Evaluation of newly synthesized phosphoramide derivatives as mild steel anti-corrosions using experimental and theoretical approaches

Abstract

Three new phosphoramide derivatives with the general formula of (R)2P(O)[C9H21N2] (R= Ph, A), (R= OPh, B) (R= OEt, C) were synthesized and characterized by using spectroscopy methods. The inhibition effectiveness of synthesized compounds was inspected using potentiodynamic polarization (PDP), impedance measurement spectroscopy (EIS) and scanning electron microscopy (SEM). The synthesized compounds demonstrated acceptable protection power for the erosion of mild steel in 1 M HCl at room temperature. The PDP studies illustrated that the new phosphoramide derivatives behaved as mixed-type inhibitors. Density functional theory and molecular dynamics (MD) simulations were employed to support experimental results. The molecular electrostatic potential plot, the highest occupied molecular orbital and the lowest unoccupied molecular orbital profiles, thermochemical parameters, and quantum chemical descriptors such as electronic electronegativity, chemical hardness of the ground state, and electrophilicity index were calculated and discussed from a corrosion inhibition view point. With the aim of identifying the most stable configuration of inhibitor-HCl, the HCl molecule was approached to all probable reactive sites of inhibitors determined by MEP plots. The molecule A with the most inhibition efficiency (87.25%) and negative inhibitor-HCl interaction energy (-2.56 kcal mol−1) was chosen to study its adsorption behavior on the Fe (1 1 0) using MD simulations at T = 298, 308, and 318 K and in the presence of n = 1-4 inhibitor molecules. The corrosion behavior was investigated with the help of binding energies, radial distribution function analysis, equilibrated configurations, and mean square displacement (MSD) analysis. The theoretical results were in good accordance with the experimental results.