Adsorption and Corrosion Mitigation Effect of Two New Salen-type Schiff Bases on Mild Steel in Acidic Medium: Experimental and Computational Studies

The quest for more green inhibitors for suppression of material corrosion continues to appreciate due to rising industrialization and advancement in technology. In this work, the abilities of two new salen-type Schiff bases: bis(3,5-dibromosalicylaldehyde) ethylenediamine (DBSE) and bis(3,5- dichlorosalicylaldehyde) ethylenediamine (DCSE) to suppress corrosion of mild steel in 1 M HCl solution were investigated by weight loss method, scanning electron microscopy (SEM), conceptual DFT calculation and molecular dynamics (Monte-Carlo) simulation. The results showed that these compounds are excellent suppressors of mild steel degradation in the acid solution as the degradation process was efficiently retarded to the tune of 92.9% and 97.5% by DCSE and DBSE, respectively at 500 µM inhibitor concentration and 313 K. Suppression efficiency was found to increase with concentration and decrease at elevated temperature due to prevalence of desorption. Adsorption of the inhibitor molecules on mild steel surface occurred by physisorption and in compliance with the Temkin isotherm. The results of SEM analysis confirmed successful formation of protective layers of the inhibitor molecules on the steel surface. Interaction descriptors from DFT calculations and Monte Carlo simulations confirmed the observed ranking of suppression ability as DBSE > DCSE with suspected contributions from both the neutral and protonated forms of the Schiff bases. We conclude that both DCSE and DBSE can be deployed as efficient green inhibitors for the mitigation of mild steel corrosion especially at low to moderately high temperatures.