Efficient corrosion inhibition performance of mild steel in hydrochloric acid (1 M HCl) by 5,5'-(1,3-phenylenebis(1,3,4-oxadiazole-5,2-diyl))bis(benzene-1,3-diamine): theoretical and electrochemical study.

This work presents the synthesis and characterization of the compound 5,5'-(1,3-phenylenebis(1,3,4-oxadiazole-5,2-diyl))bis(benzene-1,3-diamine) (PhOx-BBD). The structure of the synthesized molecule was confirmed by a variety of analytical methods, including 1H NMR,le 13C NMR, FTIR-ATR spectroscopy, and mass spectrometry. To this end, Density Functional Theory (DFT) calculations were performed to investigate the electronic structure, frontier molecular orbitals, and global reactivity descriptors. This approach was taken to elucidate the nucleophilic/electrophilic character of the oxadiazole derivative. Molecular docking studies revealed strong interactions between PhOx-BBD and the Fe-solvation cluster, suggesting favorable adsorption behavior on the iron surface. Predictions derived from the ADMET model indicated the presence of encouraging pharmacokinetic properties and acceptable safety profiles. The corrosion inhibition performance of PhOx-BBD for mild steel in a 1 M HCl medium was evaluated through experimental electrochemical measurements. The experimental findings demonstrated a substantial decline in corrosion current density with an increase in inhibitor concentration, thereby substantiating the efficacy of the inhibitor in safeguarding the metal surface. The inhibitory effect exhibited a pronounced concentration-dependent protective effect, with its efficacy increasing from 60.21 to 94.15% across a range of concentrations from 10⁻6 to 10-3 M. Electrochemical analysis indicated that the inhibitor reduced both anodic metal dissolution and cathodic hydrogen evolution reactions, suggesting a mixed-type inhibition mechanism. Moreover, Monte Carlo and molecular dynamics simulations corroborated the experimental findings by demonstrating the strong adsorption of PhOx-BBD molecules on the Fe surface and the formation of a stable protective film. The amalgamation of experimental and theoretical findings reveals consistent trends in stability, reactivity, and adsorption behavior, underscoring the efficacy of PhOx-BBD as a corrosion inhibitor for steel protection in acidic environments and as a promising candidate for applications in surface protection and materials chemistry.