Adsorption and inhibition mechanism of pyrazole derivatives on carbon steel: combined electrochemical, surface, and DFT/MD study

Abstract

In the present work, the effectiveness of two pyrazole derivatives, i.e. (Z)-1-(1-benzyl-5-methyl-1H-pyrazol-3-yl)-3-(3-ethylpyrazin-2-yl)-3-hydroxyprop-2-en-1-one (PMB) and (Z)-1-(1-benzyl-5-methyl-1H-pyrazol-3-yl)-3-hydroxy-3-(1H-imidazol-1-yl)prop-2-en-1-one (PMI), as corrosion inhibitors for carbon steel in an acidic medium was investigated using various experimental methodologies such as potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), surface analysis, and theoretical simulation by density functional theory (DFT) and molecular dynamics (MD). The inhibition mechanism was also performed to comprehend the inhibition mechanism. The results showed that the inhibition efficiencies of PMB and PMI increase with concentration and decrease with temperature, reaching a maximum efficiency of 95.3% for PMB and 82.5% for PMI at 303 K. PDP results reveal that the two inhibitors exhibit a mixed-type inhibition process, which inhibits both the anodic dissolution of metal and the cathodic reduction reaction. The EIS results reveal that higher polarization resistance (R_p) and lower double layer capacitance (C_dl) are observed due to the adsorption of molecules and protective film formation. AFM and SEM-EDS evidence a more homogeneous and less deteriorated surface, whereas contact angle measurements and UV-vis results corroborate the enhancement in hydrophobicity and the presence of inhibitor–interface interactions. Furthermore, the theoretical results are corroborated with experimental results and provide a good explanation of the adsorption pattern of PMB and PMI chemicals, which undergo a type of chemisorption according to the Langmuir adsorption model.