A theoretical and experimental investigation using a multi-criteria decision-making approach to investigate the use of oak cupule biomass as a sustainable corrosion inhibitor for mild steel in acidic solution

This study investigates adsorption mechanism and inhibition efficiency of oak cupule (OC) biomass on mild steel (MS) corrosion in an acidic medium through quantum chemical calculations and electrochemical analysis. The chemical composition of OC was characterized using FTIR-ATR, mass spectrometry, and UV-Vis spectroscopy. Electrochemical impedance spectroscopy was conducted at varying inhibitor concentrations, complemented by surface morphology analysis via SEM and contact angle measurements after 168 h of immersion. At 250 ppm, the inhibition efficiency reached 92.5 %, attributed to the presence of tannins and polyphenolic compounds. Adsorption followed the Langmuir isotherm, with an equilibrium constant of 2.36 L mg-1 and a Gibbs free energy change of-12.08 kJ mol-1. Contact angle measurements indicated increased hydrophobicity due to the formation of protective layer. Potential of zero charge (PZC) analysis confirmed electrostatic interactions