Hydroxy- and methoxy-aromatics as corrosion inhibitors for automotive steel in 1.0 M HCl: Experimental and theoretical study

• Significant inhibition efficiencies were observed for the tested inhibitors. • The inhibitors displayed chemisorption inhibition characteristics. • Surface analysis confirmed the formation of a protective film. • Theoretical studies explained the inhibition mechanism. Corrosion protection of automotive steels is essential for extending service life and reducing maintenance costs. This study introduces three oxygen-rich aromatic compounds, 2-hydroxy-5-methoxyacetophenone (B1), 2,3,4-trimethoxybenzoic acid (B2), and 3,4,5-trimethoxybenzoic acid (B3), as novel, sustainable inhibitors for S420MC automotive steel in 1.0 M HCl. Electrochemical measurements revealed mixed-type inhibition with efficiencies exceeding 91%. Scanning Electron microscope- Energy Dispersive X-ray Spectroscopy confirmed the formation of compact protective films. Adsorption followed the Langmuir model (Kads > 9 × 10⁵ L mol⁻¹; ΔG°ads ≈ −45 kJ mol⁻¹), indicating spontaneous chemisorption. Temperature-dependent studies showed endothermic adsorption and reduced interfacial disorder. Complementary DFT, DFTB, and Monte Carlo simulations demonstrated parallel adsorption on Fe (110) via Fe–O and Fe–C coordination, consistent with experimental findings. This integrated experimental–theoretical approach identifies oxygen-bearing aromatics as a new class of efficient, environmentally compatible inhibitors.