Corrosion inhibition and adsorption behaviour of two novel quinolin-8-ols on carbon steel surface in HCl: synthesis, electrochemical, surface characterisation, and quantum chemical approaches

Two synthesised quinolin-8-ol derivatives were evaluated as corrosion inhibitors in 1M HCl medium for carbon steel (<i>C</i>/<i>S</i>). The derivatives are 1-((8-hydroxyquinolin-5-yl)methyl)urea (HQU) and 1-((8-hydroxyquinolin-5-yl)methyl)thiourea (HQT). A combination of quantum chemical approaches, scanning electron microscopy (SEM-EDX), UV-visible spectroscopy, potentiodynamic polarisation (PDP), and electrochemical impedance spectroscopy (EIS) has been used in the present work. Corrosion inhibition efficiency was found to depend on both the concentration and the structure of the compounds studied. The results demonstrated a maximum inhibition level of 94.5% for HQT and 87.3% for HQU (as determined by PPD at 303 K) at a concentration of 0.001 M, respectively. On the basis of the results of the potentiodynamic polarisation, it can be concluded that the two compounds used in this study are mixed-type inhibitors. Furthermore, according to the Langmuir adsorption model, quinolin-8-ols are adsorbed as follows. The <i>C</i>/<i>S</i> surface is where quinolin-8-ol derivatives are chemisorbed, depending on thermodynamic characteristics. Quinolin-8-ols are present, as shown by the smooth <i>C</i>/<i>S</i> surface observed by scanning electron microscopy. Results from computational methods like molecular dynamics (MDS) and density functional theory (DFT) agree well with experimental results.