Expired amoxicillin as an eco-friendly corrosion inhibitor for cast steel in sulfuric acid environment: electrochemical, surface and thermodynamic studies

During the acid pickling process, the corrosion of cast steel in acidic solutions is difficult to avoid. Thus, the utilization of inhibitors has emerged as an effective strategy for reducing the corrosion rate of cast steel. However, the conventional use of both organic and inorganic corrosion inhibitors raises environmental concerns due to their harmful properties. As a result, there is a growing interest among researchers in exploring pharmaceutical drugs as a more environmentally friendly approach to corrosion mitigation. In this study, we investigate the corrosion inhibition of cast steel using expired amoxicillin (AMXL) in a 0.5 M sulfuric acid medium. Our analysis employs gravimetric, electrochemical, and scanning electron microscopy (SEM) techniques. Electrochemical assessments conducted on cast steel electrodes indicate an increase in charge transfer resistance, and a decrease in current density when amoxicillin is introduced into the corrosive environment. Weight loss studies further confirm that amoxicillin reduces the corrosion rate of cast steel. Moreover, we observe that the inhibition effectiveness rises with increasing amoxicillin concentration but decreases with higher temperatures. Our findings also reveal that the adsorption of amoxicillin on the cast steel surface follows the Langmuir isotherm. SEM analysis is employed to visually confirm the impact of amoxicillin on the cast steel surface. The presented paper supported the effective use of outdated medications, such as amoxicillin, as corrosion inhibitors for metals, offering broad industrial applications while addressing environmental concerns. Graphical Abstract