Green corrosion inhibitors beyond efficiency: evidence convergence, mechanistic validation and industrial qualification

Abstract

Green corrosion inhibitors are promoted as sustainable substitutes for toxic or persistent additives, yet high short-term inhibition efficiency is not sufficient evidence of practical readiness. This critical review examines plant extracts, agro-industrial residues, amino acids, biopolymers, ionic liquids, deep eutectic solvents, nanoparticles, protective coatings and hybrid formulations as evidence-graded corrosion-control systems. The analysis links molecular identity, interfacial adsorption, electrochemical response, surface confirmation, microstructure, passive-film stability, toxicity, biodegradability, reproducibility and industrial qualification. Recent studies show that high efficiencies can be reached under optimized laboratory conditions when donor atoms, pi-electron density, amphiphilic organization, polymeric films, multilayer architectures or nanoparticle-assisted blocking promote surface protection. However, persistent limitations remain: poorly defined extract composition, weak batch control, short exposure windows, incomplete impedance fitting, overinterpreted quantum-chemical descriptors, scarce ecotoxicity or flow-loop validation, and limited integration with materials-engineering constraints. The review therefore proposes a qualification framework that judges green inhibitors by convergence among chemistry, electrochemistry, surface evidence, environmental compatibility, microstructural context and operational readiness rather than by inhibition efficiency alone.