Eco-friendly corrosion inhibitors based on natural extracts, biopolymers, and nanocomposites

Corrosion remains a major challenge in industrial systems because it compromises structural integrity, increases maintenance costs, and contributes to material loss and environmental burden. In response to the growing restrictions on toxic conventional inhibitors, eco-friendly corrosion inhibitors derived from natural extracts, biopolymers, and hybrid nanocomposites have emerged as promising alternatives. This systematic review synthesizes recent studies on bio-derived corrosion inhibitors, with primary emphasis on steel and steel-related substrates exposed to acidic, saline, and alkaline environments. Across the reviewed literature, many plant-derived extracts and biopolymer-based systems achieved high inhibition efficiencies, frequently exceeding 80–90% under laboratory conditions, mainly through adsorption-driven barrier formation involving heteroatoms and π-electron-rich functional groups. Hybrid systems further improved performance by enhancing film compactness, interfacial stability, and resistance to aggressive ionic species. The review also compares durability trends, environmental advantages, and cost-related considerations associated with renewable or waste-derived feedstocks. However, the available evidence remains highly heterogeneous in terms of substrate type, extraction procedure, inhibitor concentration, exposure time, and evaluation method, which limits direct cross-study comparison and prevents formal quantitative pooling. Overall, the current literature supports the strong potential of bio-derived corrosion inhibitors as sustainable alternatives to conventional systems, while also highlighting the need for standardized testing, clearer compositional characterization, and longer-term validation under realistic service conditions.