In order to evaluate the effect of the functional group present in the ligand backbone towards corrosion inhibition performances, three Schiff-base molecules namely, (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)pyridine (L¹), (E)-4-(2-(pyridin-4-ylmethylene)hydrazinyl)benzonitrile (L²) and (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)phenol (L³) were synthesized and used as corrosion inhibitors on mild steel in 1 M HCl medium. The corrosion inhibition effectiveness of the studied inhibitors was investigated by weight loss and several sophisticated analytical tools such as potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Experimentally obtained results revealed that corrosion inhibition efficiencies followed the sequence: L³ > L¹ > L². Electrochemical findings showed that inhibitors impart high resistance towards charge transfer across the metal–electrolyte interface and behaved as mixed type inhibitors. Scanning electron microscopy (SEM) was also employed to examine the protective film formed on the mild steel surface. The adsorption as well as inhibition ability of the inhibitor molecules on the mild steel surface was investigated by quantum chemical calculation and molecular dynamic (MD) simulation. In quantum chemical calculations, geometry optimized structures of the Schiff-base inhibitors, electron density distribution in HOMO and LUMO and Fukui indices of each atom were employed for their possible mode of interaction with the mild steel surfaces. MD simulations revealed that all the inhibitors molecules adsorbed in parallel orientation with respect to the Fe(110) surface.

On mild steel surface in 1 M HCl medium corrosion inhibition performances of three Schiff base inhibitors (L ¹ , L ² and L ³ ) are investigated both experimentally and theoretically (DFT and MD simulation studies).

Given the high toxicity of inorganic inhibitors, organic substances, primarily heterocycles, have been proven to be one of the most efficient, cost-effective, and practical alternatives. Severe limitations in the application of organic corrosion inhibitors, particularly their environmental toxicity, have greatly accelerated the investigation of eco-friendly and sustainable alternatives. Corrosion control has made significant use of green chemistry ideas in recent years. This involves using different sustainable materials, techniques and strategies for corrosion control. Bio-based materials, including plant extracts, natural polymers, gums, waste, amino acids, and carbohydrates, are widely employed as sustainable materials. They are considered the best eco-friendly substitutes owing to their natural origin, biodegradability, and non-accumulation. Recently, several green synthetic techniques have been used to create green synthetic inhibitors, including microwave (MW) and ultrasonic (US) irradiation, particularly in conjunction with one-step multicomponent reactions (MCRs). Besides being green and sustainable, compounds derived from MW and US irradiation are more effective inhibitors than those obtained via traditional synthesis. Synthetic inhibitors derived using sustainable chemicals, solvents, and catalysts are also regarded as green alternatives. Inhibitors synthesized using natural substrates such as AAs and carbohydrates are semisynthetic alternatives. Recently, self-healing and synergism have emerged as additional environmentally friendly corrosion prevention methods. Computational modeling and simulations such as density functional theory (DFT), molecular dynamics (MD), and Monte Carlo (MC) simulations save money and resources by minimizing the number of experimental trials. Herein, we discuss the current research on using various eco-friendly and sustainable materials, technologies, and strategies for corrosion prevention together with their challenges and opportunities.

In this work, the adsorption behavior and corresponding inhibition mechanism of two aminobenzonitrile derivatives, e.g., 2-aminobenzonitrile (2-AB) and 3-aminobenzonitrile (3-AB), in aqueous acidic medium on steel surfaces have been investigated using quantum chemical calculations and molecular dynamics (MD) simulations. Quantum chemical parameters such as E_HOMO, E_LUMO, energy gaps (ΔE), the dipole moment (μ), the global hardness (η), the softness (S), and the fraction of electron transfer from the inhibitor molecule to the metallic surface (ΔN) have been calculated and well discussed. Fukui indices analysis was performed to get local reactive sites of the studied inhibitor molecules. Furthermore, molecular dynamics simulations were applied to search for the most favorable adsorption configuration of the inhibitor over an iron (1 1 0) surface.

The purposeful incorporation of aliphatic, branched chain and substituted aromatic moieties in the molecular skeleton of organic Schiff bases, in line with corrosion inhibition performance, has been conducted. Three Schiff bases, namely, 2-((2-hydroxyethylimino)methyl)-6-methoxyphenol (L¹), 2-((1-hydroxybutan-2-ylimino)methyl)-6-methoxyphenol (L²) and 2-(2-hydroxy-3-methoxybenzylideneamino)phenol (L³) were synthesized and subsequently assessed for the inhibition of mild steel corrosion in 1 M HCl medium. The corrosion inhibition proficiencies of the synthesized inhibitors on the mild steel surface have been investigated by gravimetric measurements, electrochemical analysis (potentiodynamic polarization, electrochemical impedance spectroscopy), surface morphological studies (FESEM and AFM), contact angle measurement and, most importantly, theoretical studies. The results obtained from the gravimetric as well as electrochemical measurements revealed that the studied Schiff bases are mixed-type inhibitors that show maximum inhibition efficiency up to ∼97% at the concentration of 5 mM. In theoretical studies, atomic-level calculations give deeper insights into the corrosion inhibition mechanism and the relative performance of present inhibitors. However, it has been found that normal density functional theory (DFT) calculations are not sufficient to deal with the interactions between inhibitors and metal surfaces in complex systems. As such, in order to investigate inhibitor–metal interactions, herein, the density functional tight binding (DFTB) approach has been introduced as formulated by Hohenberg, Kohn and Sham (KS-DFT). Furthermore, for more insightful studies, e.g., growth characteristics, as well as the selection of a more stable surface of the α-Fe crystal morphology studies, have also been performed using the “morphology” module. The morphology of the α-Fe crystal in equilibrium was analyzed using the Wulff construction plot. In DFTB calculations, the trans3d Slater–Koster library set has been implemented for possible pairs of interactions between inhibitor–metal complex systems (C, N, O, H and Fe). Some salient features like equilibrium adsorption configuration and charge density difference obtained from DFTB calculations have been described in detail. Furthermore, for comparison with the real world of corrosion inhibition, molecular dynamics (MD) simulation was employed in the presence of all concerned species (inhibitor molecule, Fe surface, H₂O, H₃O⁺ and Cl⁻), which revealed the actual adsorption configurations of the inhibitor molecule on the desired metallic surfaces.