Adsorption and inhibition effect of tetraaza-tetradentate macrocycle ligand and its Ni (II), Cu (II) complexes on the corrosion of Cu10Ni alloy in 3.5% NaCl solutions

Abstract

In an attempt to search for high performance, effective and ecofriendly corrosion inhibitors, the macrocyclic compartmental ligand: (2E)-3,6,10,13-tetramethyl-2,7,9,14-tetraaza-1,8(1,4)dibenzena cyclotetradecaphane-2,6,9,13-tetraene (PDHDH) and its Ni (II), Cu (II) complexes have been synthesized and characterized by elemental and spectroscopic techniques. For corrosion inhibition studies of Cu10Ni alloy, different concentrations of synthesized inhibitors were added to 3.5 % NaCl as corrosive media and surveyed by potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. The surface of alloy samples treated with these inhibitors was analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) to confirm the existence of adsorbed protected film. PDP curves showed that the PDHDH and its Ni (II), Cu (II) complexes behave as mixed type inhibitors. The data demonstrated that the synthesized inhibitors could assist as active inhibitors for Cu10Ni alloy corrosion in 3.5 % NaCl solutions and their protection capacity reached to 95.7 % at 100 μM additive concentration. The synthesized inhibitors obey Freundlich adsorption isotherm, furthermore, the adsorption of these inhibitors on Cu10Ni is physisorption. DFT calculations, Fukui indices, Mulliken atomic charges and molecular electrostatic potential (MEP) mapping were accomplished to support the adsorption features and the corrosion inhibition mechanism of the investigated inhibitors.