Corrosion performance and adsorption mechanism of a green Cu₂O–Guiera senegalensis nanocomposite coating for tin in chloride media

Abstract

Corrosion of tin-based materials in chloride-rich environments presents a significant challenge for industrial applications, particularly when conventional coatings fail or degrade. In this study, a sustainable nanocomposite anticorrosion coating incorporating Cu₂O nanoparticles and phytochemicals derived from Guiera senegalensis was developed and evaluated for corrosion protection of tin substrates in saline media. The nanocomposite coating was formulated by dispersing Cu₂O nanoparticles and aqueous plant extract within an epoxy matrix and applied to tinplate panels. Corrosion resistance was assessed using gravimetric immersion testing in 5 wt% NaCl solution and accelerated salt-spray exposure according to ASTM B117. Phytochemical screening confirmed the presence of glycosides, tannins, flavonoids, saponins, and carbohydrates, which contribute to adsorption-driven inhibition through formation of protective surface films. The nanocomposite coating exhibited significantly lower corrosion rates, reaching a minimum of ~0.17 mm y^⁻¹ at 1.0 wt% additive loading, compared with ~1.34 mm y^⁻¹ for the additive-free coating. Salt-spray results showed substantial suppression of rust propagation, with rustcreep lengths below 2 mm and corroded areas below 5% after prolonged exposure. Adsorption isotherm analysis (Langmuir, Temkin, Freundlich, and El-Awady models) indicated spontaneous inhibitor adsorption with ΔG° ads values between −9 and −12 kJ mol^⁻¹, suggesting predominantly physisorption mechanisms. Kinetic modelling further demonstrated that incorporation of Cu₂O nanoparticles significantly reduced corrosion propagation rates and shifted corrosion behaviour toward a barrier-controlled regime. The results highlight the synergistic role of plant-derived inhibitors and nanostructured fillers in producing environmentally friendly, high-performance coatings for corrosion protection of tin in chloride environments.