Experimental, quantum chemical calculations, and molecular dynamic simulations insight into the corrosion inhibition properties of 2-(6-methylpyridin-2-yl)oxazolo[5,4-f][1,10]phenanthroline on mild steel

2-(6-Methylpyridin-2-yl)oxazolo5,4-f]1,10]phenanthroline (MOP) was synthesized and characterized by elemental analysis and Fourier-transform infrared (FT-IR), ¹H nuclear magnetic resonance (NMR), and ¹³C NMR spectra. MOP was evaluated as a corrosion inhibitor for carbon steel in 0.5 M H₂SO₄ solution using the standard gravimetric technique at 303–333 K. Quantum chemical calculations and molecular dynamic (MD) simulations were applied to analyze the experimental data and elucidate the adsorption behavior and inhibition mechanism of MOP. Results obtained show that MOP is an efficient inhibitor for mild steel in H₂SO₄ solution. The inhibition efficiency was found to increase with increase in MOP concentration but decreased with temperature. Activation parameters and Gibbs free energy for the adsorption process using statistical physics were calculated and discussed. The adsorption of MOP was found to involve both physical and chemical adsorption mechanisms. Density functional theory (DFT) calculations suggest that nitrogen and oxygen atoms present in the MOP structure were the active reaction sites for the inhibitor adsorption on mild steel surface via donor–acceptor interactions between the lone pairs on nitrogen and oxygen atoms together with the π-electrons of the heterocyclic and the vacant d-orbital of iron atoms. The adsorption of MOP on Fe (1 1 0) surface was parallel to the surface so as to maximize contact, as shown in the MD simulations. The experiments together with DFT and MD simulations provide further insight into the mechanism of interaction between MOP and mild steel.