 ± 0.2 and -6.1 ± 0.1, respectively. The Pb-ISE sensor worked best in the pH range from 3 to 8. The validation process has been carried out by comparing the measurements results of the artificial samples, at the concentrations from 25 to 100 ppm, with those of the real sample from Angke river water. The outcome was outstanding and comparable to that of the standard UV-Vis spectrophotometry measurement methods. Keywords: MB28 copolymer, photo-polymer, Pb-ISE, PGE and p-Py-Cl.

Abstract A new corrosion inhibitor, namely, 1H-1,2,4-triazol-4-amine, 3, 5-diphenyl-N-(phenyl methylene) (HTADP), has been synthesised, and its inhibiting action on ordinary steel corrosion in an acidic media has been investigated by weight loss and various electrochemical techniques. The obtained results revealed that this organic compound is a very good inhibitor. Its inhibition efficiency (IE) exceeded 90%, even at very low concentrations. HTADP was able to reduce steel corrosion more effectively in 1 M HCl. Potentiodynamic polarization studies showed that HTADP is a mixed type inhibitor, predominantly influenced by the cathodic process. The adsorption of this inhibitor onto the ordinary steel surface in 1 M HCl was found to follow the Langmuir’s adsorption isotherm. The adsorption and activation thermodynamic data were determined and discussed. A protective film was formed on the steel surface, which changed the processes at the metal-solution interface. Keywords: corrosion, steel, inhibition, adsorption and acidic media.

Abstract Mild steel (MS) corrosion inhibition by Terminalia mantaly (TM), in 1.0 M HCl, was studied using weight loss and linear polarization methods, at different reaction conditions. Gas chromatography-mass spectrometry (GC-MS) was used to determine the possible extract components. Fourier transformed infrared spectroscopy (FTIR) and optical microscopy were used to investigate the interaction of the plant extract phytochemicals with the MS surface. The obtained results revealed that the inhibition efficiency percentage (IE%) increased with a decrease in the TM concentration, and decreased with a rise in temperature (T). The IE% also decreased as the hydrochloric acid (HCl) concentration increased. Inhibition occurred through the TM phyto-molecules adsorption onto the MS surface. The corrosion inhibition kinetics followed a zero order reaction, and it was uni-molecular. The linear polarization showed that TM is a mixed-type inhibitor. Gibb’s free energies values confirmed a spontaneous process, while TM adsorption onto the MS surface was found to obey physisorption, aligning with the Langmuir’s and El-Awady’s adsorption isotherm models. Keywords: Terminalia mantaly, activation energy, corrosion, Gibb’s free energy, linear polarization and MS.

Abstract Ethylenediamine (EDA), diethylenetriamine (DETA) and N,N,N',N'-tetrakis (2-hydroxypropyl) ethylenediamine (THPrED) are used relatively often in galvanic processes. Tetra-substituted derivatives, such as N, N, N ', N'-tetrakis (2-hydroxyethyl) ethylenediamine, (THEtED) are quite biologically stable and hardly degradable. In recent years, much attention has been devoted to electrochemical oxidation, using anodes with a high over-potential of O2 evolution, such as the boron-doped diamond (BDD). DETA and THPrED electrochemical treatment using a BDD anode was herein studied. The degradation efficiency of the amines was evaluated under different current intensities and reaction times. To determine the products formed in the oxidation process, ion chromatography (IC) was used. A high decrease in the current between the first and the second CV scan indicated the polymer film formation on the BDD electrode surface. Hydroxyl radicals formed at a potential of about 2 V and higher caused further oxidation of the electrode reaction products. It was found that NH4+, CH3-COOH, N2, EDA, CO2 and NO3- were formed in a short reaction time, and at low current intensity. The mineralization occurred during substrates electrolysis, due to rapid DETA and THPrED decomposition. After 180 min of reaction, αTOC and αN values for DETA were 94% and 18%, respectively. For THPrED, αTOC was 98.6% and αN was 43.6%. Therefore, the electrochemical approach was considered a very promising method in practical application for the treatment of wastewater containing amines. Keywords: EDA, DETA, THPrED, hydroxyl radicals, BDD anode, direct and mediated oxidation and mineralization.

Abstract A graphene oxide-triazole hybrid anti-corrosive coating was done by fabricating a triazole derivative – 2-(5-mercapto-4-((3-nitrophenyl)amino)-4H-1,2,4-triazol-3-yl)isoindoline-1,3-dione (4-NBT) on a graphene oxide (GO) coated Cu electrode. The GO-4-NBT hybrid coating effect on the Cu surface corrosion behavior was electrochemically monitored through cyclic voltammetry (CV), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The fabrication of a protective coating was done in two steps. Firstly, GO was electrochemically deposited on the Cu electrode in two different aggressive media (1 M HCl and 0.1 M Na2SO4), separately. Secondly, different 4-NBT concentrations were employed to reinforce GO corrosion resistant properties. CV studies revealed that GO-4-NBT effectively suppressed the metal oxidation and oxygen reduction. EIS studies suggested that the electrochemical process on the Cu surface with GO and GO-4-NBT was charge transfer controlled. The corrosion inhibition efficiency (IE) measured by PDP and EIS was enhanced with a related raise in 4-NBT concentration. Electrochemical studies revealed that the GO-4-NBT was a mixed type of inhibitor that predominantly inhibited the anodic reaction, especially in the case of 0.1 M Na2SO4. Adsorption studies further indicated the involvement of a stable and spontaneous adsorption mechanism, most probably by chemisorption. GO-4-NBT has shown significant corrosion protection activity in 0.1 M Na2SO4. Keywords: GO-4-NBT, Cu electrode, anti-corrosion coating, electrochemical studies by, PDP and EIS, and adsorption studies.

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.