Potential of dibenzo-18-crown-6-ether derivatives as a corrosion inhibitor on mild steel in HCl medium: electrochemical and computational approaches

The extent of corrosion inhibition of macrocyclic crown ether compounds namely 2,14-bis(benzo[d]thiazol-2-yl)-6,7,9,10,17,18,20,21-octahydrodibenzo[b,k][1,4,7,10,13,16]hexaoxacyclo octadecine [BOH] and 2-(6,7,9,10,17,18,20,21-octahydrodibenzo[b,k][1,4,7,10,13,16]hexa oxa cyclooctadecin-2-yl)benzo[d]thiazole [OHB] was investigated experimentally and theoretically on mild steel in a 15% hydrochloric acid medium. The experimental investigation was completed through gravimetric and electrochemical (EIS and potentiodynamic polarization) methods. The outcomes from these methods inferred that the inhibitor BOH was a more efficient inhibitor with 98.57% efficiency at 303 K and 150 ppm. The potentiodynamic polarization outcomes reveal the inhibition activity of the inhibitor was under mixed control. The adsorption of inhibitors on the exposed metal surface acted as a prominent factor for inhibition. The surface investigation on the uninhibited and inhibited surface was made through FE-SEM, AFM and XPS analysis to justify the presence of adsorbed inhibitor molecules on the surface. Theoretical investigations by quantum chemical calculation (DFT) and Monte Carlo simulation were correlated with experimental outcomes. The adsorption mechanism of corrosion inhibition was supported by the best fitted Langmuir Adsorption isotherm. All outcomes from the above-investigated methods mutually supported each other.