A comprehensive investigation of expired dextromethorphan HBr drug as a carbon steel corrosion inhibitor using gravimetric, electrochemical, and theoretical computational approaches

This study investigates the potential of expired Dextromethorphan HBr (EDM-HBr) as a corrosion inhibitor for carbon steel in 1 M hydrochloric acid (HCl) solution. Utilizing a combination of gravimetric, electrochemical, and theoretical computational methods, the research reveals that EDM-HBr demonstrates significant corrosion inhibition, with maximum inhibition efficiencies reaching 95.3% at a concentration of 600 mg l^-1, as determined by weight loss measurements. Electrochemical polarization studies further confirm this finding, with a peak inhibition efficiency of 97.3% at the same concentration. The results indicate that despite being expired, EDM-HBr retains effective corrosion protection, with a slight decrease in efficiency over time. The activation energy increased to 32.16 kJ mol^-1 in the presence of the EDM-HBr, confirming that EDM-HBr raises the energy barrier for corrosion reactions. Adsorption studies reveal that the Freundlich isotherm model best describes the data, while a standard Gibbs free energy (ΔG°) value of approximately 20 kJ mol^-1 indicates that physisorption is the primary mechanism of adsorption. At temperatures above 298 K, the ΔG° values range from - 26.4 to -28.0 kJ mol^{- 1}, confirming a mixed adsorption mechanism involving both physical and chemical interactions. Theoretical studies corroborate the experimental findings, supporting the viability of expired EDM-HBr as an eco-friendly and cost-effective corrosion inhibitor. This research highlights the potential for repurposing expired pharmaceuticals in industrial applications, contributing to sustainable practices in corrosion management.