Preparation and characterization of novel alkylpiperazinylbenzo[h]quinoline derivatives and evaluation of their performance as corrosion inhibitors for carbon steel by electrochemical and theoretical studies

This study investigates synthesis of 2-(4-methylpiperazin-1-yl)benzo[h]quinoline-3-carbaldehyde (MPBQCA) and 2-(ethylpiperazin-1-yl)benzo[h]quinoline-3-carbaldehyde (EPBQCA) and their potential as corrosion inhibitors on carbon steel (CS) surface by electrochemical, surface examination and theoretical studies. Characterizations of the novel compounds were performed by FT-IR, mass spectrometry, ¹H NMR, and ¹³C NMR techniques. Corrosion inhibition performance was evaluated by potentiodynamic polarization (PP), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) in 1.0 M HCl. Potentiodynamic polarisation shows that both MPBQCA and EPBQCA perform well and have good corrosion inhibition in 1.0 M HCl, and both investigated inhibitors can act as mixed type corrosion inhibitors. Additionally, SEM and EDX confirmed the electrochemical results and revealed their ability to adsorbed on the surface of carbon steel. Theoretical studied was performed on CS surface using density functional theory (DFT) calculations. We employed a comprehensive approach, analysing molecular reactivity, electrostatic potential, Fukui indices, and Monte Carlo simulations to gain insights into their adsorption and inhibitory mechanisms. Our findings reveal that both inhibitors (MPBQCA and EPBQCA) performed well as corrosion inhibitors in 1.0 M HCl and acting as mixed type corrosion inhibitors as per PP measurements. Additionally, surface investigation by SEM and EDX findings support the PP results by indicating forming of the protective layer on the metal surface. These findings assured by the theoretical studies which indicate that both inhibitors (MPBQCA and EPBQCA) exhibit strong binding affinities towards the Fe surface, particularly in acidic environments. However, MPBQCA demonstrates stronger binding and higher stability due to its more favourable adsorption energies. This study provides valuable insights into the molecular-level mechanisms of corrosion inhibition by these quinoline derivatives, paving the way for further development and optimization of effective corrosion inhibitors.