Synthesis, characterization and corrosion inhibition studies of N-phenyl-benzamides on the acidic corrosion of mild steel: Experimental and computational studies

Present study aims to demonstrate the effect of electron withdrawing nitro (NO2) and electron releasing methoxy (OCH3) substituents on the inhibition behavior of N-Phenyl-benzamide derivatives (BNAs), namely N-(4-nitrophenyl) benzamide (BNA-1; NO2), N-phenylbenzamide (BNA-2; H) and N-(4-methoxyphenyl)benzamide (BNA-3; OCH3) for mild steel acidic (1 M HCl) corrosion. Results of the computational and experimental studies showed that methoxy (OCH3) substituent enhances the inhibition efficiency whereas nitro (NO2) decreases the inhibition efficiency. Electrochemical impedance spectroscope (EIS) study showed that BNAs acted as interface corrosion inhibitors and polarization study shows they acted as cathodic type corrosion inhibitors. They showed maximum efficiencies of 89.56%, 93.91% and 96.52% for BNA-1, BNA-2 and BNA-3, respectively. The BNAs strongly (high Kads values) and spontaneously (negative ∆ G0 values) adsorbed at metal/electrolyte interfaces and their mode of adsorption obeyed the Langmuir adsorption isotherm. Surface investigation of the mild steel surfaces using AFM and SEM analyses revealed that BNAs adsorb on the surface and increase the energy barrier for corrosive dissolution which is also supported by the higher values of Ea (activation energy). DFT study carried out using 3-21G, 6-31G and 6-311G basis sets provides significant support to the experimental efficiency order. DFT indices like EHOMO, ELUMO, electronegativity (χ), softness (σ), hardness (η), dipole moment (μ), energy band gap (∆ E) and fraction of electron transfer (∆ N) were derived for all basis sets. Experimental and DFT study was further supported by molecular dynamic (MD) simulations study.