Pyridine based N-heterocyclic compounds as aqueous phase corrosion inhibitors: A review

Imidazolium-Based Polymeric Ionic Liquids with Short Alkyl Chains as Green Corrosion Inhibitors for Mild Steel in 1 M HCl: Experimental and Theoretical Investigations

A novel polymeric ionic liquid (PDBA-IL-NH2) using imidazolium ionic liquids with short alkyl chains as monomers and two control ionic liquids (PDBA-IL-OH and PIL-NH2) were synthesized. Their inhibition properties and mechanisms were explored via surface analysis, weight loss tests, electrochemical studies, and adsorption isotherm analysis. The corrosion inhibition efficiency (CIE) of PDBA-IL-NH2 gradually increased with increasing concentration, and the largest efficiency was 94.67% at 100 ppm. At the same concentration (50 ppm), the corrosion inhibition abilities of inhibitors were in the order of PDBA-IL-NH2 > PDBA-IL-OH > PIL-NH2 > IL-NH2. Based on the experimental investigation, the synergistic effect of electrostatic interaction, protonation, and electron donor-acceptor interaction facilitated the intensive entanglement and coverage of PDBA-IL-NH2 with the reticulated form on the metal, and the generated densest films protected the metal from the corrosive media. Ultimately, the theoretical results of molecular dynamics simulations and quantum chemical study were in high agreement with the experimental data, which confirmed the proposed inhibition mechanisms on the microscopic scale. This study contributed valuable perspectives to the design of efficient and ecofriendly corrosion inhibitors.

Imidazoline As a Volatile Corrosion Inhibitor for Mitigation of Top- and Bottom-of-the-Line CO2 Corrosion in Carbon Steel Pipelines

A fatty acid imidazoline-based inhibitor was synthesized via a facile solvent-free synthesis method between tall oil fatty acid (TOFA) and diethylenetriamine (DETA) under atmospheric conditions with a short reaction time. The as-synthesized imidazoline (S-Imd) acted as an effective inhibitor for reducing or preventing corrosion of carbon steel pipelines at both bottom of the line (BOL) and top of the line (TOL) positions under simulated conditions of a gas pipeline in a CO2-saturated environment. The inhibition efficacy was examined by both weight loss and electrochemical measurements, such as the electrochemical impedance spectrum (EIS), potentiodynamic polarization (PDP), and linear polarization resistance (LPR). The results revealed that the S-Imd, 2-(8-heptadecenyl)-2-imidazoline-1-ethanamin, at 300 ppm exhibited a superior inhibition efficiency of up to 91.6 and 89.9% for BOL and TOL corrosion tests, respectively. The surface morphology of the carbon steel test specimens was also examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), and contact angle analysis. It was found that the as-synthesized S-Imd acted as a mixed-type inhibitor that exhibited a decreased surface roughness and oxide layer on carbon steel surfaces. However, the water contact angle was found to increase, implying enhanced hydrophobicity of the surface. Adsorption of the imidazoline molecules on carbon steel surfaces followed the Langmuir adsorption isotherm. The present work provides very promising results in the synthesis and utilization of the studied imidazoline as a volatile corrosion inhibitor (VCI), especially for carbon steel pipelines in petroleum industries.

Multicomponent synthesis via acceptorless alcohol dehydrogenation: an easy access to tri-substituted pyridines

Herein, we report palladium supported on a hydroxyapatite catalyst for synthesizing tri-substituted pyridines using ammonium acetate as the nitrogen source via acceptorless alcohol dehydrogenation strategy. The strategy offers a broad substrate scope using inexpensive and readily available alcohols as the starting material. The catalyst was prepared using a simple method and analyzed by several techniques, including FE-SEM, EDS, HR-TEM, BET, XRD, FT-IR, UV-visible spectroscopy, and XPS, demonstrating the anchoring of Pd nanoparticles on hydroxyapatite in the zero oxidation state. Moreover, several controlled experiments were carried out to understand the reaction pathway and a suitable mechanism has been proposed.

Progress in the Field of Cyclophosphazenes: Preparation, Properties, and Applications

This review article provides a comprehensive overview of recent advancements in the realm of cyclophosphazenes, encompassing their preparation methodologies, distinctive properties, and diverse applications. The synthesis approaches are explored, highlighting advancements in the preparation of these cyclic compounds. The discussion extends to the distinctive properties exhibited by cyclophosphazenes, including thermal stability characteristics, and other relevant features. Furthermore, we examine the broad spectrum of applications for cyclophosphazenes in various fields, such as coatings, adhesives, composites, extractants, metal complexes, organometallic chemistry, medicine, and inorganic chemistry. This review aims to offer insights into the evolving landscape of cyclophosphazenes and their ever-expanding roles in contemporary scientific and technological arenas. Future possibilities are emphasized, and significant research data shortages are identified.

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.

Insights into the Anticorrosion Performance of Solanum lyratum Leaf Extract for Copper in Sulfuric Acid Medium

In this paper, Solanum lyratum leaves were prepared into a corrosion inhibitor by a pure water extraction method. As a natural plant, S. lyratum leaf extract as a corrosion inhibitor has green features. S. lyratum leaf extract (SLLE) can effectively inhibit the corrosion of Cu in H₂SO₄ solution. The protective effect on copper in 0.5 mol/L H₂SO₄ solution was studied by electrochemical measurement, Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and theoretical calculation. These results showed that the maximum corrosion inhibition efficiency (η) of SLLE for copper obtained in the electrochemical measurement at different temperatures is more than 90%. The adsorption of SLLE on copper surfaces conforms to the Langmuir isotherm adsorption model. FTIR and XPS showed the bonding information. SEM and AFM proved that the SLLE can protect the copper from corrosion media. The interaction and inhibition mechanism between the SLLE and copper surface was further revealed at the molecular level by theoretical calculation.

The curious case of polyphenols as green corrosion inhibitors: a review on their extraction, design, and applications

Over the past century, a substantial amount of research focused on developing corrosion inhibitors, with a special focus on green "plant-based" corrosion inhibitors. Among the various types of inhibitors, polyphenols emerged as a promising candidate due to their advantageous characteristics, which include being inexpensive, biodegradable, renewable, and, most importantly, safe for both the environment and humans. Their performance as sustainable corrosion inhibitors have encouraged many electrochemical experiments as well as theoretical, mechanistic, and computational studies, with many papers reporting inhibition efficiencies of over 85%. In this review, the majority of literature contributions on the inhibition of various types of polyphenols, their natural extraction techniques, and their applications as "greener" corrosion inhibitors for metals are thoroughly described and discussed with a focus on their preparation, inhibition mechanism, and performance. Based on the reviewed literature, it can be concluded that polyphenols have a very promising potential to be used as both green and powerful corrosion inhibitors; therefore, further investigations, experimental or computational, are still required to realize higher inhibition efficiencies reaching up to ≈ 100%.

Unraveling Bonding Mechanisms and Electronic Structure of Pyridine Oximes on Fe(110) Surface: Deeper Insights from DFT, Molecular Dynamics and SCC-DFT Tight Binding Simulations

The development of corrosion inhibitors with outstanding performance is a never-ending and complex process engaged in by researchers, engineers and practitioners. The computational assessment of organic corrosion inhibitors' performance is a crucial step towards the design of new task-specific materials. Herein, the electronic features, adsorption characteristics and bonding mechanisms of two pyridine oximes, namely 2-pyridylaldoxime (2POH) and 3-pyridylaldoxime (3POH), with the iron surface were investigated using molecular dynamics (MD), and self-consistent-charge density-functional tight-binding (SCC-DFTB) simulations. SCC-DFTB simulations revealed that the 3POH molecule can form covalent bonds with iron atoms in its neutral and protonated states, while the 2POH molecule can only bond with iron through its protonated form, resulting in interaction energies of -2.534, -2.007, -1.897, and -0.007 eV for 3POH, 3POH⁺, 2POH⁺, and 2POH, respectively. Projected density of states (PDOSs) analysis of pyridines-Fe(110) interactions indicated that pyridine molecules were chemically adsorbed on the iron surface. Quantum chemical calculations (QCCs) revealed that the energy gap and Hard and Soft Acids and Bases (HSAB) principles were efficient in predicting the bonding trend of the molecules investigated with an iron surface. 3POH had the lowest energy gap of 1.706 eV, followed by 3POH⁺ (2.806 eV), 2POH⁺ (3.121 eV), and 2POH (3.431 eV). In the presence of a simulated solution, MD simulation showed that the neutral and protonated forms of molecules exhibited a parallel adsorption mode on an iron surface. The excellent adsorption properties and corrosion inhibition performance of 3POH may be attributed to its low stability compared to 2POH molecules.

The Effect of Smart PEO-Coatings Impregnated with Corrosion Inhibitors on the Protective Properties of AlMg3 Aluminum Alloy

The protective coating with a self-organized microtubular structure was formed using plasma electrolytic oxidation (PEO) on AlMg3 aluminum alloy in the tartrate-fluoride electrolyte. This protective layer was further modified using corrosion inhibitors of the azole group (1,2,4-triazole, benzotriazole) and polymer material (polyvinilidene fluoride, PVDF). X-ray diffraction analysis and scanning electron microscopy with energy dispersive spectroscopy were used to study the morphology and composition of the obtained oxide coatings. The presence of the inhibitor in the PEO-layer was confirmed using micro-Raman spectroscopy and X-ray photoelectron spectroscopy. The level of corrosion protection of formed coatings as well as the effect of loaded inhibitors on the anticorrosion efficiency was evaluated using electrochemical impedance spectroscopy (EIS) and localized scanning techniques (SVET/SIET). The coating impregnation with corrosion inhibitors of the azole group significantly improves the corrosion characteristics of the material. Impregnation of the base PEO-layer with 1,2,4-triazole during 24 h results in a 36 times increase in the impedance modulus measured at the lowest frequency (|Z|_f=0.1Hz). Additional sealing of impregnated coating with polymer improves the corrosion stability of the treated material. On the base of the obtained data, the optimal way of protective inhibitor- and polymer-containing formation using surface treatment was suggested. The best barrier properties were established for hybrid coatings obtained by the immersion of a PEO-coated sample in 1,2,4-triazole solution for 24 h and following spraying the PVDF solution. The value of |Z|_f=0.1Hz for this protective layer increased by more than two orders of magnitude in comparison with the base PEO-layer. The three-stage mechanism of corrosion inhibition of the sample with smart inhibitor-containing coating was established.

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys-A Review: Part III-Corrosion Inhibitors and Combining Them with Other Protection Strategies

Owing to the unique active corrosion protection characteristic of hexavalent chromium-based systems, they have been projected to be highly effective solutions against the corrosion of many engineering metals. However, hexavalent chromium, rendered a highly toxic and carcinogenic substance, is being phased out of industrial applications. Thus, over the past few years, extensive and concerted efforts have been made to develop environmentally friendly alternative technologies with comparable or better corrosion protection performance to that of hexavalent chromium-based technologies. The introduction of corrosion inhibitors to a coating system on magnesium surface is a cost-effective approach not only for improving the overall corrosion protection performance, but also for imparting active inhibition during the service life of the magnesium part. Therefore, in an attempt to resemble the unique active corrosion protection characteristic of the hexavalent chromium-based systems, the incorporation of inhibitors to barrier coatings on magnesium alloys has been extensively investigated. In Part III of the Review, several types of corrosion inhibitors for magnesium and its alloys are reviewed. A discussion of the state-of-the-art inhibitor systems, such as iron-binding inhibitors and inhibitor mixtures, is presented, and perspective directions of research are outlined, including in silico or computational screening of corrosion inhibitors. Finally, the combination of corrosion inhibitors with other corrosion protection strategies is reviewed. Several reported highly protective coatings with active inhibition capabilities stemming from the on-demand activation of incorporated inhibitors can be considered a promising replacement for hexavalent chromium-based technologies, as long as their deployment is adequately addressed.

Assessing p-tolyloxy-1,3,4-oxadiazole acetamides as lipoxygenase inhibitors assisted by in vitro and in silico studies

The underlying correlation between the inflammation, innate immunity and cancer is extensively familiar and linked through a process mediated by three enzymes; cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (CYP₄₅₀). The ever increase in the reported side effects of the antiinflammatory drugs against the targeted enzymes and the resistance developed afterwards compels the researchers to synthesize new effective molecules with safer profile. On the basis of these facts, our ongoing research on 1,3,4-oxadiazole derivatives deals with the synthesis of a new series of N-alkyl/aralky/aryl derivatives of 5-((p-tolyloxymethyl)-4H-1,3,4-oxadiazole-2-ylthio)acetamide (6a-o) which were developed by the sequential conversion of p-tolyloxyacetic acid (a) into ester (1) hydrazide (2) and 5-(p-tolyloxymethyl)-4H-1,3,4-oxadiazole-2-thiol (3). The designed compounds (6a-o) were acquired by the reaction of 1,3,4-oxadiazole (3) with numerous electrophiles (5a-o) in KOH. The synthesized analogues (6a-o) were characterized by FTIR, ¹H-, ¹³C NMR spectroscopy, EI-MS and HR-EI-MS spectrometry, and were further assessed for their inhibitory potential against the soybean 15-LOX enzyme. The results showed excellent inhibitory potential of the compounds against the said enzyme, specifically 6o, 6b, 6n and 6e with inhibitory values (IC₅₀ ± SEM) of 21.5 ± 0.76, 24.3 ± 0.45, 29.1 ± 0.65 and 31.3 ± 0.78 µM, respectively. These compounds displayed < 55 % blood mononuclear cells (MNCs) cellular viability as measured by MTT assay at 0.25 mM concentration. Other compounds demonstrated moderate inhibitory activities with IC₅₀ values in the range of 33.2 ± 0.78 to 96.3 ± 0.73 µM and exhibited little cellular viability against MNCs except 6i, 6j, 6 m and 6 k that showed 61-79 % cellular viability. It was observed that most of the compounds (6o, 6b, 6n, 6e) were found more toxic towards MNCs at studied concentration of 0.25 mM. SAR studies revealed that the positions and nature of substituents accompanying phenyl ring have great influence on 15-LOX inhibitory activity. In the most active compound 6o, the amino acids Asp768 and Val126 were involved in hydrogen bonding, Thr529 was linked with π-anion interaction and π-sulphur interaction was displayed with Tyr525 and two π-alkyl interactions were formed with the benzene ring and amino acid residues Pro530 and Arg533. The in silico pharmacokinetics profiles and density functional theory calculations of the compounds further supported the in vitro findings. Further work on the synthesis of more oxadiazole derivatives is in progress in search for potential 'leads' for the drug discovery as LOX inhibitors.

Efficient Synthesis of 6,7-Dihydro-5H-cyclopenta[b]pyridine-3-carbonitrile Compounds and Their Applicability As Inhibitor Films for Steel Alloy Corrosion: Collective Computational and Practical Approaches

An effective method for designing new heterocyclic compounds of 6,7-dihydro-5H-cyclopenta[b]pyridine-3-carbonitrile derivatives (CAPDs) was presented through cyclocondensation reaction between 2,5-diarylidenecyclopentanone derivatives and propanedinitrile, and the cyclocondensation reaction succeeded using a sodium alkoxide solution (sodium ethoxide or sodium methoxide) as the reagent and the catalyst. The synthesized CAPD derivatives were employed as novel inhibitors for carbon steel (CS) corrosion in a molar H2SO4 medium. The corrosion protection proficiency was investigated by electrochemical measurements (open circuit potential vs time (E OCP vs t), potentiodynamic polarization plots (PDP), and electrochemical impedance spectroscopy (EIS)) and surface morphology (scanning electron microscopy (SEM)) examinations. The results show that the CAPD derivatives exhibit mixed type inhibitors and a superior inhibition efficiency of 97.7% in the presence of 1.0 mM CAPD-1. The adsorption of CAPD derivatives on the CS interface follows the Langmuir isotherm model, including physisorption and chemisorption. Scanning electron microscopy (SEM) exploration confirmed the adsorption of the CAPD derivatives on the CS substrate. Monte Carlo (MC) simulations and DFT calculations revealed that the efficacy of the CAPD molecules correlates well with their structures, and this protection was attributed to their adsorption on the CS surface.

One-Pot Hydrothermal Synthesized Nitrogen and Sulfur Codoped Carbon Dots for Acid Corrosion Inhibition of Q235 Steel

N and S codoped carbon dots having good water solubility have been successfully made by a novel hydrothermal method and characterized by FTIR, XPS, and TEM. The as-synthesized CDs were carbon particles rich in polar functional groups less than 10 nm in size. Electrochemical measurements, gravimetry, and surface analysis methods were utilized to examine the inhibition characteristics and adsorption mechanism of CDs on the carbon steel in acid pickling solutions. Electrochemical measurements verified that the CDs displayed adequate protection with high inhibition efficiency of 97.8%. The long-term weight-loss experiments up to 72 h further confirmed the excellent corrosion inhibition at room temperature and 313 K. The results presented are helpful for the formulation of more effective acid pickling corrosion inhibitors.

Mutual-activation between Zero-Valent iron and graphitic carbon for Cr(VI) Removal: Mechanism and inhibition of inherent Side-reaction

The low reactivity of zero-valent iron (ZVI) usually limits its application for pollutant remediation. Therefore, a microscopic galvanic cell (mGC) with short-circuited cathode and anode was synthesized to intensify its galvanic corrosion. The prepared mGC exhibited 7.14 times higher Fe(II) release performance than ordinary nanoscale-ZVI (nZVI), rendering efficient Cr(VI) removal performance. Density functional theory (DFT) revealed mutual-activation of the cathode and anode due to close proximity, dramatically enhancing the galvanic corrosion of Fe(0) in mGC. The corrosion potential of mGC was measured as -0.77 V, which was 100 mV more negative than nZVI. The released electrons and surface-bond Fe(II) from anode in mGC was proved to be the dominant reductive species. More importantly, Cr(VI) reduction was slightly inhibited by hydroxyl radicals generated by a series of inherent side-reactions in the system, which could be well eliminated by low concentrations of 4-acetamido phenol. This study provides a promising strategy for ZVI activation, and sheds light on its environmental applications.