Experimental and computational evaluation of expired anticonvulsant drugs as corrosion inhibitors for 316 stainless steel in HCl solutions

Abstract

The protective efficacy of two expired anticonvulsant medications, namely gabapentin (GAP) and oxcarbazepine (OXA), against the corrosion 316 stainless steel (316SS) in a 1.0 M HCl solution was inspected. Chemical, electrochemical, and computational analyses were employed to evaluate the corrosion inhibition performance of two expired medications. The outcomes obtained from the potentiodynamic polarization (PDP) technique showed that expired GAP and OXA effectively reduced the corrosion rate, achieving protection efficiency (PE%) of up to 93.11% and 95.12% at a concentration of 550 mg L⁻¹ for GAP and OXA, respectively. The PE% increased with lowering temperature and increasing concentrations of the expired medications.The PDP curves confirmed that both expired GAP and OXA act as mixed-type inhibitors. Electrochemical impedance spectroscopy (EIS) measurements indicated the formation of a stable inhibitor film on the 316SS surface, as evidenced by significant increases in charge transfer resistance and decreases in double-layer capacitance. The inhibitory action of GAP and OXA was attributed to their adsorption on the 316SS surface through active centers present in their molecular structures. Furthermore, both GAP and OXA functioned as pitting corrosion inhibitors by moving the pitting potential to more noble values.At all tested concentrations, OXA exhibited a stronger inhibition performance than GAP. Density functional theory (DFT) calculations were performed to analyze the electronic structures and interaction potentials of OXA and GAP with the 316SS surface. Detailed analyses of the frontier molecular orbitals, global quantum reactivity descriptors, molecular electrostatic potential (MEP) maps, and Fukui indices were conducted to identify the most reactive sites and predict the adsorption mechanisms of the inhibitors. Additionally, Monte Carlo (MC) and molecular dynamics (MD) simulations were carried out, providing dynamic insights into the adsorption configurations and interaction energies of OXA and GAP on a realistic model of the 316SS surface. The experimental findings were in excellent agreement with the theoretical results. • Expired gabapentin and oxcarbazepine inhibit 316 SS corrosion in 1.0 M HCl • Potentiodynamic polarization shows both drugs act as mixed-type inhibitors, • The protection efficacy enhanced at lower temperatures and higher concentrations. • EIS method reveals increased charge-transfer resistance and reduced double-layer capacitance, indicating robust film development. • DFT analyses identify key adsorption sites on gabapentin and oxcarbazepine. • Monte Carlo and molecular dynamics simulations exhibit favorable adsorption configurations and adsorption energies.

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