Combined Effect of Sonication and Electron Beam Irradiation on the Photocatalytic Organic Dye Decomposition Efficiency of Graphitic Carbon Nitride

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. This manuscript (carbon-3932661) describes the photocatalytic efficiency of graphitic carbon nitride (g-C3N4) for aqueous rhodamine B (RhB) decomposition was investigated. To examine the combined effects of sonication and electron beam (EB) irradiation on the photocatalytic efficiency, g-C3N4 was sonicated in 1,3-butanediol and subsequently irradiated with EB. The photocatalytic efficiency was improved by low-dose EB irradiation owing to the generation of structural defects that acted as active reaction sites. Sonication before EB irradiation induced mild exfoliation and further improved the photocatalytic efficiency. Prolonged sonication enlarged the improvement, primarily by increasing the specific surface area of g-C3N4. The positive effect of sonication was remarkable for g-C3N4 irradiated with low-dose EB compared to that for g-C3N4 irradiated with higher-dose EB. The difference between the sonication effects could be ascribed to electrostatic interactions and the resultant agglomeration among g-C3N4 particles after EB irradiation. However, several major issues need to be addressed before the manuscript can be considered for publication.
2. Can the authors provide direct evidence (e.g., zeta potential, TEM imaging) to support the claim of EB-induced electrification and particle coarsening?
3. How were the defect concentrations (e.g., N vacancies) estimated from XPS? Can the authors provide quantitative deconvolution data?
4. Were control experiments conducted to isolate the effects of photolysis and adsorption? If not, how can the authors be certain the observed degradation is photocatalytic?
5. How many replicates were performed for the photocatalytic tests? Authors needs to add the standard deviations or confidence intervals?
6. Have the authors tested the reusability or stability of the treated g-C₃N₄ over multiple photocatalytic cycles? Authors can take help from; fe-zro2 imbedded graphene like carbon nitride for acarbose (ACB) photo-degradation intermediate study.
7. Why was 1,3-butanediol chosen as the sonication medium? Could the solvent itself influence the surface chemistry or photocatalytic activity?
8. The RhB degradation kinetics appear roughly first-order; can you provide apparent rate constants (kapp) and compare quantitatively among samples?
9. What are the practical limitations of using EB irradiation at scale? Is this method energy-efficient or cost-effective for real-world applications?
10. XRD shows minimal changes, was TEM or AFM used to confirm exfoliation or particle coarsening?
11. The manuscript contains several grammatical and stylistic inconsistencies (e.g., article usage, verb tense agreement, word repetition, and informal phrasing) that occasionally obscure the intended meaning. Could the authors carefully revise the English language throughout the manuscript, preferably with professional editing or native-speaker proofreading to improve readability, grammatical accuracy, and academic tone before final submission.

Comments on the Quality of English Language

The manuscript contains several grammatical and stylistic inconsistencies (e.g., article usage, verb tense agreement, word repetition, and informal phrasing) that occasionally obscure the intended meaning. Could the authors carefully revise the English language throughout the manuscript, preferably with professional editing or native-speaker proofreading to improve readability, grammatical accuracy, and academic tone before final submission.

Author Response

1. This manuscript (carbon-3932661) describes thephotocatalytic efficiency of graphitic carbon nitride (g-C₃N₄) for aqueous rhodamine B (RhB) decompositionwas investigated. To examine the combined effects ofsonication and electron beam (EB) irradiation on the photocatalytic efficiency, g-C₃N₄ was sonicated in 1,3-butanediol and subsequently irradiated with EB. The photocatalytic efficiency was improved by low-dose EB irradiation owing to the generation of structural defects that acted as active reaction sites. Sonication before EB irradiation induced mild exfoliation and further improved the photocatalytic efficiency. Prolonged sonication enlarged the improvement, primarily by increasing the specific surface area of g-C₃N₄. The positive effect of sonication was remarkable for g-C₃N₄ irradiated with low-dose EB compared to that for g-C₃N₄ irradiated with higher-dose EB. The difference between the sonication effects could be ascribed to electrostatic interactions and the resultant agglomeration among g-C₃N₄ particles after EB irradiation. However, several major issues need to be addressed before the manuscript can be considered for publication.

 

Reply: Thank you for the precious comment. The revisions are described below.

 

 

2. Can the authors provide direct evidence (e.g., zeta potential, TEM imaging) to support the claim of EB-induced electrification and particle coarsening?

 

Reply: Thank you for the precious comment. Although the zeta potential and TEM data are not available at this moment, the coarsening of relatively small particles can be confirmed based on particle size distribution results. The particle size distributions were shown in Supplementary information (Figure S1). Additional comments were also added to the main text (lines 216–219).

 

 

3. How were the defect concentrations (e.g., N vacancies) estimated from XPS? Can the authors provide quantitative deconvolution data?

 

Reply: Thank you for the precious comment. Decrease in N amount through EB irradiation can be confirmed by quantification based on spectral deconvolution. Additionally, the EB-induced N elimination has already been reported in the previous reports. Quantification data were shown in Supplementary information (Table S1), and additional comments were added to the main text (lines239–245, 251–256, 258–260). 

 

 

4. Were control experiments conducted to isolate the effects of photolysis and adsorption? If not, how can the authors be certain the observed degradation is photocatalytic?

 

Reply: Thank you for the precious comment. The effect of physical adsorption on dye removal has already been known to be minor since the specific surface area of g-C₃N₄ is quite small, so that the control experiments under dark condition has been omitted in this study. Additional comments were added to the main text (lines 264–268).

 

 

5. How many replicates were performed for the photocatalytic tests? Authors needs to add the standard deviations or confidence intervals?

 

Reply: Thank you for the precious comment. The photocatarytic tests were carried out three times. The error bars shown in Figure 5 indicate minimum and maximum experimental values. We believe this information could be sufficient to represent the differences between the experimental data. Additional comments were added to the main text (lines 159–161).

 

 

6. Have the authors tested the reusability or stability of the treated g-C₃N₄ over multiple photocatalytic cycles? Authors can take help from; fe-zro2 imbedded graphene like carbon nitride for acarbose (ACB) photo-degradation intermediate study.

 

Reply: Thank you for the precious comment. Althouth the main topic of this study is the positive effect of sonication and EB irradiation rather than the practical characteristics such as long-term reusability, it is important anyway. Additional comments were added to the main text (lines 327–332). Moreover, the previous example shown by the reviewer was considered in the discussion [38].

 

 

7. Why was 1,3-butanediol chosen as the sonication medium? Could the solvent itself influence the surface chemistry or photocatalytic activity?

 

Reply: Thank you for the precious comment. In many cases, sulfuric acid is commonly used as medium for ultrasonic exfoliation, but if sulfuric acid is used in this case, residual acid may affect the quantification of RhB; the RhB concentration is measured by colorimetric method, and thus the color change through reaction between sulfuric acid and RhB may result in experimental errors. To avoid the color change caused by residual acid, 1,3-butanediol (organic solvent used in the previous work) was employed in this study. Additional comments were added to the main text (lines 122–126).

 

 

8. The RhB degradation kinetics appear roughly first-order; can you provide apparent rate constants (kapp) and compare quantitatively among samples?

 

Reply: Thank you for the precious comment. Estimation of the apparent first-order rate constants is possible. The obtained data were ilisted in Supplementary information (Table S2). Additional comments were also added to the main text (lines 269–277, 295–296).

 

9. What are the practical limitations of using EB irradiation at scale? Is this method energy-efficient or cost-effective for real-world applications?

 

Reply: Thank you for the precious comment. Although the energy consumption and cost effectiveness of EB irradiation method cannot be simply compared to those of other techniques, the EB irradiation can be carried out without harmful reagents and under ambient atmosphere and temperature. These would be the advantages of EB irradiation method. Additional comments were also added to the main text (lines 61–65).

 

 

10. XRD shows minimal changes, was TEM or AFM used to confirm exfoliation or particle coarsening?

 

Reply: Thank you for the precious comment. If the high-resolution TEM images and AFM data can be available and they reveal the microscopic structural alteration, they would be useful. However, unfortunately, such data are not immediately available. Of course, the authors are confident that the TEM observation is important. Additional comments were added to the main text (lines 216–219).

 

 

11. The manuscript contains several grammatical and stylistic inconsistencies (e.g., article usage, verb tense agreement, word repetition, and informal phrasing) that occasionally obscure the intended meaning. Could the authors carefully revise the English language throughout the manuscript, preferably with professional editing or native-speaker proofreading to improve readability, grammatical accuracy, and academic tone before final submission. 

 

Reply: Thank you for the precious comment. In fact, English correction by a professional proofreader has been carried out prior to the first submission, but additional proofreading of the revised manuscript has been performed again. 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript investigated the combined effect of sonication and electron beam irradiation on the photocatalytic performance of g-C3N4 catalyst. Catalysts were characterized with XRD, XPS, and surface area measurement. Some speculations on the structural-function relationship were made based on these data. However, there’s no clear evidence of why high dose electron beam leads to lower catalytic performance. While EB irradiation and sonication can both improve catalyst performance under certain conditions, there seems to be no synergistic effect with these treatments. My main comments are summarized below:

Page 2 paragraph 1: there’s no reference here on the low photocatalytic reaction efficiency of g-C3N4 photocatalyst.

Page 3 section 2.2, how much time did the EB irradiation last? Does the irradiation time affect the photocatalytic performance?

In figure 4, it is recommended to include the spectrum of the fresh C3N4 without any treatment as a comparison.

In page 6 paragraph 1, “EB irradiation altered the composition of C and N in the samples”, is there any evidence to support this claim? Were there any C/N ratio change after the treatment? Were elemental composition information (survey spectra) analyzed when collecting the XPS data? In the same paragraph, the authors claim that sonication did not cause obvious changes to the chemical structure of the catalyst, is there any data to support that?

How stable is the treated catalyst, does the reaction rate degrade over time or after multiple reuse cycles?

Author Response

This manuscript investigated the combined effect of sonication and electron beam irradiation on the photocatalytic performance of g-C₃N₄ catalyst. Catalysts were characterized with XRD, XPS, and surface area measurement. Some speculations on the structural-function relationship were made based on these data. However, there’s no clear evidence of why high dose electron beam leads to lower catalytic performance. While EB irradiation and sonication can both improve catalyst performance under certain conditions, there seems to be no synergistic effect with these treatments. My main comments are summarized below:

 

Reply: Thank you for the precious comment. Althouth the synergistic effect of the sonication and EB irradiation was not observed in this study, the "synergy" of EB irradiation and sonication is not main topic of this study. Regarding this study, we consider that the improvement of photocatalytic performance induced by the sonication followed by EB irradiation with relatively low dose is novel finding of this work. The revisions are described below.

 

 

Page 2 paragraph 1: there’s no reference here on the low photocatalytic reaction efficiency of g-C₃N₄ photocatalyst.

 

Reply: Thank you for the precious comment. Although the drawbacks of g-C₃N₄ has been widely known, some references referring the drawbacks were indicated (line 52).

 

 

Page 3 section 2.2, how much time did the EB irradiation last? Does the irradiation time affect the photocatalytic performance?

 

Reply: Thank you for the precious comment. Generally, the irradiation effect on materials' performance is examined based on irradiation dose rather than irradiation time. The EB irradiation dose has been regulated by the number of passages through the irradiation device, so that additional comments were added to the main text (lines 133–134).

 

 

In figure 4, it is recommended to include the spectrum of the fresh C₃N₄ without any treatment as a comparison.

 

Reply: Thank you for the precious comment. The C 1s and N 1s spectra of intact g-C₃N₄ were provided in Supplementary information (Figure S2).

 

 

In page 6 paragraph 1, “EB irradiation altered the composition of C and N in the samples”, is there any evidence to support this claim? Were there any C/N ratio change after the treatment? Were elemental composition information (survey spectra) analyzed when collecting the XPS data? In the same paragraph, the authors claim that sonication did not cause obvious changes to the chemical

structure of the catalyst, is there any data to support that?

 

Reply: Thank you for the precious comment. Decrease in N amount through EB irradiation can be confirmed by quantification based on spectral deconvolution. Additionally, the EB-induced N elimination has already been reported in the previous reports. Quantification data were shown in Supplementary information (Table S1), and additional comments were added to the main text (lines239–245, 251–256, 258–260). 

 

 

How stable is the treated catalyst, does the reaction rate degrade over time or after multiple reuse cycles?

 

Reply: Thank you for the precious comment. Althouth the main topic of this study is the positive effect of sonication and EB irradiation rather than the practical characteristics such as long-term reusability, it is important anyway. Additional comments were added to the main text (lines 327–332). 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The idea can be interesting, but characterization of obtained materials have to be done more seriously.

These are my comments regarding the results presented:

1. The XRD results would benefit from a more detailed discussion. A noticeable shift in diffraction peak positions is observed; however, the corresponding numerical values are not provided. Since a shift toward higher 2θ values implies a decrease in d-spacing, this aspect should be addressed and interpreted by the authors. A clearer and more comprehensive analysis of the structural changes inferred from XRD data is recommended.
2. The manuscript contains several repetitive sentences, which affect the readability and flow of the text. For instance, the paragraph spanning lines 162–172 illustrates this issue, and similar repetitions appear elsewhere. The authors are advised to revise the text for conciseness and clarity.
3. It is recommended that the authors present the specific surface area values in a table with exact numerical data rather than only in graphical form. This would make the results easier to follow and facilitate understanding of the trends discussed in the text.
4. The XPS analysis, as currently presented, lacks sufficient detail to support the conclusions drawn. Peak positions are not reported, and neither peak areas nor their ratios are provided to substantiate the repeated statements in the text. The authors should include these quantitative details to strengthen the validity of their XPS interpretation. 

Author Response

The idea can be interesting, but characterization of obtained materials have to be done more seriously.

 

These are my comments regarding the results presented:

 

Reply: Thank you for the precious comment. The revisions are described below.

 

 

1. The XRD results would benefit from a more detailed discussion. A noticeable shift in diffraction peak positions is observed; however, the corresponding numerical values are not provided. Since a shift toward higher 2θ values implies a decrease in d-spacing, this aspect should be addressed and interpreted by the authors. A clearer and more comprehensive analysis of the structural changes inferred from XRD data is recommended.

 

Reply: Thank you for the precious comment. In this case, the peak shift caused by the sonication and EB irradiation was very slight, so that the change in crystal structure would be minor. The values of 2θ were added to the figure (Figure 2). 

 

 

2. The manuscript contains several repetitive sentences, which affect the readability and flow of the text. For instance, the paragraph spanning lines 162–172 illustrates this issue, and similar repetitions appear elsewhere. The authors are advised to revise the text for conciseness and clarity.

 

Reply: Thank you for the precious comment. The manuscript was checked again, and several redundant sentences were deleted to simplify the descriptions and avoid the repetitions.

 

 

3. It is recommended that the authors present the specific surface area values in a table with exact numerical data rather than only in graphical form. This would make the results easier to follow and facilitate understanding of the trends discussed in the text.

 

Reply: Thank you for the precious comment. The numerical data were added to the figure (Figure 3). 

 

 

4. The XPS analysis, as currently presented, lacks sufficient detail to support the conclusions drawn. Peak positions are not reported, and neither peak areas nor their ratios are provided to substantiate the repeated statements in the text. The authors should include these quantitative details to strengthen the validity of their XPS interpretation.

 

Reply: Thank you for the precious comment. The peak positions were added to the figure (Figure 4). Decrease in N amount through EB irradiation can be confirmed by quantification based on spectral deconvolution. Additionally, the EB-induced N elimination has already been reported in the previous reports. Quantification data were shown in Supplementary information (Table S1), and additional comments were added to the main text (lines239–245, 251–256, 258–260). 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Comments to the author

1. I suggest the author to provide the significance of sonication and EB for g-C3N4 modification in the introduction section.
2. I suggest the author to provide the comparative study with other modification methods such as hydrothermal, plasma, chemical etching, etc.
3. The XRD and XPS have the lack of quantitative interpretation like crystallite size changes, peak fitting results, etc.
4. There are no numerical values and error bar in the BET analysis. I suggest the author to provide the same in the Figure 3.
5. I suggest the author to provide the SEM/TEM images after the modification of g-C3N4 from sonication and EB.
6. Figure 5 represents the first order kinetics and there is no k and R2 value. I suggest the author to calculate the k and R2 value for all the samples and compared the results.
7. There is no control experiment for photocatalytic degradation of RhB.
8. I suggest the author to provide the reusability and stability study.
9. Figures are not clear.
10. I suggest the author to provide the quantitative result in the abstract section.
11. Few sentences are not clear. I suggest the author to check the clarity of the statements throughout the manuscript.
12. I suggest the author to check the typographical errors in the entire manuscript.

Author Response

1. I suggest the author to provide the significance of sonication and EB for g-C₃N₄ modification in the introduction section.

 

Reply: Thank you for the precious comment. Descriptions on the novel findings were added to the main text lines (lines 106–109).

 

 

2. I suggest the author to provide the comparative study with other modification methods such as hydrothermal, plasma, chemical etching, etc.

 

Reply: Thank you for the precious comment. Although the advantages of method proposed here cannot be simply compared to other techniques, the EB irradiation can be carried out without harmful reagents and under ambient atmosphere and temperature. These would be the advantages of the proposed method. Additional comments were added to the main text (lines 61–65).

 

 

3. The XRD and XPS have the lack of quantitative interpretation like crystallite size changes, peak fitting results, etc.

 

Reply: Thank you for the precious comment. In this case, the XRD peak shift caused by the sonication and EB irradiation was very slight, so that the change in crystal structure would be minor. However, crystallite size can be estimated based on the XRD data, so that the calculated crystallite size were described in the main text (lines 172–182). 

   The XPS peak positions were added to the figure (figure 4). Decrease in N amount through EB irradiation can be confirmed by quantification based on spectral deconvolution. Additionally, the EB-induced N elimination has already been reported in the previous reports. Quantification data were shown in Supplementary information (Table S1), and additional comments were added to the main text (lines239–245, 251–256, 258–260). 

 

 

4. There are no numerical values and error bar in the BET analysis. I suggest the author to provide the same in the Figure 3.

 

Reply: Thank you for the precious comment. The specific surface areas were written in the figure (Figure 3). In many articles, indication of the error range of specific surface area is generally omitted, so that the error bars were not shown also in this figure. 

 

 

5. I suggest the author to provide the SEM/TEM images after the modification of g-C₃N₄ from sonication and EB.

 

Reply: Thank you for the precious comment. If the SEM/TEM images can be available and they reveal the microscopic structural alteration, they would be useful. However, unfortunately, such data are not immediately available. Of course, the authors are confident that the SEM/TEM observation is important. Additional comments were added to the main text (lines 216–219).

 

 

6. Figure 5 represents the first order kinetics and there is no k and R2 value. I suggest the author to calculate the k and R2 value for all the samples and compared the results.

 

Reply: Thank you for the precious comment. Estimation of the apparent first-order rate constants is possible. The obtained data were ilisted in Supplementary information (Table S2). Additional comments were also added to the main text (lines 269–277, 295–296).

 

 

7. There is no control experiment for photocatalytic degradation of RhB.

 

Reply: Thank you for the precious comment. The effect of physical adsorption on dye removal has already been known to be minor since the specific surface area of g-C₃N₄ is quite small, so that the control experiments under dark condition has been omitted in this study. Additional comments were added to the main text (lines 264–268).

 

 

8. I suggest the author to provide the reusability and stability study.

 

Reply: Thank you for the precious comment. Althouth the main topic of this study is the positive effect of sonication and EB irradiation rather than the practical characteristics such as long-term reusability, it is important anyway. Additional comments were added to the main text (lines 327–332). 

 

 

9. Figures are not clear.

 

Reply: Thank you for the precious comment. The figures were checked again and remade as much as possible (resolution, font size, etc).

 

 

10. I suggest the author to provide the quantitative result in the abstract section.

 

Reply: Thank you for the precious comment. Quantitative result on the significance of combined treatment (sonication and EB irradiation) was added to the abstract (lines 22–24).

 

 

11. Few sentences are not clear. I suggest the author to check the clarity of the statements throughout the manuscript.

 

Reply: Thank you for the precious comment. The sentences were checked again and rewritten as much as possible. In addition, proofreading of the revised manuscript has been performed as described below. 

 

 

12. I suggest the author to check the typographical errors in the entire manuscript.

 

Reply: Thank you for the precious comment. In fact, English correction by a professional proofreader has been carried out prior to the first submission, but additional proofreading of the revised manuscript has been performed again. 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

No further comments.

Author Response

Comment: No further comments.

 

Reply: Thank you for your cooperation.

Reviewer 3 Report

Comments and Suggestions for Authors

1.As the authors stated in the text written between the line 235-237, values obtained for binding energies in XPS measurements are higher than standard values characteristic for carbon -nitrogen bonds of carbon-nitride due to charging effect. It is a common problem with carbon-nitride based materials, because of its low conductivity and layered structure. Additionally, charging effect that occurs during XPS measurements is differential charging that leads to peak broadening and/or occurrence of additional peaks for the same chemical state. Shift in binding energies is not uniform for all peaks, nor the broadening of the peaks induced by charging effect.

There are additional manifestations of sample charging that, together with the two effects described above, render the XPS data in this manuscript unusable in their present form. As a result, the detailed interpretations and conclusions derived from the XPS spectra are incorrect—or, at best, highly uncertain.

If these data were published without correction, they could introduce long-term confusion into the literature. Future studies may cite these spectra as a reference, thereby normalizing charging-induced artefacts and reinforcing incorrect peak assignments and chemical-state interpretations.

I am outlining these issues in detail so that the authors fully recognize the broader implications of publishing severely distorted XPS data. Maintaining methodological accuracy and avoiding the propagation of artefactual results has always been an essential, if unwritten, scientific standard.

Author Response

Comment: As the authors stated in the text written between the line 235-237, values obtained for binding energies in XPS measurements are higher than standard values characteristic for carbon -nitrogen bonds of carbon-nitride due to charging effect. It is a common problem with carbon-nitride based materials, because of its low conductivity and layered structure. Additionally, charging effect that occurs during XPS measurements is differential charging that leads to peak broadening and/or occurrence of additional peaks for the same chemical state. Shift in binding energies is not uniform for all peaks, nor the broadening of the peaks induced by charging effect.

There are additional manifestations of sample charging that, together with the two effects described above, render the XPS data in this manuscript unusable in their present form. As a result, the detailed interpretations and conclusions derived from the XPS spectra are incorrect—or, at best, highly uncertain.

If these data were published without correction, they could introduce long-term confusion into the literature. Future studies may cite these spectra as a reference, thereby normalizing charging-induced artefacts and reinforcing incorrect peak assignments and chemical-state interpretations.

I am outlining these issues in detail so that the authors fully recognize the broader implications of publishing severely distorted XPS data. Maintaining methodological accuracy and avoiding the propagation of artefactual results has always been an essential, if unwritten, scientific standard.

 

Reply: Thank you for the precious comment. As the reviewer pointed out, the current XPS measurement results are not completely reliable and may contain problems. The major effect of charging on the spectral shape is a reduction in the signal/noise ratio due to peak broadening, which often affects quantitative analysis results. However, in the spectra obtained in this study, although peak shifts were observed, no significant changes in the signal/noise ratio were observed. Therefore, while the composition values ​​themselves may be affected by charging, we believe this effect is not significant enough to change the assertion regarding structural changes. However, as the reviewer advised, it is important to carefully consider the effect of charging when examining the results of this study. The effect of charging on XPS measurements of this material has not been thoroughly investigated and further research is needed. We have added additional comments to emphasize this point (line 237-245). We have also rewritten the relevant parts of the conclusions (line 330-338).

 

Reviewer 4 Report

Comments and Suggestions for Authors

The author revised the manuscript as per the reviewer comments. So the manuscript may be accepted for publication.

Author Response

Comment: The author revised the manuscript as per the reviewer comments. So the manuscript may be accepted for publication.

 

Reply: Thank you for your cooperation.