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Article

Structure–Activity Relationship of Ionic Liquids for Acid Corrosion Inhibition

1
Systems Engineering, Modeling and Analysis Laboratory (LIMAS), Faculty of Sciences Dhar El Mahraz, Sidi Mohamed Ben Abdellah University, BP 1796 Atlas, Fez 30000, Morocco
2
Department of Chemistry, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), P.O. Box 90950, Riyadh 11623, Saudi Arabia
3
Department of Biology, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 11623, Saudi Arabia
4
Laboratory of Electrochemistry and Corrosion, Engineering Polytechnic School, Euromed University of Fes (UEMF), Fes 30030, Morocco
5
Engineering Laboratory of Organometallic, Molecular Materials and Environment (LIMOME), Faculty of Sciences Dhar El Mahraz, Sidi Mohamed Ben Abdellah University, BP 1796 Atlas, Fez 30000, Morocco
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2025, 26(12), 5750; https://doi.org/10.3390/ijms26125750
Submission received: 5 May 2025 / Revised: 7 June 2025 / Accepted: 10 June 2025 / Published: 16 June 2025

Abstract

Novel derivatives of imidazolium-based ionic liquids with varying alkyl chains, IL-1, IL-2, and IL-3, were evaluated as corrosion inhibitors for mild steel in 1 M HCl solution. The experimental investigations used Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques. The results demonstrated exceptional corrosion inhibition efficiency (>90%), as classified by electrochemical analyses, which identified these corrosion inhibitor compounds as mixed-type. The ionic liquids’ adsorption complied with the Langmuir adsorption isotherm. The characterization of the surface via SEM and EDX confirmed the development of a protective adsorbed inhibitor layer on the steel substrate. Furthermore, the theoretical DFT method (at B3LYP/6-311G (d, p)) was conducted to describe the electronic properties and reactivity of the molecules. The Monte Carlo simulation on the surface of Fe(1 1 0) was assessed to provide in-depth understanding of the adsorption mechanisms and interactions responsible for the corrosion inhibition between the molecules and the surface of the mild steel.

1. Introduction

Mild steel (MS) has been extensively used as the main material for pipework in various industrial fields. It is commonly used in applications such as pipes, flow lines, and transport or distribution pipelines in the oil and gas industries. The corrosion of metals is an important economic and safety challenge for various industries, specifically in the fields of construction and oil refining. Acidification is a crucial technique in these industries to promote well formation and improve oil production. However, this process endangers the durability of steel equipment due to acid-induced corrosion [1,2,3,4,5]. The use of corrosion inhibitors is a common practice to protect reactive metal surfaces from degradation in various media. This method remains one of the easiest and most cost-effective methods to reduce the corrosion rate. Organic compounds rich in sulfur, oxygen, and nitrogen, especially those with π-electronic systems, are frequently recognized as effective inhibitors. Numerous studies have shown their ability to provide remarkable inhibitory efficacy [2,5,6,7,8,9,10]. Generally, the inhibitory molecules attach to the metal surface through a chemical or physical adsorption mechanism, which facilitates the creation of a protective film [11,12]. Due to stringent environmental regulations, the adoption of green corrosion inhibitors is strongly encouraged. The development of safe and eco-friendly corrosion inhibitors is actively pursued. Consequently, ionic liquids (ILs) have attracted significant interest from academic researchers and engineers for their crucial, eco-friendly, and cost-effective nature. The physical and chemical properties of ionic liquids are the primary factors in their applications across various fields, including corrosion inhibition. Recently, attention has been directed toward imidazolium ILs, a diverse class of heterocyclic compounds containing nitrogen in their structures, renowned for their ability to form cationic molten salts. The biodegradability, non-toxicity, cost-effectiveness, safety, and high solubility in water render imidazolium-based ILs an ecological and sustainable alternative for numerous industrial applications [13,14,15,16,17].
Quantum chemistry techniques have proven to be very effective in the determination of molecular structures and the analysis of electronic properties. This method allowed for the determination of essential electronic parameters of the molecules. The relationship between the inhibitory effect and the molecular structure of the studied compounds was confirmed. The mechanisms of inhibition specific to organic inhibitors can be elucidated accurately through theoretical modeling approaches. Molecular dynamics (MD) and Monte Carlo (MC) simulations can provide insights into the design of inhibitory systems with optimal properties and elucidate the adsorption mechanism [12,18,19]. This study is focused on investigating the corrosion inhibition efficiency and properties of three imidazolium-based ionic liquids, namely, 3-(2-chlorobenzoyl)-1-phenethyl-1H-imidazol-3-ium chloride(IL-1), 3-(4-chlorobenzoyl)-1-phenethyl-1H-imidazol-3-ium chloride(IL-2), and 3-(4-fluorobenzyl)-1-phenethyl-1H-imidazol-3-ium chloride(IL-3), using electrochemical tests on mild steel in hydrochloric acid medium, as well as surface analysis and quantum chemical calculations DFT and MC.

2. Results

2.1. Electrochemical Impedance Spectroscopy (EIS)

In the absence of the three inhibitors studied by EIS, the corrosion behavior of mild steel in 1 M of HCl solution was observed. Figure 1 shows the Nyquist plots of the mild steel without and with the addition of the inhibitors at different concentrations of the new ionic liquids studied at 298 K. The Bode plots of the mild steel are also shown in Figure 2. In the medium frequency range, a single-phase peak is detected in the Bode plots [20].
The resulting graphic representation of the Nyquist graph shows a depressed capacitive half-loop, indicating charge-transfer-controlled corrosion. The capacitive loop has increased due to the roughness and disorganization of the active sites on the mild steel surface [21,22]. To model the EIS results, a circuit similar to Randles’ was utilized. As depicted in Figure 3, the equation was used to calculate the CPE value. The circuit used to fit the experimental data includes the constant phase element (CPE), charge transfer resistance (Rct), and solution resistance (Rs).
ZCPE = [Q(jω)n]−1
Q represents the CPE magnitude, ω represents the angular frequency, and i2 = −1 is a non-existent number.
Table 1 shows the corrosion kinetic parameters, Cdl, Rct, and Q. The load transfer resistance values increase with the rising concentration of the synthesized products. In contrast, the Cdl values decrease as the concentration increases, which promotes the formation of adsorbed films on the mild steel [23,24] and the replacement of water at the mild steel/solution interface. This leads to a decrease in the thickness of the double electrical layer, in addition to a reduction in the dielectric constant [25,26]. The inhibition efficiency follows the order IL-2 (96.9) > IL-1 (96.6) > IL-3 (94.6) at 10−3 M. IL-2 is the most effective inhibitor due to its higher adsorption capacity.

2.2. Adsorption Isotherm Study

The efficiency and adsorption capacity of the molecule determine the degree of adsorption of the corrosion inhibitor on the metal surface. Understanding the adsorption mechanism between the studied molecules and the metal is of paramount importance when considering the adsorption process. The adsorption behavior of the imidazolium-derived ILs can be explained by the Langmuir adsorption isotherm and can be described as follows [20]:
K C i n h = θ 1 θ C i n h θ   v s   C i n h
Surface coverage is represented by θ, Cinh is the concentration of the synthesized ILs (M), and K is the adsorption equilibrium constant (L mol−1). The plots in Figure 4 show the relationship between Cinh and Cinh/θ. In addition, the equation used to calculate ΔGads was based on the expression of the standard Gibbs’ free energy of adsorption [27], expressed as
ΔGads = RTLn (55.5 K)
The solution contains 55.5 moles of H2O, and R is 8.314 J mol−1 K−1, while T is the absolute temperature.
Table 2 clearly shows the values of (R2), the linear correlation coefficients, and the slopes, confirming the Langmuir adsorption model. Thus, these results suggest that the best linear fit for the EIS data is the Langmuir model.
According to studies in the literature, adsorption between the charged inhibitor and the metal is detected when the ΔGads value is under or equal to −20 KJ mol−1. When the ΔGads value is equal to −40 KJ mol−1 or more, chemisorption may be present. The ΔGads values are close to −40 KJ mol−1 in our case [27,28]. The results obtained demonstrate that the adsorption of the ILs examined is principally chemisorption. They are adsorbed and form strong bonds on the surface of the steel.

2.3. Effect of Immersion Time on the ILs Inhibition Efficiency

Several immersion times were used to examine the development in inhibition efficiency of all the ionic liquid compounds examined on mild steel surface corrosion in 1 M of HCl at 298 K. Figure 5 presents the Nyquist curves for MS in a 1 M solution of hydrochloric acid (HCl) without (white) and with 10−3 M of ILs during various immersion phases lasting up to 12 h. In addition, Table 3 summarizes the EIS parameters from the Nyquist diagrams. When not all the compounds examined are present, the diameter of the semicircle reduces over time. This reduction in charge transfer resistance is associated with a rise in the double-layer capacitance, which could be due to the accumulation of free metal ions in the diffuse double layer. However, with the existence of ILs, the Rct values decrease over time, while the Cdl values increase. We can explain this by the weak permeability of the inhibitor film based on the ionic liquids on the surface of the MS samples. In addition, Table 3 demonstrates that the inhibition efficiency values remained almost unchanged. The value of inhibition efficiency in a half hour of immersion time (Table 3) is smaller or a slightly lower than the value after immersion, confirming the stability of the adsorbed inhibitor film formed by the ionic liquids in an acidic solution of HCl with passing time [20].

2.4. Potentiodynamic Polarization (PDP) Measurements

The values of the parameters current density (icorr), corrosion potential (Ecorr), and the anode and cathode (βa and βc) Tafel slopes were determined from the anodic and cathodic regions of the Tafel curves. To calculate the corrosion current densities (icorr), the linear segments of the anode and cathode curves were extrapolated to the corrosion potential. The inhibition efficiency was assessed based on the measured values of icorr using the following relationship.
E I P D P = i c o r r 0 i c o r r i c o r r 0
where i c o r r 0 and icorr are the corrosion current density in the absence of ILs and the presence of ILs.
Figure 6 shows the potentiodynamic polarization curves of the metal (MS) in 1 M of HCl, without and with the inhibitors, the ionic liquids, studied at various concentrations. The results in Figure 6 and Table 4 show that the introduction of the imidazolium-based ionic liquid inhibitors into the aggressive acidic medium leads to a simultaneous reduction in the anodic and cathodic current density, with a more pronounced effect as the concentration of inhibitors increases. This suggests that these ionic liquids influence the anodic dissolution of MS steel as well as the cathodic reduction hydrogen evolution mechanism [29,30], while not significantly altering the shape of the Tafel curves. The observed potential shift is attributed to the existence of a corrosion film formed on the surface of the sample. The linear segments of the Tafel curves in the cathodic and anodic regions were extrapolated to the corrosion potential (Ecorr) to determine the corresponding corrosion current densities.
According to Table 4, when the compounds are added, the icorr values decrease. This means that increasing the concentration of ILs decreases the icorr values. Also, the results indicate that the maximal values of η% for IL-1, IL-2, and IL-3 are 96.8%, 96.6%, and 95.5%, respectively, at 10−3 M. The values of η% demonstrate that IL-1 is the most effective corrosion inhibitor for MS in 1 M HCl solution. The change in corrosion potential (Ecorr) of a cathodic or anodic inhibitor must be greater than 85 mV from the uninhibited system. In contrast, this change is generally less than 85 mV in the case of a mixed inhibitor. The displacement measured in this research was lower than 85 mV, which indicates that they function as inhibitors of both types [16,23].

2.5. Effect of Temperature

The potentiodynamic polarization (PDP) method was employed to evaluate the effect of temperature on the corrosion behavior of mild steel (MS) in a 1 M HCl solution, in the absence and presence of 10−3 M of inhibitor, across a temperature range of 298 K to 328 K. Table 5 and Figure 7 present the electrochemical parameters and PDP plots of the mild steel (MS) in the presence of the ionic liquid inhibitors. Based on the results, we conclude that increasing temperature leads to a decrease in EPDP, while icorr increases with increasing temperature due to the acceleration of the electrochemical reactions and the formation of stronger chemical bonds via adsorption [20]. As the temperature rises, the inhibitor adsorption equilibrium shifts to the desorption process, resulting in decreased surface coverage and a decrease in protection against corrosion diffusion on the surface.
The evaluation of multiple thermodynamic activation parameters was based on the Arrhenius equations and their modified versions. Specifically, the activation energy (Ea), entropy (ΔSa), and enthalpy (ΔHa) are measured during the steel corrosion of the mild steel in a 1 M solution of HCl, with and without the synthesized inhibitor. An improved comprehension of the corrosion inhibition mechanisms is made possible by these thermodynamic data. This is the traditional Arrhenius equation and its reformulation based on the theory of the transition state [31,32].
i c o r r = A e x p ( E a R T )
E c o r r T = R N h exp Δ S a R e x p ( Δ H a R T )
Figure 8 shows the Arrhenius curves showing ln i0 (corrosion) and ln(i0/T) as a function of 1000/T. From the slopes and orthogonals that are at the origin of these curves, the activation energy (Ea), enthalpy (ΔHa), and entropy (ΔSa) were determined and are shown in Table 6. The results of this research show that the values of Ea obtained with the existence of the tested inhibitors exceed those measured in a 1 M HCl solution without an inhibitor. It can be argued that this increase is caused by the physical adsorption of the inhibitors on the metal mild steel surface.
In addition, the high and positive values of ΔHa show the endothermic character of the steel dissolution mechanism (MS). Also, the lower negative values of ΔSa observed in the presence of IL-3 and the positive values of IL-2 and IL-1, compared with the acid solution without an inhibitor, suggest an increase in the molecular order when the reagents are adsorbed to the steel/solution interface.

2.6. Surface Characterization (SEM-EDS)

The SEM images of the metal mild steel specimens are shown in Figure 9. Figure 9a represents the surface of the polished MS, a non-corroded surface with some scratches due to the polishing. However, after 6 h of immersion in 1 M HCl, the surface morphology was strongly corroded and damaged with cracks and pits (Figure 9b). On the contrary, the mild steel surface damage is considerably lower, and the surface of the metal is relatively smooth with the existence of the protection of inhibitors (Figure 9c–e).
The EDX spectra give a general idea about the surface composition of the metal. In this study, we use the EDX of MS specimens before and after immersion in 1 M HCl in the presence and absence of the studied inhibitors (Figure 9). The EDX spectra display peaks corresponding to the primary elements found in the MS (Fe and C). In Figure 9b’, after the immersion in HCl, we notice the appearance of the Cl resulting from the adsorption of HCl, while the presence of N and Cl with the addition of inhibitors is shown in Figure 9c’–e’. These provide evidence for the existence of the inhibitors on the mild steel surface [33,34].

2.7. Theoretical Information

The ionic liquid optimization structures are presented in Figure 10. These geometry optimization structures are optimized using the B3LYP and 6-311 G (d,p) bases in the aqueous phases. The HOMO and LUMO orbitales and EPS of the ionic liquids are shown in Figure 10. The HOMO density distributed over the structure regions of the ionic liquids is responsible for the electron’s donation capacity. Also, these regions of LUMO density are the center responsible for electron acceptance from the surface of the substrate [35,36]. The parameters calculated for the synthesized ionic liquids, HOMO and LUMO energy, and gap energy, are described in Table 7.
The high EHOMO value refers to the ability to donate free electrons to a vacant orbital of the metals. And the lower ELUMO value indicates the strong tendency of the molecules to gain electrons. The three synthesized ionic liquids have the same EHOMO, with a small difference, giving them the following ranking: ILS2 > ILS1 > ILS3. This reflects that ILS2 can share its electrons more than the other ionic liquids. Additionally, the gap energy parameter is crucial for assessing the inhibitory activity of the molecules. A smaller gap energy indicates better reactivity of the inhibitors against the corrosion rate. In our study, ILs 1 and ILs 2 have the lowest gap energy values, 0.1402 and 0.1437, respectively, which can be explained by the superior adsorption potential of ILs 1 and 2 on the surface of the mild steel. Also, the fraction of transferred electrons, ΔN, is an essential indicator of the corrosion inhibition efficiencies of the molecules. ΔN > 0 describes a great donation capacity of electrons, which can decrease the effect of corrosion on the surface of metals [36,37].
The ΔEb–d (backdonation energy) also provides insight into the stability of our molecule; a negative value of ΔEb–d indicates that the structure is more stable. In our case, the calculated values for ΔEb–d are −0.0175 eV for Ils1, −0.0179 eV for Ils2, and −0.0256 eV for Ils3, which are caused by the stabilization of these ionic liquid molecules. The electronegativity parameter is linked to the capability to donate electrons. The highest electronegativity value of an inhibitor corresponds to its lowest capacity to provide electrons. The electronegativity parameter is linked to the capability to donate electrons. The highest electronegativity value of an inhibitor corresponds to its lowest capacity to provide electrons. In the present study, the electronegativity values of our inhibitors are −0.1642, −0.1631, and −0.1312 for IL1, ILs 2, and ILs 3, respectively. These align with our results. The DFT calculation parameters display harmony with the experimental results.
To study the interaction between the synthesized ionic liquids and the mild steel surface, a Monte Carlo simulation was employed as an effective computational method. Figure 11 shows the most stable adsorption configurations for the synthesized inhibitors based on the ionic liquids on the surface of the Fe(1 1 0) in the water solution. It is clear from the top and side views of the IL molecules on the surface of the Fe(1 1 0) that the molecules are oriented parallel to the iron surface, which represents the best position for adsorption. The highly negative adsorption energy values represent the higher efficiency of inhibition, which is due to the stable and strong chemical bond formed between the inhibitors and the surface of the Fe(1 1 0). The values of the adsorption energy for the ionic liquid molecules are given in Table 8. We can explain the mechanism of adsorption through the nitrogen, oxygen, and pi electrons of the aromatic ring; these donating electrons exist in inhibitors, which can occupy the empty d orbitals, creating a protective film on the mild steel surface. The adsorption energies of our inhibitors have high negative values, −3145.745 for ILS1, −2980.188 for ILS2, and −2099.160 for ILs3, thus showing that the strong inhibition efficiency of our inhibitors is in good agreement with the experimental results obtained from the PDP and EIS techniques.

3. Materials and Methods

3.1. Synthesis of Imidazolium-Derived (IL-1, IL-2, and IL-3)

The synthetic route for the preparation of the imidazolium-based ionic liquid derivatives is illustrated in Figure 12. In a typical procedure, the alkyl halides—2-chlorobenzoyl chloride, 4-chlorobenzoyl chloride, and/or 1-(chloromethyl)-4-fluorobenzene (1.1 eq)—were added to a solution of 1-phenethyl-1H-imidazole (1.0 eq) in toluene. The reaction mixture was then irradiated at 80 °C for 20 min in a sealed vessel using a SEM microwave reactor (CEM Corp., Matthews, NC, USA). Upon mixing, a clear and homogeneous solution was observed, indicating the formation of an oily intermediate. The resulting product was extracted using ethyl acetate. All the synthesized derivatives were then dried under reduced pressure.

3.2. Mild Steel and Solutions Preparation

Samples of mild steel (0.21% C, 0.38% Si, >1% of Mn, S, P, Al, and balance by Fe) were analyzed using electrochemical analysis. For all the studies, an aggressive 1 M hydrochloric acid solution was used. All these samples were mechanically polished using various emery papers and then rinsed with methanol and water, before drying. The electrolyte solution was prepared using 37% hydrochloric acid (HCl). The concentration of the studied imidazolium IL ranged from 10−5 to 10−3 M. This work used no supporting solvent to dissolve the corrosion inhibitors directly in a 1 M HCl solution.

3.3. Characterization of IL-1, IL-2 and IL-3

3.3.1. The 3-(2-Chlorobenzoyl)-1-phenethyl-1H-imidazol-3-ium chloride (IL-1)

The 3-(2-chlorobenzoyl)-1-phenethyl-1H-imidazol-3-ium chloride (IL-1) can be characterized as follows. FT-IR, cm−1: ν = 765 (C-H, CH2), 1154 (C-N), 1561 (C=N), 1672 (C=O), and 2674 and 3100 (Ar-H). 1H NMR (400 MHz, CDCl3) (Figure 12): δH = 3.16 (t, 2H, CH2), 4.55 (t, 2H, CH2), 7.14–7.74 (d, 2H, Ar-H), 7.01–7.40 (m, 9H, Ar-H), and 9.27 (s, 1H, Ar-H); 13C NMR (100 MHz, CDCl3) (Figure 12): δC = 36.7 (CH2), 50.9 (CH2), 119.6 (CH), 121.1 (CH), 127.5 (CH), 128.3 (CH), 128.6 (CH), 129.3 (CH), 131.3 (CH), 131.8 (CH), 134.9 (CH), 135.7 (C), 137.1 (C), 137.3 (C), 137.7 (CH), and 173.3 (CO); Found: C, 62.32, H, 4.57, N, 8.14%. Calcd. for C18H16Cl2N2O, C, 62.26, H, 4.64, N, 8.07%.

3.3.2. The 3-(4-Chlorobenzoyl)-1-phenethyl-1H-imidazol-3-ium chloride (IL-2)

The 3-(4-chlorobenzoyl)-1-phenethyl-1H-imidazol-3-ium chloride (IL-2) can be characterized as follows. FT-IR, cm−1: ν = 747 (C-H, CH2), 1154 (C-N), 1561 (C=N), 1707 (C=O), and 2687 and 3100 (Ar-H). 1H NMR (400 MHz, CDCl3) (Figure 13): δH = 3.12 (t, 2H, CH2), 4.50 (t, 2H, CH2), 7.22–7.85 (d, 2H, Ar-H), 7.01–7.39 (m, 9H, Ar-H), and 9.27 (s, 1H, Ar-H); 13C NMR (100 MHz, CDCl3) (Figure 12): δC = 36.5 (CH2), 50.8 (CH2), 119.6 (CH), 121.3 (CH), 126.7 (CH), 127.3 (CH), 128.9 (CH), 131.8 (CH), 134.9 (CH), 135.7 (C), 137.1 (C), 137.3 (C), 137.7 (CH), and 167.6 (CO); Found: C, 62.35, H, 4.58, N, 8.12%. Calcd. for C18H16Cl2N2O, C, 62.26, H, 4.64, N, 8.07%.

3.3.3. The 3-(4-Fluorobenzyl)-1-phenethyl-1H-imidazol-3-ium chloride (IL-3)

The 3-(4-fluorobenzyl)-1-phenethyl-1H-imidazol-3-ium chloride (IL-3) can be characterized as follows. FT-IR, cm−1: ν = 751 (C-H, CH2), 1150 (C-N), 1508 (C=N), and 2843 and 3135 (Ar-H). 1H NMR (400 MHz, CDCl3) (Figure 13): δH = 3.14 (t, 2H, CH2), 4.51 (t, 2H, CH2), 5.46 (s, H, CH2), 7.21–7.53 (d, 2H, Ar-H), 6.90–7.41 (m, 9H, Ar-H), and 10.15 (s, 1H, Ar-H); 13C NMR (100 MHz, CDCl3) (Figure 12): δC = 36.3 (CH2), 51.0 (CH2), 52.2 (CH2), 116.1 (CH), 116.4 (CH), 121.7 (CH), 122.4 (CH), 128.7 (CH), 128.9 (CH), 130.9 (CH), 131.2 (C), 135.6 (C), 136.9 (CH), and 167.6 (C); Found: C, 68.32, H, 5.68, N, 8.90%. Calcd. for C18H18ClFN2, C, 68.24, H, 5.73, N, 8.84%.

3.4. Electrochemical Measurements

To carry out the electrochemical tests, we need a mild steel used as a working electrode with a surface area of 1 cm2, a counter electrode consisting of platinum (Pt), and also a reference electrode consisting of Ag/AgCl. The EIS measurement was performed with an amplitude of 5 mV, a frequency range of 100 kHz to 100 MHz, using an AC signal at the open-circuit potential (OCP). All the experiments were conducted at ambient temperature, without agitation. The curves of polarization were established according to the potential, ranging between −250 and +250 mV, with respect to the OCP. After reaching a scan speed of 1 mV/s, the OCP was stabilized for 30 min. The equations below can estimate the inhibition efficiency of each inhibitor [38,39].
E I E I S = R C R C 0 R C
E I P D P = i c o r r 0 i c o r r i c o r r 0

3.5. Surface Characterization

The mild steel specimens underwent a 6 h immersion in 1 M HCl at room temperature and 10−3 M of inhibitors for surface analysis. The Quattro ESEM-FEG is a type of scanning electron microscope (SEM) (Thermo Fisher Scientific, Waltham, MA, USA) that combines Environmental Scanning Electron Microscopy (ESEM) and Field Emission Gun (FEG) technologies. This technique was used to obtain SEM images by assessing the accelerating voltage of 20 kV at 1000× magnification, associated with X-ray photoelectron spectroscopy (EDX) (Thermo Fisher Scientific, Waltham, MA, USA).

3.6. Theoretical Details

3.6.1. Density Functional Theory (DFT)

The DFT methods were calculated using Gaussian 09 and Gauss view software 6.0 [40], with a hybrid function of the Beeke parameters Lee, Yang, and Parr B3LYP and G-311G (d,p) comes basis set [41] was also calculated in water utilizing the integral equation formalism variant of the polarizable continuum module (IEFPCM). The properties of the molecules via the energies of the highest occupied molecular orbital EHOMO and lowest unoccupied molecular orbital ELUMO can be explained using the quantum chemical descriptor premised on the default calculation. These descriptors can be calculated using the HOMO and LUMO energies, including the energy gap (ΔEgap), harness (η), softness (σ), chemical potential (µ), electronegativity (χ), electrophilicity (ω), nucleophilicity (ε), fraction of electrons transferred (ΔN), and back donation energy (ΔEb–d), and they were calculated as follows [42,43,44]:
Δ E g a p = E L U M O E H O M O
η = Δ E g a p 2 = E L U M O E H O M O 2
σ = 1 η = 2 E L U M O E H O M O
χ = E L U M O + E H O M O 2
ω = χ 2 2 η
Δ N = Φ F e χ i n h 2 ( η F e + η i n h )
ε = 1 ω
Δ E b d = η 4
The Φ value for the Fe (1 1 0) surface is 4.82 eV and η F e is null.

3.6.2. Monte Carlo Simulation (MC)

To study the interaction of the ILs with the surface of the mild steel, we used the MC simulation in the Biovia Material Studio 2020 software. The geometry optimization of the surface of the Fe was explored using GGA/PBE on the castep module, and the ILs were explored using the Dmol3 (GGA, PBE). We used the Fe (1 1 0) surface due to its higher stabilization energy and packed surface [45]. The adsorption locator module was exploited to investigate how these molecules interacted and reacted with the surface of the metal, we used the compass force field [46,47] for the adsorption study because of its effectiveness in the field of corrosion modeling [15]. The crystal of the Fe was constructed with an edge of 60 A to ascertain that enough depth was achieved, and the 10 × 10 super cell. The adsorption study was carried out under solvation conditions using ILs + 100 H2O + 3 H3O+ + 3Cl. The optimization structures of the ILs, Fe, H2O, H3O+, and Cl were calculated to obtain the most stable adsorbed configuration.

4. Conclusions

The effect of the ionic liquids IL-1, IL-2, and IL-3 on the inhibition of mild steel corrosion in 1 M HCl solutions was investigated. The results showed that the ionic liquids act as effective corrosion inhibitors. Additionally, the adsorption of the compounds IL-1, IL-2, and IL-3 in 1 M HCl solution followed the Langmuir isotherm, and they also function as mixed-type corrosion inhibitors. Furthermore, the theoretical calculations (DFT) and MC simulations produced results consistent with the experimental findings. The results indicated that IL-1 and IL-2 exhibited the highest inhibition efficiencies, with 96.6% and 96.9%, respectively.

Author Contributions

Conceptualization, A.O.A. and A.T.; Software, A.O.A.; Investigation, W.E.; Resources, W.E.; Data curation, M.M., W.E. and F.E.-H.; Writing—original draft, M.M., B.H. and F.E.-H.; Writing—review & editing, B.H.; Funding acquisition, F.E.-H. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported and funded by the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University (IMSIU) (grant number IMSIU-DDRSP2502).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Verma, C.; Olasunkanmi, L.O.; Ebenso, E.E.; Quraishi, M.A.; Obot, I.B. Adsorption behavior of glucosamine-based, pyrimidine-fused heterocycles as green corrosion inhibitors for mild steel: Experimental and theoretical studies. J. Phys. Chem. C 2016, 120, 11598–11611. [Google Scholar] [CrossRef]
  2. Guo, L.; Zhu, S.; Zhang, S.; He, Q.; Li, W. Theoretical studies of three triazole derivatives as corrosion inhibitors for mild steel in acidic medium. Corros. Sci. 2014, 87, 366–375. [Google Scholar] [CrossRef]
  3. Srivastava, V.; Haque, J.; Verma, C.; Singh, P.; Lgaz, H.; Salghi, R.; Quraishi, M.A. Amino acid-based imidazolium zwitterions as novel and green corrosion inhibitors for mild steel: Experimental, DFT and MD studies. J. Mol. Liq. 2017, 244, 340–352. [Google Scholar] [CrossRef]
  4. Chauhan, D.S.; El-Hajjaji, F.; Quraishi, M.A. Chapter 18—Heterocyclic ionic liquids as environmentally benign corrosion inhibitors: Recent advances and future perspectives. In Ionic Liquid-Based Technologies for Environmental Sustainability; Elsevier: Amsterdam, The Netherlands, 2022; pp. 279–294. [Google Scholar]
  5. Olasunkanmi, L.O.; Obot, I.B.; Kabanda, M.M.; Ebenso, E.E. Some quinoxalin-6-yl derivatives as corrosion inhibitors for mild steel in hydrochloric acid: Experimental and theoretical studies. J. Phys. Chem. C 2015, 119, 16004–16019. [Google Scholar] [CrossRef]
  6. Alibakhshi, E.; Ramezanzadeh, M.; Bahlakeh, G.; Ramezanzadeh, B.; Mahdavian, M.; Motamedi, M. Glycyrrhiza glabra leaves extract as a green corrosion inhibitor for mild steel in 1 M hydrochloric acid solution: Experimental, molecular dynamics, Monte Carlo and quantum mechanics study. J. Mol. Liq. 2018, 255, 185–198. [Google Scholar] [CrossRef]
  7. Zhang, K.; Xu, B.; Yang, W.; Yin, X.; Liu, Y.; Chen, Y. Halogen-substituted imidazoline derivatives as corrosion inhibitors for mild steel in hydrochloric acid solution. Corros. Sci. 2015, 90, 284–295. [Google Scholar] [CrossRef]
  8. Asadi, N.; Ramezanzadeh, M.; Bahlakeh, G.; Ramezanzadeh, B. Utilizing Lemon Balm extract as an effective green corrosion inhibitor for mild steel in 1 M HCl solution: A detailed experimental, molecular dynamics, Monte Carlo and quantum mechanics study. J. Taiwan Inst. Chem. Eng. 2019, 95, 252–272. [Google Scholar] [CrossRef]
  9. Yıldız, R. An electrochemical and theoretical evaluation of 4, 6-diamino-2-pyrimidinethiol as a corrosion inhibitor for mild steel in HCl solutions. Corros. Sci. 2015, 90, 544–553. [Google Scholar] [CrossRef]
  10. Saha, S.K.; Dutta, A.; Ghosh, P.; Sukul, D.; Banerjee, P. Novel Schiff-base molecules as efficient corrosion inhibitors for mild steel surface in 1 M HCl medium: An experimental and theoretical approach. Phys. Chem. Chem. Phys. 2016, 18, 17898–17911. [Google Scholar] [CrossRef]
  11. Saha, S.K.; Ghosh, P.; Hens, A.; Murmu, N.C.; Banerjee, P. Density functional theory and molecular dynamics simulation study on corrosion inhibition performance of mild steel by mercapto-quinoline Schiff base corrosion inhibitor. Phys. E Low-Dimens. Syst. Nanostructures 2015, 66, 332–341. [Google Scholar] [CrossRef]
  12. Cao, Z.; Tang, Y.; Cang, H.; Xu, J.; Lu, G.; Jing, W. Novel benzimidazole derivatives as corrosion inhibitors of mild steel in the acidic media. Part II: Theoretical studies. Corros. Sci. 2014, 83, 292–298. [Google Scholar] [CrossRef]
  13. Qiang, Y.; Zhang, S.; Guo, L.; Zheng, X.; Xiang, B.; Chen, S. Experimental and theoretical studies of four allyl imidazolium-based ionic liquids as green inhibitors for copper corrosion in sulfuric acid. Corros. Sci. 2017, 119, 68–78. [Google Scholar] [CrossRef]
  14. El-Hajjaji, F.; Messali, M.; Aljuhani, A.; Aouad, M.R.; Hammouti, B.; Belghiti, M.E.; Chauhan, D.S.; Quraishi, M.A. Pyridazinium-based ionic liquids as novel and green corrosion inhibitors of carbon steel in acid medium: Electrochemical and molecular dynamics simulation studies. J. Mol. Liq. 2018, 249, 997–1008. [Google Scholar] [CrossRef]
  15. Chu, T.-S.; Mai, W.-J.; Li, H.-Z.; Wei, B.-X.; Xu, Y.-Q.; Liao, B.-K. Insights into the Corrosion Inhibition Performance of Plant Extracts of Different Genera in the Asteraceae Family for Q235 Steel in H2SO4 Medium. Int. J. Mol. Sci. 2025, 26, 561. [Google Scholar] [CrossRef]
  16. Palumbo, G.; Święch, D.; Górny, M. Guar Gum as an Eco-Friendly Corrosion Inhibitor for N80 Carbon Steel under Sweet Environment in Saline Solution: Electrochemical, Surface, and Spectroscopic Studies. Int. J. Mol. Sci. 2023, 24, 12269. [Google Scholar] [CrossRef]
  17. El-Nagar, R.A.; Khalil, N.A.; Atef, Y.; Nessim, M.I.; Ghanem, A. Evaluation of ionic liquids based imidazolium salts as an environmentally friendly corrosion inhibitors for carbon steel in HCl solutions. Sci. Rep. 2024, 14, 1889. [Google Scholar] [CrossRef]
  18. Ansari, K.R.; Quraishi, M.A.; Singh, A. Schiff’s base of pyridyl substituted triazoles as new and effective corrosion inhibitors for mild steel in hydrochloric acid solution. Corros. Sci. 2014, 79, 5–15. [Google Scholar] [CrossRef]
  19. Xu, B.; Yang, W.; Liu, Y.; Yin, X.; Gong, W.; Chen, Y. Experimental and theoretical evaluation of two pyridinecarboxaldehyde thiosemicarbazone compounds as corrosion inhibitors for mild steel in hydrochloric acid solution. Corros. Sci. 2014, 78, 260–268. [Google Scholar] [CrossRef]
  20. Zeng, C.; Zhou, Z.; Mai, W.J.; Chen, Q.H.; He, J.; Liao, B.K. Exploration on the corrosion inhibition performance of Salvia miltiorrhiza extract as a green corrosion inhibitor for Q235 steel in HCl environment. J. Mater. Res. Technol. 2024, 32, 3857–3870. [Google Scholar] [CrossRef]
  21. Ansari, K.R.; Ramkumar, S.; Chauhan, D.S.; Salman, M.; Nalini, D.; Srivastava, V.; Quraishi, M.A. Macrocyclic compounds as green corrosion inhibitors for aluminium: Electrochemical, surface and quantum chemical studies. Int. J. Corros. Scale Inhib. 2018, 7, 443–459. [Google Scholar]
  22. Nam, N.D.; Bui, Q.V.; Mathesh, M.; Tan, M.Y.J.; Forsyth, M. A study of 4-carboxyphenylboronic acid as a corrosion chemical engineering communications 13 inhibitor for steel in carbon dioxide-containing environments. Corros. Sci. 2013, 76, 257–266. [Google Scholar] [CrossRef]
  23. Cui, F.; Ni, Y.; Jiang, J.; Ni, L.; Wang, Z. Experimental and theoretical studies of five imidazolium-based ionic liquids as corrosion inhibitors for mild steel in H2S and HCl solutions. Chem. Eng. Commun. 2021, 208, 1580–1593. [Google Scholar] [CrossRef]
  24. Roy, P.; Karfa, P.; Adhikari, U.; Sukul, D. Corrosion inhibition of mild steel in acidic medium by polyacrylamide grafted Guar gum with various grafting percentage: Effect of intramolecular synergism. Corros Sci. 2014, 88, 246–253. [Google Scholar] [CrossRef]
  25. Lopez, D.A.; Simison, S.N.; de Sanchez, S.R. The influence of steel microstructure on CO2 corrosion. EIS studies on the inhibition efficiency of benzimidazole. Electrochim. Acta 2003, 48, 845–854. [Google Scholar] [CrossRef]
  26. Murulana, L.C.; Singh, A.K.; Shukla, S.K.; Kabanda, M.M.; Ebenso, E.E. Experimental and quantum chemical studies of some bis (trifluoromethyl-sulfonyl) imide imidazolium-based ionic liquids as corrosion inhibitors for mild steel in hydrochloric acid solution. Ind. Eng. Chem. Res. 2012, 51, 13282–13299. [Google Scholar] [CrossRef]
  27. Zhang, S.; Tao, Z.; Liao, S.; Wu, F. Substitutional adsorption isotherms and corrosion inhibitive properties of some oxadiazol-triazole derivative in acidic solution. Corros. Sci. 2010, 52, 3126–3132. [Google Scholar] [CrossRef]
  28. Omotosho, O.A.; Okeniyi, J.O.; Oni, A.B.; Makinwa, T.O.; Ajibola, O.B.; Fademi, E.O.J.; Obi, C.E.; Loto, C.A.; Popoola, A.P.I. Inhibition and mechanism of Terminalia catappa on mild-steel corrosion in sulphuric-acid environment. Prog. Ind. Ecol. Int. J. 2016, 10, 398–413. [Google Scholar]
  29. Hassan, H.H.; Abdelghani, E.; Amin, M.A. Inhibition of mild steel corrosion in hydrochloric acid solution by triazole derivatives: Part I. Polarization and EIS studies. Electrochim. Acta 2007, 52, 6359–6366. [Google Scholar] [CrossRef]
  30. Zhang, J.; Kong, M.; Feng, J.; Yin, C.; Li, D.; Fan, L.; Chen, Q.; Liu, H. Dimeric imidazolium ionic liquids connected by bipyridiyl as a corrosion inhibitor for N80 carbon steel in HCl. J. Mol. Liq. 2021, 344, 117962. [Google Scholar] [CrossRef]
  31. El Hajjaji, F.; Salim, R.; Messali, M.; Hammouti, B.; Chauhan, D.; Almutairi, S.; Quraishi, M. Electrochemical Studies on New Pyridazinium Derivatives as Corrosion Inhibitors of Carbon Steel in Acidic Medium. J. Bio-Tribo-Corros. 2019, 5, 4. [Google Scholar] [CrossRef]
  32. Go, L.C.; Depan, D.; Holmes, W.E.; Gallo, A.; Knierim, K.; Bertrand, T.; Hernandez, R. Kinetic and thermodynamic analyses of the corrosion inhibition of synthetic extracellular polymeric substances. PeerJ Mater. Sci. 2020, 2, e4. [Google Scholar] [CrossRef]
  33. Alaoui, A.O.; Elfalleh, W.; Hammouti, B.; Titi, A.; Messali, M.; Kaya, S.; EL IBrahimi, B.; El-Hajjaji, F. Theoretical prediction of corrosion inhibition by ionic liquid derivatives: A DFT and molecular dynamics approach. RSC Adv. 2025, 15, 2645–12652. [Google Scholar]
  34. Junaedi, S.; Al-Amiery, A.A.; Kadihum, A.; Kadhum, A.A.H.; Mohamad, A.B. Inhibition Effects of a Synthesized Novel 4-Aminoantipyrine Derivative on the Corrosion of Mild Steel in Hydrochloric Acid Solution together with Quantum Chemical Studies. Int. J. Mol. Sci. 2013, 14, 11915–11928. [Google Scholar] [CrossRef] [PubMed]
  35. Gómez-Sánchez, G.; Olivares-Xometl, O.; Arellanes-Lozada, P.; Likhanova, N.V.; Lijanova, I.V.; Arriola-Morales, J.; Díaz-Jiménez, V.; López-Rodríguez, J. Temperature Effect on the Corrosion Inhibition of Carbon Steel by Polymeric Ionic Liquids in Acid Medium. Int. J. Mol. Sci. 2023, 24, 6291. [Google Scholar] [CrossRef]
  36. Kanzouai, Y.; Ech-chihbi, E.; Al Houari, G.; Arrousse, N.; Salim, R.; El-Hajjaji, F.; Rais, Z.; Taleb, M. Adsorption and Corrosion Inhibitive Properties of Some Aldehyde Derivatives on Mild Steel in 1 M HCl Solution: Electrochemical and Computational Investigations. J. Bio-Tribo-Corros. 2021, 7, 101. [Google Scholar] [CrossRef]
  37. EL-Hajjaji, F.; Salim, R.; Ech-chihbi, E.; Titi, A.; Messali, M.; Kaya, S.; El Ibrahimi, B.; Taleb, M. New imidazolium ionic liquids as eco-friendly corrosion inhibitors for mild steel in hydrochloric acid (1 M): Experimental and theoretical approach. J. Taiwan Inst. Chem. Eng. 2021, 123, 346–362. [Google Scholar] [CrossRef]
  38. El-Hajjaji, F.; Messali, M.; de Yuso, M.V.M.; Rodríguez-Castellón, E.; Almutairi, S.; Bandosz, T.J.; Algarra, M. Effect of 1-(3-phenoxypropyl) pyridazin-1-ium bromide on steel corrosion inhibition in acidic medium. J. Colloid Interface Sci. 2019, 541, 418–424. [Google Scholar] [CrossRef]
  39. Liu, F.G.; Du, M.; Zhang, J.; Qiu, M. Electrochemical behavior of Q235 steel in saltwater saturated with carbon dioxide based on new imidazoline derivative inhibitor. Corros. Sci. 2009, 51, 102–109. [Google Scholar] [CrossRef]
  40. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A.; et al. Hada GAUSSIAN 09 R’evision; Gaussian, Inc.: Wallingford, CT, USA, 2009. [Google Scholar]
  41. Adardour, M.; Lasri, M.; Ait Lahcen, M.; Maatallah, M.; Idouhli, R.; Alanazi, M.M.; Lahmidi, S.; Abouelfida, A.; Mague, J.T.; Baouid, A. Exploring the efficacy of benzimidazolone derivative as corrosion inhibitors for copper in a 3.5 Wt.% NaCl solution: A comprehensive experimental and theoretical investigation. Molecules 2023, 28, 6948. [Google Scholar] [CrossRef]
  42. Verma, D.K.; Aslam, R.; Aslam, J.; Quraishi, M.A.; Ebenso, E.E.; Verma, C. Computational modeling: Theoretical predictive tools for designing potential organic corrosion inhibitors. J. Mol. Struct. 2021, 1236, 130294. [Google Scholar] [CrossRef]
  43. Obot, I.B. Recent Advances in Computational Design of Organic Materials for Corrosion Protection of Steel in Aqueous. In Developments in Corrosion Protection; IntechOpen: London, UK, 2014; p. 123. [Google Scholar]
  44. Toukal, L.; Foudia, M.; Haffar, D.; Aliouane, N.; Al-Noaimi, M.; Bellal, Y.; Elmsellem, H.; Abdel-Rahman, I. Monte Carlo simulation and electrochemical performance corrosion inhibition whid benzimidazole derivative for XC48 steel in 0.5 M H2SO4 and 1.0 M HCl solutions. J. Indian Chem. Soc. 2022, 99, 100634. [Google Scholar] [CrossRef]
  45. Chen, L.; Lu, D.; Zhang, Y. Organic compounds as corrosion inhibitors for carbon steel in HCl solution: A comprehensive review. Materials 2022, 15, 2023. [Google Scholar] [CrossRef] [PubMed]
  46. Hsissou, R.; Dahmani, K.; El Magri, A.; Hmada, A.; Safi, Z.; Dkhireche, N.; Galai, M.; Wazzan, N.; Berisha, A. A combined experimental and computational (DFT, RDF, MC and MD) investigation of epoxy resin as a potential corrosion inhibitor for mild steel in a 0.5 M H2SO4 environment. Polymers 2023, 15, 1967. [Google Scholar] [CrossRef]
  47. Kasprzhitskii, A.; Lazorenko, G.; Nazdracheva, T.; Yavna, V. Comparative computational study of l-amino acids as green corrosion inhibitors for mild steel. Computation 2020, 9, 1. [Google Scholar] [CrossRef]
Figure 1. Nyquist diagrams for MS in a 1 M HCl solution at 298 K that has different concentrations of IL-1, 2, and 3.
Figure 1. Nyquist diagrams for MS in a 1 M HCl solution at 298 K that has different concentrations of IL-1, 2, and 3.
Ijms 26 05750 g001
Figure 2. Bode plots for MS in a 1 M HCl solution at 298 K that has different concentrations of IL-1, IL-2, and IL-3.
Figure 2. Bode plots for MS in a 1 M HCl solution at 298 K that has different concentrations of IL-1, IL-2, and IL-3.
Ijms 26 05750 g002
Figure 3. The experimental impedance equivalent circuit.
Figure 3. The experimental impedance equivalent circuit.
Ijms 26 05750 g003
Figure 4. Langmuir adsorption isotherm plots for the mild steel of the ionic liquids (ILs) at 298 K.
Figure 4. Langmuir adsorption isotherm plots for the mild steel of the ionic liquids (ILs) at 298 K.
Ijms 26 05750 g004
Figure 5. Nyquist diagrams for MS in 1 M HCl with and without the studied ILs after different immersion times.
Figure 5. Nyquist diagrams for MS in 1 M HCl with and without the studied ILs after different immersion times.
Ijms 26 05750 g005
Figure 6. Tafel plots for MS in 1 M HCl solution at 298 K, in the presence and absence of various concentrations of synthesized ILs.
Figure 6. Tafel plots for MS in 1 M HCl solution at 298 K, in the presence and absence of various concentrations of synthesized ILs.
Ijms 26 05750 g006
Figure 7. PDP plots for MS in 1 M HCl in the presence and absence of three ILs in 10−3 M at different temperatures.
Figure 7. PDP plots for MS in 1 M HCl in the presence and absence of three ILs in 10−3 M at different temperatures.
Ijms 26 05750 g007
Figure 8. Arrhenius plots: (a) ln icorr versus 1000/T, (b) ln icorr/T versus 1000/T for MS in 1 M HCl with and without synthesized ILs.
Figure 8. Arrhenius plots: (a) ln icorr versus 1000/T, (b) ln icorr/T versus 1000/T for MS in 1 M HCl with and without synthesized ILs.
Ijms 26 05750 g008
Figure 9. Surface morphology and corresponding EDX analysis of MS samples: (a,a’) Polished, (b,b’) Immersed in 1 M HCl (blank), and treated with (c,c’) IL-1, (d,d’) IL-2, and (e,e’) IL-3.
Figure 9. Surface morphology and corresponding EDX analysis of MS samples: (a,a’) Polished, (b,b’) Immersed in 1 M HCl (blank), and treated with (c,c’) IL-1, (d,d’) IL-2, and (e,e’) IL-3.
Ijms 26 05750 g009aIjms 26 05750 g009b
Figure 10. Optimized structures, HOMO, LUMO, and EPS of the studied ionic liquid inhibitors.
Figure 10. Optimized structures, HOMO, LUMO, and EPS of the studied ionic liquid inhibitors.
Ijms 26 05750 g010
Figure 11. The top and side views of the most stable energy configuration of the Il inhibitors on the Fe(1 1 0) surface.
Figure 11. The top and side views of the most stable energy configuration of the Il inhibitors on the Fe(1 1 0) surface.
Ijms 26 05750 g011
Figure 12. Procedure to synthesize imidazolium chloride inhibitors (IL-1, IL-2, IL-3).
Figure 12. Procedure to synthesize imidazolium chloride inhibitors (IL-1, IL-2, IL-3).
Ijms 26 05750 g012aIjms 26 05750 g012b
Figure 13. 1H NMR spectrum (1), 13C NMR spectrum (2) in CDCl3 (400 MHz), and DEPT-135 NMR spectrum in CDCl3 (100 MHz) (3) of IL-1, IL-2, and IL-3.
Figure 13. 1H NMR spectrum (1), 13C NMR spectrum (2) in CDCl3 (400 MHz), and DEPT-135 NMR spectrum in CDCl3 (100 MHz) (3) of IL-1, IL-2, and IL-3.
Ijms 26 05750 g013
Table 1. EIS parameters for MS in 1 M hydrochloric acid in the absence and presence of studied ILs in various concentrations.
Table 1. EIS parameters for MS in 1 M hydrochloric acid in the absence and presence of studied ILs in various concentrations.
MediumConc.
(M)
Rs
(Ω cm2)
Rct
(Ω cm2)
CPEQ
(µF Sn−1)
Ɵƞimp
%
Cdl (µFcm−2)ndl
Blank---1.73389.10.784312.70------
IL-110−51.8116.744.20.830107.70.71771.7
5 × 10−51.8216.433.20.82578.70.84784.7
10−41.9404.518.40.79350.50.91891.8
5 × 10−41.3700.915.70.76947.40.95395.3
10−31..0989.012.20.70345.30.96696.6
IL-210−51.9165.826.20.82766.80.80180.1
5 × 10−51.7210.624.50.81564.70.84384.3
10−41.538419.60.82546.20.91491.4
5 × 10−41.179011.90.75637.30.95895.8
10−30.810818.80.70235.20.96996.9
IL-310−51.695.352.80.791159.00.65465.4
5 × 10−51.8107.843.30.828108.40.69469.4
10−41.6202.330.50.82474.50.83783.7
5 × 10−41.8402.418.50.81845.10.91891.8
10−31.3616.517.00.76943.20.94694.6
Table 2. EIS thermodynamic parameters obtained by using the Langmuir isotherm at 298 K.
Table 2. EIS thermodynamic parameters obtained by using the Langmuir isotherm at 298 K.
Compound.K (L/mol)ΔGads (KJ/mol)R2Slopes
IL-116.13 × 104−39.60.999991.03
IL-216.80 × 104−39.70.999981.02
IL-37.03 × 104−37.60.999881.04
Table 3. EIS parameters for MS in 1 M hydrochloric acid in the absence and presence of studied ILs after various immersion times.
Table 3. EIS parameters for MS in 1 M hydrochloric acid in the absence and presence of studied ILs after various immersion times.
MediumTime
(h)
Rs
(Ω cm2)
Rct
(Ω cm2)
CPEQ
(µF Sn−1)
ηEIS
%
Cdl
(µF cm−2)
ndl
Blank½1.733.089.10.784312.70--
11.626.4122.70.810364.90--
21.626.3122.80.810364.80--
41.521.4267.00.834627.00--
61.019.4349.40.796963.80--
121.210.4419.50.764949.2--
IL-1½1.098912.20.70345.396.6
11.294315.40.73748.997.2
21.390918.30.73959.097.2
41.878422.60.76766.897.3
61.671525.00.80073.297.3
121.361530.80.82680.998.3
IL-2½0.810818.80.70235.296.9
10.512807.50.74732.697.9
20.899811.80.73737.897.4
41.085313.00.73443.197.4
60.775414.90.72451.697.4
121.263518.20.72262.998.3
IL-3½1.3616.517.00.76943.294.6
11.6555.220.20.79157.695.2
21.6457.521.70.79256.594.2
41.4386.426.00.79865.994.4
61.5258.028.80.79976.992.5
121.2179.834.60.786102.694.2
Table 4. EIS parameters obtained by the concentration effect.
Table 4. EIS parameters obtained by the concentration effect.
MediumConc.
M
−Ecorr mV/Ag/AgClicorr
µA cm−2
−βc
mV dec−1
βa
mV dec−1
ηPDP
%
1 M HCl---413944139128----
IL-11 × 10−541226312410872.1
5 × 10−541013712711285.5
1 × 10−44117712911491.8
5 × 10−44093813312295.9
1 × 10−34103013512596.8
IL-21 × 10−541917212711281.8
5 × 10−542013512811385.7
1 × 10−44138313212291.2
5 × 10−43983613512596.2
1 × 10−33973213812696.6
IL-31 × 10−541533513012164.5
5 × 10−541728213411870.1
1 × 10−441115213611983.8
5 × 10−44108313511691.2
1 × 10−33934313212095.4
Table 5. Electrochemical parameters obtained under 4 temperatures with and without ILs.
Table 5. Electrochemical parameters obtained under 4 temperatures with and without ILs.
MediumTemperature
K
−Ecorr
mV/ECS
icorr
µA cm−2
−βc
mV dec−1
βa
mV dec−1
ηPDP
%
Blank298413944139128---
3084101690137129---
3184112328126125---
3284123387120133---
IL-12984103013512596.8
3084148812712794.7
31844018713511991.9
32841640212212888.1
IL-22983973213812696.6
3084369213512494.5
31841119013012891.8
32841241313212387.8
IL-32983934313212095.4
30841910713012393.7
31841820813112291.0
32843144212712686.9
Table 6. Values of Ea, ΔHa, and ΔSa without and with treatment of IL compounds.
Table 6. Values of Ea, ΔHa, and ΔSa without and with treatment of IL compounds.
MediumEa (KJ/mol)ΔHa (KJ/mol)ΔSa (J/mol K)
Blank33.831.2−82.7
IL-169.566.98.5
IL-268.565.75.0
IL-362.259.6−13.2
Table 7. DFT calculated chemical parameters of the Ils molecules.
Table 7. DFT calculated chemical parameters of the Ils molecules.
ParametersIls 1Ils 2Ils3
EHOMO−0.2343−0.2350−0.2336
ELUMO−0.0941−0.0913−0.0288
ΔEgap (eV)0.14020.14370.2048
η (eV)0.07010.07180.1024
σ (eV−1)14.265313.92759.7656
χ (eV)−0.1642−0.1631−0.1312
ω 0.19230.18520.0840
ε5.20005.399511.9047
ΔN11035.550634.701224.1757
ΔEb–d (eV)−0.0175−0.0179−0.0256
Table 8. Monte Carlo simulation (MC) of Il inhibitors on Fe(110) surface.
Table 8. Monte Carlo simulation (MC) of Il inhibitors on Fe(110) surface.
StructuresTotal EnergyAdsorption EnergyRigid Adsorption Energy
Fe(1 1 0)@ILs 1@H2O−2459.130−3145.745−2521.515
Fe(1 1 0)@ILs 2@H2O−2293.572−2980.188−2347.356
Fe(1 1 0)@ILs 3@H2O−2029.694−2099.160−2088.581
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Omari Alaoui, A.; Messali, M.; Elfalleh, W.; Hammouti, B.; Titi, A.; El-Hajjaji, F. Structure–Activity Relationship of Ionic Liquids for Acid Corrosion Inhibition. Int. J. Mol. Sci. 2025, 26, 5750. https://doi.org/10.3390/ijms26125750

AMA Style

Omari Alaoui A, Messali M, Elfalleh W, Hammouti B, Titi A, El-Hajjaji F. Structure–Activity Relationship of Ionic Liquids for Acid Corrosion Inhibition. International Journal of Molecular Sciences. 2025; 26(12):5750. https://doi.org/10.3390/ijms26125750

Chicago/Turabian Style

Omari Alaoui, Aymane, Mouslim Messali, Walid Elfalleh, Belkheir Hammouti, Abderrahim Titi, and Fadoua El-Hajjaji. 2025. "Structure–Activity Relationship of Ionic Liquids for Acid Corrosion Inhibition" International Journal of Molecular Sciences 26, no. 12: 5750. https://doi.org/10.3390/ijms26125750

APA Style

Omari Alaoui, A., Messali, M., Elfalleh, W., Hammouti, B., Titi, A., & El-Hajjaji, F. (2025). Structure–Activity Relationship of Ionic Liquids for Acid Corrosion Inhibition. International Journal of Molecular Sciences, 26(12), 5750. https://doi.org/10.3390/ijms26125750

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