Assessment of inhibition performance of expired chloroquine phosphate on 304 L stainless steel corrosion in hydrochloric acid solution: An experimental and computational study

This study comprehensively investigates the corrosion inhibition properties of expired chloroquine phosphate (CLQ) in 1 M hydrochloric acid (HCl), simulating industrial acid cleaning processes, through a combination of weight loss, electrochemical, surface analysis techniques, and DFT calculations. The findings reveal that CLQ exhibits a concentration-dependent inhibition efficiency, reaching over 91 % at 1 g/L and 25°C. Notably, the inhibition performance slightly increases with temperature, attributed to enhanced molecular mobility and diffusion of CLQ, which facilitate improved surface coverage and the filling of surface imperfections, thereby strengthening the protective barrier on the steel. PDP analysis implies that CLQ behaves as a mixed-type inhibitor. Surface analyses, including SEM, EDS, 3D profilometry, and FTIR, conducted after a 24-h immersion period substantiate the development of a protective layer on the steel surface. Computational studies highlight that the aromatic heterocyclic and aliphatic amine regions of CLQ are pivotal in facilitating electron transfer during adsorption, as evidenced by analyses of the HOMO, LUMO, & molecular electrostatic potential (MEP). These analyses support a mixed physisorption and chemisorption mechanism, with the aromatic moiety identified as the primary adsorption site. The coherence between experimental and computational results underscores CLQ's effectiveness as a corrosion inhibitor. Moreover, the utilization of expired chloroquine not only offers a cost-effective solution but also promotes environmental sustainability by repurposing pharmaceutical waste, thereby reducing pollution.