Investigation of corrosion inhibition performance of expired fluconazole drug on mild steel in 0.5M H2SO4 medium

•The disposal of the expired Fluconazole drug threatens the environment, but still, it contains active components.•The potentiality of the active components utilized to guard the mild steel corrosion in0.5M H2SO4 medium.•Fluconazole inhibitor molecules control both anodic and cathodic processes and function as mixed inhibitors.•SEM with EDS and contact angle analysis confirms that inhibitor molecules cover the mild steel surface and build it more hydrophobic nature.•DFT (Quantum chemical mechanics) studies and MD Simulation confirm the chemical surface interactions via inhibitor molecular orbitals and the Fe-atomic orbitals. Fluconazole is a pharmaceutical drugused for the treatment of fungal infections.The disposal of the expired Fluconazoledrug threatens the environment, but still, it contains active components. The potentiality of the active components of the expired Fluconazole drug was utilized to guard the mild steel corrosion in0.5M sulphuric acid medium. Electrochemical and mass loss studies were used to evaluate the drug's capacity to protect mild steel surfaces against corrosion. The outcomes of the studies demonstrate that Fluconazole effectively inhibits the corrosion of mild steel in sulphuric acid solution at various temperatures.The maximum inhibition efficiency obtained by the mass loss method was 93.75% at 110 ppm drug concentration. Fluconazole molecules have been determined to follow the Langmuir adsorption isotherm model. The SEM images visualized that, in the presence of drug molecules th mild steel surface was least affected by the acid solution compared to the blank solution. The water contact angle data revealed that the adsorption of Fluconazole molecules builds mild steel surfaces that are more hydrophobic in nature. The inhibitor molecules retard both anodic and cathodic reactions in an acid medium and act as a mixed-type inhibitor. DFT calculations and Molecular dynamics simulations further elucidated the chemical interactions between Fluconazole and the mild steel surface.