Investigation of some phenolic-type antioxidants compounds extracted from biodiesel as green natural corrosion inhibitors; DFT and molecular dynamic simulation, comparative study

Abstract

To solve the problem of environmental pollution during the metal cleaning process, new compounds extracted from biodiesel such as Pyropyl-Gallate (L1), Pyrogallol (L2), 4-Methyl-catecho (L3) and Protocatechuic-acid (L4) were investigated as green corrosion inhibitors by using density functional theory (DFT) and Molecular dynamic simulation (MDS) methods. The computed quantum chemical parameters obtained from DFT for instance the total energy (ET), the energy of the highest occupied molecular orbital (EHOMO), the energy of the lowest unoccupied molecular orbital (ELUMO), the dipole moment (µ) and the polarizability (α) indicate that those examined molecules were efficient corrosion inhibitor. The tested molecules present a general planar structure. This structure unit may be in favor of the important interaction zone if the molecule adsorbed on the metal surface at nearly 0° contact angle. As can be seen from Molecular electrostatic potential (MEP), it is clear that more electron rich regions are largely located around the heteroatoms and the conjugated double bonds, means that L1, L2, L3 and L4 can promote the formation of a complex on the metal surface by transferring electrons and forming a coordinate covalent bond through the chemical adsorption. From MDS study, the binding energy of the adsorption system (Inhibitor-Fe) is more important, showing that this adsorption system is very stable, and has high inhibitory efficiency. According to the study of quantum chemistry, the oxygen atoms of the molecules tested can give electrons to the unoccupied iron orbital “d” to form coordination bonds while the orbital π of aromatic rings can accept electrons from the iron orbital “d” to form coordination bonds. A good agreement was found between DFT and MDS methods.