Electrochemical study and modeling of an innovative pyrazole carboxamide derivative as an inhibitor for carbon steel corrosion in acidic environment

The impact of N,1-dibenzyl-5-methyl-1H-pyrazol-3-carboxamide (BPC) on the carbon steel (CS) corrosion in hydrochloric acid (1 M) was studied in this work, considering concentration and temperature effects. Electrochemical investigation indicated that BPC functions as a mixed-type inhibitor. For an optimal BPC concentration of 125 ppm, the inhibition efficiency of 91.55% was obtained at 298 K. According to adsorption isotherm of Langmuir, the BPC adheres to the CS with standard adsorption free energy (ΔG°_ads) of − 26.76 kJ mol⁻¹. Furthermore, the calculation of dissolution activation parameters revealed an increase in energy (E_a) from 46.48 to 94.97 kJ mol⁻¹, an elevation in the enthalpy (∆H_a) from 43.89 to 92.37 kJ mol⁻¹, and a rise in the entropy (∆S_a) from − 91.17 to 51.43 J mol⁻¹ K⁻¹ in the presence of 125 ppm of BPC. The experimental results were confirmed by quantum chemistry calculations based on density functional theory (DFT) and molecular simulations using the Monte Carlo method. These theoretical approaches also allowed for a comparison of the inhibitory performances of BPC with its protonated form, BPCH, the latter being found more effective. Moreover, the study of the radial distribution function g(r) predicted that the nature of the bond formed with the steel surface is of a chemical type.