Application of Herbal Extracts in Corrosion Inhibition of Valuable Metals: A Review

Corrosion is a natural chemical or electrochemical process that results in the deterioration of metals and other materials due to their interaction with the surrounding environment. The most common contribution to the acceleration of corrosion is oxygen, although other atmospheric gases including sulphur oxides, nitrogen oxides, halogens, and hydrogen sulphide also play a significant impact. Inorganic and synthetic organic inhibitors have historically been used to prevent corrosion, however many of these substances are costly, hazardous, and non-biodegradable. Green and sustainable corrosion inhibitors are becoming the subject of more study due to growing environmental concerns. In harsh acidic environments, plant extracts that are abundant in phytochemicals including alkaloids, flavonoids, terpenoids, phenolics, and other compounds that include oxygen, nitrogen, and sulphur have shown encouraging adsorption capabilities and corrosion prevention effectiveness. Comprehensive analysis of surface shape, adsorption processes, and inhibitor performance has been made possible by sophisticated analytical and electrochemical methods, including as SEM, EDX, XRD, FTIR, XPS, AFM, UV–Visible spectroscopy, and Electrochemical Impedance Spectroscopy (EIS). Phytochemical adsorption on metal surfaces, which is frequently explained using isotherm models like Langmuir adsorption, is essential for creating protective coatings that lower corrosion rates. This study underscores the significance of environmentally friendly corrosion inhibitors and the possibility of herbal extracts as sustainable substitutes for traditional inhibitors.