Experimental and DFT study of the corrosion inhibition potential of expired diclofenac potassium on stainless steel in hydrochloric acid solution

This study investigates, for the first time, the efficacy of expired diclofenac potassium (DFP) as a corrosion inhibitor for 304 L stainless steel in 1 M HCl, mimicking industrial acid cleaning conditions. A comprehensive evaluation combining weight loss analyses, electrochemical analyses at varying temperatures (25, 40, and 60 °C), and advanced surface characterization (SEM, EDS, 3D profilometry, FTIR). DFP revealed about 90 % inhibition efficiency at a concentration of 500 ppm at all the studied temperatures. DFP acted as a mixed-type inhibitor, adhering to the Langmuir isotherm and forming a uniform protective monolayer. Density Functional Theory (DFT) calculations indicated synergistic physisorption and chemisorption, with electron transfer primarily involving the aromatic and amine regions of the molecule. This dual adsorption mechanism was supported by HOMO, LUMO, and MEP analyses. The robust inhibition performance, coupled with the potential for repurposing expired pharmaceuticals, highlights DFP as a cost-effective, eco-friendly alternative for corrosion prevention in pipelines, heat exchangers, and desalination systems, aligning industrial and environmental priorities. This study demonstrates the dual advantages of utilizing expired pharmaceuticals for industrial corrosion prevention, emphasizing both economic and ecological benefits. The integration of experimental and computational methods ensures a thorough understanding of DFP’s inhibition capabilities