Corrosion Inhibition of Carbon Steel in Hydrochloric Acid Solution Using Ethoxylated Nonionic Surfactants Based on Schiff Base: Electrochemical and Computational Investigations

Two ethoxylated nonionic surfactants (L400 and L600) based on Schiff base are prepared from polyoxyethylene, glyoxalic acid, and phenylenediamine. They are evaluated electrochemically as carbon steel corrosion inhibitors in 1 M HCl by electrochemical impedance spectroscopy (EIS) and Tafel techniques and complemented with microscopic analysis methods. The obtained Tafel data indicate the mixed-type behavior of the inhibitor used. The inhibition efficiency touches the peak at 1 × 10–4 M, exhibiting 92 and 94% for L400 and L600, respectively. The presence of the tested inhibitors decreases corrosion current density (icorr) and double-layer capacitance (Cdl) due to the formation of a protective adsorption layer in place of the already adsorbed water and aggressive Cl– ions. Both L400 and L600 adsorption modes follow Langmuir adsorption isotherm. The density functional theory (DFT) calculated indices (ΔEgap and EHOMO) indicate the superiority of L600 over the L400 counterpart as a reactive compound. Adsorption of L600 and L400 over the Fe(1 1 0) in simulated acidic medium is investigated by Monte Carlo (MC) simulation to verify their inhibition performance and are matched with adsorption free energy ΔGads calculated values. Both experimental and theoretical data are in agreement.