An Experimental and Computational Approach for the Utilization of Expired Escitalopram as a Corrosion Inhibitor for Carbon Steel

Corrosion of carbon steel in acidic medium remains a major industrial concern, requiring efficient and economical corrosion inhibitors. In this work, expired Escitalopram was examined as a potential waste-derived corrosion inhibitor for carbon steel in 1 M HCl using experimental and computational approaches. The protection efficiency increased with inhibitor concentration but decreased with elevated temperature, indicating an adsorption-controlled inhibition mechanism. The optimum inhibition efficiency of 97.34% was determined at 150 ppm after 4 h immersion at 25 °C through gravimetric analysis. Similar behaviour was demonstrated through potentiodynamic polarization (PDP), where an efficiency of ~97% was recorded at 150 ppm. In EIS analysis, charge-transfer resistance increased with inhibitor concentration. Thermodynamic and kinetic parameters were evaluated to elucidate the inhibition mechanism. Surface characterization using SEM, EDX, and FTIR provided supporting evidence consistent with reduced surface deterioration and inhibitor–surface interaction. Computational analysis complemented the experimental results, supporting favourable adsorption of expired Escitalopram. The findings demonstrate the potential of expired Escitalopram as an effective corrosion inhibitor and a possible route for value-added reuse of expired pharmaceutical material under acidic corrosion conditions.