Density functional theory studies on the corrosion inhibition of benzoin, benzil, benzoin-(4-phenylthiosemicarbazone) and benzil-(4-phenylthiosemicarbazone) of mild steel in hydrochloric acid

Abstract

The density functional theory (DFT) calculations were performed on benzoin (BN), benzil (BL), benzoin-(4-phenylthiosemicarbazone) (BN4PTSC) and benzil-(4-phenylthiosemicarbazone) (BL4PTSC) used as corrosion inhibitors for mild steel in acidic medium. The quantum chemical parameters/descriptors, namely, E HOMO (highest occupied molecular orbital energy), E LUMO (lowest unoccupied molecular orbital energy), the energy difference (ΔE) between E HOMO and E LUMO, dipole moment (μD), electron affinity (A), ionization potential (I), the absolute electronegativity (χ), absolute hardness (η), softness (σ), polarizability (α), the Mulliken charges, and the fraction of electrons (ΔN) transfer from inhibitors to iron, were calculated and correlated with the experimental IE%. Condensed Fukui functions have been used to determine the sites for electrophilic and nucleophilic attacks on each of the inhibitors.