Theoretical, electrochemical and computational inspection for anti-corrosion activity of triazepine derivatives on mild steel in HCl medium

The two triazepine derivatives, 2-amino-9-(1H-indol-3-yl)-4-(4-methoxyphenyl)-7-oxo-1,7-dihydropyr ido[1,2-b][1,2,4]triazepine-3,8,10-tricarbonitrile [AITT] and ethyl 2-amino-8,10-dicyano-9-(2-hydroxy3-methoxyphenyl)-4-(4-methoxyphenyl)-7-oxo-1,7-dihydropyrido [1,2 -b][1,2,4]triazepine-3-carboxy late [EHTC] were successfully synthesized and demonstrated as corrosion inhibitor for mild steel in 15% HCl medium. Their auspicious inhibiting performance was measured by weight loss measurement and the electrochemical impedance spectroscopic method. The adsorption of inhibitors chemically or physically on the exposed metal surface is the main key factor behind the protection mechanism. The investigation at an optimum concentration of 200 ppm (303 K) showed the inhibitor AITT and EHTC with 96.88% and 95.56% inhibition efficiency. The functional groups attached to inhibitor AITT encourages the electron density over the whole molecule and makes it more efficient as a corrosion inhibitor than EHTC. The minimization of cathodic as well as anodic reactions from the potentiodynamic polarization method reveals the inhibitors as mixed-type inhibitors which is also supported by the computed free energy of adsorption values from best fitted Langmuir Adsorption isotherm. The extreme improvement in damaged surface (inhibitor-free medium) was found on the application of inhibitors which is characterized by the surface topographical analyses FESEM and AFM. The elemental analysis of the inhibited metal surface was executed by XPS analysis. The computational methods as Monte-Carlo Simulation, DFT and Fukui calculations, were also employed for the justification of outcomes from experimental methods. All the observations were mutually supported. (C) 2021 Elsevier B.V. All rights reserved.