Adsorption and corrosion inhibition potentials of salicylaldehyde-based Schiff bases of semicarbazide and p-toluidine on mild steel in acidic medium : experimental and computational studies

Abstract

Experimental studies, supported by comprehensive density functional theory (DFT) and Monte Carlo simulation studies have been carried out on 2-(2-hydroxybenzylidene)hydrazinecarboxamide (SEMISCAD) and 2-((p-tolylimino)methyl)phenol (p-TOLUSCAD), to describe their corrosion inhibition potentials for mild steel in hydrochloric acid (HCl). The newly synthesized Schiff bases inhibit corrosion of mild steel in 1 M HCl, and their corrosion inhibition efficiencies increase with increase in concentration. Inhibition efficiencies of 79 % and 86 % were obtained for SEMISCAD and p-TOLUSCAD, respectively at 303 K and minute concentration (5 × 10-4 M). The results further revealed that p-TOLUSCAD could be an averagely efficient formulation to exhibit 50% inhibition efficiency, even at elevated temperature (343 K). Both compounds were found to inhibit corrosion at the anodic and cathodic sites on the steel, and they are therefore mixed-type inhibitors. Electrochemical impedance spectroscopy (EIS) data revealed the adsorptive nature of the molecules on the steel surface. SEMISCAD and p-TOLUSCAD inhibit steel corrosion by adsorbing at steel/HCl interface via physisorption and chemisorption mechanisms. Reactivity parameters predicted from DFT calculations suggested the involvement of protonated forms of the molecules in the inhibitive process, and p-TOLUSCAD as a potentially better corrosion inhibitor than SEMISCAD, which is also supported by the adsorption characteristics derived from Monte Carlo simulations.