Electrochemical And DFT Investigations of Anticorrosive Potentials of Selected Sulphonamides Based On Adsorption At Aluminium/Aqueous Acid Interface

The anticorrosive properties of six (6) selected sulphonamide derivatives on the aluminium surface were investigated in order to reveal their mechanism and mode of adsorption on Al/HCl interface, as well as the strength of the interactions between the inhibitor and Al surface. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques were utilised to evaluate the inhibition efficiencies of the selected compounds, while scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy techniques were utilised to understand the surface morphology of Al and adsorption sites of the sulphonamides. Density functional theory (DFT) calculations were utilised to investigate the strength of interactions between the inhibitor molecules and Al. Corrosive electrolyte of 1 M hydrochloric acid was employed in the study. All the studied sulphonamides showed excellent corrosion inhibition efficiencies with maximum values of up to 95%-97% at the optimum concentrations (4 × 10 -5 M - 4 × 10 -5 M), based on EIS measurements. The EIS parameters further revealed adsorbed film of the sulphonamides on the Al surface with capacitive-inductive characters. All the six sulphonamides reduced the corrosion current densities for both anodic and cathodic half-reactions and shifted the corrosion potentials to some anodically nobler values as revealed by the PDP data. Adsorption of the sulphonamides at the Al/HCl interface was described by the Langmuir isotherm model. Surface protection properties of the sulphonamides were further confirmed by SEM plates that showed less damaged surface of Al for the inhibited process compared to the uninhibited one. DFT results suggest that the binding energy for the inhibitors on the Al surface results in an energy that is less than 30 kJ/mol, which is an indication that the interactions are van der Waal type of interaction, suggesting physisorption mechanism.