Adsorption, corrosion inhibition mechanism, and computational studies of Azadirachta indica extract for protecting mild steel: Sustainable and green approach. (June 2022)

• Record Type: Journal Article
• Authors: Kumar, Harish; Yadav, Vikas; Kumari, Anu
• Is Part Of: Journal of physics and chemistry of solids. Volume 165(2022)
• Publication Date: 2022-06
• Subjects: Azadirachta indica -- DFT -- Green corrosion inhibitor -- Impedance spectroscopy -- Mild steel -- Molecular dynamics simulation; AI Azadirachta indica -- DFT Density Functional Theory -- MS Mild Steel -- HOMO Highest Occupied Molecular Orbital -- LUMO Lowest Occupied Molecular Orbital -- CIE Corrosion Inhibition Efficiency -- FMO Frontier Molecular Orbital -- MD Molecular Dynamics -- MIT Metallurgical Imaging Technique -- GI Green Inhibitor -- OCP Open Circuit Potential -- CR Corrosion Rate; Solids -- Periodicals; Solides -- Périodiques; Solids; Periodicals; 530.41
• DOI: 10.1016/j.jpcs.2022.110690
• Languages: English
• ISSNs: 0022-3697

Abstract

Abstract: The extract of Azadirachta indica (AI) leaves has been explored as a green inhibitor for mild steel (MS) in 5.0 m hydrochloric acid by computational (DFT, Langmuir/Freundlich adsorption, frontier molecular orbital, and molecular dynamics simulation) and experimental (polarization, gravimetric, gasometric, and impedance) techniques. Corroded surfaces have been investigated by metallurgical microscopy and SEM techniques. The impedance parameters and inhibition efficiency were found to increase with AI extract concentration, the latter from 50.64% to 89.25%. Various theoretical parameters, such as electronic charge in the HOMO/LUMO, Fukui function, metal−inhibitor interaction energy (−22.12 kJ/mol), adsorption energy (7.86 kJ/mol), back-donation energy, chemical potential (3.95 eV), and global hardness (1.75 eV), imply high adsorption of AI extract (flavonoid as major constituent) on MS. SEM and metallurgical imaging techniques have proved the growth of a uniform barrier film on the surface of MS with increasing AI extract concentration. The numbers and intensities of pits and cracks decrease with increasing AI extract concentration. A maximum of 89.25% inhibitory efficiency was shown by AI. Wastewater from gravimetric experiments was examined for biocompatibility and biodegradability, and was found within the permissible range. Graphical abstract: The extract of Azadirachta indica leaves was investigated as a green inhibitor for mild steel in 5 M HCl by theoretical and experimental techniques. Experimental techniques like gravimetric, polarization, gasometric, and impedance were used. Theoretical techniques like DFT, Langmuir adsorption, Frontier molecular orbital, and molecular dynamics simulation were used. The corroded surface was investigated by metallurgical microscopy and SEM techniques. The inhibition efficiency was found to increase with AI concentration that is 0.1–4 g/L. Polarization study shows that AI acts as a mixed control. The solution resistance and charge transfer resistance increase with AI concentration. The theoretical parameters like electron distribution in HOMO/LUMO, Fukui indices per atom, interaction energy, adsorption energy, back donation energy, chemical potential, global hardness, etc. prove strong adsorption of AI molecules on Fe (110) surface. SEM and metallurgical imaging techniques prove the growth of uniform, barrier film on the surface of mild steel with AI concentration. The number and intensity of pits decreases with AI concentration. AI shows 89.25% inhibition efficiency for MS at 4 g/L in 5 M HCl. Image 1 Highlights: Azadirachta indica (AI) leaf extract has been tested as a green corrosion inhibitor. Gravimetric, polarization, impedance, and microscopy techniques have been applied. Experimental and computational studies prove strong adsorption. AI acts as a very good inhibitory, anti-cracking, and anti-pitting agent for mild steel. A maximum of 89.25% corrosion inhibition efficiency was achieved.