Eco-friendly anti-corrosion performance of chitosan modified with fused heterocyclic compound on mild steel in acidic medium

This study aims to explore the prevention of chitosan modified with a fused heterocyclic compound as a sustainable corrosion inhibitor for mild steel in 1 M HCl. Electrochemical instruments, including potentiodynamic polarization techniques, and electrochemical impedance spectroscopy (EIS), were employed to evaluate the corrosion protection performance. The outcomes showed that the chitosan modified with a fused heterocyclic compound has outstanding inhibition performance, with an inhibition effectiveness of 98.25 % at 100 ppm. The anti-corrosion features of modified chitosan were ascribed to the presence of hetero atoms in modified chitosan composite which leads to the creation of a protective layer, The modified chitosan composite behaved as mixed-typed inhibitors, as shown by the PDP results. The modified chitosan composite adsorbs on mild steel in the investigated corrosive media via chemisorption interactions, and its adsorption followed the Langmuir adsorption model. Furthermore, increasing the temperature from 303 to 333 K enhanced the corrosion rate, most likely due to the desorption of the inhibitor agent from the steel surface.

Stepwise versus Concerted: Theoretical Insights into the Stereoselectivity in Aryl Imine Formation Assisted by Acid and Water

The wide applications of the aryl Schiff base require extensive understanding of the mechanism of its formation, which remains unclear. In this work, the detailed formation mechanisms between benzaldehyde and aniline or 4-(9-anthryl) ethynyl aniline were investigated at the CCSD(T)//B3LYP level, and the influence of water molecules and acid catalysis and the stereoselectivity were addressed. The results show that the participation of explicit water molecules greatly accelerates the reactions by alleviating the ring tension of the transition states, and acid catalysis strongly favors the imine formation and provides driving force for the forward reaction. In acidic conditions, both N-protonated carbinolamine formations and imine formations are achieved under mild conditions with the assistance of water molecules, and the proton transfer is more advanced than the C-N and C═N bond formation, which is in good agreement with the experimental observations. In contrast, under neutral conditions, even with the assistance of two water molecules, the reaction is hard to take place at room temperature owing to the high Gibbs free energy barriers with the proton transfer and the C-N or C═N bond formation concerted. The analysis of stereoselectivity shows that the formation of trans imine is both kinetically and thermodynamically more favorable than the cis one under the acidic condition with the assistance of water molecules, and the presence of conjugated substituent 4-(9-anthryl) ethynyl of aniline marginally raises the energy barriers. This work provides a systematic view of the mechanism for the formation of aryl imine and is expected to offer insights for the control of the dynamic covalent chemistry and the synthesis of covalent organic frameworks.

Interfacial Adsorption and Corrosion Inhibition Behavior of Environmentally Friendly Imidazole Derivatives for Copper in the Marine Environment

Copper and copper alloys are commonly used in industry due to their excellent mechanical properties, making research on the corrosion resistance of copper of great significance. The corrosion inhibition properties of 2-imidazolidinone and allantoin for copper in 3.5 wt % NaCl were studied by weight loss and electrochemical tests. Changes in the density of the copper corrosion current and the impedance module indicated that 2-imidazolidinone and allantoin exhibited cathodic corrosion inhibitors and a valid protective effect. Meanwhile, the weight loss tests showed that the inhibition efficiency of 2-imidazolidinone and allantoin at 3 mM reached 98.94% and 97.82%, respectively. The surface physiochemical properties were qualitatively and quantitatively studied by using SEM-EDS, XPS, white light interferometry, and contact angle analysis. The interfacial adsorption behavior revealed by QCM, synchrotron radiation micro-infrared, and adsorption isotherm analysis indicated that both imidazole derivatives formed an effective and rigid physical adsorption film and obeyed the Langmuir adsorption model on copper, while both the mass and thickness of the adsorption film formed by 2-imidazolidinone were higher than those of allantoin. This study contributed to an in-depth understanding of the interfacial adsorption behavior and corrosion inhibition ability of 2-imidazolidinone and allantoin and provided guidelines for the design and development of novel heterocycles as potential corrosion inhibitors for copper in marine environments. In particular, copper was used as a corrosion inhibitor in seawater storage and transport equipment.

Evaluation of synthesized biosurfactants as promising corrosion inhibitors and alternative antibacterial and antidermatophytes agents

This study investigated different amino acid-based surfactants (AASs), also known as biosurfactants, including sodium N-dodecyl asparagine (AS), sodium N-dodecyl tryptophan (TS), and sodium N-dodecyl histidine (HS) for their potential anticorrosion, antibacterial, and antidermatophyte properties. The chemical and electrochemical techniques were employed to examine the copper corrosion inhibition efficacy in H₂SO₄ (1.0 M) solution at 298 K. The results indicated their promising corrosion inhibition efficiencies (% IEs), which varied with the biosurfactant structures and concentrations, and the concentrations of corrosive medium. Higher % IEs values were attributed to the surfactant adsorption on the copper surface and the production of a protective film. The adsorption was in agreement with Langmuir adsorption isotherm. The kinetics and mechanisms of copper corrosion and its inhibition by the examined AASs were illuminated. The surfactants behaved as mixed-kind inhibitors with minor anodic priority. The values of % IEs gained from weight loss technique at a 500 ppm of the tested surfactants were set to be 81, 83 and 88 for AS, HS and TS, respectively. The values of % IEs acquired from all the applied techniques were almost consistent which were increased in the order: TS > HS ≥ AS, establishing the validity of this study. These surfactants also exhibited strong broad-spectrum activities against pathogenic Gram-negative and Gram-positive bacteria and dermatophytes. HS exhibited the highest antimicrobial activity followed by TS, and AS. The sensitivity of pathogenic bacteria varied against tested AASs. Shigella dysenteriae and Trichophyton mantigrophytes were found to be the most sensitive pathogens. HS exhibited the highest antibacterial activity against Shigella dysenteriae, Bacillus cereus, E. coli, K. pneumoniae, and S. aureus through the formation of clear zones of 70, 50, 40, 39, and 35 mm diameters, respectively. AASs also exhibited strong antifungal activity against all the tested dermatophyte molds and fungi. HS caused the inhibition zones of 62, 57, 56, 48, and 36 mm diameters against Trichophyton mantigrophytes, Trichophyton rubrum, Candida albicans, Trichosporon cataneum, and Cryptococcus neoformans, respectively. AASs minimal lethal concentrations ranged between 16 to 128 µg/ml. HS presented the lowest value (16 µg/ml) against tested pathogens followed by TS (64 µg/ml), and AS (128 µg/ml). Therefore, AASs, especially HS, could serve as an effective alternative antimicrobial agent against food-borne pathogenic bacteria and skin infections-associated dermatophyte fungi.

Ionic liquid as an effective green inhibitor for acid corrosion of aluminum composite: experimental and theoretical considerations

Results of anticorrosive performance of ionic liquid 1-methyl-1-propyl-piperidinium bromide (MPPB) on corrosion of 6061Al-10vol% SiC composite (Al-MMC) in 0.05 M HCl solution. Electrochemical techniques were adopted to study corrosion and corrosion inhibition rates. Experiments were conducted in the temperature range of 308–323 K by varying concentrations of MPPB. Conditions were standardized to accomplish maximum inhibition efficiency. Kinetic parameters were evaluated. Results were fitted into various adsorption isotherm models and they fitted best into the Langmuir adsorption isotherm. Using data from adsorption isotherms, thermodynamic parameters were calculated. The surface morphology was examined by energy-dispersive X-ray spectroscopy (EDAX), atomic force microscope (AFM), and scanning electron microscope (SEM). FTIR–spectra and X-ray diffraction (XRD) studies were performed to reaffirm the adsorption of MPPB. Adsorption of the inhibitor and mechanistic aspects of corrosion inhibition were supported and supplemented by quantum chemical calculations using density functional theory (DFT). The investigation revealed that percentage inhibition efficiency (% IE) improved with the increase in the concentration of MPPB, while it decreased with a rise in temperature. Maximum efficiency of 60% was observed with 400 ppm MPPB at 308 K. MPPB acted as a mixed inhibitor, obeyed the Langmuir adsorption model, and the mode of adsorption was physisorption. Quantum chemical calculations validated the results of the adsorption study.

Graphical abstract

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.

Experimental and theoretical insights into copper corrosion inhibition by protonated amino-acids

The effects of cysteine (Cys) and l-methionine (l-Met) on copper corrosion inhibition were examined in 1 M HNO₃ solution for short and long exposure times. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were used. The EIS determined the potential for zero charges of copper (PZC) in the inhibitor solution. SEM and AFM have been used to study material surfaces. Energy-dispersive X-ray spectroscopy (EDS) was used to identify surface elemental composition. DFT and molecular dynamics simulations explored the interaction between protonated amino acids and aggressive media anions on a copper (111) surface.

The effects of cysteine (Cys) and l-methionine (l-Met) on copper corrosion inhibition were examined in 1 M HNO₃ solution for short and long exposure times.

Inhibition Evaluation of Chromotrope Dyes for the Corrosion of Mild Steel in an Acidic Environment: Thermodynamic and Kinetic Aspects

In this report, two chromotrope dyes, chromotropic acid (CA) and chromotrope 2R (CR), were explored as inhibitors against mild steel corrosion in 1.0 M sulfuric acid solutions at 303 K. Electrochemical, spectroscopic, chemical, and microscopic techniques, namely, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy, mass loss, and scanning electron microscopy (SEM), have been employed to evaluate the inhibition efficiencies (%IEs) of the examined organic dyes. The %IEs were found to increase with the inhibitors' concentrations, while they decreased with rising temperature. The outcomes of the PDP technique displayed that the examined inhibitors operated as mixed-type inhibitors with anodic prevalence. The impedance spectra described by Nyquist and Bode graphs in the corrosive environment and in the presence of various concentrations of the examined inhibitors showed single depressed capacitive loops and one-time constants. This behavior signified that the mild steel corrosion was managed by the charge transfer process. The SEM micrographs of the surfaces of mild steel samples after adding the examined inhibitors revealed a wide coverage of these compounds on the steel surfaces. Thus, the acquired high %IEs of the examined inhibitors were interpreted by strong adsorption of the organic molecules on the mild steel surface. This constructed a shielding layer separating the alloy surface from the corrosive medium, and such adsorption was found to follow the Langmuir isotherm. Furthermore, the evaluated thermodynamic and kinetic parameters supported that the nature of such adsorption was mainly physical. Results obtained from all employed techniques were consistent with each other and revealed that the %IE of the CR inhibitor was slightly higher than that of CA under similar circumstances. Finally, the mechanisms of both corrosion of mild steel in sulfuric acid solutions and its inhibition by the tested organic dyes were also discussed.

Cubic Liquid Crystals of Polyoxometalate-Based Ionic Liquids

Thermotropic ionic liquid crystals of polyoxometalate (POM)-based ionic liquids (POM-based ILs), which are formed by a POM, K₇PW₁₁O₃₉, and cationic surfactants, tetra-n-alkylammonium bromide ((C_nH_2n+1)₄N⁺Br^-, n = 6 and 7), are first proposed. As a model system, the cubic phase structure of a POM-based IL, {(C₇H₁₅)₄N⁺}₇PW₁₁O₃₉, was determined to form in a wide range of temperatures, exhibiting good thermostability, excellent mechanical strength, and high viscosity. Furthermore, the lyotropic ionic liquid crystals formed by {(C₇H₁₅)₄N⁺}₇PW₁₁O₃₉ in solvents such as chloroform or toluene still maintained a cubic structure. These cubic ionic liquid crystals (CILCs) were used as anticorrosion coatings both in acidic and neutral environments. The electrochemical measurements of Cu and Fe surfaces coated by CILCs showed an excellent ability of anticorrosion, indicating that the metals can be perfectly protected by the CILC coatings with high resistance and low capacitance. We assume that the CILCs may serve as barriers to stop oxygen diffusing to metals and interrupt the electron tunnels between the metal surfaces and the electrolyte solutions. Such environmentally friendly CILCs of POMs-based ILs are convenient for coating and removal, being vital to versatile industrial and academic applications.

Electrochemical Investigation of Tetrazolium Violet as a Novel Copper Corrosion Inhibitor in an Acid Environment

Tetrazolium violet (TZV) is an important pharmaceutical intermediate for the preparation of various medicines, taking into account microbiological studies and TZV as a new inhibitor of heterocyclic compound. The corrosion inhibiting action of TZV for copper in 0.5 M H₂SO₄ solutions was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy. The corroded copper surfaces were evaluated by scanning electron microscopy. Thereafter, the thermodynamics of TZV adsorption onto copper was computed and evaluated. As a result, the target TZV compound shows great corrosion inhibition performance to protect copper in sulfuric acid. Thermodynamic test results reveal that the Langmuir, Dhar-Flory-Huggins, and Bockris-Swinkels isotherm models provide a better description for the adsorption process of TZV on the metal surface. The calculated values of ΔG _ads ⁰ indicate a spontaneous adsorption process of TZV on the copper surface accompanied by two kinds of interactions, physical adsorption and chemisorption.

Water Pipes Corrosion Inhibitors for Q235 Steel in Hydrochloric Acid Medium Using Spiropyrazoles Derivatives

Water pipes and drinking water quality deterioration in distribution systems and sea water desalination impose the use of corrosion inhibitors. The protective effect of spiropyrazole derivatives against Q235 steel and its adsorption performance were examined in solution of 1 M HCl utilizing TP (Tafel polarization), electrochemical frequency modulation (EFM), and electrochemical impedance spectroscopy (EIS) tests. The outcome data from hindrance efficiency rise with the dose of inhibitor. The orders of %IE of spiropyrazole derivatives are given: (1) > (2) > (3).It was noted that the values of EHOMO and ELUMO dropping in order run parallel to the improvement in %IE, which support the preceding order. EIS spectra exhibited one capacitive loop and approve the protective ability. Molecular docking was utilized to get a full picture on the binding mode among spiropyrazoles derivatives and the receptor of 3tt8-hormone of crystal structure examination of Cu human insulin derivative. The morphology of protected Q235 steel was evaluated by checking electron magnifying instrument innovation with energy dispersive X-beam spectroscopy (SEM–EDX).

Microstructural and Corrosion Characteristics of Al-Fe Alloys Produced by High-Frequency Induction-Sintering Process

Al-x wt.% Fe bulk alloys were fabricated from a powder mixture of pure Al and x wt.% of Fe, where x = 2 wt.%, 5 wt.% and 10 wt.%. Initially, as-mixed mixtures were processed using a mechanical-alloying (MA) technique in an attritor for 4 h. The milling was performed in an argon atmosphere at room temperature followed by the sintering of the milled powders in a high-frequency induction furnace to produce bulk samples. Scanning electron microscopy (SEM) was used to study the morphology of the produced alloys, and X-ray diffraction (XRD) to determine the phases formed after the sintering process and their crystallite size. The corrosion behavior of the fabricated samples was studied by immerging them in a 3.5% sodium chloride (NaCl) solution at room temperature using cyclic-polarization (CP) and electrochemical-impedance-spectroscopy (EIS) techniques. The SEM results showed that Fe was uniformly distributed in the Al matrix, and XRD revealed the formation of Al and intermetallic, i.e., Al6Fe and Al13Fe4, phases in the Al-Fe alloys after sintering. The hardness of the Al-Fe alloys was increased with the addition of Fe due to the formation of intermetallic compounds. Electrochemical results showed that there was a proportional relationship between the percentage of Fe additives and corrosion potential (Ecorr) where it shifted toward a nobler direction, while corrosion current density (icorr) and corrosion rate decreased with an increasing Fe%. This observation indicates that the addition of Fe into an Al matrix leads to an improvement in the corrosion resistance of the alloys.

Corrosion Protection of N80 Steel in Hydrochloric Acid Medium Using Mixed C15H15NO and Na2WO4 Inhibitors

A novel inhibitor based on mixed Mannich base (C15H15NO) and Na2WO4 was developed for the corrosion prevention of N80 steel in hydrochloric acid solution. Infra-red spectrum, electrochemical measurements, X-ray Photoelectron Spectroscopy, and Scanning Electron Microscopy were used to understand the inhibition efficiency and mechanism. The results showed that the mixed inhibitors reduced the corrosion current density and increased the interface resistance. The inhibition efficiency is the highest when the ratio of C15H15NO to Na2WO4 is 1:1 in the mixture. Observed from the surfaces, the number of pits and small cracks was reduced on the surface in the presence of the optimized inhibitors. The inhibition film can successfully hinder the chloride ions from reaching the bulk steel.

Corrosion inhibition of copper in aqueous chloride solution by 1H-1,2,3-triazole and 1,2,4-triazole and their combinations: electrochemical, Raman and theoretical studies

Triazoles are well-known organic corrosion inhibitors of copper. 1H-1,2,3-Triazole and 1,2,4-triazole, two very simple molecules with the only difference being the positions of the nitrogen atoms in the triazole ring, were studied in this work as corrosion inhibitors of copper in 50 mM NaCl solution using a set of electrochemical and analytical techniques. The results of electrochemical tests indicate that 1H-1,2,3-triazole exhibited superior inhibitor properties but could not suppress anodic copper dissolution at moderate anodic potentials (>+300 mV SCE), while 1,2,4-triazole, although it exhibited higher anodic currents, suppressed anodic copper dissolution at very anodic potentials. Density functional theory calculations were also performed to interpret the measured data and trends observed in the electrochemical studies. The computational studies considered either the inhibitors isolated in the gaseous phase or adsorbed onto Cu(111) surface models. From the calculations, the mechanisms of the inhibitive effects of both triazoles were established and plausible mechanisms of formation of the protective films on the Cu surface were proposed. The results of this study hold positive implications for research in the areas of catalysis, and copper content control in water purification systems.

Linkage, charge state and layer of L-Cysteine on copper surfaces

The control of linkage and charge state between biomolecules and metals represents a key issue for the architect of bioactive systems. In this paper, the linkage, charge state and layer of L-Cysteine (L-Cys) self-assembled films were handled on copper surfaces at pH=6.86. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed to measure the film quality and the details of self-assembled progress. X-ray photoelectron spectroscopy (XPS) and quantum chemical calculations of density functional theory (DFT) were used to characterize the linkage, charge state and layer of the L-Cys molecules on copper surfaces. The results indicate that, from 0s to 24h, the self-assembled process can be classified as three steps, fast adsorption at the beginning, and then rearrangement to form a monolayer, and then the formation of double layer. And L-Cys molecules link to the copper surface through CuS bond, not CuN bond. The thickness of monolayer is 10.5Å. Then the L-Cys molecules of second layer recline on the first layer. Finally, by the interaction of amine group and carboxylic acid group between the two layers, the second self-assembled film stands uprightly, and the -S^- group of the second layer point outward. The thickness of the double layer is 19.7Å. All the Cu/L-Cys films have negative charges because the pH (6.86) of the self-assembled solution is more than the isoelectric point of the L-Cys (5.05).