Determination of Activation Energy from Decolorization Reactions of Synthetic Dyes by Fenton Processes Using the Behnajady–Modirshahla–Ghanbary Kinetic Model

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

In this study, the initial reaction rates and the activation energy (Ea) from the decolorization of synthetic dyes by Fenton processes mediated by Fe3+ reducers were studied using the BMG kinetic model. The novelty of this work is unclear. It must be highlithed in accordance with the literature review. It is also written like a report and lacks discussion. So, I think it cannot be considered for publication in this version.

Author Response

Point by point response to reviewer’s comments

We would like to thank the Editor and Reviewers time and efforts in reviewing our manuscript. The changes in this corrected version were highlighted in blue in the manuscript. Sincerely yours.

Reviewer 1

In this study, the initial reaction rates and the activation energy (Ea) from the decolorization of synthetic dyes by Fenton processes mediated by Fe3+ reducers were studied using the BMG kinetic model. The novelty of this work is unclear. It must be highlithed in accordance with the literature review.

Authors: In the Introduction section, the last paragraph justifies the use of the BMG model to calculate activation energy. However, we have added a sentence to the previous paragraph to provide clearer justification for this work: “To the best of our knowledge, no studies have been conducted to calculate the Ea using 1/m values from the degradation of different dyes, used as target pollutants, by Fenton processes.”

It is also written like a report and lacks discussion. So, I think it cannot be considered for publication in this version.

Authors: In this new version of the manuscript, we have included a more detailed discussion for each of Figures 5-9. Additionally, two new paragraphs were added on page 10 for a joint discussion of the results.

Comments:

Introduction: must be improved.

Authors: This topic already adresses the main aspects of Fenton reaction to degrade dyes. We presented the fundamentals of Fenton chemistry, susceptibility of dyes to hydroxyl radicals, advantages, limitations, effect of adding reducers, kinetic of reactions, and types of kinetic models. Even so, some improvements were added.

References: can be improved.

Authors: We have inserted other seven references in this new version of the manuscript.

Research design: Must be improved.

Authors: We have improved the text to better clarify how the work was conducted.

Methods: Can be improved

Authors: We have included other relevant aspects in this topic, such as how the control experiments were conducted.

Results clearly presented: Must be improved.

Authors: We have improved the discussion of the results by addressing a more detailed analysis of the figures.

Conclusions: Must be improved.

Authors: This topic has been improved to clearly present the results and the main outcomes of the research. Although it is now slightly shorter, it is more concise and objective.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This work aimed to continue studies of reaction kinetics based on the degradation of synthetic dyes via Fenton processes mediated by reducing compounds. However, there are still big problems in the text. I suggest that this work should be reevaluated after extensive revision.

 

1. The degradation mechanisms of different target dyes are different, and the types of free radicals that play a leading role will also be different, whether the BMG model will not be applicable. Just how much the activation energy calculated by the BMG model differs from the data measured by other authoritative methods should be reflected in the paper, although the authors make a slight mention of this in the introduction of the four previously reported works.

2. Compared with the published papers, the amount of data listed in this paper is also insufficient. A logarithmic curve makes only four test points, which makes the conclusions of the study unreliable.

3. In addition, in the section of Results and Discussion, the experimental data presented by the authors is extremely limited, and most of the graphic data are from previously published work (from Fig. 5 to Fig. 9), which makes the paper less like an original research article and more like a Comment article.

4. The whole paper lacks a summary of catalytic mechanisms, and is more like a list of published data, that is, an experimental report.

Author Response

Point by point response to reviewer’s comments

We would like to thank the Editor and Reviewers time and efforts in reviewing our manuscript. The changes in this corrected version were highlighted in blue in the manuscript. Sincerely yours.

Reviewer 2

This work aimed to continue studies of reaction kinetics based on the degradation of synthetic dyes via Fenton processes mediated by reducing compounds. However, there are still big problems in the text. I suggest that this work should be reevaluated after extensive revision. 

1. The degradation mechanisms of different target dyes are different, and the types of free radicals that play a leading role will also be different, whether the BMG model will not be applicable. Just how much the activation energy calculated by the BMG model differs from the data measured by other authoritative methods should be reflected in the paper, although the authors make a slight mention of this in the introduction of the four previously reported works.

Authors: We have added two new paragraphs on these aspects on page 10.

2. Compared with the published papers, the amount of data listed in this paper is also insufficient. A logarithmic curve makes only four test points, which makes the conclusions of the study unreliable.

Authors: We cannot agree with this statement because studies evaluating four temperature values to calculate activation energy are commonly found in literature (Santos et al., 2011; Tony & Mansur, 2019; Kumar et al., 2019). This information was included on page 6 in this new version of the manuscript.

3. In addition, in the section of Results and Discussion, the experimental data presented by the authors is extremely limited, and most of the graphic data are from previously published work (from Fig. 5 to Fig. 9), which makes the paper less like an original research article and more like a Comment article.

Authors: We cannot agree with this statement because half of the results shown in Figures 5-9 were obtained in the present study. The other half was published in previous works, but they are shown in the same figures for comparison purposes between the reaction kinetics models, from which their rate constants were used to calculate activation energy.

4. The whole paper lacks a summary of catalytic mechanisms, and is more like a list of published data, that is, an experimental report.

Authors: We have improved the catalytic mechanisms promoted by each type of reducer in Supplementary Material (Figures S6-S10), although the effect of phenolic compounds was described since the first version of the manuscript. We have attempted to clarify in the text that this is not merely a compilation of published works, as half of the results depicted in Figures 5-9 were obtained in the present study. The other half was published in previous works, but they are shown in the same figures 5-9 for comparison purposes.

Other comments:

Introduction: must be improved.

Authors: This topic already adresses the main aspects of Fenton reaction to degrade dyes. We presented the fundamentals of Fenton chemistry, susceptibility of dyes to hydroxyl radicals, advantages, limitations, effect of adding reducers, kinetic of reactions, and types of kinetic models. Even so, some improvements were added.

References: can be improved.

Authors: We have inserted other seven references in this new version of the manuscript.

Research design: Must be improved.

Authors: We have improved the text to better clarify how the work was conducted.

Methods: Must be improved

Authors: We have included other relevant aspects in this topic, such as how the control experiments were conducted.

Conclusions: Must be improved.

Authors: This topic has been improved to clearly present the results and the main outcomes of the research. Although it is now slightly shorter, it is more concise and objective.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study is about the determination of activation energy for the Fenton´s process for dye decolorization with or without reducers using the BMG model, but some aspects should be revised in the manuscript. This work misses the comparison of this model with other models for kinetics determination.

The first time that the acronym of BMG appear should be defined.

Why the authors use this model to determine the Ea? This is not clear in the work.

Which are the present results of Figure 3 since the authors define as data from previous work.

For Figure 3 is missing the data of each dye without Fenton, since the temperature can interfere in the 1/m for these dyes.

The authors should also compare dye decolorization results by the reducers without Fenton, since the reducers can interfere in the decolorization.

Author Response

Point by point response to reviewer’s comments

We would like to thank the Editor and Reviewers time and efforts in reviewing our manuscript. The changes in this corrected version were highlighted in blue in the manuscript. Sincerely yours.

Reviewer 3

This study is about the determination of activation energy for the Fenton´s process for dye decolorization with or without reducers using the BMG model, but some aspects should be revised in the manuscript. This work misses the comparison of this model with other models for kinetics determination.

Authors: This work precisely compares the BMG with others more commonly used kinetic models to calculate activation energy (Ea) from their rate constants. In this new version, we have added two paragraphs on the aspects aforementioned on page 10.

The first time that the acronym of BMG appear should be defined.

Authors: Corrected.

Why the authors use this model to determine the Ea? This is not clear in the work.

Authors: In the Introduction section, the last paragraph justifies the use of the BMG model to calculate activation energy. However, we have added a sentence to the previous paragraph to provide clearer justification for this work: “To the best of our knowledge, no studies have been conducted to calculate the Ea using 1/m values from the degradation of different dyes, used as target pollutants, by Fenton processes.”

Which are the present results of Figure 3 since the authors define as data from previous work.

Authors: Figure 3 was constructed using previous data, which were not presented in figure form in prior works. Its purpose here is to illustrate the increase in 1/m with rising temperature. By utilizing the 1/m values depicted in this figure, we were able to calculate the Ea values in the current study.

For Figure 3 is missing the data of each dye without Fenton, since the temperature can interfere in the 1/m for these dyes.

Authors: In the methodology section, we have inserted the following sentence: “The solutions were kept in a water bath for 10 min to reach the designed temperature and then Fe ions were added to start the reactions. This time interval also demonstrated that there was no decolorization of any of the dyes due to the unique effect of temperature.”

The authors should also compare dye decolorization results by the reducers without Fenton, since the reducers can interfere in the decolorization.

Authors: Considering the unique effect of reducers, the reaction medium contains much more sulfuric acid (which is a strong acid) than the reducers (generally weak acids). If the reviewer assumes that hydrolysis reactions could decolorize the dyes, these reactions would hardly be catalyzed by the reducers. It is important highlighting that all reactions (and controls) were evaluated in the presence of sulfuric acid (1 mmol.L-1). On the other hand, if the reviewer assumes that reduction reactions could promote decolorization, no anthraquinone-type dyes, which are susceptible to reductive transformation, were evaluated in this study. Anyway, we now include the following sentence: “Controls involving the reagents separately (including only the reducers, Fe salts, or H₂O₂) were conducted in previous our studies and did not present decolorization”.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Please clearly indicate in the text which data in Fig. 5-9 are based on published data and which are new data and conclusions of this work. In addition, supporting materials Figure S1-5 are not mentioned in the content of the paper and what their functions are.

Author Response

Point by point response to reviewer’s comments

We would like to thank the Editor and Reviewers time and efforts in reviewing our manuscript. The changes in this corrected version were highlighted in blue in the manuscript.

Sincerely yours,

The authors

Reviewer 2

Please clearly indicate in the text which data in Fig. 5-9 are based on published data and which are new data and conclusions of this work.

Authors: In this new version of the manuscript, we have made improvements to better clarify Figures 5-9, aiding in the comprehension in comparing activation energy values calculated in this study using the BMG model and those obtained through conventional methods in our previous studies. Additionally, justification and conclusions were improved.

In addition, supporting materials Figure S1-5 are not mentioned in the content of the paper and what their functions are.

Authors: Figures S1 to S5 in the suplementary material has been mentioned since the first version of the manuscript. On Page 5, it is stated: “The parity plot between the experimental and the predicted data can clarify if a kinetic model is suitable in describing a reaction system [38-40]. Figures S1 to S5 (available in the Supplementary Materials) show the parity plots between the experimental data of decolorization at different temperatures and the results predicted through the equations obtained from the BMG kinetic model. For most of the reaction systems, the predictions of the models are in good agreement with the respective experimental results. Only one R² value was slightly lower than 0.8, which is the parity graph referring to Safranin T decolorization by Fe²⁺/H₂O₂/Ascorbic Acid system. In this way, through the analysis of parity plot, the BMG model was adequate to describe the decolorization of the dyes by Fenton processes.”

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The authors adressed all the concerns in the revision. Therefore, the manuscript can be accepted

Author Response

Point by point response to reviewer’s comments

We would like to thank the Editor and Reviewers time and efforts in reviewing our manuscript. The changes in this corrected version were highlighted in blue in the manuscript.

Sincerely yours,

The authors

Reviewer 3

The authors adressed all the concerns in the revision. Therefore, the manuscript can be accepted

Authors: We thank its comments.

Author Response File: Author Response.pdf