Sustainable Corrosion Mitigation Using Aqueous Spent Coffee Grounds Extract: Comparative Performance in Different Acidic Media

This study investigates the efficiency of green corrosion inhibitors derived from spent coffee grounds (SCGs) for OL 37 carbon steel in 0.5 M H2SO4 and 1 M HCl environments. The aqueous extracts, labeled K1 and K2, were obtained through specialized extraction techniques and characterized by HPLC. Their protective performance was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). FT-IR spectroscopy and SEM-EDX analysis confirmed the presence of a protective inhibitor film on the OL 37 surface, attributed to the adsorption of organic molecules from the SCGs extract (K1 and K2). The adsorption behavior followed the Langmuir isotherm, with high adsorption constants and standard free energy values (ΔG°ads), indicating a mixed-mode adsorption mechanism. Furthermore, the negative Gibbs free energy values of adsorption confirm the spontaneity of the adsorption process. Thermodynamic studies conducted between 293 K and 333 K demonstrated the temperature dependence of the inhibition process. Results showed that at a concentration of 800 ppm and 1000 ppm, both inhibitors exhibited high efficiency, reaching 96% for K1 and 95% for K2.