Eco-Friendly Corrosion Inhibition of Carbon Steel Using Schiff Base Derivatives of p-Tolualdehyde Chitosan in Acidic Media

In this study, a novel chitosan based nanohybrid corrosion inhibitor was successfully synthesized and thoroughly characterized. The new synthesized compound: a chitosan Schiff base derivative with multiple active sites was evaluated for its efficacy as a green corrosion inhibitor for AISI 4140 steel in an acidic medium. The formation of the Schiff base was confirmed using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), and elemental analysis. The successful synthesis of silver nanoparticles (AgNPs) and the corresponding nanohybrid (NHc) was further validated through UV–visible spectroscopy and scanning electron microscopy (SEM). The resulting compounds, PTc (the chitosan Schiff base) and NHc (the AgNPs incorporated nanohybrid), demonstrated excellent corrosion inhibition efficiencies of 86.99% and 96.00%, respectively, at a concentration of 500 ppm. The enhanced efficiency observed with the NHc compound underscores the synergistic interaction between the chitosan matrix and the silver nanoparticles. Thermodynamic analysis indicated that the adsorption of both inhibitors onto the steel surface was spontaneous, with Gibbs free energy values (ΔGads) ranging from −26.00 to −33.45 kJ/mol. Furthermore, density functional theory (DFT) calculations were employed to support experimental findings and to elucidate the adsorption behavior and inhibition mechanisms at the molecular level.