Nitrogenated derivatives of furfural as green corrosion inhibitors for mild steel in HCl solution

The ability of nitrogenated derivatives of furfural to act as corrosion inhibitors for mild steel in 1molL−1 HCl solution was evaluated using weight-loss measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The imine 2-((furan-2-ylmethylene)amino)ethan-1-ol (1) and the mixture of 2-(furan-2-yl)-1,3-oxazinane and 3-((furan-2-ylmethylene)amino)propan-1-ol (2a+b) presented, respectively, 81.9% and 84.4% of inhibition efficiency towards the mild steel acidic corrosion at 5×10−3molL−1, room temperature and 2-h immersion time. Polarization curves showed more effective inhibition in the cathodic process. EIS plots indicated an increase in the polarization resistance with enhancement of inhibitor concentration. The adsorption of the evaluated inhibitors obeyed the Langmuir adsorption isotherm. The ΔG°ads and ΔH°ads values obtained suggest a physical nature adsorption of inhibitors (1) and (2a+b). The physisorption could be explained by the coulombic interaction between the protonated forms of the inhibitor molecules due to the acid medium with the negatively charged surface. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphologically and chemically, respectively. Quantum chemical calculations were applied to correlate electronic structure parameters of inhibitors with their corrosion inhibition efficiency.