Suppression of mild steel corrosion in acidic niche by synergistic inhibition effect of zinc oxide nanoparticle-expired clindamycin drug: synthesis, characterization, acidimetric, electrochemical, and computational investigations

Fabricating a new, effective, and environmentally friendly corrosion inhibitor is essential for protecting mild steel (MS) in acidic environments. For the first time, a blend of zinc oxide nanoparticles (ZnONPs) and expired clindamycin (ECLI) was used to mitigate MS corrosion in an acidic niche. The ZnONPs synthesized from Opuntia fragalis leaves (OFL) were characterized using UV-vis, SEM, XRD, and FT-IR spectroscopy. The corrosion inhibition efficacy was examined using weight loss via the central composite design-response surface methodology (CCD-RSM), acidimetric, electrochemical, surface topology, quantum chemical calculations (QCC), and molecular dynamics simulation (MDS). The findings demonstrated that the synergy between ECLI and ZnONPs (ECLI-ZnONPs) significantly inhibited MS corrosion, with an inhibition efficiency of 84.24% compared to the single inhibitor at 65.82%, thereby exhibiting a cooperative synergistic effect (synergy > 1). Potentiodynamic polarization investigations revealed that ECLI-ZnONPs function as a mixed-type inhibitor. The EIS results showed that as the inhibitor was incorporated into the HCl solution, the charge-transfer resistance increased, which is attributed to the adsorption of the synergised inhibitors onto the surface of MS. The structure-activity relationship between the molecular conformation of the blend ECLI-ZnONPs and its corrosion inhibition efficiency was visualized using QCC and MDS to elucidate molecular-level interactions.