Novel 8-Hydroxyqionoline Derivatives as Effective Corrosion Inhibitors for Mild Steel in HCl Solution: Synthesis, Characterization, Gravimetric, Electrochemical, Surface Morphological and UV-Visible Spectrometry

Two newly substituted quinoline derivatives, namely 5-(((2-hydroxyethyl) thio) methyl) quinolin-8-ol Q-OH and 5-(((2-aminoethyl) thio) methyl) quinolin-8-ol Q-NH2 were synthesized and characterized by elemental analysis data, H-1 and C-13 Nuclear Magnetic Resonance Spectroscopy. Their inhibitory performance was studied against the corrosion of mild steel in 1.0 M hydrochloric acid at 298 K. Data obtained from EIS measurements has been examined and characterized by weight loss, Tafel polarization and electrochemical impedance spectroscopy (EIS). The experimental results reveal that the studied compounds have good inhibiting effects on the corrosion for mild steel in 1.0 M HCl medium. The protection efficiency increases with increasing inhibitor concentration but decrease with temperature. Good agreement between the results obtained from weight loss and electrochemical measurements. It has been determined that the adsorption for the studied inhibitors on mild steel complies with the Langmuir adsorption isotherm at all studied temperatures. The kinetic and thermodynamic parameters for mild steel corrosion and inhibitor adsorption, respectively, were determined and discussed. On the bases of thermodynamic adsorption parameters, comprehensive adsorption (physisorption and chemisorption) for the studied inhibitors on mild steel surface was suggested. Results show that the order of inhibition efficiency is Q-OH > Q-NH2. Potentiodynamic polarization studies have shown that compounds studies acts as a mixed type of inhibitor's. However, in order to get information on bonding mechanism of mild steel surface/inhibitors/1.0 M HCl solution system, the corrosion protection was also investigated by UV-visible spectrophotometry. Scanning Electron Microscopy was also performed and discussed for surface morphology study of mild steel samples.