Computational insights into the corrosion inhibition mechanism of hyoscyamine and zonisamide on mild steel: A combined DFT, MD, and NCI analysis

Abstract

This study employed density functional theory (DFT) and molecular dynamics (MD) simulations to investigate the mechanisms by which hyoscyamine (HYO) and zonisamide (ZNS) inhibit acid corrosion in mild steel. Examining electrical characteristics, surface binding, and inhibitory mechanisms, the study aimed to elucidate the relationship between molecular architectures and protective efficacy. Although protonation in acidic environments alters the effectiveness of both chemicals, DFT simulations show that they both efficiently decrease corrosion. The high electron-donating and accepting capabilities of the frontier electron spectroscopic HOMO and LUMO orbitals enabled the formation of strong charge-transfer bonds with iron atoms. The more effective alternative was ZNS as compared to HYO, which had a bigger energy gap (5.29 eV). The strong interactions between metals and inhibitors have been explained by finding reactive areas on oxygen, nitrogen, and sulfur atoms by molecular electrostatic potential studies and Fukui indices. The MD simulations confirmed the stable surface adsorption; HYO had a lower binding energy (256.217 kcal/mol) compared to ZNS (293.588 kcal/mol). The chemical adsorption of both inhibitors at a 3.5 Å radius from the surface was mainly driven by hydrogen bonding and van der Waals forces. Computational methods, combined with experimental data, indicate that both compounds exhibit high corrosion resistance. With more active binding sites, a narrower energy gap, and greater surface binding, ZNS outperforms the other. These results shed light on a potential approach to mitigating industrial acid corrosion and provide valuable insights for developing more effective corrosion inhibitors.