Density Functional Theory (DFT) calculations were performed on two quinoline
molecules namely 2-hydroxyquinoline-3-carboxylic acid (2-HQCA) and 2-mercaptoquinoline-3-
carboxylic acid (2-MQCA) to investigate their possible role as steel corrosion inhibitor.
Calculations were carried out for neutral and protonated forms both in gas and aqueous phases for
comparison. The quantum chemical properties and descriptors most relevant to their inhibition
potentials such as EHOMO, ELUMO, Energy gap (ΔE), dipole moment (D), softness (S), hardness (η),
fraction of electrons transferred (ΔN), electrophilicity (ω), total energy change (ΩT) have been
calculated and compared. The interaction energy between the inhibitors and iron atom was also
computed and discussed. The results from the calculations indicate that 2-MQCA should have
better corrosion inhibition properties for steel than 2-HQCA. This is solely due to the substitution
of O with S.
Keywords: Corrosion inhibition, DFT, modelling studies, quinoline, steel.
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