Plant leaf extracts as green corrosion inhibitors of steel in acidic and seawater environments: a review

T he growing emphasis on environmentally friendly corrosion inhibitors has attracted substantial interest within academic circles, driven by the goal of addressing the persistence issue of corrosion. The application of plant leaf extracts as agents to mitigate metal degradation in harsh environments has emerged as a significant area of study. As the use of mild steel, pipeline steel, and stainless steel becomes more prevalent in corrosive settings like acidic and seawater environments across various industries, demand for environmentally benign and relatively efficient corrosion inhibitors has grown. A comprehensive review of existing literature reveals that plant leaf extracts contain phytochemical compounds such as tannins, polyphenols, and glycerides, which form strong bonds with metal surfaces, effectively obstructing active sites and reducing the ingress of corrosive agents. Functional groups and heteroatoms such as oxygen (O), sulfur (S), nitrogen (N), and phosphorus (P), along with aromatic rings, enrich these extracts, adhering to metal surfaces and inhibiting corrosion. Analysis of the surveyed literature demonstrates that inhibition efficiency rises with increasing inhibitor concentration, with the Langmuir model emerging as the dominant absorption model. Researchers employed electrochemical and weight loss techniques to investigate corrosion mechanisms and absorption models. Notably, most leaf extracts exhibit inhibition efficiencies surpassing 90%, with a minimum of 60% inhibition recorded within the reviewed literature. The paper also discusses the prospects and challenges associated with commercializing these environmentally friendly corrosion inhibitors. Overall, this review highlights the promising potential of plant leaf extracts as corrosion inhibitors while addressing the considerations and obstacles surrounding their practical implementation.