Recycling of expired Ceporex drug (CPX) as a corrosion inhibitor for carbon steel in a hydrochloric acid medium.

The management of hazardous waste is one of society's current problems. Expired pharmaceuticals fall into this category; they are a type of waste that is not recycled and is typically disposed of by incineration Interestingly, these drug compounds have been demonstrated to possess corrosion-inhibiting properties for various metals and corrosive solutions. This study specifically investigates the corrosion tendency of carbon steel (CS) in 1 M HCl upon application of unused Ceporex drug medication as a potential corrosion inhibitor. The inhibition efficiency of CPX was measured using three techniques: weight loss (WL), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) tests. The inhibition efficiency (% IE) steadily improved as the drug concentration increased from 5 × 10-6 to 11 × 10-6 M. This increase in the CPX dose led to an increase in the corrosion inhibition (% IE) up to 89.3% (EIS), 86.6% (PDP), and 87.8% (WL). Conversely, the inhibition efficiency decreased with increasing temperature, decreasing from 87.8% at 25 °C to 81.8% at 55 °C (all at a concentration of 11 × 10-6 M). The PDP data indicated that CPX decreased the corrosion current density via a mixed mode mechanism. Surface analyses, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM), demonstrated the development of a protective layer on the carbon steel (CS) surface, where CPX adsorption followed the Langmuir adsorption isotherm. A deeper understanding of the inhibitory mechanism was achieved through DFT-based quantum chemical indices. The quantum chemical parameters (E LUMO, E HOMO, and ΔE) showed a strong correlation with the protection efficiency of the drug under investigation. Furthermore, molecular dynamics (MD) simulations were used to predict the conformational adsorption modification of the inhibitor on the iron surface. Importantly, the results obtained from all employed techniques were found to be in good agreement.