Synthesis and characterization of two 8-quinolinol derivatives and their application as corrosion inhibitors for carbon steel in hydrochloric acid solution

Two derivatives of 8-quinolinols, namely 2-amino-N-((8-hydroxyquinolin-5-yl)methyl)acetamide (AHQA) and 2,2,2-trifluoro-N-((8-hydroxyquinolin-5-yl)methyl)acetamide (TFQA), were synthesized, characterized, and evaluated as corrosion inhibitors for the dissolution of carbon steel (CS) in 1 M HCl solution. The inhibition effects of AHQA and TFQA on CS corrosion in 1 M HCl solutions were investigated using open circuit potential (OCP) curves, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), UV-visible spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), as well as density functional theory (DFT) and molecular dynamics (MD) simulations. The results show that AHQA and TFQA are excellent anti-corrosion inhibitors within the temperature range of 303–333 K, and their inhibition performance depends on temperature and concentration; notably, at 10−3 M, the corrosion inhibition efficiencies were 96.3% for AHQA and 95.3% for TFQA. The PDP results indicate that AHQA and TFQA act as mixed-type inhibitors. The chemisorption of these compounds on the CS surface follows the Langmuir adsorption isotherm. The substrate surface composition analysis employed by UV-visible spectroscopy and the surface characterization investigated by SEM-EDX and AFM confirmed that TFQA and AHQA adsorb onto the CS surface to form the 8-quinolinols-Fe protective film, which successfully shields the CS from corrosive ions. Quantum chemical parameters align well with the experimental results, supporting a higher inhibition efficiency of AHQA due to the electron-donating effect of the -CH2-NH2 substituent, compared to TFQA, which contains the electron-withdrawing -CF3 group. Additionally, the MD simulation shows that AHQA and TFQA adsorb onto the Fe(110) surface in a flat orientation.