Insights into Corrosion Inhibition Behavior of a 5-Mercapto-1, 2, 4-triazole Derivative for Mild Steel in Hydrochloric Acid Solution: Experimental and DFT Studies

Round 1

Reviewer 1 Report

In the manuscript "Insights into corrosion inhibition behavior of a 5-mercapto-1, 2, 4-triazole derivative for mild steel in hydrochloric acid solution complemented with adsorption and DFT studies" Authors reported excellent corrosion inhibition efficiencies of 97% s at 303 K. The compound is promising material for applications in environments where corrosion inhibition is very paramount. In the overall, the work is scientifically sound. The methodology is well expressed for reproducibility and the results are convincing. It is a good contribution to the area of corrosion inhibition study. I consider the manuscript worthy of consideration for publication after a minor revision based on the comments that follow:

1. Check the equation 1. Change “c” by “d”.
2. In section 3.1 author can explain bit more about the process and its phenomenon.
3. Author seems very hurry to submit the revised manuscript therefore he has not even checked the equation numbers properly (please check and put eq. number correctly).
4. Equation 1 to 4 (section 2.5) there is a gap between E and LUMO, please revise it.
5. Figure 8 can be modified (for reference see the following articles and cite)

https://doi.org/10.1016/j.molstruc.2021.130822

https://doi.org/10.1016/j.molliq.2021.116184

https://doi.org/10.1016/j.matchemphys.2021.124613

https://doi.org/10.1007/s40090-020-00222-0

https://doi.org/10.1007/s42452-020-04079-x

6. There are some grammatical and typological errors, please check the entire manuscript and revise it carefully.
7. Author can replace some old paper citations with some newly published articles:

https://doi.org/10.1007/s13369-019-04270-2

https://doi.org/10.1007/s40735-020-00340-3

https://doi.org/10.1007/s40735-020-00368-5

https://doi.org/10.1007/s42452-020-04079-x

https://doi.org/10.1007/s40090-020-00222-0

Author Response

Dear Sir,

Thank you for your useful comments and suggestions all were conducted point by point, so please see the revised manuscript.

Thank you 

Best Regards

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript looks much better now and can be proceeded for publication.

Author Response

Dear Sir,

Thank you for your useful comments and suggestions all were conducted point by point, so please see the revised manuscript.

Thank you 

Best Regards

Reviewer 3 Report

The paper has been strongly improved by the authors that provided an higher quality work: the English was more fluent and comprehensible, several comments with comparisons with literature data were added and the aim and obtained results were better discussed and presented.

Some errors are still present in the work and I provided an attached pdf file which contains all the details of my suggestions. I think that at its present state the proposed paper can be considered for publication only after a further revision.

Here after some general comments:

I suggest a modification of the title of the article (In particular, please, eliminate the word “complemented”)

Introduction

Eliminate the repetion of two identical sentences (see pdf file)

Section 2.2

You have to present in a different way data related to the percentage of elements and the peaks in the FTIR curves. I think that the FTIR curves need to be added to the work.

Section 3.1

The graphs are now more significant, anyway I think you need to improve the image quality and standardize the graphs style. When you present points which are an average of several experimental (or calculated) data, you need to add the error bars referring to the standard deviation.

(Same comments for section 3.2)

Section 3.3

In the previous review I wrote the following comment:

A table with the results of activation energy with different inhibitor concentration in the corroding solution must be added.

When enthalpy and entropy were discussed, only two values were reported, with and without inhibitor, why? You assess that the value of H depends on the slop of the straight lines and I can see one straight line for each inhibitor concentration! Please, can you better explain how the calculation were carried out?

I can see that the section was partially rewritten and there is Table 3 in which all the values were reassumed (pay attention: Table 3 is present in the word file but not in the pdf file!)

Looking at the table I can understand that the values of activation energy are very similar for each concentration of inhibitor: I think you suppose that it is the same for the different concentration of inhibitor. This hypothesis needs to be explained and justified in the text. Furthermore the standard deviation can help to understand if the approximation is tolerable.

Please do not disregard each comments in the pdf file: there are further suggestions which are indispensable for improving the work and let it be published.

Comments for author File: Comments.pdf

Author Response

Dear Sir,

Thank you for your useful comments and suggestions all were conducted point by point, so please see the revised manuscript.

Thank you 

Best Regards

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The manuscript have been adequately modified but some comments of the review were ignored: here after the points missing.

Please note that if the last point (*) will be ignored as in the previous report the paper cannot be considered adequate for publishing in my opinion.

 

Pag. 4 : Please, indicate the density in g/cm3

Pag. 4 : The numbering of the equations is still wrong! You cannot use the same number for indicating several equations, please correct!

Pag. 9 : the data in the Table 3 are referred only to HCl solution with EMTP! Please, add the value for 0 ppm of EMTP or modify the Table caption.

(*) Pag. 9 : For the third time I repeat the same comment:

              When enthalpy and entropy were discussed, only two values were reported, with and without inhibitor, why? You assess that the value of DH depends on the slop of the straight lines and I can see one straight line for each inhibitor concentration! Please, can you better explain how the calculation were carried out?

Looking at the table 3 I can understand that the values of activation energy are very similar for each concentration of inhibitor: I think you suppose that it is the same for the different concentration of inhibitor. This hypothesis needs to be explained and justified in the text.

In the cover letter the authors assess at this comment “Done, please see the revised manuscript” but no comments or explanation about the use of only one value of Activation energy for the solution with inhibitor in several concentrations were added!! This manner is not adequate.

Author Response

Dear Reviewer,

Thank you for useful comments and suggestions all have been done point by point so please see the revised manuscript

Best regards

Author Response File: Author Response.docx

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

General comments

The proposed work is an analysis of the effect of an inhibitor in acid solution with the aim to protect mild steel form corrosion process. The research activity was well structured because several concentration of inhibitor were tested and several parameters were evaluated: the efficiency of the inhibitor was evaluated by the mass loss and the effect of time and temperature were investigated to. Then the enthalpy and entropy of activation where evaluated, the inhibition mechanisms was studied and also the quantum parameters.

Although the work seems well organized, it is not well exposed and presents several inaccuracies and errors that makes it not suitable for publication.  Some statements are totally incomprehensible, all the paper need to be rewritten in a more suitable English form (some suggestions are present in this file and in the attached pdf file). Analytic methods are presented with superficiality and more attention is required for the comments of the results which need to be compared with other results in literature.

Nevertheless, it is not clear why the authors propose EMTP as inhibitor for corrosion of mild steel in acidic solutions. In the paper there is not a clue about the advantage of this compound.

Hereafter all my suggestions and comments.

Abstract

• A triazole heterocyclic compound namely 3-(4-ethyl-5-mercapto-1, 2, 4-triazol-3-yl)-1-phenylpropanone (EMTP) was examined for its corrosion protection against mild steel in 1 M hydrochloric acid medium utilizing gravimetric techniques.

I think that EMTP protect mild steel against 1 M HCl medium, thus the sentence is unclear and need to be rewritten.

• Please remember to specify the meaning of the acronyms when used for the first time (more specific comments on the pdf file)

 

Introduction

 

• Inhibitors have been used to prevent metallic materials from corroding by limiting metal solubility and consumption.

Please, modify the sentence as suggested:

“Inhibitors can prevent the corrosion of metallic materials by…”

Materials and Method

2.1 Corrosive media

• Dilution of reagent grade 37 percent HCl with deionized water yielded the corrosive solution (1 M HCl).

This sentence is unclear: the corrosive solution is 1M HCl, but I cannot understand if it is obtained by diluting with deionaized water a 37%vol HCl acqueous solution (commercial? Where you purchased it?)

• For inhibition studies, inhibitor with concentrations of 100, 200, 300, 400, 500, and 1000 ppm were produced by dissolving the necessary quantity of EMTP in 1 M HCl and at 303 K as stirring temperature.

This statement need to be modify. Please follow the suggestions on the pdf file or, in any case, rephrase it in a more formal manner. Furthermore when you speak about the stirring, you have to specify if the temperature  is referred to the plate or to a control thermocouple immersed in the solution. Please add also the tyoe of hot stirring plate.

• Mild steel specimen was abraded with various grade emery sheets and rinsed with methyl alcohol, dimethyl ketone, and distilled water before being dried and weighed.

What do you mean with “various grade emery sheets”? I think it is necessary to specify the procedure and to let understand if every sample is worked with the same procedure.

• Mild steel specimen was exposed to various inhibitor concentrations in hanging position with nylon line at 303 K and the mid steel specimen mass loss were for different time periods (1, 5, 10, 24 and 48 h).

Some correction for this statement were proposed in the pdf file. Anyway the meaning is unclear: maybe the authors want to say that an average mass loss for the steel specimens was evaluated for differet exposure time? Again, the statement is written in such a way that the temperature seems to be referred to the nylon strand (and not nylon line). Please rephrase all the statement following the suggestion in here and in the pdf file.

• Triplicated experiments were carried and average value was determined.

This sentence need to be rewritten: Experiments were repeated for three times in order to determine average values

??%=[??(absence)−??(presence)?×100]

• When the protection efficiency is defined the meaning of Cr(absence) and Cr(presence) need to be specified:  absence= without inhibitor and presence=with inhibitor. Furthermore this formula can be wrong: in my opinion the numerator must be C_R(absence). There is a typo error or you defined in this way the corrosion rate? In this last case, why?

 

2.2 Computational Details

In this section the authors are required to describe the equations and in particular the meaning of the symbols: E,  s, h, c. There is also an error in numbering the equations (number 1 and 2 have been already used in the previous section)

 

3. Results and Discussion

3.1. Weight Loss Techniques

Fig 2-6: Units of measurement must be add into the graphs. Furthermore, it could be useful to put all the graphs together so that the trends according to time can be pretty visible. In any case it is appropriate to use always the same dimension for the axis.

• Compared with the triazoles corrosion inhibitors investigated previously in Table 1, EMTP showed more favorable corrosion-inhibiting performance.

Table 1 is not referred to the triazole corrosion inhibitors. I think it is necessary to add the reference to the previous work in which the authors discussed this other inhibitors.

 

• At 500 ppm, the inhibitor examined was determined to have the highest inhibitory efficacy.

Please rephrase according to the following suggestion: When the inhibitor is add to the corroding solution with a concentration of 500 ppm, the highest inhibitory efficacy was obtained.

• Because the inhibitor molecules are adsorbed from the metal surface with increasing immersion time and there is no significant increase in the inhibition efficiency after 5 hours of immersion time.

This sentence is incomprehensible, please try to modify it in order to let understand the meaning.

 

3.2 Effect of Immersion time

- The immersion time was selected best on the optimum results which was 10 hours.  

This sentence is totally unclear: please rewrite.

Fig 6-10: As in the other graphs: Units of measurement must be add into the graphs. Furthermore, it could be useful to put all the graphs together so that the trends according to temperature can be pretty visible. In any case it is appropriate to use always the same dimension for the axis.

When the activation energy for the corrosion process was evaluated, I think a deeper discussion about this method has to be carried out. In this way the process cannot be considered reliable.

A table with the results of activation energy with different inhibitor concentration in the corroding solution must be added.

When enthalpy and entropy were discussed, only two values were reported, with and without inhibitor, why? You assess that the value of DH depends on the slop of the straight lines and I can see one straight line for each inhibitor concentration! Please, can you better explain how the calculation were carried out?

 

3.3 Adsorption isotherm

• In general, the protection performance of an EMTP molecule depends on its adsorption capability on the mild steel surface. In general, the protection performance of an EMTP molecule depends on the abilities of these molecules to be adsorbed on the mild steel surface.

These two sentence are a repetition.

• Inhibition of the surface of mild steel based on how the inhibitor molecules are adsorbed on the surface of the metal, in addition to nature and structure of the inhibitor molecules

This sentence in unclear, please rewrite.

• A straight line was obtained from plotting of ??⁄ ?? ? as in Figure 13, and the value of linear correlation coefficient (R2) was found to be close to unity, which indicates that the adsorption mechanism of tested inhibitor molecules in acidic solution on mild steel surface follows Langmuir adsorption model.

Observing Fig 13 it is evident that for T=303K a straight line can well represent the trend of the “experimental” points. Instead, for the other temperatures the trend can be approximated with a straight line but it is very difficult to believe that R² is close to 1. Thus, what do you mean with “close to unity”? Can you add the value of correlation factor for each straight line?

Furthermore, for 1000 ppm the value of C/θ is exactly on the straight line for each value of T. I think that this trend is very strange. For T=313, 323, 333 K the trend seems more parabolic or logarithmic for points corresponding to 100, 200, 300, 400 and 500 ppm and then there is a counter trend for 1000 ppm: how can you explain this phenomenon? There is some error in graph?

 

3.5. Inhibition Mechanism

• The corrosion inhibition occurs through the substituent of water molecules by the inhibitor’s ability toward particular the tested inhibitor molecules adsorption on the MS surface

This sentence is unclear, please rewrite.

Conclusions

More details need to be highlighted, furthermore is not clear what is the advantage of using EMPT as corrosion protection instead of other possible candidates.

 

Reference

From 14 to 19 there is a repetition of the numbers

Comments for author File: Comments.pdf

Reviewer 2 Report

The authors reported in their manuscript the investigation of the compound EMTP as an effective corrosion inhibitor for mild steel substrate in the acidic medium. Honestly, the literature is congested with similar studies about studying the corrosion inhibition properties of various organic compounds which makes the novelty of the current manuscript somehow limited. One approach to enhance the level of novelty of such studies is to compare the inhibition efficiency of the studied compound vs. a commercial corrosion inhibitor formulation. Nevertheless, the current manuscript can be useful to researchers in the corrosion inhibition field and it can be considered for publication after the authors addressing the following comments:

1. It is not clear in the manuscript whether the synthesized triazole EMTP is a novel compound or not? Kindly comment on this.
2. The carbon-13 NMR data of EMTP compound should be added to the manuscript.
3. Figures 2-10: kindly add the unit to the legend of the Y & Z axes.
4. Section 3.2: kindly change “best on” to “based on”.
5. How the authors validated the use of “6-31G*” as a basis set for their DFT calculations? Why not a higher basis set?

 

Reviewer 3 Report

1. The title of the article should be modified, as it does not give a scientific idea about the research.
2. The author should add some results in the form of numerical values in the abstract section.
3. In the Abstract and introduction section: the authors need to improve with more specific short results and conclusions, i.e. academic novelty and technical advantages.
4. The author should cite some recently published articles in the introduction section.
5. The introduction section should be finished with the aim of the research.
6. The elemental composition of the used mild steel is missing, please add it.
7. Make x, y, and z-axis symmetrically for figures 2-10.
8. The author should add weight loss results and compare the outcomes for all the conditions.
9. In table 1, put all the values symmetrically (make 2 or 3 digits after the dot) for example 2.33 or 2.330.
10. The author can improve the inhibition mechanism.
11. In the conclusion section, the author should add the outcomes of their investigations and explain them.