2-Aminobenzene-1,3-dicarbonitriles as green corrosion inhibitor for mild steel in 1Â M HCl: Electrochemical, thermodynamic, surface and quantum chemical investigation

The three 2-aminobenzene-1,3-dicarbonitriles derivatives (ABDNs) namely 5′-amino-2,4-dihydroxy-4″-methyl-1,1′:3′,1″-terphenyl-4′,6-dicarbonitrile (ABDN-1), 5′-amino-2,2″,4-trihydroxy-1,1′:3′,1″-terphenyl-4′,6′-dicarbonitrile (ABDN-2) and 5′-amino-2,3″,4-trihydroxy-1,3-methoxy,1′:3′,1″-terphenyl-4′,6′-dicarbonitrile (ABDN-3) were synthesized and their corrosion inhibition properties on mild steel in 1 M HCl were investigated using weight loss and electrochemical techniques. Among the compounds investigated, ABDN-3 exhibited the best inhibition efficiency of 97.83% at 100 mg/L. Scanning electron microscopy (SEM) and dispersive X-ray spectroscopy (EDX) examinations was performed on inhibited and uninhibited mild steel samples to show the presence of ABDNs on mild steel surface. The potentiodynamic polarization studies reveal that all three studied inhibitors were of mixed type and their adsorption on the mild steel surface in 1 M HCl follows the Langmuir adsorption isotherm. Quantum chemical calculations studied were also performed to support weight loss and electrochemical experimental observations.