Corrosion Inhibition Performances of Imidazole Derivatives-Based New Ionic Liquids on Carbon Steel in Brackish Water

Round 1

Reviewer 1 Report

1. Judging from semi-circular data shown in Figure 2, the data accuracy of IE% estimated by authors must be too good.

 

2. Line 157-160 and Figure 3

From the viewpoint of the above point 1 and Figure 3, the sentences such as “the optimal concentration for IL1 is 80 ppm and for IL2 is 100 ppm” are not adequate. “IE% curve becomes almost flat in the range from 80(or 60) to 120ppm” or other expressions should be better.

 

3. Table 2

Error values of IE% were added in Table 2 in the revised manuscript. From just the same reason of the above point, the error values must be not correct. Especially, the error values of 0.00 for several data are utterly strange.

 

4. Figure 4

In this figure, Langmuir and Temkin models are used.

The two models are based on different concept of absorption such as absorption mechanism or absorption energy dependence on concentration. The reviewer recommends the author to describe the difference of concepts of the two models for readers’ understanding and also to describe the applicable concentration range (or applying concentration range) of the two models in Figure 4 to estimate the thermodynamic values such as Tables 3 and 4. (especially for Langmuir model)

 

5. Line 240-242 and Figure 5

Arrhenius type of equation is applied to estimate activation energy in Figure 5. However, apparently almost all data do not show a linear tendency in Figure 5 except several conditions. The author should describe what range of the data in Figure 5 are applied to estimate the energy values or how to estimate the slope for non-linear data.

At least, from the data at the 4 different temperatures (Figure 5 (a)&(b)), it is not possible to estimate the slopes (or activation energies) at the 4 different temperatures (Figure 5 (c)&(d))

 

6. Equation (8)

Is really the equation correct? (or is Equation (7) correct?)

If it is correct, the authors shoudld describe the explanation on difference of equation meanings between Equations (7) & (8).

The reviewer recognizes that I corr is a kind of parameters expressing a corrosion reaction rate(speed). It is not correct, is it?

 

(Miscellaneous)

7. Line 202

If Eq. (3) is applied, the expression of “The intercept section (b) equal to the Kads value”must be “The reciprocal value (b) of the intercept section . . . “

 

8. Figure 4 (a)

The reviewer recommends the authors to change the scale of the figure to include “Zero” value (C=0) as for X axis, because the authors carried out estimation of the intercept section from the figure.

Author Response

Reviewer # 1

 

1. Judging from semi-circular data shown in Figure 2, the data accuracy of IE% estimated by authors must be too good.

Answer and Correction from the Authors:

The authors have revised and expanded the judging from semi-circular data shown in Figure 2 in the manuscript.

1. Line 157-160 and Figure 3

From the viewpoint of the above point 1 and Figure 3, the sentences such as “the optimal concentration for IL1 is 80 ppm and for IL2 is 100 ppm” are not adequate. “IE% curve becomes almost flat in the range from 80(or 60) to 120ppm” or other expressions should be better.

 Answer and Correction from the Authors:

The authors have added and revised the explanation for  Figure 3 the sentences of “the optimal concentration for IL1 is 80 ppm and for IL2 is 100 ppm” in the manuscript.

1. Table 2

Error values of IE% were added in Table 2 in the revised manuscript. From just the same reason of the above point, the error values must be not correct. Especially, the error values of 0.00 for several data are utterly strange.

Answer and Correction from the Authors:

Thank you for the comments, the authors agree with this correction. This Table has been revised based on the previous comment of a reviewer, so the authors followed that comment. But, now the authors are back to the real data we have.

1. Figure 4

In this figure, Langmuir and Temkin models are used.

The two models are based on different concept of absorption such as absorption mechanism or absorption energy dependence on concentration. The reviewer recommends the author to describe the difference of concepts of the two models for readers’ understanding and also to describe the applicable concentration range (or applying concentration range) of the two models in Figure 4 to estimate the thermodynamic values such as Tables 3 and 4. (especially for Langmuir model)

 Answer and Correction from the Authors:

The authors have added the explanation on the differences of Langmuir and Temkin isotherm models in the manuscript.

1. Line 240-242 and Figure 5

Arrhenius type of equation is applied to estimate activation energy in Figure 5. However, apparently almost all data do not show a linear tendency in Figure 5 except several conditions. The author should describe what range of the data in Figure 5 are applied to estimate the energy values or how to estimate the slope for non-linear data.

At least, from the data at the 4 different temperatures (Figure 5 (a)&(b)), it is not possible to estimate the slopes (or activation energies) at the 4 different temperatures (Figure 5 (c)&(d))

  Answer and Correction from the Authors:

The data in Figure 5 are used to estimate the  activation energy with the linier equation was arranged to

So, Ln (Icorr ) is linier function to 1/T, also it can be used to get the Ea  values at various temperatures. The authors have revised the Figure 5 (a&b).

1. Equation (8)

Is really the equation correct? (or is Equation (7) correct?)

If it is correct, the authors shoudld describe the explanation on difference of equation meanings between Equations (7) & (8).

The reviewer recognizes that I corr is a kind of parameters expressing a corrosion reaction rate(speed). It is not correct, is it?

Answer and Correction from the Authors:

The equations (7) & (8) are correct. The reviewer recognizes that I corr is a kind of parameters expressing a corrosion reaction rate(speed), it is true, the authors have added the statement about Icorr in the manuscript.

1. Line 202

If Eq. (3) is applied, the expression of “The intercept section (b) equal to the Kads value”must be “The reciprocal value (b) of the intercept section . . . “

 Answer and Correction from the Authors:

Yes, it means. Eq.3 used for expressing the values of Kads, which can be used to determine the delta G ads.

1. Figure 4 (a)

The reviewer recommends the authors to change the scale of the figure to include “Zero” value (C=0) as for X axis, because the authors carried out estimation of the intercept section from the figure.

Answer and Correction from the Authors:

The authors have revised the Figure 4(a) in the manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper, corrosion inhibition performances of imidazole derivatives-based new ionic liquids on carbon steel in brackish water, written by Megawati Zunita et al., investigated the anti-corrosion behavior of two types of ionic liquids on carbon steel and gave a proposed adsorption mechanism that fitted Langmuir adsorption isotherm model.

 

Since I am not an expert in the anti-corrosion field, I would like only to give the suggestions in my knowledge domain.

 

1. The chemical structures in Figure 1 should redraw, and I recommend to use ‘ACS Document 1996’ format. Moreover, what is the anion? And where is the charge?
2. Line 318-322, I double the absorption mechanism supposed here. In my opinion, the interface of the steel and saltwater might be more complex than presented. The oxygen atom is difficult to be an important role, and electrostatic interaction might be stronger then pi-Fe interaction. Of course, all of these need to be demonstrated by detailed experiments (not in this paper, but for further research).

 

I recommend accepting this paper after minor modification. But, as I mentioned, I am not an expert in this field, so please consider suggestions from other reviewers more.

Author Response

1. The chemical structures in Figure 1 should be redrawn, and I recommend to use ‘ACS Document 1996’ format. Moreover, what is the anion? And where is the charge?

Answer and Correction from the Authors:

The authors have redrawn of Figure 1. The anion of IL1 and IL2 are iodine ion and the charge has been drawn in the chemical structure in Figure 1.

 

1. Line 318-322, I double the absorption mechanism supposed here. In my opinion, the interface of the steel and saltwater might be more complex than presented. The oxygen atom is difficult to be an important role, and electrostatic interaction might be stronger then pi-Fe interaction. Of course, all of these need to be demonstrated by detailed experiments (not in this paper, but for further research).

 Answer and Correction from the Authors:

Thank you for the comments. Figure 6 showed a general demonstration of IL1 and IL2 in protecting the metal surfaces. For deep studies of some interactions including electrostatic interaction, The authors agree with the reviewer’s comment to publish in a new paper.

 

I recommend accepting this paper after minor modification. But, as I mentioned, I am not an expert in this field, so please consider suggestions from other reviewers more.

Reviewer 3 Report

The work entitled “Corrosion Inhibition Performances of Imidazole Derivatives-based New Ionic Liquids on Carbon Steel in Brackish Water” describes the preparation new imidazole derivatives-based ILs (1,3-dipropyl-2-(2-propoxyphenyl)-4,5-diphenylimidazole iodide (IL1) and 1,3-dibutyl-2-(2-butoxyphenyl)-4,5-diphenylimidazole iodide (IL2)) and their use as corrosion inhibitors. In particular, the inhibition effects of ILs were investigated on carbon steel in brackish water media. The approach is similar to previous works reported by the authors, that use a non-ionic similar compounds. Finally, the adsorption mechanisms of IL1 and IL2 on carbon steel surfaces were also determined which followed the Langmuir adsorption isotherm model. I would like to recommend the manuscript for publication but there are many major revisions and relevant literature should be added.

In the introduction, the literature of Ionic Liquids must be improve (line 58-61). In particular, more recent paper can be added (for example Chem. Sci., 2020,11, 6405-6422, Phys. Chem. Chem. Phys., 2017, 19, 8201—8209, Biophysical Reviews, 2018, 10(3), pp.691-706, Journal of Thermal Analysis and Calorimetry (2019) 138, 3335–3345)

A NMR, FTIR, and HR-ESI-MS spectrum are needed (for example in supporting information) for purity determination of ILs.

Line 153 “The IE% of IL2 was higher than IL1 due to the presence of three butyl chains in IL2 that increased hydrophobicity and this decreased the interaction between steel surfaces and corrosion agents”. This assumption was expanse ad analyzed in deep with some similar example reported in literature.

Line 177 The authors report that the ILs are insoluble in water. This is partially confirmed by inhibition experiments. Also, for a correct quantification of leaching, it is necessary to establish the water solubility for the two ILs in the range 25-55°C. Furthermore, the increase of solubility in function of temperature could justify the trend reported in table 2. Please Author comment on this aspect.

In table 6 different values of DH* and DS* were obtained for the blank. The trend was confirmed in all range of concentration with exception of 60 ppm value. If the data are confirmed, how the authors explain this?

Author Response

The work entitled “Corrosion Inhibition Performances of Imidazole Derivatives-based New Ionic Liquids on Carbon Steel in Brackish Water” describes the preparation new imidazole derivatives-based ILs (1,3-dipropyl-2-(2-propoxyphenyl)-4,5-diphenylimidazole iodide (IL1) and 1,3-dibutyl-2-(2-butoxyphenyl)-4,5-diphenylimidazole iodide (IL2)) and their use as corrosion inhibitors. In particular, the inhibition effects of ILs were investigated on carbon steel in brackish water media. The approach is similar to previous works reported by the authors, that use a non-ionic similar compounds. Finally, the adsorption mechanisms of IL1 and IL2 on carbon steel surfaces were also determined which followed the Langmuir adsorption isotherm model. I would like to recommend the manuscript for publication but there are many major revisions and relevant literature should be added.

In the introduction, the literature of Ionic Liquids must be improve (line 58-61). In particular, more recent paper can be added (for example Chem. Sci., 2020,11, 6405-6422, Phys. Chem. Chem. Phys., 2017, 19, 8201—8209, Biophysical Reviews, 2018, 10(3), pp.691-706, Journal of Thermal Analysis and Calorimetry (2019) 138, 3335–3345)

 Answer and Correction from the Authors:

The authors have added the references as suggested by reviewer in the manuscript.

A NMR, FTIR, and HR-ESI-MS spectrum are needed (for example in supporting information) for purity determination of ILs.

 Answer and Correction from the Authors:

The authors have added the characterization data of IL1 and IL2 in the manuscript in the result and discussion section.

Line 153 “The IE% of IL2 was higher than IL1 due to the presence of three butyl chains in IL2 that increased hydrophobicity and this decreased the interaction between steel surfaces and corrosion agents”. This assumption was expanse and analyzed in deep with some similar example reported in literature.

 Answer and Correction from the Authors:

The authors have added, expanded, and analyzed in deep based on the similar reported literature.

Line 177 The authors report that the ILs are insoluble in water. This is partially confirmed by inhibition experiments. Also, for a correct quantification of leaching, it is necessary to establish the water solubility for the two ILs in the range 25-55°C. Furthermore, the increase of solubility is function of temperature could justify the trend reported in table 2. Please Author comment on this aspect.

Answer and Correction from the Authors:

The authors have conducted measurement of ILs solubility with Solvatochromic shifts of Reichardt’s dye method in the range 25-55°C and the results showed that the ILs are relatively non-polar and consistent with their lower solubility in water at the high temperature.

In table 6 different values of DH* and DS* were obtained for the blank. The trend was confirmed in all range of concentration with exception of 60 ppm value. If the data are confirmed, how the authors explain this?

Answer and Correction from the Authors:

Thank you for the correction. In our experiments, we used different blanks for IL1 and IL2 tested as corrosion inhibitor in brackish water. We did not mix both of IL1 and IL1 into one system, but we observed with two different system and same compositions of blank and the results of DH* and DS* are relatively close around 23-28 (kJ/mol), and for 60 ppm the authors have revised the DH* value, which was a typographical  error in the manuscript.

Round 2

Reviewer 1 Report

Figure 5 (a) (b)

ΔG was estimated from pseudo-Arrhenius plots of Figure 5(a) and (b).
In the cases of no or low IL adding conditions, linear relations can be observed in the figures, then ΔG can be estimated. However, In the case of high IL adding conditions, the plots apparently show non-linear relations. Thus, ΔG cannot be estimated from the non-linear plots properly. This means that almost data of Table 6 should be unreliable.

Even if the authors want to estimate ΔG value in a limited condition from those figures, they should describe why the value can be estimated in the limited condition with some justifying reasons.

Author Response

Please see the attachment for our response.

Author Response File: Author Response.docx

Reviewer 3 Report

Now the manuscript can be accepted in present form.

Author Response

We thank the reviewer for accepting our paper.

Round 3

Reviewer 1 Report

First, the reviewer insists that this paper shows interesting results for corrosion inhibition properties of imidazolic ionic liquids (ILs) with different alkyl groups on carbon steel in blackish water.

Figures 5(a)&(b) are important figures which provide fundamental and insightful information on inhibition activity as a function of temperature and ILs’ concentration.

However,

some of thermodynamic analyses of this paper are not adequate. So, the reviewer strongly recommends the authors to revise the manuscript or remove non-adequate part of the discussion.

 

Figures 5(a)&(b) and Table 5

The analysis of data or estimation of parameters relating to the figures is not adequate.

The authors tried to analyze the data by the Arrhenius type of analysis. The Arrhenius analysis can be applicable when linear dependence of the tendency is observed. In this sense, no or low IL addition data have such a linear tendency, thus the analysis can be used to estimate activation energy or other thermodynamic parameters. But, data with high IL concentrations apparently have non-linear tendencies (decreasing curves with convex shape). This feature indicates that the reaction is not a simple one and the Arrhenius analysis cannot be applied. In some cases, such type of tendency is analyzed by the Arrhenius plot under a limited consideration such as within a narrow temperature range in order to estimate “apparent” activation energies or thermodynamic parameters. The authors may insist that analysis in this paper was performed under such a limited condition, However, in the case, the deviation of each data from the fitting line is very large so that the accurate fitting cannot been achieved. Then, obtained thermodynamic data must have a large error.

Therefore, as for data of Table 5, the data is not reliable. Even if the author dare to carry out this type of analyses (with large errors), the author must describe the limited condition and the limited applicability of the data (and description of data accuracy).

The review recommends the authors not to carry out this type of analyses if possible.

 

Table 6

The authors did not show the Arrhenius plot to obtain the thermodynamic parameters in Table 6 using Equation 8. However, the authors must have carried out the plots. The value of ln(Icorr/T) is plotted against 1/T in the plots, instead of the value of ln(Icorr) in Figures 5(a)&(b). The plots should show similar decaying tendencies to the Figure 5 (a)&(b) (see the description (**) shown below). We can easily find the similar tendency from the data of Figures 5 (a)&(b). Thus, from the same reason in Figure 5, the estimation method of thermodynamic data should not be applicable to estimate the thermodynamic data in Table 6. Even if the analysis is applied to the data, the authors describe the fact of non-linear relation and the error contained in the obtained data.

 

 

Even not using Tables 5&6 and Figure 5(c)&(d), Figure 5 shows the corrosion inhibition activity of IL. From the figure, the important results of corrosion inhibition property in this paper itself should not change.

Addition to the point that corrosion activity of IL could be observed, the tendency that the activity is prominent for lower temperatures is observed, (On the other hand, the activity becomes lower for higher temperatures.)  

 

 

(**)

In Figure 5, ln(Icorr) of y-axis changes from about 16.5 to about 18.0-19.0, which means that Icorr largely changed about 5-15 times. On the other hand, (1/T) changes from about 3.05 to about 3.35 by about 10% difference. From those, the value of Icorr/T should change about 4.5-13.5 times. Thus ln(Icorr/T) of y-axis of the Arrhenius plots for Table 6 must have almost the same decaying tendency with increasing 1/T as that shown in Figure 5 for each IL concentration data. (Each data for samples with higher ILs’ concentrations show a decreasing curve with a convex shape.)

 

Author Response

Please see the attachment

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

In this paper, the authors tested an inhibition property of new ionic liquids and shows that they has as inhibition property on corrosion reaction in brackish water in some degree. This result itself should be interesting. However, thermodynamic analyses on obtained results should not be adequate.

For example,

(1)Some usage of thermodynamic words such as "spontaneous" should not be correct.

(2) Applicability of the models on their results and reliability of obtained thermodynamic values must be checked more carefully.

(3) Accuracy of data should be more carefully discussed.

(4) Due to the inappropriate evaluation of data accuracy, some interpretations of some Figures or Tables should become non-adequate.

Author Response

 

Please see the attachment

Author Response File: Author Response.doc

Reviewer 2 Report

General comments

The present article reports the corrosion inhibition performance of two ionic liquids on carbon steel surface in brackish water. However, the final purpose of this paper isn’t fully clear. Also, why were these ionic liquid types investigated? This manuscript isn’t well organized and is scientifically lack. English has to be remarkably improved and several sentences have to be rewritten. Other sentences are repeated too much times. Conclusions are not sounded. I don’t recommend the present paper for publication.

 

Other specific comments

Introduction, page 2, line 59: ionic liquids cannot be generally defined as “non-toxic”.

Figure 2 should successively be reported with respect to Figure 3.

Table 2: can the authors really estimate an IL content of 19.72 (IL1) and 17.85 (IL2) ppm? It would be better to indicate 20 and 18 ppm, respectively. The error bars contain too many unit digits (i.e., 32.49 ± 0.38 should be replaced with 32.5 ± 0.4).

Figure 3 (AC responses) should be reported in square scale.

Why was a plateau (Figure 2) observed above 80 ppm of IL? Why is the optimal IL concentration equal to 80 ppm? A reasonable explanation should be given.

The authors cannot claim that the best IL concentrations using the direct-coating method are 20 and 18 ppm, respectively, as they have investigated no other IL content.

No comment is provided for Figure 4.

Figure 5 should be more deeply discussed.

Author Response

Please see the attachment

Author Response File: Author Response.doc

Round 2

Reviewer 2 Report

Even if the authors have tried to improve the manuscript, several remarks weren’t addressed. Detailed comments are listed in the followings.

- English was improved, but it has to be checked again through the whole paper

- The lines from 115 through 119 and from 138 through 139 are repetitions of lines from 100 through 104 and from 134 through 135, respectively. Please, check.

- Page 2, line 59: the authors insist that several (maybe, some) ionic liquids are non-toxic, but it is relevant for this manuscript? Are the investigated ionic liquids non-toxic?

- Figure 2 (Inhibition efficiency vs concentration) is obtained from Figure 3 (Nyquist plots). Therefore, the latter should be reported prior Figure 2.

- The error bar has to fall on the last digit unit. Therefore, the values (Table 2) 99.3 ± 1.0, 50.6 ± 1.0 and 33.6 ± 1.0 have to be reported as 99 ± 1, 51 ± 1 and 34 ± 1, respectively.

 - The Nyquist plots have to be reported in square scale and with the same full scale. This is not only for graphical reasons but, overall is fundamental for interpreting the AC responses.

- The authors didn’t explain why the corrosion inhibition decreases upon 80 ppm for IL1 and 100 ppm for IL2.

- The explanation on Figure 5 is confuse.

Therefore, the manuscript isn’t still publishable in the present form.

Author Response

Replies to Reviewer’s Comments

 

General Comment

Even if the authors have tried to improve the manuscript, several remarks weren’t addressed. Detailed comments are listed in the followings.

Response

We thank the reviewer for the comments and we carried out all the corrections pointed out by the reviewer in the revised paper.

Comment

1. English was improved, but it has to be checked again through the whole paper

Response

The paper was checked again for proper English usage and necessary corrections were carried out.

Comment

2. The lines from 115 through 119 and from 138 through 139 are repetitions of lines from 100 through 104 and from 134 through 135, respectively. Please, check.

Response

The redundancies pointed out in the method section were corrected. The statements were not repeated in the revised manuscript.

Comment

3. Page 2, line 59: the authors insist that several (maybe, some) ionic liquids are non-toxic, but it is relevant for this manuscript? Are the investigated ionic liquids non-toxic?

Response

The statement on non-toxic nature of ionic liquids was deleted as we did not test the toxicity of the ILs.

Comment

4. Figure 2 (Inhibition efficiency vs concentration) is obtained from Figure 3 (Nyquist plots). Therefore, the latter should be reported prior Figure 2.

Response

We agree with the reviewer. Thanks for pointing out this sequence. We changed the figures in the revision. Now, Nyquist plots are listed as Figure 2 and Inhibition Efficiency plot is in Figure 3.

Comment

5. The error bar has to fall on the last digit unit. Therefore, the values (Table 2) 99.3 ± 1.0, 50.6 ± 1.0 and 33.6 ± 1.0 have to be reported as 99 ± 1, 51 ± 1 and 34 ± 1, respectively.

Response

The error bars digits are corrected in Table 2 as suggested.

Comment

6. The Nyquist plots have to be reported in square scale and with the same full scale. This is not only for graphical reasons but, overall is fundamental for interpreting the AC responses.

Response

Nyquist plots were corrected with square scale as suggested.

Comment

7. The authors didn’t explain why the corrosion inhibition decreases upon 80 ppm for IL1 and 100 ppm for IL2.

Response

The following explanation is provided for the difference in optimum IL concentrations for IL1 and IL2 in the revision (lines 298-304).

When the IL concentration was increased higher than 80 ppm, the performance of IL1 decreased. This is because IL1 tend to saturate and agglomerate at concentration above 80 ppm. The same phenomenon happened for IL2 when the concentration was increased to higher than 100 ppm. Therefore, the optimum concentration for IL1 is 80 ppm and the optimum concentration for IL2 is 100 ppm at room temperature (25° C). The experimental results by the EIS method show that IL1 and IL2 have good corrosion inhibitor activities on carbon steel surfaces under the brackish water condition. These data were validated by the Tafel method as described below.

 

Comment

8. The explanation on Figure 5 is confusing.

Response

The explanation for Figure 5 was rewritten to make it clear.

 

Round 3

Reviewer 2 Report

The authors have devoted effort for matching the referee recommendations. However, a few issues have still to be addressed for publishing this manuscript.

English still need to be refined.

The error bars of Table 2 are still wrong. For instance, it isn’t correct to report 99 ± 0.45, but 99 ± 1 is right (the error bar has to fall always on the last digit unit of the reported value). All other error bars in Table 2 have to be changed accordingly.

Line 69: Imidazolium-based (not imidazole) ILs cannot be defined as all poorly hydrophobic. For instance, the hydrophobicity depends on the nature of the anion (i.e., if coupled with perfluoroalkylsulfonyl instead BF4 or PF6, imidazolium cations give highly hydrophobic ILs).

Author Response

Please see the attachment for the reply to reviewer's comments

Author Response File: Author Response.doc