Investigation on corrosion protection behavior and adsorption of carbohydrazide-pyrazole compounds on mild steel in 15% HCl solution: Electrochemical and computational approach

Abstract

The behavior of synthesized (E)-5-amino-3-(4-methoxyphenyl)-N′-(1-(4-methoxyphenyl)ethylidene)-1H-pyrazole-4-carbohydrazide [AMPC] and (E)-5-amino-N′-(4-chlorobenzylidene)-3-(4-chlorophenyl)-1H-pyrazole-4-carbohydrazide [ACPC] towards the corrosion protection of mild steel (MS) in 15% HCl solution was studied by gravimetric and electrochemical methods. The inhibitor AMPC and ACPC at an optimum concentration of 300 ppm showed 98.26% and 96.21% inhibition efficiency, respectively at 303 K temperature. Thermodynamic results conquer that both inhibitors followed mixed adsorption and results from polarization suggests the retardation of the cathodic as well as anodic reactions in presence of inhibitors. The Langmuir adsorption isotherm suggests the monolayer adsorption of inhibitors on the MS facet. The formation of protective layers of inhibitors on MS surface was confirmed by the outcomes of FESEM and AFM topographical details. The composition of adsorbed layers on the MS surface was studied by XPS analysis. The energy related to molecular orbital of inhibitors, and adsorption behavior was computationally examined by Density Functional Theory (DFT), calculation of Fukui functions and Monte-Carlo simulation (MCS) studies.