Electrochemical and Computational Studies of Some Carbazole Derivatives as Inhibitors of Mild Steel Corrosion in Abiotic and Biotic Environments

Abstract

The potentials of three carbazole derivatives, namely 2,3,4,9-tetrahydro-1H-carbazole-8-carboxylic acid (THCZCA), 6-methyl-2,3,4,9-tetrahydro-1H-carbazole (MTHCZ) and 9-methyl-9H-carbazole-3-carboxylic acid (MCZCA) as anticorrosion agents for mild steel in abiotic, 1 M HCl and biotic, Desulfovibrio vulgaris (D. vulgaris) media have been investigated by electrochemical and weight loss techniques. The compounds were found to suppress mild steel corrosion in both 1 M HCl and D. vulgaris media. Potentiodynamic polarization data suggested that the presented carbazoles exhibit mixed-type inhibitive behaviour with hugely cathodic effect. Adsorption of the compounds was best described by Langmuir (for THCZCA) and Frumkin (for MTHCZ and MCZCA) isotherms. Scanning electron microscopy analyses indicated that the studied carbazoles formed protective film on mild steel surface both in the 1 M HCl and SRB media. The N and O heteroatoms and aromatic π-electron fragments of the molecules interact chemically with the mild steel as suggested by FTIR spectra. Quantum chemical calculations also suggested that the N and O atoms are the most susceptible sites of interactions with mild steel and the trends of the derived reactivity indices correlate fairly well with experimental inhibition efficiencies. Monte Carlo simulations also showed that the carbazole molecules have a great tendency to displace water from metallic surface and adsorb strongly on the steel surface as revealed by the high magnitudes of adsorption energies in the Fe(110)/inhibitor/50 H2O systems.