Comparative corrosion inhibition of expired favipiravir and hydroxychloroquine sulfate: An In Silico and In Vitro study

Abstract

The present study investigates the corrosion inhibition performance of expired Favipiravir and Hydroxychloroquine sulfate for low-carbon steel in 2 M H₂SO₄ medium. Gravimetric testing, thermometric measurements, and potentiodynamic polarization were employed to quantify the inhibition response, while Density Functional Theory (DFT) modeling supported mechanistic interpretation. Both expired drugs effectively suppressed metal dissolution, achieving maximum inhibition efficiencies of 92.61 % for Favipiravir and 96.55 % for Hydroxychloroquine sulfate at 500 ppm and 303 K. Langmuir adsorption isotherm analysis indicated monolayer adsorption governed by a synergistic physisorption–chemisorption mechanism. Microscopic examinations confirmed reduced surface roughness and corrosion product formation in inhibited systems. DFT results revealed favorable frontier orbital energies, high dipole moments, and strong electron-donor capability, correlating well with experimental observations. This study uniquely demonstrates the comparative inhibition efficiency and adsorption behavior of two structurally distinct expired antiviral drugs, revealing a structure–activity relationship that links electronic properties with corrosion resistance. The findings highlight a novel valorization pathway for expired pharmaceuticals as sustainable, cost-effective, and eco-friendly corrosion inhibitors for industrial applications.