Quantum chemical and molecular dynamics study of quince extract as a corrosion inhibitor for St37 steel in acidic solution

This study explored the corrosion behavior of low-carbon steel in a 1 M hydrochloric acid (HCl) solution with increasing temperatures, using varying concentrations of Quince Extract (QE) as an eco-friendly, natural corrosion inhibitor. The extract, scientifically known as Cydonia oblonga , contains functional groups such as amino acids and flavonoids, which contribute to its corrosion-inhibiting properties. These functional groups were analyzed using Fourier Transform Infrared Spectroscopy (FTIR). Electrochemical impedance spectroscopy (EIS) and polarization tests were conducted to assess the inhibition efficiency of QE within a temperature range of 308–328 K. The electrochemical results revealed that the inhibition efficiency of QE decreases with rising temperatures but improves with higher extract concentrations in the solution. According to polarization test data, at a QE concentration of 1000 ppm, the inhibition efficiency reached 91 % at 308 K but dropped to 81 % when the temperature increased to 328 K. The adsorption of QE onto the low-carbon steel surface was modeled using the Langmuir isotherm. Activation and thermodynamic parameters were calculated to analyze the interaction between the inhibitor and the metal surface. The ∆G°ads values at different temperatures were approximately −21 kJ·mol −1 , indicating physical adsorption. The activation energy (Ea) was found to increase from 37.40 kJ·mol −1 in the absence of QE to 72.36 kJ·mol −1 at a QE concentration of 1000 ppm, further supporting the physical adsorption mechanism. To evaluate the effect of temperature on the adsorption of the inhibitor onto the steel surface, molecular dynamics (MD) simulations were performed. The results identified 4-O-caffeoylquinic acid (CQA) as the most effective component among the QE derivatives for corrosion inhibition. Additionally, Monte Carlo (MC) and MD simulations confirmed a decrease in inhibition efficiency with increasing temperature, consistent with the experimental findings.