Synthesis, experimental and computational studies on the anti-corrosion performance of substituted Schiff bases of 2-methoxybenzaldehyde for mild steel in HCl medium

Abstract

Corrosion inhibition performance of two synthesized Schiff base ligands; (E)-2-((2-methoxybenzylidene)amino)phenol L1 and (E)-2-((4-methoxybenzylidene)amino)phenol L2 were carried out by weight loss measurement in 0.1 M hydrochloric acid (HCl) solution. Density Functional Theory (DFT) and Molecular dynamics (MD) simulation were applied to theoretically explain the inhibitors’ intrinsic properties and adsorption mechanism in the corrosion study. The result of the inhibition performances carried out at varying concentrations and temperatures were compared. The corrosion inhibition efficiencies of L1 and L2 at an optimal concentration of 10 × 10–4 M were 75% and 76%. Langmuir isotherm model fits the data obtained from the experiment with a correlation coefficient (R2) value closer to unity. The adsorption mechanism of inhibitor on the surface of the Fe metal occurred via chemisorption inferred from the Gibbs free energy (ΔGads). Scanning electron microscopy showed a mild degradation on the surface of the mild steel immersed in the L1, and L2 inhibited acid solution, which could be due to surface coverage. The energy dispersive X-ray spectroscopy showed the metal surface’s elemental composition and the existence of the chlorine peak, which emanates from the HCl medium. DFT calculations revealed that the hybrid B3LYP functional performed better than the M06-2X meta-functional in estimating the energies of the synthesized Schiff bases for corrosion inhibition as seen in the lower ΔE values of 3.86 eV and 3.81 eV for L1 and L2. The MD simulation revealed that the orientation of inhibitors on the surface of the metal resulted in the coordination bond formation and that the interaction energy of L2 was −746.84 kJ/mol compared to −743.74 kJ/mol of L1. The DFT and MD results agreed with the observed trend of the experimental findings.