N–hydroxybenzothioamide derivatives as green and efficient corrosion inhibitors for mild steel: Experimental, DFT and MC simulation approach

•THA-OCH3 is better inhibitor than other; its maximum inhibition efficiency was 94.26% for MS in 1 M HCl.•PDP analysis suggests that all studied inhibitors are mixed type.•XRD and SEM-EDS surface analysis support the experimental results.•DFT and MC simulation exhibited high electron donating and adsorption nature of THAs.•Theoretical results confirmed the experimental studies. In this research work, the thiohydroxamic acid derivatives included N–hydroxybenzothioamide (THA–H), 4–bromo–N–hydroxybenzothioamide (THA–Br), and 4–methoxy–N–hydroxybenzothioamide (THA–OCH3) were first introduced as effective and green corrosion inhibitors for mild steel in 1M HCl.The inhibition behaviours of THA–H, THA–Br and THA–OCH3 were first–fully characterized by weight loss (WL), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS).The obtained experimental results suggested that the maximum inhibition efficiency of THA–H, THA–Br and THA–OCH3 were over 90% at 300 ppm.The surface characterization of the metal surfacewas investigated by X–ray diffraction analysis (XRD), scanning electron microscope (SEM) and electron diffraction X–ray spectroscopy (EDS) analysis; the obtained results confirmed that the selected inhibitors formed the protective filmon the metal surface. The quantum chemical analysis and Monte Carlo (MC) simulationwere also performed to determine the nature of adsorption, possible adsorption orientation of inhibitor molecules on the metal surface, the correlation between the inhibition properties and molecular structures. Adsorption isotherm suggests that the selected molecules are mixed type of corrosion inhibitors related to Langmuir isotherm.