Combined molecular simulation, DFT computation and electrochemical studies of the mild steel corrosion protection against NaCl solution using aqueous Eucalyptus leaves extract molecules linked with zinc ions

Abstract

Being low cost and non-hazardous, the inhibitors from green sources have become one of the most popular materials used for metals protection against corrosion nowadays. Despite the satisfying efficiencies of these compounds in acidic environments, they show poor performance in neutral atmospheres. One way to overcome this weakness is the employment of insoluble metallic ions in the inhibition system. In this study, we have investigated the synergistic impact between the eucalyptus leaves extract (ELE) and divalent zinc ions. Surface characterization was accomplished by ultra-violate visible analysis (UV–Vis), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), atomic force microscope (AFM), grazing incidence X-ray diffraction (GIXRD), Fourier transmission infrared (FTIR) spectroscopy and contact angle (CA) measurements. The electrochemical behavior of different ratios of ELE:Zn was evaluated by EIS and potentiodynamic spectroscopy (PDS). Moreover, the computational studies were utilized to scrutinize the nature of the interactions between the organic and inorganic compounds. Results showed that 200 ppm ELE + 600 ppm Zn had the highest inhibition efficiency and synergistic impact. The efficiency in this sample reached 90% after 48 h which is a desirable value. This performance is attributed to the hydrophobic complexes and chelates formed on the surface of the substrate. The theoretical investigations disclosed that the ELE:Zn complexes adsorbed on the steel surface mostly based on donor-acceptor adhesion mechanism.