Recycling pharmaceutical waste (vancomycin) as sustainable corrosion inhibition for API 5 L X60 carbon steel in 1 M hydrochloric acid: a combined electrochemistry and theoretical study

Repurposing expired vancomycin drug as an effective corrosion inhibitor for API 5 L X60 carbon steel (X60-CS) in 1 M hydrochloric acid (HCl). The pharmaceutical drugs that have expired are included in this category; they are a waste type that is usually burned rather than recycled. It’s interesting to note that certain drug compounds exhibit characteristics that prevent corrosion in a variety of metals and corrosive liquids. This study aimed to comprehensively evaluate vancomycin based on concentration on X60-CS in acidic environments. A variety of techniques were employed to assess the corrosion-mitigating properties of vancomycin. To assess vancomycin’s remarkable performance, we used extensive procedures, including weight loss (WL) and sophisticated electrochemical methods such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). By increasing vancomycin concentration, the inhibition efficiency will increase. The outcomes are remarkable: 94.2% (weight loss), 92.3% (polarization), and 95.3% (EIS) were the best inhibitory efficiencies attained at 298 K. With a good fit, vancomycin follows the Langmuir isotherm. The data obtained for activation energy increased from (50.82–80.35 kJ mol⁻¹), providing physical adsorption mechanisms in the interaction of the vancomycin inhibitor with the X60-CS surface. PDP results indicate that the corrosion current density ( I corr ) decreases from 244 to 54 µA cm⁻² at inhibitor concentrations of 20 and 100 ppm, respectively. Along with weight-loss studies, surface analysis was carried out using Fourier Transform Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM), Energy Dispersive X-Ray (EDX), and Scanning Electron Microscopy (SEM), and vancomycin adsorption on the X60-CS surface was evidenced. The quantum chemical parameters (E LUMO , E HOMO, and \(\:\varDelta\:\) E) have a strong relationship with the protection efficiency of the investigated drug. The vancomycin inhibitor conformational adsorption modification on the iron surface was also predicted using molecular dynamics (MD) simulations. Results gained for all techniques used are in good agreement.