L-tryptophanium picrate as novel anticorrosion agent for mild steel in 5% HCl: A detailed experimental and in silico investigation

• L-tryptophanium picrate shows excellent anticorrosion for mild steel in acid medium. • Gravimetric analysis confirms superior corrosion inhibition performance. • XPS data reveals donor-acceptor interactions between inhibitor and iron atoms. • MD modeling shows planar alignment of inhibitors on the metal surface . • Radial distribution function evidences chemisorption mechanism. Acidizing in petroleum recovery often leads to severe corrosion of mild steel, necessitating the development of highly effective corrosion inhibitors. In this study, L-tryptophanium picrate ( [Trp][Pic]), an amino acid derivative synthesised by one-step synthesis involving two-component acid–base reaction between L-tryptophan and picric acid, is investigated as a novel corrosion inhibitor for mild steel in 5% HCl. A comprehensive experimental and theoretical approach was employed to evaluate its performance. Weight loss measurements, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) were used to determine the inhibition efficiency. At 30°C, [Trp][Pic] significantly increased the polarization resistance from 81.08 Ω cm² in the uninhibited solution to 462.15 Ω cm² in the presence of 100 ppm of [Trp][Pic], achieving an inhibition efficiency of 82.46%. PDP results confirmed its mixed-type behavior, reducing both anodic and cathodic reactions. Surface analysis through SEM and AFM demonstrated the formation of a uniform protective film of [Trp][Pic] that shielded the steel surface. X-ray photoelectron spectroscopy (XPS) supported the role of donor-acceptor interactions between heteroatoms and Fe atoms in the chemisorption mechanism. Molecular dynamics (MD) simulations identified key binding sites responsible for the strong adsorption of [Trp][Pic], providing insight into the molecular-level mechanism of inhibition. These findings highlight the potential of [Trp][Pic] as a promising corrosion inhibitor for industrial applications.