Effectiveness of a novel C4-substituted heterocyclic organic pyrazolone as a corrosion inhibitor for mild steel in 1.0 M HCl: electrochemical, surface analytical and theoretical studies

This study investigates the corrosion inhibition performance of a novel C4-substituted pyrazolone-based heterocyclic compound, namely 3-(5-methyl-3-oxo-2,3-dihydro-1<i>H</i>-pyrazol-4-yl)-3-phenylpropanoic acid (C4-PRZ-1), on mild steel (MS) in a 1 M hydrochloric acid (HCl) environment. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods were employed to evaluate the inhibitor's protective capabilities. The effects of varying inhibitor concentrations and temperature on inhibition efficiency were systematically examined. Results demonstrated that increasing the inhibitor concentration improved corrosion protection, with a maximum efficiency of 85% observed at 5.0 mM. Furthermore, raising the temperature from 298 to 328 K caused a decrease in the inhibitive efficiency of the examined compound. The adsorption behavior of C4-PRZ-1 on the MS surface followed the Langmuir's isotherm model. Thermodynamic parameters associated with the adsorption process were determined to provide further insight into the inhibition mechanism. Surface morphology and elemental composition analyses using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) confirmed the formation of a protective film on the steel surface. Additionally, density functional theory (DFT) calculations were conducted to explore the electronic interactions, particularly the charge transfer between chloride ions and the steel substrate. Monte Carlo simulations, in conjunction with simulated annealing algorithms (SAA) and adsorption locator techniques, further elucidated the molecular interactions between the inhibitor and the metal surface, supporting the experimental findings.