The corrosion inhibition performance of expired Beloc drug: theoretical and experimental study

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In this study, expired Beloc containing metoprolol (ML) and tartaric acid (TA) was thoroughly analyzed to determine its efficiency in inhibiting the corrosion of mild steel (MS) in a 0.5 M HCl solution. Both experimental and theoretical approaches were utilized. Density functional theory (DFT) with the B3LYP 6–311++G(d,p) basis set was employed to investigate the quantum chemical properties of ML and TA. The electronic properties were determined, revealing that certain characteristics such as dipole moment and energy band gap of the primary constituents effectively inhibit the corrosion of mild steel in 0.5 M HCl. The experimental study involved electrochemical impedance spectroscopy (EIS) at various concentrations (200, 300, 400 and 500 ppm) of ML-TA and different immersion times (1–168 h). Additionally, SEM images were taken to compare the surface morphology in the absence and presence of ML-TA. During a 1-h immersion period, the polarization resistance values were 39, 212.3, 249.5, 255.8, and 382.8 Ω cm2, and the corresponding inhibition efficiencies (IE%) were 81.6%, 84.4%, 85.3%, and 89.8% for 200, 300, 400, and 500 ppm MEM, respectively. For prolonged immersion at 500 ppm ML-TA, the IE% values increased to 88.2%, 91.5%, 93.7%, and 95.5% at 24, 48, 96, and 168 h, respectively.