Corrosion inhibition studies of ferrocenyl Schiff bases in a mild acidic medium through experimental methods and DFT calculations†
Abstract
In this research, we report a study on the synthesis of a new series of ferrocene based Schiff bases 4,4′-(((((methane-1,2-diylbis(oxy))bis(4,1-phenylene))bis(methaneylylidene))bis(azan eylylidene))bisferrocene FcA), 4,4′-((((methane-1,2-diylbis(oxy))bis(2-methoxy-1,4pheny lene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene FcB and 4,4′ ((((methane-1,2-diylbis(oxy))bis(2-ethoxy-1,4-phenylene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene FcC. These Schiff bases were characterized by using several spectroscopic techniques such as FT-IR, 1H and 13C NMR. The inhibitive effect of these Schiff bases on the corrosion of aluminium alloy in 0.1 M HCl medium was explored by weight loss measurement, Tafel polarization, electrochemical impedance spectroscopy and FT-IR spectroscopy. The influence of molecular configuration on the corrosion inhibition behavior of the inhibitors has been explored by quantum chemical calculations. The experimental findings demonstrated that FcB and FcC showed better anticorrosion efficiency than FcA. Weight loss measurement revealed the comprehensive adsorption of inhibitors. The assessed inhibition efficiencies are 79%, 80% and 81% for FcA, FcB and FcC, respectively. These results confirm the superior corrosion inhibition properties of FcB and FcC for aluminum alloy corrosion in 0.1 M HCl due to the presence of electron donating alkoxy groups (–OCH3 and –OC2H5). Polarization curves also indicated that the studied ferrocenyl Schiff bases were mixed inhibitors and their inhibition efficiencies are (FcA) 91.67%, (FcB) 97.15% and (FcC) 97.16%. Among all the examined Schiff bases, FcB and FcC show the lowest corrosion current density icorr, which makes them good inhibitors with high inhibition efficiencies. Parameters obtained from the quantum mechanical calculations revealed a correlation between corrosion inhibition efficiency and the molecular structure, stressing the structure–activity relationship. FT-IR spectroscopy confirmed chemisorption of these ferrocene based Schiff bases on the surface of the aluminium alloy.