Portugaliae
Electrochimica Acta

Plant extracts containing heteroatoms can be used as corrosion inhibitors as they are non-polluting, cheap and eco-friendly. The present work focuses on Asparagus Racemosus (Shatavari) as a corrosion inhibitor of aluminium in acidic medium. The techniques that have been used include weight loss method, quantum chemical analysis and scanning electron microscopy. It was seen that at 4000 ppm concentration of inhibitor the corrosion inhibition efficiency was 72.28%. The inhibition efficiency increased with increase in concentration. The best description of adsorption isotherm was seen to follow Langmuir adsorption isotherm. In order to elucidate the reactivity and molecular structure of inhibitor, quantum chemical parameters were utilized. The surface properties of the metal specimen were determined by SEM.

In this work, activated carbon was produced from residue of fruit of Sapindus and used for the application of adsorption removal of malachite green dye from simulated aqueous solution. Adsorption kinetics of malachite green onto actived carbon was studied in a batch system. The effects of pH and contact time were examined. The malachite green maximum adsorption occurred at pH 6 (4.5 mg/g) and the lowest adsorption occurred at pH 2 (4.1 mg/g). The apparent equilibrium was reached after 120 min. Optimal experimental conditions were determined. In order to determine the best-fit-adsorption Kinetics, the experimental data were analyzed using pseudo-first-order, pseudo-second-order, pseudo-third-order, Esquivel, and Elovich models. Linear regressive and non-linear regressive methods were used to obtain the relative parameters. The statistical functions were estimated to find the suitable method which fit better the experimental data. Both methods were suitable to obtain the parameters. The non-linear pseudo-first-order model was the best to fit the equilibrium data. The present work showed that activated carbon can be used as a low cost adsorbent for the malachite green removal from water.

Benzaldehyde oxime can be readily converted to the corresponding benzaldehyde in biphasic medium. The reaction was carried out with platinum electrodes at room temperature in an undivided cell within constant biphasic medium consisting of chloroform containing benzaldehyde oxime and an aqueous solution of potassium perchlorate as a mediator with a catalytic amount of H2SO4. The electrochemical oxidation was optimized with various experimental parameters to result in the high yield of benzaldehyde (80%).

Bitter leaves extract as inhibitive agent in HCl medium for the treatment of mild steel through pickling was studied. Thermometric, gravimetric and potentiodynamic polarization methods were employed in the corrosion inhibition study. The bitter leaves extract was analyzed using gas chromatography-mass spectrometer. The analysis of the extract revealed the presence of C6H8O (96 g/mole: 2,4-Hexadienal); C7H12 (96 g/mole: 3,4-Heptadiene; 1,3-Diethylallene) and C10H18O2 (170 g/mole: 2-Decenoic acid) as the predominant chemical constituents. The activation energy for the corrosion inhibition process ranged from 39.831 to 77.533 kJ/mol, while the heat of adsorption ranged from -16.093 to -30.224 kJ/mol. These values showed that exothermic and spontaneous adsorption of the extract on the mild steel followed the mechanism of physical adsorption. Maximum inhibition efficiency of 85.4% was obtained. The extract was highly efficient in the corrosion inhibition function. The plant-based inhibitor of bitter leaves extract is a suitable additive for pickling, cleaning and descaling operations.

We made a nano-porous alumina membrane by anodization under 40 V by two steps (10 minutes and 120 minutes) in oxalic acid, followed by chemical treatment in phosphoric acid assisted by an ultrasonic bath. Thus, we achieved a total relatively short time (3 h 30 min) for the synthesis, having all physicochemical processes been done at room temperature (25 °C). We verified a hexagonal arrangement structure with 56 nm inter-pore diameter, and density of 1010 pores/cm2, characteristic of the self-ordered porous alumina. Therefore, our membranes can be used as a template for fast synthesis of nanostructures as nanowires, nano-tubes.