Reusing an Expired Drug as a Sustainable Corrosion Inhibitor for Bronze in 3.5% NaCl and Simulated Acid Rain Solutions

In recent years, the concept of reusing expired pharmaceuticals as corrosion inhibitors has attracted considerable attention due to the increasing demand for sustainable and eco-friendly solutions. This paper investigates the potential of an expired drug, called Fluimucil, containing N-acetylcysteine (NAC, 300 mg/3 mL), as a green corrosion inhibitor of bronze exposed to 3.5 wt.% NaCl solution and simulated acid rain (pH = 3.4). Potentiodynamic polarization measurements revealed that the drug acted mainly as a cathodic-type inhibitor in both electrolytes. Inhibition efficiency increased with drug concentration, reaching the maximum values of 86.7% in the presence of 36 mM NAC in the saline solution and 90.2% in the presence of 6 mM NAC in simulated acid rain. The anticorrosive effect of the drug was likely due to the adsorption of NAC on the bronze surface, which hindered to some extent the charge transfer reaction and corrosion product formation, thereby offering enhanced protection. Disregarding the nature of the corrosive electrolyte, NAC adsorption on the bronze followed the Langmuir isotherm model, involving a combination of physisorption and chemisorption processes. Surface examination by SEM-EDX confirmed that expired Fluimucil significantly mitigated the surface degradation and the corrosion products on the bronze.