The Degradation of Rhodamine B by an Electro-Fenton Reactor Constructed with Gas Diffusion Electrode and Heterogeneous CuFeO@C Particles
, Xin Su 1, Yifan Li 2, Yang Zhang 1,*, Yunmei Du 1,* and Yuanhong Ding 1,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsSee the attachment
Comments for author File: 
Comments.pdf
Must be improved
Author Response
Response to the Reviewer 1’s comments
The manuscript needs major revision before proceeding further. Many abbreviations have not been defined. In the discussion, the authors used to claim but there are no technical justifications for their claim. The discussion of results is extremely poor. The discussion is not in sequence and there is no coherence in the discussion. Following are my observation;
We greatly appreciate reviewer for the important comments on this manuscript, and thank you for giving us an opportunity to polish it, all abbreviations have been defined in advance, and some paragraphs were rearranged or rewritten to meet the Reviewer’s expectation. Below are our responses according to the comments point by point, because some present sentences and words are revised or deleted, and some new ones are inserted, thus, the line number of revised version is different from that of the original manuscript, please pay attention to it.
Point 1: There are several grammatical errors throughout the manuscript. It is recommended that the manuscript be edited by a certified English editing service or a native English speaker.
Response 1: Thanks for your suggestion, we had revised the full text of this manuscript in detail, and hope to meet the requirement of this Journal.
Point 2: The abstract contains numerous abbreviations that need to be defined. The authors should revise the abstract to ensure it can stand alone from the rest of the paper.
Response 2: Thanks for your important suggestion, assuredly, many abbreviations may result in difficulty of understanding. To describe clearly the used GDE cathode and based r-GO materials, all the abbreviation of GDE, r-GO and Rh B have been replaced with “gas diffusion electrode”, “r-graphene oxide” and “Rhodamine B”, respectively.
Point 3: The introduction lacks coherence and is written in fragments. Additionally, the text formatting is inconsistent. The introduction should be thoroughly revised for clarity and flow.
Response 3: Thanks for your important suggestion, the Introduction section has been revised in detail again, we wish it could meet your expectation, if not, please return right away, we will carefully revise it again.
Point 4: The compound with which r-GO reacts is not mentioned in the first paragraph of Section 2.1. Please ensure that the reactive compound or reagent used in the interaction with r-GO is clearly stated in this section for better clarity and understanding of the experimental process.
Response 4: Thanks for your important suggestion, two paragraphs were inserted into the Section 2.1 (later adjusted as Section 2.2) to describe clearly the preparation process of r-GO and NSB-r-GO composite.The inserted paragraphs were as follows:
The nickel foam was designated as the supporting plate material of GDE, on which surfaces elements N-S-B and r-GO compounds was pasted. The pretreatment process of nickel foam was as follows: it was cut into rectangular plates with 5 cm length and 2.5cm width, then cleaned with deoiling and deoxidizing process, continuously, placed ultrasonically in anhydrous ethanol for 30 min, after that, cleaned with deionized water and placed sequentially in 0.5mol /L diluted hydrochloric acid for ultrasonic process for 15 min, fourthly, it was washed with deionized water until neutral, and immersed ultrasonically again in deionized water for 15 min. Finally, it was dried and sealed at 80℃for the subsequent preparation of GDE.
All the surface-modified materials such as r-GO and NSB-r-GO composite were made from graphene oxide (GO) and chemical reagents containing elements N-S-B, which were purchased directly from chemical reagents corporations.
Point 5: The dimensions of casted electrode are not mentioned in section 2.1. Please clearly state for clarity.
Response 5: Thanks for your important suggestion, the dimensions of casted electrode named GDE electrodes was 5 cm length and 2.5cm width, respectively, it was mentioned in the inserted paragraphs in present Section 2.2.
Point 6: The section 2.4 should be before section 2.1 and authors can explain the characterization methods in a separate heading.
Response 6: Thanks for your important suggestion, we have re-adjusted the Section 2, in which the chemical reagents was newly listed as Section 2.1 and the former Section 2.4 was now listed as Section 2.5. Its content was focused on the characterization of r-GO, NSB-r-GO composites and CuFeO@C particles.
Point 7: Authors should cite the reason of choosing Ti/RuSn anodes. They also clearly mention that the catalytic CuFeO@C particles electrode acts as anode or cathode. What is the purpose of this in the system?
Response 7: Thanks for your important suggestion, in this work, Ti/RuSn plate is used as a kind of DSA (Dimensionally Stable Anode), its surficial layer is composed of catalytic elements of Ru-Sn and has good selectivity for oxygen. If the oxygen atoms of H2O are absorbed on it, the hydrogen-oxygen bonds are likely broken to generate active hydrogen radicals, while some corresponding hydroxyl ions from the ionization of H2O is possibly transformed into hydroxyl free radicals by losing electron on Ti/RuSn anodes, it likely reacts with Rh B and results in the decomposition of Rh B, as showed in equation (a) and (b).
H2O-2e→2OH-+2 H+ (a)
OH--e→OH. (b)
As known, Rh B is mainly decomposed by the constructed electro-Fenton process, in which H2O2 and Fe2+ is generated in-situ on the surface of GDE cathode and CuFeO@C particles, respectively, in order to decompose Rh B deeply on the surface of anode either, Ti/RuSn plate is selected as anode in the electrolytic process. On the other, amounts of CuFeO@C particles is suspended between GDE cathode and Ti/RuSn anode in the wastewater, and could be polarized into tiny positive and negative electrodes, besides generating Fenton reagent of Fe2+, it works actually as a kinds of tiny conducting particles electrodes in a conceptual three-dimensional electrolytic reactor.
Point 8: Section 3.3.1: How authors could claim that N2 adsorption desorption is equally good for O2 adsorption over the material because both molecules have different radii and characteristics. Please add the justification for readers. Same comment for CV discussion.
Response 8: Thanks for this very important comment, we agree deeply with it, assuredly, N2 adsorption desorption is not equally good for O2 adsorption over the material because both molecules have different radii and characteristics. However, in this work, N2 is designated and used as a test gas in BET (Brunauer-Emmett-Teller) method for universal measurement of the specific surface areas and distribution of micropores in materials. In this work, GDE plate electrode is made of nickel foam which surface is modified by NSB r-GO compounds, its specific surface areas and distribution of micropores is only measured by BET method using N2 as test gas, but the measured results could be used to estimate the mesoporous structure of electrode, here, the electrode is specially referred to GDE cathode, and its mesoporous structure likely accelerates the mass transfer efficiency of O2 and the yield of H2O2.
About CV curves, the reactivity of oxygens absorbed on GDE electrode could be affected obviously by the doping elements, therefore Figure 2 and Figure 3 shows that the transferring efficiency and reactivity of O2 on NSB r-GO GDE was better than that on r-GO GDE.
Point 9: Section 3.1.3: three-dimensional interconnecting frameworks claim needs to be verified because where is third dimension? And how authors count surface folds of Composite and r-GO?
Response 9: Thanks for this very important comment, Rh B was decomposed by an electro-Fenton process, both H2O2 and Fe2+ were generated in situ as Fenton reagents by GDE cathode and suspended CuFeO@C particles, however, the CuFeO@C particles could be polarized into tiny positive and negative electrodes, and works actually as a kinds of tiny conducting particles electrodes that could be regarded as third electrodes between cathode and anode plates in a “conceptual Three-Dimensional Electrolytic Reactor (TDER)”.
Among all cathode materials for H2O2 generation, carbon-based materials such as graphene oxide and activated carbon fiber, is selected generally due to their high conductivity and large specific surface area, some heteroatoms (such as N, S, B, F, P, O, etc.) are also doped into the carbon-based skeleton of cathode materials. On the other, to guarantee the mesoporous GDE not to be submerged and jammed with electrolyte, its surface is generally modified by adding an amount of PTFE (Polytetrafluoroethylene) emulsion to obtain hydrophobicity. Therefore, the internal structure of GDE used in this work, was porous and hydrophobic, and had gas-liquid-solid three phase contact surface, which ensures the transmission, diffusion and reaction utilization of O2 to generate H2O2 smoothly.
Finally, we are very sorry for observing merely the surface folds of composite and r-GO by SEM and TEM images.
Point 10: What extra information the authors want to draw through TEM which is still left after SEM? Please justify.
Response 10: Thanks for this very important comment, the external characteristics of GDE electrode could be obtained by SEM analysis in detail, while its internal structure was measured by TEM method which adopted more smaller measure scale than SEM.
TEM images of internal r-GO and NSB-r-GO materials showed that the edges of the graphene nanosheets were wrinkled with wavy and transparent filaments due to local stress caused by oxygen deficiency. On the one hand, in the hydrothermal process, due to the reduction reaction of graphene materials and the doping of heteroatoms (N, S and B), the interconnections between graphene layers would produce ripples and grooves, resulted in uneven/structural defects of edges and voids, exposed high-density active sites and formed more electron bridges, thereby accelerated electron transfer and reduced conduction loss. On the other hand, the three-dimensional porous lattice structure and the presence of non-uniform/structural defects could also accelerate the adsorption and diffusion process of ions in the electrolyte, and further improved the electrocatalytic activity.
Point 11: Section 3.1.3: Authors claimed in XPS discussion that they selected NSB r-GO material for electrode. From how many materials they selected this composite? It is not explained anywhere in the manuscript.
Response 11: Thanks for this very important comment, the initial target of this work is that a new type of Fenton process could be constructed without any addition of conventional chemical reagent such as H2O2 and Fe2+, then based on literatures, only r-GO and NSB-r-GO materials was selected and explored whether H2O2 could be generated smoothly, and only heterogeneous CuFeO@C particles was manufactured to testify whether Fe2+ could be generated either, then as an ultimate object, we want to investigate whether Rh B could be degraded successfully as the same as conventional Fenton process, therefore, in this manuscript, lots of details about characteristics of GDE electrode and CuFeO@C particles was insufficient, thus sincerely, we are very sorry for our imperfect work and manuscript.
Point 12: Section 3.1.4: The results have been explained without any mechanistic background which could hardly inspire the potential reader.
Response 12: Thanks for this very important comment, one paragraph is inserted into the Section3.1.4 to explain the possible generating way of hydrogen peroxide.
Point 13: How suddenly a CuFeO@C particle comes into picture? What shortcomings the authors faced with NSB r-GO?
Response 13: Thanks for this very important comment, in this work, Fe2+ is supplied by heterogeneous CuFeO@C particles, therefore, it is necessary to testify whether ferric ion is synthesized into the particles by SEM and XRD images. On the other, we think, NSB r-GO GDE has the shortcomings of complicated manufacturing process.
Point 14: Please add the results of RhB degradation without catalytic particles? Response 14: Thanks for this very important comment, the removal efficiencies of RhB degradation without catalytic particles has been inserted into the Figure 10 (e). indeed, Rh B could be degraded by H2O2 generated on GDE cathode without catalytic particles, but its removal efficiencies were lower than expected.
Point 15: Section 3.3: The discussion lacks the mechanistic details in all the sections.
Response 15: Thanks for this very important comment，three-paragraphs sentences have been inserted in Section3.3 to strengthen the discussion.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
The manuscript presented for review is devoted to construction of electron-Fenton reactor for investigation of wastewater treatment (from synthetic Rhodamine B (Rh 13 B)). The research is of interest from both a fundamental and an applied point of view The manuscript is well written and carried out on high experimental level. I recommend the manuscript for publication after addressing a number of minor recommendations that may improve this article:
1) It would be desirable for the convenience of perception to combine some of the equations into one scheme (for example, equations 1-4).
2) It is necessary to provide citations in the journal format (reference numbers, not transcripts).
3) In my opinion, Figure 1 is more suitable for presentation in Supplementary materials. Directly in the article, you can depict the installation in a schematic form.
4) Figure 3 also may be transferred into Supplementary materials.
5) I think that Conclusion section is very short. Probably, this part should be expanded in terms of a clearer and more detailed presentation of the results and their novelty.
6) Page 1: the text in introduction have different font size; page 5: some text is yellow colored.
Author Response
Response to the Reviewer 2’s comments
The manuscript presented for review is devoted to construction of electron-Fenton reactor for investigation of wastewater treatment (from synthetic Rhodamine B (Rh 13 B)). The research is of interest from both a fundamental and an applied point of view The manuscript is well written and carried out on high experimental level. I recommend the manuscript for publication after addressing a number of minor recommendations that may improve this article:
Thank Reviewer for evaluating the manuscript and giving us very important comments, we have checked it in detail and recognized the severity of these errors and problems. Here below are our responses to these comments and suggestions.
Point 1: It would be desirable for the convenience of perception to combine some of the equations into one scheme (for example, equations 1-4).
Response 1: We understand the Reviewer’s concern, thanks for this very important comment. The places of some equations has been adjusted to read it easily.
Point 2: It is necessary to provide citations in the journal format (reference numbers, not transcripts).
Response 2: We understand the Reviewer’s concern, thanks for this important suggestion, the format of cited places and sort order of references in full text has been revised as required.
Point 3: In my opinion, Figure 1 is more suitable for presentation in Supplementary materials. Directly in the article, you can depict the installation in a schematic form.
Response 3: We understand the Reviewer’s concern, thanks for this important suggestion, this photograph of the electro-Fenton reactor in laboratory has been replaced by a schematic form.
Point 4: Figure 3 also may be transferred into Supplementary materials.
Response 4: We understand the Reviewer’s concern, thanks for this important suggestion, firstly, Figure 3 merely showed that NSB-r-GO GDE electrode had higher reactivity of oxygen than that of r-GO GDE electrode, this image assuredly should be transferred into supplementary materials. However, we want to demonstrate all the necessary image in this one file named “Response to the Reviewer” without another supplementary materials file. Therefore, we retain Figure 3 in this manuscript yet. Could you please agree with our opinion?
Point 5: I think that Conclusion section is very short. Probably, this part should be expanded in terms of a clearer and more detailed presentation of the results and their novelty.
Response 5: We understand the Reviewer’s concern, thanks for this important suggestion, the Conclusion section has been expanded by adding some advantages of electro-Fenton process.
Point 6: Page 1: the text in introduction have different font size; page 5: some text is yellow colored.
Response 6: We understand the Reviewer’s concern, thanks for this important suggestion, the text in introduction with different font size has been revised as the same font as text of this paragraph, however, the yellow color text of page 5 in this typeset manuscript, has been likely revised by editor.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsN/A
Comments on the Quality of English LanguageN/A
Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors have completed all comments as per suggestion. Therefore, I recommend the manuscript for publication in present form.
