Mechanistic Insights and Performance of Pyrazole-Based Corrosion Inhibitors for Carbon Steel in Acidic Media: Experimental and Computational Approaches

In an attempt to mitigate steel corrosion, the present work delves into the adsorption and inhibitory performance of newly synthesized pyrazole-derived ligands, specifically 1-benzyl-5-methyl-1H-pyrazole-3-carboxylic acid (B5MPyAc), 1-benzyl-5-methyl-1H-pyrazole-3-carbohydrazide (B5MPy), and ethyl 1-benzyl-5-methyl-1H-pyrazole-3-carboxylate (EB5MPy), on C48 carbon steel in a 1.0 mol/L hydrochloric acid solution, at a temperature range from 298 to 318 K. This evaluation employed a diverse array of chemical, electrochemical, and surface characterization techniques, including potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), weight loss (WL) assessment, and scanning electron microscopy (SEM), supplemented by theoretical calculation methods. Inhibition efficiencies were observed to reach 94.77, 90.03, and 82.86% for B5MPyAc, B5MPy, and EB5MPy, respectively, at an optimal concentration of 103 µM L−1. EIS data revealed an increase in polarization resistance and a notable decrease in double-layer capacitance (Cdl) values, attributable to the adsorption of inhibitors at the metal/solution interface. Potentiodynamic polarization curves indicated that B5MPyAc, B5MPy, and EB5MPy function as mixed-type corrosion inhibitors. Additionally, inhibitor adsorption was found to conform to the Langmuir adsorption isotherm. Scanning electron microscopy (SEM) images, coupled with UV–visible absorption analysis, confirmed that the efficacy of all three inhibitors could be linked to the formation of a protective layer on the metal surface. Density Functional Theory (DFT) calculations have shown that quantum chemical parameters do not align well with the experimental inhibition performance. In contrast, Molecular Dynamics (MD) simulations suggested a parallel orientation in the adsorption of inhibitors, with findings particularly supporting the superior efficiency of B5MPyAc. This study would serve as a foundation for further development of effective pyrazole-based corrosion inhibitors.