Sustainable Nanohybrid Coating from Sugarcane-Bagasse Silica and F. sycomorus Extract for Long-Term Corrosion Resistance of Metal Surfaces

Abstract

The study reports a sustainable nanohybrid coating that integrates biogenic silica nanoparticles (SiO₂ NPs) from sugarcane bagasse with Ficus sycomorus leaf extract in an epoxy matrix to protect metal surfaces against corrosion. Silica was prepared by a sol–gel route from acid-leached bagasse ash and characterized usingFT-IR, XRD and SEM. The SiO₂ NPs were amorphous and silanol-rich, forming strong interfacial interactions with epoxy and creating a dense, tortuous barrier. The F. sycomorus extract, rich in phenolics, flavonoids, and alkaloids, served as a green inhibitor via adsorption and metal-ion complexation. Coatings containing only extract (P), only silica (NP), and the combined nanohybrid (NH) were applied to tin-plate and evaluated by neutral salt spray (up to 360 h) and NaCl immersion. Relative to neat epoxy, all modified films reduced degradation, with NH performing best: rust creep 50% for the control; P and NP were intermediate (creep ≤3 mm, area ≤16–18%). Immersion testing showed corrosion-rate suppression from ~1.0×10⁻⁴ mm·h⁻¹ (control) to 80%; NP and P achieved ~60% and ~40%, respectively. Kinetic analysis confirmed diffusion-controlled growth for all systems, with parabolic rate constants kₚ decreasing from 0.0998 (control) to 0.00007 mm²·h⁻¹ (NH), and power-law exponents n ≈ 0.4–0.5. The synergy between SiO₂-induced barrier densification and bio-extract chemisorption/passivation underpins the gains in durability. Leveraging agricultural waste and plant-derived inhibitors, this nanohybrid advances circular-economy coatings while delivering high corrosion resistance in saline environments.