Some New Synthesized Gemini Cationic Surfactants as Corrosion Inhibitors for Carbon Steel in Hydrochloric Acid Solution

The effect of newly synthesized gemini surfactants on the corrosion of carbon steel in 1-M HCl was investigated. The outcomes show that the inhibition effectiveness of the compounds is affected by the increasing concentration and the capability to produce micelles in an aqueous solution. Weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques were used in the investigation. The obtained results show that these surfactants behave as good corrosion inhibitors. With increasing surfactant concentrations, the inhibition efficiency of the investigated compounds increases. The results show that the inhibition efficiency for the best inhibitor has 97.9% at 100 ppm. Changes in impedance parameters (charge transfer resistance, Rct, and double-layer capacitance, Cdl) were indicative of surfactant adsorption on the metal surface, resulting in the formation of a protective film, according to EIS results. The measurements of potentiodynamic polarization revealed that the inhibitors are mixed type. Physical and chemical adsorption are demonstrated by these gemini surfactants and is governed by the Langmuir adsorption isotherm. The morphology of the C-steel surface and the protective film on the surface was studied using SEM, AFM, and XPS characterization. The results of the various procedures agreed very well.


Introduction
Carbon steel is extensively used in industry: marine requirements, nuclear plants, shipping, chemical processing, etc. [1][2][3][4].The broad applications of carbon steel owing to its low cost and suitable mechanical properties [5][6][7].Carbon steel corrodes in a variety of media and hydrochloric acid is commonly used for various purposes, for example, cleaning equipment, acid pickling, the removal of rust, the acidification of oil wells in oil rescue, and petrochemical methods [8][9][10].
Many authors have investigated the use of surfactants as corrosion inhibitors [27][28][29][30][31][32][33][34][35][36][37][38][39].Surfactant inhibitors have numerous advantages, including high inhibition efficiency, low cost, low toxicity, and ease of manufacture [40].Therefore, the study of the relationship between adsorption and corrosion inhibition is very important.Gemini surfactants are prepared using two conventional surfactants joined by a spacer [41][42][43][44].As a result, gemini surfactants exhibit superior properties compared to traditional types of surfactants.It has a low critical micelle concentration, high surface tension lowering ability, and high biological activity [45].Thus, higher inhibition efficiencies are expected at lower concentrations compared to monomeric equivalents.Many studies have demonstrated the high inhibition efficiency of gemini surfactants [46][47][48][49][50]. From an ecological standpoint, the toxicity of gemini surfactants is lower than that of their monomeric equivalents [51][52][53][54][55].The goal of this paper is to investigate the efficacy of some new gemini cationic surfactants as corrosion inhibitors.Since these compounds possess positively charged N + ions, we expect the inhibitory effect of the compounds through electrostatic attraction on the negative charge induced on the iron surface.Heterocyclic compounds possessing a quaternized nitrogen were established to have corrosion hindrance [45].In this study, we used weight loss and electrochemical methods for the kinetic studies, and SEM, AFM, and XPS as tools for surface inspection.

Weight Loss Method
C-steel coupons with dimensions of (2.0 × 2.0 × 0.2) cm were used.Coupons were abraded using emery papers with different grit sizes (400, 800, and 1200) and then the coupons were weighed after washing with water and acetone and drying well.C-steel coupons were dipped in 100 ml of 1-M HCl with and without surfactants.The coupons were weighed every hour for 6 hours.The previous steps were repeated using a water bath at various temperatures ranging from 298 to 318 K with an accuracy of ±0.1 o C .After a certain time of immersion, the C-steel coupon is rinsed and weighed after drying using a four-digit balance.

Electrochemical Techniques
A three-electrode glass cell was used.The working electrode area of 1 cm 2 was fixed to a Teflon holder.The counter electrode was a platinum sheet fixed to a wire covered with a glass rod and the SCE was used as the reference electrode.The C-steel electrodes were polished with 400, 800, and 1200 grit to ensure their smoothness, washed with double distilled water, degreased with acetone, and then dried.An alternative voltage is applied and the electrode potential changes from − 250 to + 250 mV with respect to the opencircuit potential (E OCP ) at a sweep rate of 2 mV.s −1 .The relationship between Tafel polarization and current density was obtained and plotted with a potentiostat device.EIS experiments were performed at 298 K with a frequency range of 100 kHz to 0.2 Hz and OCP with a 10-mV amplitude.Experiments were performed using (potentiostat/galvanostat/ZRA (Gamry Reference 3000)).

Effect of Concentration
Using Eqs. 1 and 2, the efficiencies and corrosion rates were calculated after the addition of different concentrations of the investigated compounds.
where W uninhibited and W inhibited are the weight loss of coupons with and without the inhibitor, respectively.The variation in the weight loss with time is shown in Figs. 1, 2, and 3, and the inhibition efficiencies of the examined surfactants are summarized in table S1.
Figures 1, 2, and 3 and Table S1 show the decrease in corrosion rate with increasing surfactant concentration.The inhibitory effect is due to the blocking of corrosion sites and reduction of metal dissolution by surfactants adsorbed on metal surfaces [57].Table S1 shows that the order C3 > C2 > C1 has the highest inhibitory efficiency.This behavior confirms the high inhibition efficiency of the longest hydrocarbon chains [58].C3 efficiency was found to decrease at concentrations above 100 ppm.This may be related to the very low CMC value of this surfactant.When the surfactant reaches its critical micelle concentration, the inhibitor agglomerates away from the C-steel surface, increasing the area exposed to the corrosive medium and increasing the corrosion rate [59].

Effect of Temperature
The effect of temperature on the corrosion rate of carbon steel in 1-M hydrochloric acid with different surfactant concentrations was investigated.The temperature range is 298K-318K.Figures 4, 5 and S3.The inhibition increases as the temperature rises, which means the chemical adsorption of surfactant on the C-steel surface.In chemisorption, high activation energy is required, heat raises the energy of molecules until it exceeds the activation energy for adsorption, and then more molecules were adsorbed [60].

Kinetic and Thermodynamic Parameters of Corrosion
The activation energies of the corrosion reactions were calculated at different temperatures using the Arrhenius and transition state Eqs. 3 and 4, respectively.
where K corr is the corrosion rate of C-steel in 1-M HCl at a particular temperature, T, Ea is the activation energy for this reaction, and R is the general gas constant.For C1 activation Table S4 summarizes the results of various thermodynamic parameter calculations.Knowing that N is the Avogadro number and h is the Planck's constant.
From Table S4, the activation energy increases with increasing surfactant concentration, indicating an increase .  in the energy required for the corrosion reaction [61].The endothermic nature of the corrosion reaction was indicated by a positive enthalpy change value [62] and an increase in enthalpy value as inhibitor concentration increases, revealing the efficiency of the inhibitor and decreasing corrosion rate of the C-steel [63].Entropy change also has negative values, which is a sign of a decrease in disorder [64].This indicates that activated complexes tend toward the association process rather than dissociation.This means less disturbance when transitioning from the reactants to the activated complex and better adsorption of the inhibitors to the metal surface.

Adsorption Isotherms
Inhibitor efficiency depends on the adsorption of inhibitor molecules to the surface of C-steel.Adsorption isotherms are used to understand the nature of the interaction between the produced film and the metal surface [65].Adsorption occurs by displacing water molecules on the metal surface with inhibitor molecules, as in Eq. 5 [66].Adsorption depends on a number of factors, including the type of metal and its surface properties and corrosive properties, medium used, pH value, and temperature.
where (I) is the inhibitor added to the corrosive medium and (X) is the number of water molecules on the carbon steel surface displaced by the inhibitor.Using the surface coverage values calculated from the weight loss method, the relationship between surface coverage and different concentrations ( 5) of surfactants prepared at different temperatures was drawn.The greatest fit belonged to the Langmuir adsorption model with correlation coefficients (R 2 = 0:99) for all surfactants.The Langmuir model correlation is displayed in Eq. 6.
where K ads is the adsorption constant, θ is the inhibitor surface coverage, and C is the surfactant concentration.where ΔG • ads is the free energy of adsorption, 55.5 represented the water concentration in an acid solution, T is the temperature in Kelvin, and R is the universal gas constant (J mol −1 K −1 ).
Figure 15 represents the relation between logK ads and 1000/T.From the slope of the linear relation, the change in enthalpy was calculated.Studied and calculated different   parameters for the adsorption process were mentioned in Table S5.Changes in enthalpy were estimated by the slope of the linear relation between temperatures in Kelvin and standard free energy of adsorption as in Fig. 16.
As shown in Table S5, the adsorption constant rises as the temperature rises.ΔG • ads for the investigated compounds was negative, indicating a spontaneous adsorption process (30).

It is known that when the value of ΔG •
ads is less than -20 kJ/ mol, the adsorption process by physical adsorption occurs, but when the value of ΔG • ads is large, more than -40 kJ/mol., this indicates that a chemisorption process is occurring.From the data in Table S5, the values of ΔG • ads are less than -40 kJ/ mol but greater than -20 kJ/mol.This means that physical or chemical adsorption processes take place and there is a strong tendency toward physisorption [67].
A positive sign associated with the enthalpy change ( ΔH • ads ) indicates that the adsorption process is endothermic.This indicates that the adsorption of surfactants on carbon steel surfaces is endothermic [68].The value of ΔH • ads is greater than 40kJ/mol and less than 100kJ/mol, implying physical and chemical adsorption.A negative sign confirms a more regular system.The adsorption of the surfactant on the C-steel surface reduces the degree of distribution and increases the negative value [69].

Potentiodynamic Polarization
Tafel polarization was studied for carbon steel in 1-M HCl without and with different inhibitor concentrations at 25 °C (Figs.17,18,19).Electrochemical parameters including Tafel slope (βa, βc), current density of corrosion ( i corr ) , corrosion potential (E corr ), inhibitor efficiency (%IE), and surface coverage (θ) were calculated.These parameters are summarized in Table S6.where I 0 corr denotes the corrosion current density of the blank solution and I corr denotes the corrosion current densities of the inhibited solutions.
According to Table 6S, the current density decreased as the inhibitor concentration increased.This indicates a high adsorption of compounds on the surface of carbon steel.Compare the decrease in corrosion current density for C1, C2, and C3.We found that C3 had the lowest value i corr .The efficiencies can be ordered as C3 > C2 > C1.This order of efficiency is consistent with increasing carbon chain length.From the potentiodynamic polarization curves, both the anodic and cathodic curves shifted to lower current densities compared to the blank.This speculated that the investigated compounds reduced both anodic dissolution and cathodic hydrogen evolution [70].Moreover, increasing concentrations of the compounds did not significantly alter the values of the βa and βc slopes.This suggests that the mechanism was accomplished by simply blocking the anodic and cathodic sites on the C-steel surface.E corr of C-steel shifted from the blank value by less than 25 mV in the cathodic direction.It has been reported that they can be classified as cathodic or anodic inhibitors if the change in E corr exceeds 85 mV compared to the blank E corr [71].This indicates that all investigated inhibitors act as mixedtype inhibitors with higher cathodic values.

Electrochemical Impedance Spectroscopy
The impedance of the investigated surfactants was investigated at 298 K in the absence and presence of various concentrations of the compounds.Figures 20,21 All variables obtained from impedance spectroscopy are shown in Table S7.Inhibition efficiency was calculated using Eqs.11 and 12.
where R • ct is the resistance of charge transfer for uninhibited solutions and R ct is the resistance of charge transfer for inhibited solutions.Where C dl is the double-layer capacity and f max is the highest angular frequency.
Equations 11 and 12 are used to calculate the charge transfer resistance; R ct is the the double-layer capacitance; C dl is the inhibition efficiency (η), and surface coverage is denoted as (θ).The data are summarized in Table S7.We used the program ZSimpWin3.60 to fit the experimental data to comparable loop models (Fig. 26).R1 is the solution and CPE1 is the constant phase element, associated with the capacitive performance of the film on the surface parallel to the resistance (R2); a constant phase element (CPE) is used instead of a capacitor.
Surfactant molecules are adsorbed on metal surfaces, and as the concentration increases, the adsorption layer thickens and the bilayer thins [72].Results obtained from EIS show increased inhibition with increasing surfactant concentrations.This implies a more adsorbed layer on the metal surface and increased inhibition due to an increased molecular weight, with good agreement between the results obtained from various tests.

SEM Technique
To investigate the surface morphology [73], C-steel bars were immersed in corrosive medium (1-M HCl) and corrosive medium containing 100-ppm C3 at 298 K. and 318 K for 24 h. Figure 27(a-c) shows the effect of adding C3 to the surface of C-steel. Figure 27b represents the surface of the C-steel in corrosive media without any addition of inhibitor C3, confirming the formation of rust on the metal surface due to exposure to corrosive media oxygen, water molecules, and chloride ions as given in Eqs. 13 and 14. ( 12) The figure indicates the formation of a protective adsorbed layer on the surface of the C-steel.

Atomic Force Microscopy (AFM) Analysis
The surface morphology photos of the C-steel surface were taken.Another set of experiments involved photographing C-steel immersed in 1-M HCl in the absence and presence of 100-ppm C3 inhibitor for 24 h at 298 K. Images are shown in Fig. 28(a-c).The parameters are summarized in Table S8, where S a represents the roughness, S q is a symbol for the root mean square, S p is a sign for peak high, S m represents the mean value, Sv is the valley depth, and Sy is a symbol for the peak valley height [74][75][76].
From the data, we can conclude that the roughness of the blank increases as temperature increases.In the presence of C3, the surface roughness decreased with increasing temperature, which confirms the chemical adsorption of the inhibitor.

X-Ray Photoelectron Technique
The binding energy is plotted against the number of electrons escaped per second.The position of the peak of this curve represents the adsorbed atoms and the intensity represents the concentration of the adsorbed element [77].The C-steel bar is released in a corrosive medium (1-M HCl) for 24 h in the presence of 100 ppm of the investigated surfactant.
Inhibitor adsorption of C3 was investigated by XPS as shown in Fig. 29(a-f).From the XPS data, there is adsorption of the inhibitor to the metal surface.As shown in Fig. 29, the maximum intensity of the entire spectrum increases from C1 to C3.This means that as the carbon chain length of the hydrophilic moiety increases, greater adsorption occurs and inhibitor effectiveness increases.

The Adsorption Mechanism
Various types of adsorption can occur during the inhibition process: (a) electrostatic attraction between charged metal surfaces and other charged ions, (b) interactions between lone pairs of electrons present in N/O atoms and metals, (c) interaction of pi-electrons with metals, or (d) a combination of the above [78].
Since the surface of carbon steel has a positive charge, the Cl − ions from the addition of hydrochloric acid and surfactant are attracted to the metal surface, causing the positively charged metal surface to flip to a negatively charged surface.This negative charge attracts molecules containing (N +).Through the various calculated parameters, a combination of adsorption mechanisms is involved.The inhibition efficiency is affected by several factors, including the density of adsorption sites and their charge, the formation of complexes with metal surfaces, and molecular size.In turn, the molecular weight of the inhibitor affects its efficiency, and more surface corrosion sites are covered by the inhibitor [79,80].That is what happened when the carbon chain length of the gemini cationic surfactant was increased.The efficiency can be ordered as C3 > C2 > C1.

Conclusion
The collected results lead to the following conclusions.

Scheme 1 Scheme 2 Scheme 3
Scheme 1 Chemical structure of C1 , 6, and 7 show the weight loss(1) ) C.R = weight loss time variation with time at different temperatures for C-steel in the absence and presence of 100 ppm from different compounds under investigation.Various parameters considered from the weight loss data are shown in Tables S2

Fig. 1 Fig. 2
Fig. 1 Weight loss vs. time for dissolution of C-steel without and with different concentrations of C1 in 1-M HCl at (298 K) from the slope of the relationship between 1000/T and log K corr as shown in Figs.8, 9, and 10.The change in enthalpy was calculated from the slope of the line and the entropy change from the intercept, as shown in Figs.11, 12, and 13.

( 10 )Fig. 14 CFig. 15 Fig. 16
Fig. 14 C against concentration (C), Langmuir adsorption isotherm model for different concentrations of the three surfactants at 298 K , and 22 show the Nyquist plots, whereas Figs. 23, 24, and 25 show the Bode plots of the studied compounds.

Fig. 24 Fig. 25 Fig. 26
Fig. 24 Bode plotting for C-steel present in 1-M HCl without and with different concentrations of C1

Fig. 27 a
Fig. 27 a C-steel free, b C-steel in the blank at 298 K, and c C-steel in 100 ppm C3 at 298K

( 1 )
The corrosion-inhibiting properties of N, Nʹ-((1, 4-phenylene bis(oxy)) bis(2-oxoethane-2,1-diyl)) derivatives were investigated.According to the results of the testing, the produced surfactants are effective inhibitors of carbon steel corrosion in 1-M HCl.(2)The inhibition efficiencies of the investigated compounds increase with increasing inhibitor concentrations (3) The order of the inhibition efficiency decreases in the order C3 > C2 > C1, which is same as the order of decreasing in the hydrocarbon chain length.(4) The results show that the adsorption of the investigated compounds follows Langmuir's adsorption isotherm.(5)The inhibitors behave as mixed-type inhibitors.(6)The results obtained from weight loss, potentiodynamic, and EIS are in good agreement.(7)The results obtained from chemical and electrochemical methods are supported by SEM and AFM analytical techniques.

Fig. 29 a
Fig. 29 a-f XPS for steel immersed in HCl for 24 h in the presence of 100ppm of C3, where a C1s spectrum, b for N1S spectrum, C for O1S spectrum, d for Fe 2P spectrum, e represented a survey for adsorption, and f XPS survey for different three surfactants ◂ which has a molecular weight of 832.14 g/mol and its chemical formula is C 44 H 80 N 4 O 6 Cl 2 .C3 is N,N′-((1,4-