HKUST-1 MOF as Corrosion Inhibitor on AISI 5140 Steel in 3.5 wt% NaCl Medium

The current study examines the corrosive inhibitory effectiveness of HKUST-1, a copper-based metal–organic framework (MOF) on AISI 5140 steel in a 3.5 wt% NaCl solution at temperatures between 30 °C and 50 °C. Potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and weight loss tests demonstrated that HKUST-1 creates an adsorptive barrier on the steel surface, greatly lowering the rate of corrosion. Its remarkable temperature-dependent performance is confirmed by the lowest corrosion rate of 0.249 mm y⁻¹ and the maximum inhibition efficiency of 88.9% at 50 °C (0.005 g L⁻¹). The development of a compact, protective coating over the metal surface was further confirmed by SEM and EDS investigations. The enthalpy of adsorption values indicates that the process follows a mixed physisorption-chemisorption mechanism, with chemisorption being dominant. The best fit isotherm is the Langmuir adsorption isotherm. These findings point to HKUST-1 as a possible environmentally acceptable corrosion inhibitor for saline environments.