Portugaliae
Electrochimica Acta

Examination of the physical (colour, odour, pH, solubility in various solvents) and chemical (GCMS and FTIR) characteristics of Ficus benjamina gum revealed that the gum is yellowish in colour, mildly acidic and ionic in nature. Major constituents of the gums were found to be sucrose and d-glucose, which constituted 60.92 % of their chemical constituents, while various carboxylic acids [(albietic acid (1.00%), hexadecanoic acid (4.41 %), 9-octadecanoic acid (1.00 %), octadecanoic acid (3.01 %), oleic acid (0.10 %), octadecanoic acid (9.12 %) and 6,13-pentacenequinone (20.43 %)] accounted for the remaining constituents. Functional groups identified in the gum were found to be those typical for other carbohydrates. From the knowledge of the chemical structures of compounds that constitute the gum, the corrosion inhibition potentials of the gum were ascertained and from weight loss analysis, the gum was found to be an active inhibitor against the corrosion of aluminum in solutions of tetraoxosulphate (VI) acid. The gum acted as an adsorption inhibitor that favours the mechanism of chemical adsorption and supported the Frumkin and Dubinin-Radushkevich adsorption models.

Electrochemical monitoring techniques were employed in this study to assess anticorrosion performance of Phyllanthus muellerianus leaf-extract on concrete steel-reinforcement in 0.5 M H2SO4, used for simulating industrial/microbial environment. For this, steel-reinforced concretes admixed with different concentrations of the natural plant leaf-extract were partially immersed in the acidic test-solution and subjected to electrochemical monitoring of corrosion potential, corrosion current and corrosion rate. Test responses analysed as per ASTM G16¬-95 R04, showed that the corrosion rate correlated, r = 84.93%, ANOVA p-value = 0.0403, with the leaf-extract concentration admixed in concrete and the ratio of the standard deviation of potential to the standard deviation of current. These identified the 0.3333% Phyllanthus muellerianus (per weight of cement) with optimum effectiveness at inhibiting steel-reinforcement corrosion both by the experimental model, η = 91.662.51%, and by the prediction from the correlation fitting model, η = 85.5414.44%. Fittings of both the experimental and the predicted data followed the Flory–Huggins and the Frumkin adsorption isotherms which suggest prevalent mechanism of physical adsorption (physisorption) of the extract on steel-rebar surface. These support the use of Phyllanthus muellerianus as environmentally-friendly admixture for inhibiting concrete steel-reinforcement corrosion in the industrial/microbial service-environment.

The influence of cathode material on the electrochemical degradation of methyl orange (MO), methylene blue (MB) and malachite green (MG) dyes was investigated. The cathode materials used were platinum (Pt), copper (Cu), zinc (Zn) and aluminum (Al). The electrochemical activity of the selected dyes on the metal cathodes was examined by cyclic voltammetry (CV). The electrochemical treatment was carried out in both divided and undivided cells. The degradation process was monitored by UV-Visible spectroscopy and chemical oxygen demand (COD) measurement. The influence of pH on discoloration and degradation of dyes was studied. The power consumption and current efficiency of the treatment process involving different cathode materials was computed and compared. The role of cathode material in the degradation of dyes has been established.

The degradation of Alizarin Red S by electro-generated species using Pt and BDD electrodes was performed. The results were explained by the generation of OH* radical, S2O82− at BDD electrode and active chlorine species at Pt electrode. The slow degradation is affected by the current density, initial pH, temperature, initial dye concentration and the nature of the supporting electrolyte. However, the ionic strength showed a negligible effect on both electrodes. In the presence of KCl, the intermediates produced during the degradation are similar at both electrodes. In the presence of sulfate (at BDD electrode), the rate and the mechanism of the degradation are different from those in the presence of KCl. TOC analysis showed total mineralization of AR S.

The perovskite BaPb0.9Sb0.1O3 was prepared through the ceramic route and, after being chemical, structural and electrochemically characterized, it was used in the electrochemical oxidation of guaiacol, using Na2SO4 as electrolyte, at current densities of 5 and 10 mA cm-2 and initial guaiacol concentrations of 50, 100 and 200 mg L-1. The guaiacol degradation was followed by UV-Visible absorbance measurements, Chemical Oxygen Demand (COD) tests and Dissolved Organic Carbon (DOC) analysis. The combustion efficiency was also determined. Results have shown COD removals between 40 and 85 % and DOC removals from 34 to 66 % after 120 h assays. The absolute COD and DOC removals increase with guaiacol initial concentration and applied current density. The mineralization tendency, measured as the combustion efficiency, was maximum for the applied current density of 10 mA cm-2 and a guaiacol initial concentration of 200 mg L-1.