Evaluation and Optimization of Tour Method for Synthesis of Graphite Oxide with High Specific Surface Area

Round 1

Reviewer 1 Report

The manuscript “Evaluation and Optimization of Tour Method for synthesis of graphite oxide with high specific surface area” presents an interesting point of view on the main variables that affect the synthesis of graphite oxide. The paper mainly focuses on a statistical analysis on the influence of temperature, time and amounts of reagents (KMnO₄ and H₂O₂) on the properties of the synthesized material (GrO) such as the SSA, percentage of carbon (%C) and t-Plot micropore volume.

All the GrO samples are the extensive characterized by BET, elemental analysis, XRD, Raman and SEM.

All of the data combined provide a summary of the most important factors in the synthesis of GrO materials so that they can be prepared with the necessary properties and used in specific applications.

The paper offer important fundamental information for the GrO synthesis and can be accepted in present form.

Author Response

Referee 1:

“The manuscript “Evaluation and Optimization of Tour Method for synthesis of graphite oxide with high specific surface area” presents an interesting point of view on the main variables that affect the synthesis of graphite oxide. The paper mainly focuses on a statistical analysis on the influence of temperature, time and amounts of reagents (KMnO₄ and H₂O₂) on the properties of the synthesized material (GrO) such as the SSA, percentage of carbon (%C) and t-Plot micropore volume.

All the GrO samples are the extensive characterized by BET, elemental analysis, XRD, Raman and SEM.

All of the data combined provide a summary of the most important factors in the synthesis of GrO materials so that they can be prepared with the necessary properties and used in specific applications.

The paper offer important fundamental information for the GrO synthesis and can be accepted in present form.”

We thank the reviewer for the valuable comments and suggestions. Thank you very much for your time and interest.

Author Response File: Author Response.pdf

Reviewer 2 Report

In the manuscript "Evaluation and optimization of Tour Method for synthesis of graphite oxide with high specific surface area" by H. Bukovska et al., the authors study the effect of temperature, amount of oxidants used and the reaction time on the selected parameters of graphite oxide produced in the reaction and report  optimized conditions yielding material of high surface area.

The manuscript is exceptionally well written, the ideas of authors are presented in clear and succinct manner, the results are internally consistent and the conclusions are well based on the presented results.

In my view, the manuscript can be accepted for publication in C after minor text editing to correct typos. The authors should also carefully revise the reference list, as there are several issues there like missing references (refs. 54 and 55), missing authors (ref. 27), probably missing pages (ref. 72) and non-uniform formatting style (e.g., compare refs. 27, where the full list of 8 authors is given, and ref. 25, when the first authors is followed by "et al.").

- The sentence in line 34 is not quite informative.

- Please check the way you abbreviate "experimental design": it goes as "E.D" in line 249, "ED" in line 247, "E.A" in line 468, "E.D." in line 111

- Line 322: please change to: "According to..., a significant discrepancy is observed between..."

- Line 324: please change to: "... SSA, while..."

- Lines 355-356: please change to: "...conductivity, while..."

- Line 418: please use decimal point (0.94)

- Line 453: please change to: "... to Table 5a"

- Line 522: please change to: "For I_D/I_G, a total range of ... can be observed"

- Lines 553 and 554: do you mean "Figure 8d"?

Author Response

Referee 2:

“In the manuscript "Evaluation and optimization of Tour Method for synthesis of graphite oxide with high specific surface area" by H. Bukovska et al., the authors study the effect of temperature, amount of oxidants used and the reaction time on the selected parameters of graphite oxide produced in the reaction and report optimized conditions yielding material of high surface area.

The manuscript is exceptionally well written, the ideas of authors are presented in clear and succinct manner, the results are internally consistent and the conclusions are well based on the presented results.

In my view, the manuscript can be accepted for publication in C after minor text editing to correct typos.”

Thank you very much for your comments on the article.

Regarding the suggestions for necessary changes, I am very grateful for your contributions to this paper. All your comments have helped me to correct and improve the manuscript. Thank you very much for your time and interest.

Below I comment on each of the suggestions and changes made in blue:

1-The authors should also carefully revise the reference list, as there are several issues there like missing references (refs. 54 and 55), missing authors (ref. 27), probably missing pages (ref. 72) and non-uniform formatting style (e.g., compare refs. 27, where the full list of 8 authors is given, and ref. 25, when the first authors is followed by "et al.").

References 54 and 55 have been added. All references have been added automatically using EndNote using the Vancouver format. The difference between references with "et. al." and those with the names of all authors is due to the number of authors. There is a limit number above which is shortened by "et. al.". 

2-Comments on the Quality of English Language

- The sentence in line 34 is not quite informative. – This comment is changed, highlighted in yellow in the manuscript

- Please check the way you abbreviate "experimental design": it goes as "E.D" in line 249, "ED" in line 247, "E.A" in line 468, "E.D." in line 111. – This comment is changed throughout the text, highlighted in yellow in the manuscript

- Line 322: please change to: "According to..., a significant discrepancy is observed between...". -Changed, highlighted in yellow in the manuscript

- Line 324: please change to: "... SSA, while..." – This comment is changed, highlighted in yellow in the manuscript

- Lines 355-356: please change to: "...conductivity, while..." – This comment is changed, highlighted in yellow in the manuscript

- Line 418: please use decimal point (0.94). – This comment is changed, highlighted in yellow in the manuscript

- Line 453: please change to: "... to Table 5a" – This comment is changed, highlighted in yellow in the manuscript

- Line 522: please change to: "For I_D/I_G, a total range of ... can be observed" – This comment is changed, highlighted in yellow in the manuscript

3-Lines 553 and 554: do you mean "Figure 8d"?

The reference is to Figure 6 in the Results part of the XRD section.

Author Response File: Author Response.pdf

Reviewer 3 Report

This is an interesting manuscript that adds to the existing practical knowledge of graphite oxide sytnesis. As such, it is of interest for a large number of scientists which use GO as a starting material for graphene based nanomaterial synthesis.

The purpose and novely claims are clearly described and they certainly justify that the manuscript is published in this journal. Also, the used statistical and optimization approach (even though may be  updated with other parameters or extended with more data) is professional in the sense that it considers parameters simultaneously. Therefore I suggest publication after minor revisions.

My questions/suggestions for clarifying some details are as follows:

- optimal SSA of graphene ≅ 2600 m²/g: I think it is not "optimal" but "ideal" or geometrical. A single layer of carbon atoms of the graphene structure has this exact value considering atomic weights of carbon and the interatomic distances.

- The conclusion about exact masses of KMnO₄ and volume of H₂O₂ should be improved: these numerical values depend on the initial mass of graphite as well, so it is better to specify, possibly to mass of graphite or at least mention that these values refer only the provided synthesis recipe.

- Also, it is important to note that these optimized values very likely relate only the exact type of graphite used....larger flakes are oxidized slower. So the optimized reaction times can also vary a lot of the graphite source. I'd indicate that optimization might needed for different particle size distributions (which is of course, is a challenge...).

- "In 1958, Hummers and Offelman" : very well to refer to the procedure as "Hummers-Offeman"! But please use correct spelling. Also, I suggest to use "Marcano-Tour" because of the student's contribution, or even mentioning the equal first-authors.

- Nevertheless, naming Tour method is correct in the sense that it applies a new ingredient, phosphoric acid and removing NaNO₃. However, it is not sure at all that phophoric acid improves the synthesis. In the original article it was not investigated. Also, the method, just as the present one, uses a lot of solvents. Anyway this comments needs no action from the authros. 

- "In this work, a study of all the variables that can influence the GrO synthesis process is addressed simultaneously." should be polished: not all variables were addressed that can influence the oxidation but only the most important ones. So I would add "all the major variables".

- "both the oxidation process and the CO₂ generation are higher, leading" should be rephrased: oxidation process and generation are not "higher", but their rate or extention can be higher.

- XRD spectrum : it is not a spectrum (becasue wavelength does not vary). It is a diffractogram or a pattern.

- in Figure 5, it is not very clear that which patterns refer to the different temperatures. What does the vertical line mean? Please improve the figure significantly.

- why was the shape factor 0.94 used as compared to the usual 0.9? Was it cited from the literature? If so, how can the authors justify this use for non-experts?

- The discussion about Figure 6 should be improved. First the authors are modest about the possiblity of CO₂ bubble formation. They write "This could be due to a slight accumulation of CO₂ bubbles". However, at the end of the section the claim "All these facts are depicted in Figure 6.". I think, thought that the scenario of bubble formation would need further confirmation to accept fully. At the present, it is only an interesting possibility and kind of speculative. Indeed at different temperatures the energy and mobility of gas bubble are different. In the present case, however, it is not clear what causes the change of the interlayer distances. It might even be differences in the degrees of hydration of differently oxidized samples. It has been demonstrated for long time (even before 2010) that hydrated GOs can have a variety of d-spacings depending on the type of GO, composition, or even the ambient humidity levels etc. So, 0.81 and 0.87 nm are not very much different when one considers GO interlayer spacings for air-dry samples. If the authors think about investigating this possible bubble formation effect, it can be interesting, but needs some more effort to keep other factors that can vary interlayer spacings constant.

- Figure 6, even if bubble formation is true, not precise: where are the functional groups from the interior of particles? Would there be pure carbon lamellae filled with CO₂? What about those functional groups that do not transform to CO₂? 

Author Response

Referee 3:

“This is an interesting manuscript that adds to the existing practical knowledge of graphite oxide sytnesis. As such, it is of interest for a large number of scientists which use GO as a starting material for graphene based nanomaterial synthesis.

The purpose and novely claims are clearly described and they certainly justify that the manuscript is published in this journal. Also, the used statistical and optimization approach (even though may be  updated with other parameters or extended with more data) is professional in the sense that it considers parameters simultaneously. Therefore I suggest publication after minor revisions.”

Thank you very much for your comments on the article.

Regarding the suggestions for necessary changes, I am very grateful for your contributions to this paper. All your comments have helped me to correct and improve the manuscript. Thank you very much for your time and interest.

Below I comment on each of the suggestions and changes made in blue:

- optimal SSA of graphene ≅ 2600 m²/g: I think it is not "optimal" but "ideal" or geometrical. A single layer of carbon atoms of the graphene structure has this exact value considering atomic weights of carbon and the interatomic distances. –This comment is changed, highlighted in green in the manuscript.

- The conclusion about exact masses of KMnO₄ and volume of H₂O₂ should be improved: these numerical values depend on the initial mass of graphite as well, so it is better to specify, possibly to mass of graphite or at least mention that these values refer only the provided synthesis recipe. –This comment is added in the conclusions section, highlighted in green in the manuscript.

- Also, it is important to note that these optimized values very likely relate only the exact type of graphite used....larger flakes are oxidized slower. So the optimized reaction times can also vary a lot of the graphite source. I'd indicate that optimization might needed for different particle size distributions (which is of course, is a challenge...). –This comment is added in the conclusions section, highlighted in green in the manuscript.

- "In 1958, Hummers and Offelman": very well to refer to the procedure as "Hummers-Offeman"! But please use correct spelling. Also, I suggest to use "Marcano-Tour" because of the student's contribution, or even mentioning the equal first-authors. – This comment is changed, highlighted in green in the manuscript.

- Nevertheless, naming Tour method is correct in the sense that it applies a new ingredient, phosphoric acid and removing NaNO₃. However, it is not sure at all that phophoric acid improves the synthesis. In the original article it was not investigated. Also, the method, just as the present one, uses a lot of solvents. Anyway this comments needs no action from the authros. –Thank you for the comment, I will keep it in mind for future research and publications.

- "In this work, a study of all the variables that can influence the GrO synthesis process is addressed simultaneously." should be polished: not all variables were addressed that can influence the oxidation but only the most important ones. So I would add "all the major variables".

–This comment is changed, highlighted in green in the manuscript.

- "both the oxidation process and the CO₂ generation are higher, leading" should be rephrased: oxidation process and generation are not "higher", but their rate or extention can be higher.

– This comment is changed, highlighted in green in the manuscript.              

- XRD spectrum: it is not a spectrum (becasue wavelength does not vary). It is a diffractogram or a pattern. –This comment is changed, highlighted in green in the manuscript.              

- in Figure 5, it is not very clear that which patterns refer to the different temperatures. What does the vertical line mean? Please improve the figure significantly.

–Changed, highlighted in green in the manuscript.The vertical line marks an arbitrary division between the diffractograms of GrO synthesised at 45º and those of GrO synthesised at 60ºC. An explanation has been added both in the text and in the figure (highlighted in green in the manuscript).

- why was the shape factor 0.94 used as compared to the usual 0.9? Was it cited from the literature? If so, how can the authors justify this use for non-experts?

-The usual value of K=0.9 refers to spherical particles. In our case, the particles have not been considered spherical. As there are different shapes of sheets stacked one on top of the other, we have considered it more appropriate to change the K to an approximate octahedral shape. 

- The discussion about Figure 6 should be improved. First the authors are modest about the possiblity of CO₂ bubble formation. They write "This could be due to a slight accumulation of CO₂ bubbles". However, at the end of the section the claim "All these facts are depicted in Figure 6.". I think, thought that the scenario of bubble formation would need further confirmation to accept fully. At the present, it is only an interesting possibility and kind of speculative. Indeed at different temperatures the energy and mobility of gas bubble are different. In the present case, however, it is not clear what causes the change of the interlayer distances. It might even be differences in the degrees of hydration of differently oxidized samples. It has been demonstrated for long time (even before 2010) that hydrated GOs can have a variety of d-spacings depending on the type of GO, composition, or even the ambient humidity levels etc. So, 0.81 and 0.87 nm are not very much different when one considers GO interlayer spacings for air-dry samples. If the authors think about investigating this possible bubble formation effect, it can be interesting, but needs some more effort to keep other factors that can vary interlayer spacings constant. - Changed, highlighted in blue.

We appreciate the comment from the reviewer. The figure has been changed, adding water molecules and more oxygenated functional groups in the GrO structure synthesized at 60ºC. The explanation of Figure 6 has been modified and more literature has been added. All these changes are marked in green in the manuscript.

- Figure 6, even if bubble formation is true, not precise: where are the functional groups from the interior of particles? Would there be pure carbon lamellae filled with CO₂? What about those functional groups that do not transform to CO₂? 

The oxygenated functional groups are represented as darker blue spheres in Figure 6. Further oxygenated groups have been incorporated between the sheets of the GrO structures synthesized at 60°C.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper presents studies on the synthesis of graphite oxide by the Tour oxidation method. This is done to obtain the highest specific surface area (SSA) values. After processing, the oxidized graphite was examined by various methods, during which it was found that the maximum achieved specific surface area is 67.04 m²·g^-1 at a temperature of 60 ° C, a time of 12 h, a volume of 50 ml H₂O₂ and 29.4 g KMnO₄. Such material can be used for hydrogen storage, water decontamination or supercapacitors.

Despite a number of advantages of the presented work, there are a number of comments:

1.                 In the text line 111 «… allowing us to verify the method used in the E.D.» is it not clear the use of E.D. Meant experimental design (ED)?

2.                 The largest specific surface area was obtained with the characteristics specified in Table 2, line 242. With the exception of processing time, all parameters have maximum values, why were not large values used?

3.                 In Figure 6, line 473. It may be worth changing the designation in the figure that gray is not graphite, but graphene sheets of which graphite consists.

4.                 It is necessary to check the design of the "Links" section again. In the text, reference 16, lines 679 and 680 are indicated with a sentence break.

Comments for author File: Comments.pdf

Author Response

Referee 4:

“The paper presents studies on the synthesis of graphite oxide by the Tour oxidation method. This is done to obtain the highest specific surface area (SSA) values. After processing, the oxidized graphite was examined by various methods, during which it was found that the maximum achieved specific surface area is 67.04 m²·g^-1 at a temperature of 60 ° C, a time of 12 h, a volume of 50 ml H₂O₂ and 29.4 g KMnO₄. Such material can be used for hydrogen storage, water decontamination or supercapacitors.

Despite a number of advantages of the presented work, there are a number of comments.”

Thank you very much for your comments on the article.

Regarding the suggestions for necessary changes, I am very grateful for your contributions to this paper. All your comments have helped me to correct and improve the manuscript. Thank you very much for your time and interest.

Below I comment on each of the suggestions and changes made in blue:

1-In the text line 111 «… allowing us to verify the method used in the E.D.» is it not clear the use of E.D. Meant experimental design (ED)?

Yes, E.D. and ED refer to experimental design. It is already corrected as ED. It has been changed throughout the text, highlighted in yellow.

2-The largest specific surface area was obtained with the characteristics specified in Table 2, line 242. With the exception of processing time, all parameters have maximum values, why were not large values used?

Maximum and minimum experimental parameter values generally used to carry out the Tour method, according to the literature, have been used. Therefore, the ED used is a screening one and the aim is to make a sweep over the experimental conditions that are usually used. In addition, excessively high values of temperature, KMnO₄ and H₂O₂ have some disadvantages, so they are not normally used. High temperatures cause thermal exfoliation and reduction of GrO, which in case of excessive temperatures lead to the creation of many defects and fragmentation of their sheets. Excessive H₂O₂ can lead to reduction of functional groups and chemical etching with formation of many defects and fragmentation of GrO sheets. Finally, excess KMnO₄ can cause over-oxidation, leading to the same effect of leaf fragmentation that occurs with excess H₂O₂ and temperature. For these reasons, experimental conditions below the values at which these phenomena occur are used in the literature, as they result in lower SSA.

3-In Figure 6, line 473. It may be worth changing the designation in the figure that gray is not graphite, but graphene sheets of which graphite consists. –This comment is modified on the figure.

4-It is necessary to check the design of the "Links" section again. In the text, reference 16, lines 679 and 680 are indicated with a sentence break. –This comment is changed.

Author Response File: Author Response.pdf

Reviewer 5 Report

The authors carried out extensive analysis of synthesis process of GrO and did the investigation of the relationship between different process variables.

The results are clearly but in details explained.

Minor comments:

Line 51: the stability of pure graphene is probably not the biggest issue for various applications. alternative explanation: direct band gas, necessity for functionalization, production issues, ...

Lines 90 and 91: GBM replaced to GRM?

pages 4 and 5: Characterization methods might be described in more details, for example details of BET analysis.

Only minor changes and language polishing required.

Author Response

Referee 5:

“The authors carried out extensive analysis of synthesis process of GrO and did the investigation of the relationship between different process variables.

The results are clearly but in details explained.”

Thank you very much for your comments on the article.

Regarding the suggestions for necessary changes, I am very grateful for your contributions to this paper. All your comments have helped me to correct and improve the manuscript. Thank you very much for your time and interest.

Below I comment on each of the suggestions and changes made in blue:

Line 51: the stability of pure graphene is probably not the biggest issue for various applications. alternative explanation: direct band gas, necessity for functionalization, production issues, ...      –This comment is modified, highlighted in gray in the manuscript

Lines 90 and 91: GBM replaced to GRM? –This comment is changed, highlighted in gray in the manuscript.

pages 4 and 5: Characterization methods might be described in more details, for example details of BET analysis. –This comment is modified, highlighted in gray in the manuscript.

Author Response File: Author Response.pdf

Reviewer 6 Report

The topic of this manuscript entitled: "Evaluation and Optimization of Tour Method for synthesis of graphite oxide with high specific surface area" falls within the profile and scope of the Journal of Carbon Research.

Comment:

The article treats about specific surface area of graphene-based materials. I would be worth to add that graphene-oxide can be an effective microwave absorber.

Author Response

Referee 6:

“The topic of this manuscript entitled: "Evaluation and Optimization of Tour Method for synthesis of graphite oxide with high specific surface area" falls within the profile and scope of the Journal of Carbon Research.”

Thank you very much for your comments on the article.

Regarding the suggestions for necessary changes, I am very grateful for your contributions to this paper. All your comments have helped me to correct and improve the manuscript. Thank you very much for your time and interest.

Below I comment on each of the suggestions and changes made in blue:

The article treats about specific surface area of graphene-based materials. I would be worth to add that graphene-oxide can be an effective microwave absorber. –This comment is added and highlighted in pink in the manuscript.

Author Response File: Author Response.pdf