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

Abstract

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.

Introduction

Corrosion originates from the Latin words “redre” (to grow) and “corroder” (to grow to pieces) and refers to the chemical or electrochemical deterioration of materials, particularly metals, when exposed to reactive environments. It occurs due to interactions between metals and gases such as oxygen, sulphur oxides, nitrogen oxides, hydrogen sulphide, and halogens, with oxygen being the primary cause of most metallic corrosion. Although commonly associated with metals, corrosion-like surface degradation also affects materials such as ceramics, plastics, rubber, and wood. The process significantly reduces the functionality and lifespan of components and has a massive global economic impact, costing trillions of dollars annually. Consequently, understanding corrosion mechanisms is essential, particularly for systems operating in aggressive environments.

Advancements in corrosion research have been supported by modern surface analytical techniques, including XPS, XRD, SEM, AES, FTIR, and AFM, which provide detailed information on oxide composition, structure, and surface morphology.

Corrosion inhibitors are substances added in small quantities to aggressive environments to reduce metal deterioration. Both organic and inorganic inhibitors have been widely used; however, many conventional inhibitors are expensive, toxic, and non-biodegradable. Growing environmental and health concerns have driven the search for eco-friendly alternatives, leading to the development of green corrosion inhibitors, particularly plant-based extracts.

Herbal corrosion inhibitors, derived from plant extracts rich in phytochemicals such as alkaloids, terpenoids, flavonoids, phenolics, and organic acids, have gained considerable attention. These compounds often contain functional groups with O, N, and S atoms that enhance adsorption onto metal surfaces, improving anti-corrosive performance. Plant extracts are renewable, biodegradable, cost-effective, and environmentally safe, making them promising substitutes for traditional inhibitors. Various studies demonstrate their effectiveness in acidic environments (e.g., HCl solutions), showing mixed-type inhibition behavior and adsorption mechanisms often described by the Langmuir adsorption model.

The mechanism of corrosion inhibition primarily involves adsorption of inhibitor molecules onto the metal surface, forming a protective layer that blocks active corrosion sites. Strong inhibition occurs when molecules form coordinate bonds through electron donation, particularly via heteroatoms such as nitrogen, sulphur, and phosphorus (bond strength trend: O < N < S < P). Electrochemical techniques, especially electrochemical impedance spectroscopy (EIS), are widely used to evaluate inhibitor performance by analyzing electrode–electrolyte interface behavior.

To assess corrosion protection efficiency, researchers employ various experimental methods. The weight loss test is commonly used, alongside advanced analytical techniques such as SEM, EDX, XRD, Raman spectroscopy, FTIR, UV-Vis spectroscopy, atomic absorption spectroscopy (AAS), XPS, and AFM. These methods help characterize surface morphology, oxide composition, elemental analysis, crystal structure, and adsorption mechanisms, thereby validating corrosion inhibition processes.

Overall, the text emphasizes the significance of corrosion as a global industrial challenge, highlights the limitations of conventional inhibitors, and underscores the growing importance of environmentally friendly plant-based corrosion inhibitors supported by advanced analytical and electrochemical evaluation techniques.

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Conclusion

Corrosion is still a major and expensive global problem that affects construction materials, transportation, oil and gas, and industrial infrastructure. To increase material longevity and lower financial losses, it is crucial to comprehend corrosion mechanisms and create efficient mitigation techniques. Conventional corrosion inhibitors have proven effective, but their long-term viability is limited by their high cost, non-biodegradable nature, and environmental toxicity. Because of their renewable source, low toxicity, biodegradability, and affordability, plant-based corrosion inhibitors have become more attractive green substitutes in recent years. The adsorption capacity of phytochemicals with ?-electron systems and heteroatoms (O, N, S, and P) on metallic surfaces is enhanced, resulting in protective coatings that prevent anodic and/or cathodic processes. Overall, green corrosion inhibition strategies align with the principles of sustainable development and green chemistry, offering environmentally responsible solutions for protecting metals in aggressive environments.

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Copyright

Copyright © 2026 Kansara D, Singh G, Dochania M. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.