Portugaliae
Electrochimica Acta

Abstract Novel sulphur (S)-containing Schiff’s bases, N-((1H-indol-3-yl)methylene)thiazol-2-amine (I3A2AT) and(13E)-N1,N2-bis((thiophene-2-yl)methylene) cyclohexane-1,2-diamine (T2CDACH), were synthesized. The structures were deep-rooted by mass, UV-visible, Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analyses. The ligands inhibition efficiency (w%) on carbon steel (CS) corrosion in 1 M hydrochloric acid (HCl) was studied using gravimetric analysis, electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation (PDP), electrochemical noise (ECN), quantum chemical and surface studies. Both Schiff’s bases acted as excellent inhibitors on CS corrosion in 1 M HCl. The excellent inhibitors performance was confirmed by the formation of protective adsorption films onto the CS surface. The inhibitors adsorption onto the CS surface followed Langmuir’s adsorption isotherm. Energies of the highest and lowest occupied molecular orbitals (EHOMO and ELUMO), number of electrons transferred (∆N), electronegativity, chemical hardness, and so forth, were evaluated by quantum chemical studies. An acceptable correlation was observed between the results of quantum chemical calculations and other corrosion monitoring techniques. Keywords: adsorption, w%, PDP, quantum chemical approach and S-containing corrosion inhibitors.

Abstract Metals and alloys corrosion is one of the most challenging and damaging occurrence that is linked with enormous economic and safety losses, and it becomes more severe during some manufacturing processes by which metallic surfaces are treated for other industrial application processes. The use of corrosion inhibitors is one of the best way to protect metals and alloys against damage. The problem of the environmental toxicity of some of the employed inhibitors and the high cost involved in controlling and preventing corrosion have prompted this review. Computational chemistry methods are mostly significant in reducing the cost of protecting metals and alloys against corrosion. This review article begins with the summary of the most used computational methods, parameters and, finally, summarizes the results of some studies made by different authors in the field of corrosion science and engineering. Keywords: density functional theory (DFT), Hartree-Fock (H-F), Ab-initio, semi-empirical, acid corrosion, inhibition and alloys.

Abstract The high toxicity of industrial metal corrosion inhibitors raises various environmental and health problems. Thus, the study of metals and alloys corrosion inhibition, in acidic media, by eco-compatible organic compounds, has become a very attractive research field. In this paper, garlic (Allium Sativum) extract inhibition efficiency (IE) against API X60 carbon steel (CS) and 316L stainless steel (SS) corrosion, in a 1 M sulphuric acid (H2SO4) solution, has been investigated using electrochemical techniques, including potentiodynamic polarization (PPD) and electrochemical impedance spectroscopy (EIS). The experimental results showed the remarkable corrosion inhibitive performance of garlic extract (GE). The corrosion IE, which depends on the inhibitor concentration, increased up to 90%, for SS, and 67% for CS, as shown from the PPD tests. EIS analysis showed that the corrosion resistance (CRST) was increased in the medium with GE, indicating the properties improvement of the passive films formed on the steels surfaces. Keywords: corrosion, steel, H2SO4, green inhibitor and GE.

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.