Dispersive adsorption of Xylopia aethiopica constituents on carbon steel in acid-chloride medium: A combined experimental and theoretical approach

Ethanol extract of Xylopia aethiopica pod was investigated as a green corrosion inhibitor for the protection of Q235 carbon steel in 0.25 M H2SO4 + 0.5 M NaCl solution using a combined experimental, density functional study (DFT) and molecular dynamic simulations (MDS). The nature of organic species present in the extract was assessed using combined gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR). Gravimetric data showed that the corrosion mitigating efficacy increased with extract concentration but decreased only slightly over prolonged exposure. Electrochemical impedance spectroscopy (EIS) and water contact angle goniometer results revealed adsorption of organic species from the extract on the steel surface, while potentiodynamic polarization (PDP) results revealed a potential dependent adsorption-desorption of the inhibiting species with the potential of unpolarizability around 100 mV versus Ecorr. The physical protective effects of the adsorbed extract constituents were confirmed by various advanced surface microscopy examinations. Density functional theory calculations and molecular dynamics simulations (MDS) were undertaken to describe the electronic and adsorption properties of the individual extract active constituents including the synergistic/dispersive interactive effects of the multiple adsorptions of the various active constituents in the inhibitor film on the iron surface.