Proline nitrate ionic liquid as high temperature acid corrosion inhibitor for mild steel: Experimental and molecular-level insights

The synthesis of novel l-proline nitrate ionic liquid referred to as [Pro][NO3] (IL), was performed and the 1H, 13C NMR, and FT-IR spectroscopic techniques were used to elucidate the chemical structure. The inhibition properties of the [Pro][NO3] IL were evaluated for mild steel (MS) corrosion in 1 M HCl using gravimetric measurement, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) measurement, FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle measurement, scanning electron microscopy (SEM), density functional theory (DFT) and Monte Carlo (MC) simulation studies. As indicated by electrochemical and weight loss techniques the tested [Pro][NO3] IL was established as an excellent mixed type high-temperature acid corrosion inhibitor for MS; the optimal temperature and concentration being 70 °C and 300 ppm, respectively. Furthermore, the contact angle measurement and surface studies revealed water-repelling property and the protecting capability, respectively of the investigated inhibitor. The electronic property of [Pro][NO3] IL has been explored using density functional theory (DFT) and the sites susceptible for electron sharing were identified through Fukui indices analysis. Furthermore, molecular dynamics simulation based on the Monte Carlo method has been employed to envisage the spontaneous adsorption of [Pro][NO3] IL on MS surface.