Highly effective inhibition of steel corrosion in 1.0 M HCl solution using a novel non-ionic surfactant with coumarin moiety: Practical and computational studies

A new non-ionic organic coumarin-based surfactant was synthesized and applied to the surface of the steel in 1.0 M HCl solution. The response of the steel surface to the corrosion suppression was probed by measuring polarization, impedance, and frequency modulation in different concentrations (0.5 x 10(-4) M to 7.5 x 10(-4) M). While fitting the experiments to different adsorption isotherms, the steel-inhibitor interface interacted according to the Langmuir model. The maximum efficiencies of 84.18 % and 97.93 % were obtained for the inhibitor's lowest and highest concentrations, respectively based on the impedance spectroscopy measurements. The inhibitor was able to combat the anodic and cathodic reactions simultaneously showing a mixed-type inhibition ability. The free energy Delta G(ads) was calculated to be from 36.75 to - 38.62 kJ/mol based on the Langmuire model, indicating chemical adsorption on steel surface. A narrow energy gap of 3.012 eV was predicted by DFT calculations in consistency with high inhibition efficiency. The molecular reactivity was attributed to the contiguous system of many p orbitals on naphthalene, chromone, thiazole, and diazene entities. In turn, the p-electrons of the oxaheptadecane chains exhibit a lower contribution to the adsorption of the surfactant on the metal surface. New experimental and theoretical insights were derived and related to corrosion inhibition.