engleski

Plant polyphenols as environmentally friendly corrosion inhibitors

Plant extracts have became important as an environmentally admissible, readily available and renewable source of materials for wide range of corrosion prevention. In this work corrosion inhibition of spectroscopically pure iron was studied in chloride solution in presence of environmentally friendly polyphneols such as (+)-catechin, gallic acid in different concentrations and neutral phenolic fractions of plant extract of the species Satureja montana L. (winter savory). Spectroscopic, electrochemical and quantum-chemical methods were used. Spectroscopic research of the plant extracts showed presence of tannic compounds, especially condensed tannins, which are known as a good non-toxic corrosion inhibitors. Potentiodynamic polarization research showed that (+)-catechin, gallic acid and fractionated (phenolic) plant extracts of Satureja montana L. were effective as cathodic inhibitors of iron corrosion process. Inhibition efficiency was dependant on (+)-catechin and gallic acid concentration, and maximum value was achieved at highest concentration. Langmuir adsorption isotherm was used for adsorption process analysis on iron. Calculated Gibbs energy values indicated a physical adsorption of (+)-catechin and gallic acid on the electrode surface. Passive layer thickness was calculated from cyclic voltamograms on iron, which indicated a decrease in presence of (+)-catechin, and the lowest value was determined for the highest concentration. Impedance spectra measured on open circuit potential on iron in presence of (+)-catechin, gallic acid and neutral phenolic fractions of plant extract of the species Satureja montana L. showed an increase of passive layer resistance. Maximum value of passive layer resistance was achieved for the highest concentration of gallic acid and (+)-catechin. Results of quantum-chemical research indicated a good accordance of the calculated molecular properties (HOMO energy) with their behaviour as corrosion inhibitors. Research given in this work has confirmed positive effects of plant polyphenols as environmentally acceptable corrosion inhibitors.

iron, corrosion, polyphenols, (+)-catechin, gallic acid

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