Expired pharmaceutical compounds as green corrosion inhibitors for low carbon steel in acidic conditions

This research explores the corrosion inhibition potential of the expired pharmaceutical drug Frisium in acidic environments, focusing on its efficiency across varying concentrations. Using the weight loss method, the study evaluated the protective behavior of Frisium on low-carbon steel immersed in 1 M HCl solution. The findings revealed a clear concentration-dependent improvement in inhibition efficiency, reaching a maximum of 91.66% at 500 ppm. To elucidate the underlying inhibition mechanism, density functional theory (DFT) calculations and infrared (IR) spectroscopy were conducted, demonstrating strong interactions between the drug’s active functional groups and the steel surface. Surface morphological investigations via scanning electron microscopy (SEM) and atomic force microscopy (AFM) provided visual evidence of smoother, less corroded surfaces in the presence of the inhibitor, confirming the formation of a protective adsorbed film. Furthermore, electrochemical impedance spectroscopy (EIS) indicated enhanced charge transfer resistance, while potentiodynamic polarization studies established Frisium as a mixed-type inhibitor, influencing both anodic and cathodic reactions. The combined experimental and theoretical results consistently affirmed that inhibition efficiency increases with concentration due to effective adsorption of the drug molecules. Overall, the study highlights the promising potential of repurposing expired drugs like Frisium as eco-friendly, sustainable, and cost-effective corrosion inhibitors, offering a green alternative for industrial corrosion control.