Modification of Graphite Sheet Anode with Iron (II, III) Oxide-Carbon Dots for Enhancing the Performance of Microbial Fuel Cell

Round 1

Reviewer 1 Report

The manuscript Modification of graphite sheet anode with Iron(II, III) oxide-carbon dots for enhancing the performance of microbial fuel cell from Soumya Pandit et al submitted to Catalysts present the synthesis and characterization of a new catalyst for Microbial Fuel Cell. The text is clear, usual characterizations are presented, the studied system is new and the performances are pretty good for a microbial fuel cell.I thus consider that the manuscript is suitable for publication and the subject is in agreement with the special issue Recent Advances on Nano-Catalysts for Biological Processes”. However, I will recommend the following minor revisions:

The study is devoted to Fe3O4@PSA-C which is introduced in the introduction without any explanation of the acronym. I considerthat it is necessary to explain the meaning of this acronym at the beginning of the paper for clarity.

Similarly, the material and method part is located at the end of the manuscript and I consider that most of the acronyms especially those specific of electrochemistry (CV and EIS) should be explained when introduced in the discussion. The results presented for the samples MFC-1 to MFC-5 are discussed and the explanation of the difference only appear latter  in the tables which does not favor the understanding of the message.

Finally, I suggest to suppress the table 1 since its content is reported in Table 2 for the MFC samples. A few lines can be written to explain the differences with the three references cited in the table.

Author Response

A point-by-point response to the comments

Reviewer’s comments

Title: Modification of graphite sheet anode with Iron (II, III) oxide-carbon dots for enhancing the performance of microbial fuel cell

First, the authors would like to thank all reviewers for their valuable suggestions and corrections in enhancing our manuscript. Apart from those, the authors have included a few relevant points to improve the quality of the manuscript

#Reviewer 1:

Comments to author

1. The study is devoted to Fe3O4@PSA-C which is introduced in the introduction without any explanation of the acronym. I consider that it is necessary to explain the meaning of this acronym at the beginning of the paper for clarity.

Response: Line 104-107; Fe3O4@PSA-C assigned for Iron oxide @ sodium poly-acrylate-Carbon dot where Iron oxide (Fe3O4) is synthesized with sono- chemical method in presence of sodium poly-acrylate and after chemical sonication process with C-dot, finally we got Fe3O4@PSA-Cdot nanocomposite (annotated version).

2. Similarly, the material and method part are located at the end of the manuscript and I consider that most of the acronyms especially those specific of electrochemistry (CV and EIS) should be explained when introduced in the discussion.

Response: Line 260-264; explanation of cyclic voltammetry has been added. Line 289-297; explanation of electrochemical impedance spectroscopy has been added (annotated version).

3. The results presented for the samples MFC-1 to MFC-5 are discussed and the explanation of the difference only appear latter in the tables which does not favor the understanding of the message.

Response: As suggested by the reviewer the explanation of MFC-1 to MFC-5 has been added in the text (line 255-258) (annotated version).

 

4. Finally, I suggest to suppress the table 1 since its content is reported in Table 2 for the MFC samples. A few lines can be written to explain the differences with the three references cited in the table.

Response: Table 1 is removed and the remaining ones are renumbered (annotated version).

 

Reviewer 2 Report

Do the authors check the possibility of a higher loading rate of the anode catalyst as the highest one used in the study gave the best result clearly indicating further increment can be of better use? Please clarify.

Details about some experiments are missing like SEM, XRD, FTIR, RAMAN, etc. in the Materials and Method section. Please take good care of it. 

Please clarify the details of Figure 2. Whether it's a Cdot or Fe3O4@PSA  as mentioned in the write-up. 

Please provide some clear SEM figures if possible.

Please add these important references:

https://doi.org/10.1016/j.ijhydene.2018.02.188

https://doi.org/10.1016/j.electacta.2014.03.011

https://doi.org/10.1016/j.bej.2019.04.004

https://doi.org/10.1007/s11581-019-03083-5

https://doi.org/10.1016/j.psep.2020.06.043

https://doi.org/10.1016/j.biortech.2014.07.027

Author Response

#Reviewer 2:

1. Do the authors check the possibility of a higher loading rate of the anode catalyst as the highest one used in the study gave the best result clearly indicating further increment can be of better use? Please clarify

Response: Line 108-111; Higher amount of Fe3O4@PSA-C like 1.25mg/cm² was showing minute increase/ no increase in power density as compared to 1mg/cm² which can be neglected hence the amount of Fe3O4@PSA-C was taken till the highest power density observed (annotated version).

2. Details about some experiments are missing like SEM, XRD, FTIR, RAMAN, etc. in the Materials and Method section. Please take good care of it.

Response: Line 461-474; Details about above mentioned experiments has been added in the revised manuscript (annotated version).

3. Please clarify the details of Figure 2. Whether it's a Cdot or Fe3O4@PSA as mentioned in the write-up.

Response: Thank you so much sir for your valuable suggestion. As per your requirement Fe₃O₄-c name is replaced with Fe3O4@PSA -Cdot in image (line 454) (annotated version).

4. Please provide some clear SEM figures if possible.

Response: SEM images

 Sem of Fe3O4@PSA with grain size

 

Sem of Fe₃O₄@PSA-C with grain size

Comments 5. Please add these important references:

Responses: All the necessary references have been included. Reference journal paper no. 4,5, 9,10,11

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript reported the use of carbon dots coated with Fe₃O₄ for its application as an anode in MFCs, and the Fe3O4@PSA-C was synthesized by the hydrothermal-assisted probe sonication method. The maximum power density was observed in MFC with a 1 mg/ml concentration of Fe₃O₄@PSA-C was 440.01 mW/m², 1.54 times higher than MFCs using bare graphite sheet anode. The elevated interaction area of carbon dots permits pervasive Fe₃O₄ crystallization and leads to enhanced cell attachment capability. This significantly improved the performance and made Fe₃O₄@PSA-C modified graphite sheets a good choice as the anode for its application in MFCs.

I consider the content of this manuscript will definitely meet the reading interests of the readers of the Catalysts journal. However, there are certain English spelling and grammar issues, and also the discussion and explanation should be further improved.

 

Therefore, I suggest giving a minor revision and the authors need to clarify some issues or supply some more experimental data to enrich the content. This could be comprehensive and meaningful work after revision.

Detailed comments can be found in the PDF file.

Comments for author File: Comments.pdf

Author Response

#Reviewer 3:

1. For grammar issues, it is suggested that the author double-check the small grammar errors in the full text, especially the lack of and redundant use of definite articles.

Response: The manuscript has been checked thoroughly and edited wherever needed.

2. For the Keywords, hydrothermal assisted probe sonication, power density, and biocompatibility should be added in order to attract a broader readership.

Response: Line 39-40; As suggested by the author Keywords, hydrothermal assisted probe sonication, power density, and biocompatibility are included in the manuscript (annotated version).

3. Line 41 Bioelectricity generated by electrochemically active bacteria (EAB) has gained much attention, with promising significance for renewable energy generation, wastewater re-mediation, and metallic nanoparticle fabrication [1],[2]. Renewable energy is a hot technology in the context of global decarbonization. How does MFC combine with renewable energy? Here I suggest a more detailed description to attract readers' interest. For example, renewable energy sources are typically unstable and intermittent during generation. To tackle this issue, the employment of energy storage systems may greatly improve the utilization rate and stability of renewable energy [ChemSusChem 15.1 (2022): e202101798]. Can MFC be helpful to solve such kind of issue?

Response: This paper mainly focuses on anode modification with Fe₃O₄@PSA-C catalyst to generate highest power density possible by increasing small amount of nanoparticle in different MFC system. So, the properties and importance of anode material are well explained. Moreover, wastewater treatment and renewable energy is altogether a vast topic of discussion which cannot be added here.

4. Line 45, On the surface of the anode, biodegradable waste is oxidized and generates electrons, protons, and other by-products, electrons and protons combined with oxygen at the cathode to complete the reaction [3]. Is any proton exchange membrane or anion exchange membrane used in MFC? How are the protons transported in the system in order to combine with oxygen?

Response: Line 48-49; transport of protons from anodic chamber to cathode was done because of the presence of ionic membrane (annotated version).

5. Line 99, In the aforementioned research, Fe3O4@PSA-C (0.25 mg/ml, 0.5 mg/ml, 0.75 mg/ml, and 1 mg/ml) were used to change graphite sheet anodes. It should be In this paper/work, not aforementioned research, since it seems the content of other literature. And the anode should be solid, why the unit is used as mg/ml? That seems the solution/liquid.

Response: Line 102-103; The sentence is edited. The nanoparticle Fe3O4@PSA-C was added on the anode surface, hence the unit mg/ cm2 is used, necessary corrections were made in the revised manuscript.

6. Line 144, The atom% of C and Fe for Fe3O=@PSA are 9.83 and 36.55, respectively, as shown in fig 2(c), whereas the atom% of C and Fe for Fe3O4@PSA-C nanocomposite are 33.33 and 23.19, respectively, as shown in fig 2(d). The mass percentage of Fe decreases with the addition of C in syn-thesized functionalized nanocomposites. The first sentence, Fe3O=@PSA is a typo, = should be 4. And it is clear that when C is added to the mixture, the mass percentage of Fe decreases, and it is impossible to keep constant or even increase when more carbon-based materials are added to the mixture. But this should not be the effective information that is obtained by the SEM and EDX techniques.

Response: Line 151-158; The authors are highly thankful to observe this typo error and the error in the EDX analysis. The authors have corrected this Fe3O4@PSA-C nanocomposite. The authors have also modified the EDX section. The compositions of Fe3O4@PSA and Fe3O4@PSA-C nanocomposite was determined by X-ray energy-dispersive spectroscopy (EDS), as shown in Fig. 2 c and d. The EDS analysis of the Fe3O4@PSA samples showed peaks with weight percentages for Fe (67.65%), O (28.43%) and C (3.92%). The EDS analysis of the Fe3O4@PSA-C composite showed peaks for Fe (54.17%), O (29.08%) and C (16.75%), which reveal the implantation of the C-dots in the Fe3O4@PSA nanoparticles. The carbon- dots agglomerated over the Fe3O4@PSA surface.

7. Line 221, After 180 minutes of irradiation, no significant change in fluorescence in-tensity was detected, showing the great stability of Fe3O4@PSA-C5. Consequently, bacte-rial cells are unable to reach the surface. What are the relations between fluorescence intensity, stability of Fe3O4@PSA-C5, and bacterial cells? Why is in the MFC applications bacteria also very important? This issue should be further explained.

Response: This part has been removed in the updated version of manuscript.

8. How about the long-term stability of MFC equipped with the obtained anodes? Why no confocal laser scanning microscope images of bacteria on the anode after operation for certain months are shown? And how about the voltage output of MFC equipped with the obtained anodes in different types of wastewater? And what is the correlation between COD removal efficiency and maximum power density of the obtained anodes? These can be very interesting points to be further supplied if possible. See the literature [Advanced Materials 30.22 (2018): 1800618; Science of The Total Environment 713 (2020): 136483] for more details.

Response: Goal of this study was to analyse the reliability of Fe₃O₄@PSA-C as an active catalyst for anode for power density. COD and its relation with power density are not dealt in this manuscript but they could be a possible scope for next research (annotated version).

9. Line 391 For the synthesis of C-dot, a fixed amount of cow milk was taken for the hydrothermal treatment at 120°C for 4 hours in a 100 mL stainless steel au-toclave [20]. Milk is not a standard reagent, and the author has not provided the specific parameters of milk, such as density, concentration, and viscosity, which undoubtedly brings significant difficulties to repeating the experiment. Is it possible to provide more details on milk raw materials? How does the author guarantee the repeatability of this kind of experiment?

Response: Line 427-436; The specification of cow milk used for isolation of C-dots has been added in the revised manuscript (annotated version).

10. Line 400, The prepared solution was kept under probe sonication at a fixed temperature (60°C), power (90%), and pulse rate (3 sec on/off). What is the meaning of power (90%)? This may be 90% of the nominal power, but it should be a value, not just a percentage.

Response: Line 442-444; Thank you for observing this error. The authors have done the correction in this section. The prepared solution was kept in the probe sonicator system (Labman Pro650) with frequency 20-25kHz and 6mm probe. The settings for the probe sonicator are pulse rate (3 sec on/off), power 585 watt and the cut off temperature 65°C.

11. Line 441, The anodic chamber and cathode of MFCs were separated by a 16 cm2 cation exchange membrane (Ultrex, USA), which allowed H+ ions to move from the anodic chamber to the air-cathode interaction junction. Why the Ultrex membrane is selected instead of Nafion membranes? Their advantages over Nafion should be explained, based on structure, proton conductivity, resistance, selectivity, cross-over resistance, etc [Electrochimica Acta 378 (2021): 138133], since Ultrex membrane is not as popular as Nafion membranes.

Response:  Nafion is a homogeneous cation exchange membrane which is predominantly use in PEM fuel cell technology; on a contrary, Ultrex is a heterogeneous cation exchange membrane which is also useful to with stand high hydrostatic pressure while treating wastewater. Earlier reports suggest successful use of the Ultrex as IEM in MFCs. Following are some examples

1. J. Hernández-Fernández, A. Pérez de los Ríos, F. Mateo-Ramírez, C. Godínez, L.J. Lozano-Blanco, J.I. Moreno, F. Tomás-Alonso,New application of supported ionic liquids membranes as proton exchange membranes in microbial fuel cell for waste water treatment,Chemical Engineering Journal,Volume 279,2015,Pages 115-119,ISSN 1385-8947,https://doi.org/10.1016/j.cej.2015.04.036.
2. Prachi Vikas Moharir, A.R. Tembhurkar,Comparative performance evaluation of novel polystyrene membrane with ultrex as Proton Exchange Membranes in Microbial Fuel Cell for bioelectricity production from food waste, Bioresource Technology, Volume 266,2018,Pages 291-296,ISSN 0960-8524,https://doi.org/10.1016/j.biortech.2018.06.085.
3. The Effect of Membrane Type on the Performance of Microbial Electrosynthesis Cells for Methane Production. Journal of The Electrochemical Society, 164 (3) H3015-H3023 (2017) .
4. Sotres, A., Díaz-Marcos, J., Guivernau, M., Illa, J., Magrí, A., Prenafeta-Boldú, F.X., Bonmatí, A. and Viñas, M. (2015), Microbial community dynamics in two-chambered microbial fuel cells: effect of different ion exchange membranes. J. Chem. Technol. Biotechnol., 90: 1497-1506. https://doi.org/10.1002/jctb.4465

 

12. The paper should have a conclusion part, now only the introduction, results, discussion, and materials & methods seem incomplete for the whole structure of the manuscript. I suggest results part rename as Results and discussion, and the discussion part becomes Conclusion.

Response: As suggested by the author, the section of results is named as result and discussion and the discussion section is renamed as the conclusion for better understanding (annotated version). Although, earlier it followed the format/ template provided from the journal

 

 

Author Response File: Author Response.pdf