Experimental, quantum chemical and molecular simulation studies on the action of arylthiophene derivatives as acid corrosion inhibitors

The corrosion inhibition properties of two newly synthesized arylthiophene derivatives, namely 2-(4-amidinophenyl)-5-[(4-dimethylamino) phenyl] thiophene hydrochloride (MA-1315) and 2-(4-amidino-3-fluorophenyl)-5-[(4-dimethylamino) phenyl thiophene hydrochloride (MA-1311) on C-steel in 1.0 M HCl solution were evaluated using experimental measurements such as chemical method (weight loss)and electrochemical (electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) and electrochemical frequency modulation (EFM)) techniques. The calculated inhibition efficiencies (%IE) at the optimum concentration used (21 × 10−6 M) were 93.3% and 91.1% for MA-1315 and MA-1311, respectively at 328 K. It was observed that %IE increases with increasing the concentration of inhibitors and the temperature of the acid medium. The thermodynamic adsorption and kinetic parameters of the tested systems were calculated and discussed. The adsorption of the investigated inhibitors on C-steel followed Langmuir adsorption isotherm. The PDP curves showed that the studied arylthiophenes act as mixed-type inhibitors and the EIS results revealed that the investigated inhibitors formed a thin protective film on the metal surface. The adsorption of these compounds on C-steel surface was confirmed via Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX), Atomic Force Microscopy (AFM) and Fourier Transform Infrared (FT-IR). Inhibitory action of arylthiophenes at the molecular level was deeply explored by DFT computations, Natural Bonding Orbital (NBO) analysis and Monte Carlo simulations. The high value of %IE corresponds to the compound with higher EHOMO and lower ELUMO. N and S atoms are the most possible active centers for bonding with the Fe surface through donating electrons to the empty d-orbitals of Fe atoms as well as accepting electrons from the metal surface. The theoretical results were in good agreement with experimental measurements.