Plant Extracts as ''Green'' Corrosion Inhibitors: A Mini Review

Plant extracts represent an alternative to conventional corrosion inhibitors, primarily due to their low cost and biodegradability. This review presents the results of 35 relevant studies from the Scopus and Web of Science databases in order to evaluate the application of plant extracts in this area. The analysis of the work shows that the most effective extracts are those containing high content of phenols, flavonoids, tannins, alkaloids and saponins. These compounds contain heteroatoms (N, S, O) and aromatic systems, which are easily adsorbed on metal surfaces and thus form a protective film. It is described in scientific papers that the inhibitory effect is most often attributed to physical and chemical adsorption, which is confirmed by Langmire/Freundlich adsorption models and changes in electrochemical behavior and surface morphology. The effectiveness of the inhibition itself depends on the type of plant, extraction method, extract concentration, temperature and exposure time; thus, in most studies, the corrosion efficiency is over 70%, while under optimal conditions it exceeds over 90%. However, for plant extracts to be used in industry, it is necessary to determine whether they remain effective on a large scale and over a long period of time.