Enhanced anticorrosion performance of antipyrine derivatives on mild steel in an acidic environment: an experimental and theoretical analysis

Abstract

Efficient and structurally diverse organic corrosion inhibitors remain a major challenge for mild steel protection in acidic environments. In this study, three novel adamantyl amide derivatives of 4-aminoantipyrine, M1, M2, and M3, were synthesized and evaluated to investigate the influence of steric effects and accessibility of donor sites on corrosion inhibition performance. The corrosion inhibition performance was examined by weight loss measurements, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and surface characterization techniques, such as SEM, EDX, FESEM, and XPS, along with density functional theory (DFT) calculations. Among the investigated compounds, M1 exhibited superior inhibition efficiency, achieving up to 98.92% at 0.5 mM in 1.0 M HCl, outperforming its sterically hindered analogs M2 and M3. The inhibition efficiency increased with concentration and immersion time but decreased with temperature, indicating a predominantly physisorption-driven process. The thermodynamic parameters (E_a ≈ 44–55 kJ mol⁻¹; ΔG ≈ −10 to −16 kJ mol⁻¹) further support a mixed adsorption mechanism with dominant electrostatic interactions. The electrochemical results revealed a significant reduction in the corrosion current density and enhanced polarization resistance, confirming the formation of a protective inhibitor film. Surface analyses demonstrated the formation of a compact and adherent layer, particularly for M1, which correlated with its superior performance. DFT analysis enabled molecular-level understanding of the process, which showed that adsorption was favored by low energy gaps, high softness values, and high electron transfer ability. Compared to conventional antipyrine-based Schiff bases, the presence of an adamantyl amide moiety offers dual functionality for surface shielding and steric modulation for electron donation. The present investigation has established the importance of steric effects around the adsorption active sites for the effective design of high-performance organic inhibitors for corrosion protection.