2D Nanomaterial—Based Electrocatalyst for Water Soluble Hydroperoxide Reduction
Round 1
Reviewer 1 Report
1- Abstract is not well written. For example, this sentence cannot be understood:
Hydroperoxides emerge upon lipid peroxidation: they are highly reactive, tend to form free radicals when decomposing, and therefore their elevated levels indicate lipid deterioration.
Please revised the abstract with results oriented too. (mention the name of composite formed)
2- In introduction, it is recommended to add a paragraph about the graphene materials for the different applications by citing the references such as Journal of Environmental Chemical Engineering 9 (5), 106111, Applied Nanoscience 11 (4), 1291-1302.
3- Is there any advantage of using 2D nanomaterials in the electrochemical reduction of hydroperoxide. Please mention in introduction.
4- The quality of figures and language should be improved.
5. Please rectify all typo and grammatical mistakes like line 215, 286....etc
6. Please check all figure numbering in the text specially Fig 2-1. (line 192)
7 why the author choose the doping of cobalt derivative.
Author Response
Responses to Referee #1
Q1- Abstract is not well written. For example, this sentence cannot be understood:
“Hydroperoxides emerge upon lipid peroxidation: they are highly reactive, tend to form free radicals when decomposing, and therefore their elevated levels indicate lipid deterioration. “
Please revised the abstract with results oriented too. (mention the name of composite formed).
A: Thank you for the suggestions. The first sentence of the Abstract as well as the second one were rewritten. The main results have been included in the Abstract from the very beginning. The composite “name” is Co-g-C3N4/Nafion, which was not mentioned due to the limits of 200 words for the Abstract, however now was added.
Q2- In introduction, it is recommended to add a paragraph about the graphene materials for the different applications by citing the references such as Journal of Environmental Chemical Engineering 9 (5), 106111, Applied Nanoscience 11 (4), 1291-1302.
A: A recent review article dedicated to 2D –nanodimensional materials and their applications in biomedical research has been added to the Introduction. The suggested articles by Mohamad Nasir Mohamad Ibrahim and co-workers consider too narrow area of applications and their connection to our research is not seen. Graphene and carbon nitride differ substantially (in terms of catalytic properties and electrical conductivity), so that an eventual comparison between them will be hard to explain.
Q3- Is there any advantage of using 2D nanomaterials in the electrochemical reduction of hydroperoxide. Please mention in introduction.
A: In the additional paragraph added to the Introduction it was said: “Their unique catalytic properties and large surface-to-volume ratio makes them suitable for a wide spectrum of applications, such as environmental catalysis, drug delivery, sensory, and energy applications.”
Q4- The quality of figures and language should be improved.
A: Thank you for the critical notes. Indeed, the quality of Figures needed improvements, and two of the Figures – Fig.1 and Fig. 6 have been re-plotted. As suggested by the Editor, the sensitivity was re-calculated for each type of catalyst by dividing it to the electrochemically accessible surface area, determined electrochemically.
The language spelling and grammar has been checked, and the technical omissions were corrected. Where possible, the sentences were also simplified so that to improve the readability of the text.
Q5. Please rectify all typo and grammatical mistakes like line 215, 286....etc.
A: Thank you for pointing out to these technical issues. All the indices (subscripts and superscripts) have been checked and amended where found.
Q6. Please check all figure numbering in the text specially Fig 2-1. (line 192).
A: Thank you for the notification. Fig 2-1 was a short indication for Fig. 2, series 1. Now it is corrected.
Q7 why the author choose the doping of cobalt derivative.
A: As it was stated in the Introduction: cobalt oxides possess i) electrochemical activity in our target reaction (lines 76-78); and ii) the spinel cobalt oxides have structure-improving effect on the doped carbon nitride (lines 73-76).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this work the performances of metal oxides – doped graphitic carbon nitride are examined as catalyst influencing the electrochemical reduction of hydrogen peroxide and tert-butyl hydroperoxide. The article is interesting in nature, but it should be modified before it becomes publishable. Some suggestions are as below:
1. The introduction discusses the electrochemical methods for the determination of hydroperoxides such as electrochemical oxidation or reduction of hydrogen peroxide; and then describes the type of catalysts used for the electroreduction of H2O2 (including nobel metal nanoparticles, metal oxide nanoparticles, and carbon nanomaterials). Here the importance of the research, and the main reason based on which the study is conducted is not very clear. Please clearly discuss the target and importance of the research.
2. Since the target of the research is based on assessing the catalytic performance of g-C3N4 materials (or nanomaterials), the article must include further information about the catalysts used; such as (a) the concentration (mass loading) of the catalysts on glassy carbon working electrode; (b) the size and distribution of catalysts on glassy carbon working electrode examined by microscopy studies; and (c) the crystalline structure of the catalysts examined by X-ray diffraction pattern.
3. the results obtained need to be compared with those of alternative catalysts reported in the literature.
Author Response
Responses to Referee #2
In this work the performances of metal oxides – doped graphitic carbon nitride are examined as catalyst influencing the electrochemical reduction of hydrogen peroxide and tert-butyl hydroperoxide. The article is interesting in nature, but it should be modified before it becomes publishable. Some suggestions are as below:
- The introduction discusses the electrochemical methods for the determination of hydroperoxides such as electrochemical oxidation or reduction of hydrogen peroxide; and then describes the type of catalysts used for the electroreduction of H2O2 (including nobel metal nanoparticles, metal oxide nanoparticles, and carbon nanomaterials). Here the importance of the research, and the main reason based on which the study is conducted is not very clear. Please clearly discuss the target and importance of the research.
A: The practical importance of the study has been highlighted by stating that the “purpose of this study is to develop and characterize a sensitive chemically modified glassy carbon electrode (GCE) for the determination of water-soluble peroxides such as hydrogen peroxide and tert - butyl hydroperoxide in aqueous media by using as a modifying phase graphitic carbon nitride (g-C3N4) doped with metal oxides, and Nafion™ polymer suspension as a binding agent as a first step towards the development of an electrochemical peroxide test.”
- Since the target of the research is based on assessing the catalytic performance of g-C3N4 materials (or nanomaterials), the article must include further information about the catalysts used; such as (a) the concentration (mass loading) of the catalysts on glassy carbon working electrode; (b) the size and distribution of catalysts on glassy carbon working electrode examined by microscopy studies; and (c) the crystalline structure of the catalysts examined by X-ray diffraction pattern.
A: Authors thank to this reviewer for the helpful suggestions.
- The catalyst load was indicated both in the text and in the Figure legends, below each Figure. The mass of the catalysts was varied between 0.010 mg and 1 mg. The electrochemically accessible surface area was also determined, as suggested by the Editor of the Journal, and in order to compare the catalytic activity of differently modified electrodes, the sensitivities were recalculated by dividing the already established one to the surface for each electrode type – Fig. 1 and Fig. 6.
- The size and the distribution of catalysts has been studied by SEM (Fig. S2 in the Supporting information) and by polarization microscopy (Fig. S3-A) and reflected light microscopy (Fig. S3B). These photos can be found in the Supplementary information.
- A full instrumental examination of metal oxides – doped carbon nitrides has been done in our previous studies (TEM, XRD, FT-IR, ICP-OES, BET etc.). Because these studies have been already published in an open access source (ref. #30, ref. #32), and are currently under consideration for another journal, we do not find it correct to present them again.
- the results obtained need to be compared with those of alternative catalysts reported in the literature.
A: Thank you for this suggestion. A comparison of the discussed results with earlier studies performed with noble metals co-deposits, has been provided in the Discussion section. We have run also another experiment reducing H2O2 on the surface of a platinum disc electrode with the same geometric surface, and have noted that the catalytic activity of our electrode is ca. ~30% of the Pt. Moreover, under equivalent experimental conditions, the amperometric records of the Pt electrode were much noisier, with a high background current and hardly-reachable steady-state response, which is undesired when aiming at analytical applications.
Author Response File: Author Response.pdf
Reviewer 3 Report
In this manuscript, Mariya Pimpilova et. al. reported the electrocatalytic effect of metal oxide-doped g-C3N4 in combination with conductive polymer on the electrochemical reduction of H2O2 and tBHP. The topic of this manuscipt is interesting and fits well with this journal. Besides, the work is well presented. I can recommend acceptance of this manuscript after addressing the following minor points.
1. The potentials used in this studies should be calibrated into RHE.
2. In Figure 1, the subscripts of all materials are not corrected. The same mistakes can be also found in Figs. 5 and 6.
3. There is no any characterizations for Co-g-C3N4 or reference samples. I strongly suggest authors to do careful characterizations for Co-g-C3N4 and reference samples, including SEM, TEM, XPS, XRD and so on.
4. The figure design should be improved. For example, figure 4 is not well designed.
Author Response
Responses to Referee #3
In this manuscript, Mariya Pimpilova et. al. reported the electrocatalytic effect of metal oxide-doped g-C3N4 in combination with conductive polymer on the electrochemical reduction of H2O2 and tBHP. The topic of this manuscipt is interesting and fits well with this journal. Besides, the work is well presented. I can recommend acceptance of this manuscript after addressing the following minor points.
- The potentials used in this studies should be calibrated into RHE.
A: Authors thank the reviewer for their time and efforts spent in reviewing their MS. All the potentials in the text were re-calculated vs. reversible hydrogen electrode and were given together with the values measured vs. Ag|AgCl, sat. KCl reference electrode. Figures were not manipulated, so we believe this is substantial to present both values.
- In Figure 1, the subscripts of all materials are not corrected. The same mistakes can be also found in Figs. 5 and 6.
A: We are thankful for this critical note of the reviewer. Figures 1 and 6 were redrawn. The reason is that the Editor kindly suggested to recalculate the sensitivity of different electrodes by using current densities, instead of the absolute current values, so we determined the electrochemically accessible surface area of each one and replotted the two Figures with the obtained values and corrected indices.
- There is no any characterizations for Co-g-C3N4 or reference samples. I strongly suggest authors to do careful characterizations for Co-g-C3N4 and reference samples, including SEM, TEM, XPS, XRD and so on.
A: We appreciate this reviewer’s comment. Since the electrochemical characterization follows the heterogeneous-catalytic studies performed with the studied materials, these characterizations have been published already under open access policy (ref. #30 and ref. # 32). Taking this into account, we do not find it appropriate to re-publish the characterization. There is a statement in the Introduction that the materials characterization is available in the abovementioned papers.
- The figure design should be improved. For example, figure 4 is not well designed.
A: Authors accept the reviewer’s critical note. Fig. 4 A and Fig. 4 –B visualize the cyclic voltammograms of the catalytic electrode under the same conditions as the presented at Fig. 3. In order to enlarge the specific region where the electrocatalytic process becomes obvious, the presented CVs were given in a narrower potential region, than in Fig. 3.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have addressed most of the comments, unless the comment related to the characterization of the catalyst. However, I feel the article has the merit to be published in the current form.
