Portugaliae
Electrochimica Acta

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.