Effect of hydrocarbon chain length for acid corrosion inhibition of mild steel by three 8-(n-bromo-R-alkoxy)quinoline derivatives: Experimental and theoretical investigations

Frontiers and advances in N-heterocycle compounds as corrosion inhibitors in acid medium: Recent advances

The acid solution is widely used in chemical cleaning, oil well acidifying, and other fields, which also brings the problem of metal corrosion that cannot be underestimated. However, adding an inhibitor is one of the most convenient and effective ways to slow down metal corrosion. N-heterocyclic compounds with high stability and durability, in line with the strategy of sustainable development, have been widely studied in an acidic environment. Imidazole, pyridine, and quinoline compounds, as the most commonly used corrosion inhibitors, can form a compact protective film via π electron cloud shifting towards the N atoms to generate coordination function. In particular, flexible modifiability makes N-heterocyclic compounds adapt to different corrosion environments readily, conducive to the formation of chemical bonds between compounds with metal surfaces to be better adsorption, so as to avoid the blemish of traditional inhibitors (such as inorganic salt and organic amines inhibitors) due to excessive usage, surface roughness of metal or environmental factor (for instance, temperature, pH and metallic) causing loose bonding between film and metal surface. More importantly, the efficient corrosion inhibition and toxicity of N-heterocyclic compounds have close to do with their own functional groups. Combined with the latest research achievement, the effects of different substituents on the corrosion inhibition and corrosion inhibition mechanisms were systematically reviewed in the acid-corrosive solution of imidazole, pyridine, and quinoline and their derivatives in this review article, respectively. In addition, the application and function of density functional theory in predicting the corrosion inhibition effect of corrosion inhibitors are also discussed. The future development trend was prospected according to the summarized research results.

Investigation of the corrosion inhibition potentials of some 2-(4-(substituted)arylidene)-1H-indene-1,3-dione derivatives: density functional theory and molecular dynamics simulation

Background

Corrosion is a threat to material strength and durability. Electron-rich organic inhibitor may offer good corrosion mitigation potentials. In this work, anti-corrosion potentials of nine derivatives of 1H-indene-1,3-dione have been investigated using density functional theory (DFT) approach and molecular dynamics (MD) simulation. Chemical reactivity descriptors like energies of lowest unoccupied molecular orbital (ELUMO), highest occupied molecular orbital (EHOMO), electron affinity (A), ionization potential (I), energy gap (ΔEgap), global hardness (η), global softness (σ), electronegativity (χ), electrophilicity (ω), number of transferred electrons (ΔN) and back-donation (ΔEback-donation) were computed at DFT/B3LYP/6-31G(d) theoretical level. The local reactive sites and the charge partitioning on the compounds were studied using Fukui indices and molecular electrostatic potential (MEP) surface analysis. The adsorption behavior and the binding energy of the inhibitors on Fe (110) surface in hydrochloric acid solution were investigated using MD simulation.

Results

The high chemical reactivity, kinetic instability and good corrosion inhibition potentials demonstrated by the inhibitors are rationalized based on their high EHOMO, A, σ, ΔN, ΔEback-donation, and low ΔEgap, ELUMO, I and η. A wide difference of approximately 2.4–3.2 eV between the electronegativities of iron and the 1H-inden-1,3-diones suggests good charge transfer tendency from the latter to the low-lying vacant d-orbitals of iron. The heteroatoms (O and N) and the aromatic moieties are the nucleophilic sites on the inhibitors for effective adsorption on the metal surface as shown by condensed Fukui dual functions and MEP analysis. The MD simulation shows good interaction and strong binding energy between the inhibitor and Fe (110) surface.

Conclusions

Effective surface coverage and displacement of H3O+, Cl− and water molecules from Fe (110) surface by the inhibitors indicate good corrosion inhibition properties of the inden-1,3-diones. 2-((4,7-dimethylnaphthalen-1-yl)methylene)-1H-indene-1,3(2H)-dione display low energy gap, strongest binding interaction and most stabilized iron-inhibitor configuration, hence, the best anti-corrosion potential.

Graphical abstract

New QSPR model for prediction of corrosion inhibition using conceptual density functional theory

The relationship between structure and corrosion inhibition of a series of twenty-eight quinoline and pyridine derivatives has been established through the investigation of quantum descriptors calculated with PBE/6-311 +  + G** method. A quantitative structure-property relationship (QSPR) model was obtained by examining these descriptors using a genetic algorithm approximation method based on a multiple linear regression analysis. The results indicate that the efficiency of corrosion inhibitors is strongly associated with hardness (η), minimal electrostatic potential (ESP_min), and volume (V) descriptors. Furthermore, the validity of the proposed model is corroborated by an adsorption study on an iron surface Fe(110).

Electrochemical and quantum mechanical investigation of various small molecule organic compounds as corrosion inhibitors in mild steel

The corrosion inhibition property of selected small organic compounds was investigated using electrochemical measurements, including potentiodynamic polarization (PDP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and density functional theory (DFT) calculations. The inhibition efficiency (IE %) of the inhibitor on mild steel (MS) in 1 M HCl was then determined. Results show that the presence of the inhibitors resulted in decreased corrosion current density (I_corr) values and increased polarization resistance (R_p). Furthermore, the use of higher concentrations of inhibitors led to an increased inhibition efficiency. Tafel slopes and shifts in the E_corr values suggested that the inhibitors tested are mixed-type inhibitors that form a protective layer on the surface of the substrate. Of the organic compound inhibitors tested, the inhibitor 4-ethylpyridine (EP) exhibited the highest R_p values and inhibition efficiency values from the PDP, LPR, and EIS analyses, respectively. DFT calculations showed negative adsorption energies and confirmed the chemisorption of the inhibitors allowing for the formation of a hydrophobic protective film against corrosion and correlations between the quantum chemical values and electrochemical data were demonstrated. The results show the influence of the presence of electronegative O, S, and N atoms, as well as the role of aromatic rings in the promotion of surface protection by preventing aggressive ionic species from binding onto MS.