Expired Samafed drug as a nanotechnology-relevant corrosion inhibitor for carbon steel: Experimental and theoretical study

Abstract

All pharmaceuticals are unsafe after a certain period of time and may become medically toxic. However, they still contain active ingredients with chemical structures that can act as organic corrosion inhibitors and be used to protect various metallic materials. In this study, Samafed syrup, which contains Pseudoephedrine and Triprolidine, is investigated due to its ability to adsorb onto the surface of steel, thereby reducing corrosion. From a nanotechnology perspective, the adsorption of these organic molecules occurs at the nanoscale, leading to the formation of a protective nanolayer on the metal surface that enhances corrosion resistance. The inhibitor is applied at four concentrations (0.4, 2, 4, and 6 v/v%) and four temperatures (303, 313, 323, and 333 K) to evaluate polarization resistance and inhibition efficiency. The highest values of polarization resistance (5.49×10⁻³ Ω·cm²) and inhibition efficiency (92.02%) are obtained at 2 v/v% and 333 K. Surface characterization is performed using FTIR, which revealed the role of functional groups in the drug composition. Scanning electron microscopy (SEM) images showed improved surface coverage, while atomic force microscopy (AFM) analysis confirmed the formation of a uniform protective layer. AFM results further demonstrated nanoscale surface smoothing and the development of a compact nanostructured film formed by Fe–Samafed complexes. Theoretical calculations are conducted using adsorption isotherms and density functional theory (DFT). The results indicate that Samafed adsorption is predominantly physical in nature, supported by low adsorption/desorption constants and negative values of free energy, entropy, and enthalpy. Additionally, electronic property calculations confirmed the presence of active centers in the drug components capable of interacting with the steel surface. The findings highlight the importance of nanotechnology concepts in corrosion inhibition, where nanoscale adsorption and film formation play a key role in enhancing protective performance.