Modified Activated Carbon Fiber Felt for the Electrosorption of Norfloxacin in Aqueous Solution

Round 1

Reviewer 1 Report

This paper describes the use of Modified Activated Carbon Fibre Felt (MACFF) as a sorbent for Norfloxacin antibiotic (NOR). The authors have carried out a thorough investigation of the material suitability, and their work would be of interest to researchers in the field of carbon materials and environmental technologies due to the threat of NOR as a water pollutant.

I would suggest the following alterations:

In line 129, the water flow rate is specified as 0 ml/hr, is this correct?

In line 161, I do not understand the term "gash crack". I would recommend the authors revise this sentence.

In line 334, I would be hesitant to state that the result "proves" that the Langmuir model fits the data better. Only 5 data points are shown in figure 7 for the curve fitting, and the R-squared values for the two models are similar so it is not clear that one fits better to the data than the other. The text should be changed to reflect this.

Author Response

Point 1: In line 129, the water flow rate is specified as 0 ml/h, is this correct?

 

Response 1: In the experiment, after pumped water into the adsorption device, there was no water flow in the device. After the adsorption reaches equilibrium, the treated water will be flowed out of the device. The sentence was corrected into “Adsorption kinetics test: NOR solution with a concentration of 300 mg/L and a pH of 6 was used in the experiment, and a 0.6 V voltage, and 15 mm plate spacing were applied.”, at lines 143-144 and 147-148.

 

Point 2: In line 161, I do not understand the term "gash crack". I would recommend the authors revise this sentence.

 

Response 2: The "gash crack" had been replaced by “longitudinal grooves” in the revised manuscript at line 167.

 

Point 3: In line 334, I would be hesitant to state that the result "proves" that the Langmuir model fits the data better. Only 5 data points are shown in figure 7 for the curve fitting, and the R-squared values for the two models are similar so it is not clear that one fits better to the data than the other. The text should be changed to reflect this.

 

Response 3: Thank you very much for the comments. The previous sentences have been replaced by " The experimental data of NOR removal by MACFF are fitted to Langmuir model and did not fit to Freundlich model”, according to Reviwer2’s comments, at line 337-338, page 9, which marked in red. (Please see “Comments and Suggestions for Authors 10”)

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper deals with a complete and interesting study of electrosorption of norfloxacin. However, some issues need to be clarified or modified before publication.

• Section 2.2. needs to report the equipment used for FTIR characterization and methodology.
• Following the former issue, is it used the same amount of sample to analyse ACFF and MACFF materials? It is necessary to specify it in the text. The intensity of all the peaks are proportionally reduced on the sample before modification, therefore, the conclusion of the increase of surface groups by the treatment is not clear, may be affected by the use of a different amount of sample. It is very strange that treatment modify all the different oxygen surface groups in a similar proportion. Treatment by nitric acid is more likely to favour formation of acid groups.  
• I do not understand the sentence of lines 160-162: “However, after modification of ACFF, the number of spots on the surface 160 of MACFF is reduced, which makes the gash crack deeper and more regular and the fiber 161 arrangement more compact”. ¿Which is the relationship between spots and the gash crack?.
• Units are missing in table 2.
• In view of fitting parameters, discrimination between the two kinetic models proposed in section 3.3.1. cannot be performed from the experimental results obtained. The selection of kinetic model is not supported by the results at this stage. Moreover, diffusional limitations were found, which impede the correct determination of kinetic parameters. This section should be deleted and also from the conclusions the statement of lines 444-446 as it is not well supported.
• There are some spelling and English errors to correct:

            Line 37: abroad has a different meaning than that used for.

            Line 45: “is a critical factor” instead “is critical factor”

            Line 148: “the regeneration rate was calculated” instead “the regeneration rate calculated”

            Line 246: I do not understand the meaning of “ this change trend”

           

 

Author Response

Response to Reviewer 2 Comments

 

Point 1: Section 2.2. needs to report the equipment used for FTIR characterization and methodology.

 

Response 1: Thank you very much for your comments.We have added " The surface functional groups of ACFF before and after modification were analyzed by Fourier transform infrared (FT-IR, Thermo, Nicolet, USA)." to the revised manuscript at lines 104-105, page 3, which marked in red.

 

Point 2: Following the former issue, is it used the same amount of sample to analyse ACFF and MACFF materials? It is necessary to specify it in the text. The intensity of all the peaks are proportionally reduced on the sample before modification, therefore, the conclusion of the increase of surface groups by the treatment is not clear, may be affected by the use of a different amount of sample. It is very strange that treatment modify all the different oxygen surface groups in a similar proportion. Treatment by nitric acid is more likely to favour formation of acid groups.  

 

Response 2: Thank you very much for your comments. The same amount of sample was used to analyse ACFF and MACFF materials. We have specified in the revised manuscript at lines 105-106, page 3, which marked in red.

 

Point 3: I do not understand the sentence of lines 160-162: “However, after modification of ACFF, the number of spots on the surface 160 of MACFF is reduced, which makes the gash crack deeper and more regular and the fiber 161 arrangement more compact”. Which is the relationship between spots and the gash crack?.

 

Response 3: We apologize for our incorrect statement. The sentences were rewritten in the revised manuscript at lines 167-169, page 5.

 

Point 4: Units are missing in table 2.

 

Response 4: Units have added in table 2.

 

Point 5: In view of fitting parameters, discrimination between the two kinetic models proposed in section 3.3.1. cannot be performed from the experimental results obtained. The selection of kinetic model is not supported by the results at this stage. Moreover, diffusional limitations were found, which impede the correct determination of kinetic parameters. This section should be deleted and also from the conclusions the statement of lines 444-446 as it is not well supported.

 

Response 5: This section has been deleted and modified. The conclusions the statement of lines 444-446 have been deleted. For details, please see the revised manuscript in section 3.3.1.

 

Point 6: Line 37: abroad has a different meaning than that used for.

 

Response 6: We have made correction according to the Reviewer’s comments, at line 42, page 1.

 

Point 7: Line 45: “is a critical factor” instead “is critical factor”

 

Response 7: Thank you very much for the comments. We have made correction according to the Reviewer’s comments, at line 54, page 2.

 

  Point 8: Line 148: “the regeneration rate was calculated” instead “the regeneration rate calculated”

 

Response 8: Thank you very much for the comments. We have made correction according to the Reviewer’s comments, at line 154, page 2.

 

Point 9: Line 246: I do not understand the meaning of “this change trend”

 

Response 9: Originally, what we meant was “As the concentration increases, the amount of adsorption also increases.” “This change trend……” has been deleted.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript has been prepared with good information.  Samples and data have been used in a properly way. For these reasons I recommend the publication of this manuscript after revision. Therefore, I would like to mention some points about the aforementioned paper in order to be taken into account by the authors:

1. In whole manuscript please check for formatting errors, e.g. for spaces between words (i.e. abstract section and lines 24, 352 etc.).
2. In the introduction in lines 33-35 the authors mention: “The impact of antibiotic residues in the environment, especially in the aqueous environment, is gradually attracting attention”.

It is not clearly described the state of the art of the investigated problem. Please provide references from 2019 and 2020.

3. 4. Electric adsorption test, line 127, please delete the phrase: “Study on the influence of plate spacing:” it is not necessary. You have to start your paragraph: “The influence of plate spacings…..”
4. 6. Adsorption kinetics test and adsorption isotherms, lines 139 and 143 the authors mention: “0 ml/h water flow rate”, is that correct?
5. Figure 2. SEM images of ACFF (a, b, c) and MACFF (d, e, f). The SEM images are very good and well presented. In line 157, please be more specific at your comment, i.e the sentence “By comparing Figure 2. (a), (b) and (c) and Figure 2. (d), (e) and (f), it can be seen….” Must be modified as: “By comparing Figure 2. (a), (b) and (c) for ACFF and Figure 2. (d), (e) and (f) for MACFF, it can be seen..”.
6. 1.2. Analysis of specific surface area and pore structure. In lines 169 and 170 is repeated the sentence: “Table 1 shows the specific surface area”. Please in line 170 change to “”According with the values presented in Table 1, the specific surface area of MACFF is 170 increased by 30.9%, etc.”
7. Lines 172-177 check the English and rewrite the paragraph.
8. Figure 3. FTIR spectra of active carbon fiber felt. Please refer in the capture of Fig. 3 and in the diagram that is about ACFF (before modification) and MACFF (after modification), and add the same in line 179, as you use these abbreviations for the materials applied in the manuscript.
9. Line 227: “Differ little” change to “differ slightly”.
10. 3.2. Adsorption isotherms. Lines 332-333 please change the sentence “that the Langmuir isotherm adsorption model is better than the Freundlich model in fitting the experimental data of NOR removal by MACFF” with the sentence : “that the experimental data of NOR removal by MACFF are fitted to Langmuir model and did not fit to Freundlich model, as well.”
11. The literature is sufficiently critical, current, and internationally evaluated, but this is older, the references from last years are necessary, for demonstrated the actuality. Please provide references from 2019 and 2020.
12. The Abstract and the Conclusion section should refer to the study findings, i.e. the optimum adsorption capacity etc.

 

Best regards

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 3 Comments

Point 1: In whole manuscript please check for formatting errors, e.g. for spaces between words (i.e. abstract section and lines 24, 352 etc.).

 

Response 1: We apologize for our carelessness, and we have thoroughly checked and corrected all the formatting errors in the revised manuscript.

 

Point 2: In the introduction in lines 33-35 the authors mention: “The impact of antibiotic residues in the environment, especially in the aqueous environment, is gradually attracting attention”. It is not clearly described the state of the art of the investigated problem. Please provide references from 2019 and 2020.

 

Response 2: We have added relevant information to the manuscript and provided the latest research literature, at lines 36-50, page 2. Cited documents are marked in red in the 13-page Reference.

 

Hernández, F.; Calısto-Ulloa, N.; Gómez-Fuentes, C.; Gómez, M.; Ferrer, J.; González-Rocha, G.; Bello-Toledo, H.; Botero-Coy, A.M.; Boıx, C.; Ibáñez, M.; Montory, M. Occurrence of antibiotics and bacterial resistance in wastewater and sea water from the Antarctic. J. Hazard. Mater. 2019, 363, 447-456. http://doi:10.1016/j.jhazmat.2018.07.027  

Lei, K.; Zhu, Y.; Chen, W.; Pan, H.-Y.; Cao, Y.-X.; Zhang, X.; Guo, B.-B.; Sweetman, A.; Lin, C.-Y.; Ouyang, W.; He, M.-C.; Liu, X.-T. Spatial and seasonal variations of antibiotics in river waters in the Haihe River Catchment in China and ecotoxicological risk assessment. Environ. Int. 2019, 130, 104919. https://doi:10.1016/j.envint.2019.104919

Yang, X.; Zhang, X.; Wang, Z.; Li, S.; Zhao, J.; Liang, G.; Xie, X. Mechanistic insights into removal of Norfloxacin from water using different natural iron ore – biochar composites: more rich free radicals derived from natural pyrite-biochar composites than hematite-biochar composites. Applied Catalysis B: Environmental, 2019, 117752. https://doi:10.1016/j.apcatb.2019.117752 

Li, C.; Gao, Y.; Li, A.; Zhang, L.; Ji, G.; Zhu, K.; Wang, X.; Zhang, Y. Synergistic effects of anionic surfactants on adsorption of norfloxacin by magnetic biochar derived from furfural residue. Environ. Pollut. 2019, 254, 113005. https://doi:10.1016/j.envpol.2019.113005 Xu, Z.; Xue, X.; Hu, S.; Li, Y.; Shen, J.; Lan, Y.; Zhou, R.; Yang, F.; Cheng, C. Degradation effect and mechanism of gas-liquid phase dielectric barrier discharge on norfloxacin combined with H₂O₂ or Fe²⁺. Sep. Purif. Technol. 2020, 230, 115862. https://doi.org/10.1016/j.seppur.2019.115862

Jojoa-Sierra, S.D.; Silva-Agredo, J.; Herrera-Calderon, E.; Torres-palma, R.A. Torres-Palma of the antibiotic norfloxacin in municipal wastewater, urine and seawater by electrochemical oxidation on IrO2 anodes. Sci. Total Environ. 2017, 575, 1228-1238.https://doi.org/10.1016/j.scitotenv.2016.09.201

da Silva, S.W.; Navarro, E.M.O.; Rodrigues, M.A.S.; Bernardes, A.M.; Pérez-Herranz, V. Using p-Si/BDD anode for the electrochemical oxidation of norfloxacin. J. Electroanal. Chem. 2019, 832, 112-120. https://doi:10.1016/j.jelechem.2018.10.049  

Xiang, Y.; Xu, Z.; Wei, Y.; Zhou, Y.; Yang, X. Carbon-based materials as adsorbent for antibiotics removal: Mechanisms and influencing factors. J. Environ. Manage. 2019, 237, 128-138.https://doi.org/10.1016/j.jenvman.2019.02.068  

 

Point 3: 4. Electric adsorption test, line 127, please delete the phrase: “Study on the influence of plate spacing:” it is not necessary. You have to start your paragraph: “The influence of plate spacings…..”

 

Response 3: Thank you very much for your comments. We have made correction according to the Reviewer’s comments and amended "Study on the influence of initial concentration" and "Study on the influence of voltages" together, at line 127,130,133, page 4.

 

Point 4: 6. Adsorption kinetics test and adsorption isotherms, lines 139 and 143 the authors mention: “0 ml/h water flow rate”, is that correct?

 

Response 4: In the experiment, after pumped water into the adsorption device, there was no water flow in the device. After the adsorption reaches equilibrium, the treated water will be flowed out of the device. The sentence was corrected into “Adsorption kinetics test: NOR solution with a concentration of 300 mg/L and a pH of 6 was used in the experiment, and a 0.6 V voltage, and 15 mm plate spacing were applied.”, at lines 145-146 and 148-149.

 

Point 5: Figure 2. SEM images of ACFF (a, b, c) and MACFF (d, e, f). The SEM images are very good and well presented. In line 157, please be more specific at your comment, i.e the sentence “By comparing Figure 2. (a), (b) and (c) and Figure 2. (d), (e) and (f), it can be seen….” Must be modified as: “By comparing Figure 2. (a), (b) and (c) for ACFF and Figure 2. (d), (e) and (f) for MACFF, it can be seen..”.

 

Response: Thank you very much for your comments. The sentence was corrected into “By comparing Figure 2. (a), (b) and (c) for ACFF and Figure 2. (d), (e) and (f) for MACFF, it can be seen.” in the revised manuscript at lines 163-164, page 5, which marked in red.

 

Point 6: 1.2. Analysis of specific surface area and pore structure. In lines 169 and 170 is repeated the sentence: “Table 1 shows the specific surface area”. Please in line 170 change to “According with the values presented in Table 1, the specific surface area of MACFF is 170 increased by 30.9%, etc.”

 

Response 6: Thank you very much for your comments. The sentence was corrected into “According with the values presented in Table 1, the specific surface area of MACFF is increased by 30.9%, the average pore diameter is increased by 3.4%, and the micropore volume is increased by 36.4%, as also reflected in the SEM images in Figure 2.” in the revised manuscript at lines 176-177, page 5, which marked in red.

 

Point 7: Lines 172-177 check the English and rewrite the paragraph.

 

Response 7: The paragraph was checked carefully and rewritten in the revised manuscript at lines 179-183, page 5, which marked in red.

 

Point 8: Figure 3. FTIR spectra of active carbon fiber felt. Please refer in the capture of Fig. 3 and in the diagram that is about ACFF (before modification) and MACFF (after modification), and add the same in line 179, as you use these abbreviations for the materials applied in the manuscript.

 

Response 8: Thank you very much for the comments of reviewers. We have added “before modification, after modification” in the corresponding position. For details, see the revised manuscript at lines 163-164, 185-186, which marked in red. Fig. 3 is also modified together.

 

Point 9: Line 227: “Differ little” change to “differ slightly”.

 

Response 9: Thank you very much for the Reviewer's comments. We have made correction according to the Reviewer’s comments, at line 233, page 7.

 

Point 10: 3.2. Adsorption isotherms. Lines 332-333 please change the sentence “that the Langmuir isotherm adsorption model is better than the Freundlich model in fitting the experimental data of NOR removal by MACFF” with the sentence : “that the experimental data of NOR removal by MACFF are fitted to Langmuir model and did not fit to Freundlich model, as well.”

 

Response 10: Thank you very much for the Reviewer's comments. We have made correction according to the Reviewer’s comments, at lines 335-336, page 95.

 

Point 11: The literature is sufficiently critical, current, and internationally evaluated, but this is older, the references from last years are necessary, for demonstrated the actuality. Please provide references from 2019 and 2020.

 

Response 11: Thank you very much for the comments. The relevant literature of 2019-2020 related to our research was read and screened carefully. For details, please see the revised manuscript at lines 36-50 and page 13 in the References part.

Hernández, F.; Calısto-Ulloa, N.; Gómez-Fuentes, C.; Gómez, M.; Ferrer, J.; González-Rocha, G.; Bello-Toledo, H.; Botero-Coy, A.M.; Boıx, C.; Ibáñez, M.; Montory, M. Occurrence of antibiotics and bacterial resistance in wastewater and sea water from the Antarctic. J. Hazard. Mater. 2019, 363, 447-456. http://doi:10.1016/j.jhazmat.2018.07.027  

Lei, K.; Zhu, Y.; Chen, W.; Pan, H.-Y.; Cao, Y.-X.; Zhang, X.; Guo, B.-B.; Sweetman, A.; Lin, C.-Y.; Ouyang, W.; He, M.-C.; Liu, X.-T. Spatial and seasonal variations of antibiotics in river waters in the Haihe River Catchment in China and ecotoxicological risk assessment. Environ. Int. 2019, 130, 104919. https://doi:10.1016/j.envint.2019.104919

Yang, X.; Zhang, X.; Wang, Z.; Li, S.; Zhao, J.; Liang, G.; Xie, X. Mechanistic insights into removal of Norfloxacin from water using different natural iron ore – biochar composites: more rich free radicals derived from natural pyrite-biochar composites than hematite-biochar composites. Applied Catalysis B: Environmental, 2019, 117752. https://doi:10.1016/j.apcatb.2019.117752 

Li, C.; Gao, Y.; Li, A.; Zhang, L.; Ji, G.; Zhu, K.; Wang, X.; Zhang, Y. Synergistic effects of anionic surfactants on adsorption of norfloxacin by magnetic biochar derived from furfural residue. Environ. Pollut. 2019, 254, 113005. https://doi:10.1016/j.envpol.2019.113005 Xu, Z.; Xue, X.; Hu, S.; Li, Y.; Shen, J.; Lan, Y.; Zhou, R.; Yang, F.; Cheng, C. Degradation effect and mechanism of gas-liquid phase dielectric barrier discharge on norfloxacin combined with H₂O₂ or Fe²⁺. Sep. Purif. Technol. 2020, 230, 115862. https://doi.org/10.1016/j.seppur.2019.115862

Jojoa-Sierra, S.D.; Silva-Agredo, J.; Herrera-Calderon, E.; Torres-palma, R.A. Torres-Palma of the antibiotic norfloxacin in municipal wastewater, urine and seawater by electrochemical oxidation on IrO2 anodes. Sci. Total Environ. 2017, 575, 1228-1238.https://doi.org/10.1016/j.scitotenv.2016.09.201

da Silva, S.W.; Navarro, E.M.O.; Rodrigues, M.A.S.; Bernardes, A.M.; Pérez-Herranz, V. Using p-Si/BDD anode for the electrochemical oxidation of norfloxacin. J. Electroanal. Chem. 2019, 832, 112-120. https://doi:10.1016/j.jelechem.2018.10.049  

Xiang, Y.; Xu, Z.; Wei, Y.; Zhou, Y.; Yang, X. Carbon-based materials as adsorbent for antibiotics removal: Mechanisms and influencing factors. J. Environ. Manage. 2019, 237, 128-138.https://doi.org/10.1016/j.jenvman.2019.02.068  

 

Point 12: The Abstract and the Conclusion section should refer to the study findings, i.e. the optimum adsorption capacity etc.

 

Response 12: Thank you very much for the Reviewer's comments. We have made correction in the revised manuscript at lines 19-20 and 444, which marked in red according to the Reviewer’s comments.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors fulfilled all the isues arised. However, line 167 needs a small correction of editing, the sentence has no sense, there are two extra words which should be deleted: However,  after modification of ACFF, which makes the longitudinal grooves deeper...

Author Response

Point 1: The authors fulfilled all the isues arised. However, line 167 needs a small correction of editing, the sentence has no sense, there are two extra words which should be deleted: However, after modification of ACFF, which makes the longitudinal grooves deeper...

 

Response 1: Thank you very much for the Reviewer's comments. We have made correction according to the Reviewer’s comments, at line 177, page 5.

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

I thank the authors for their detailed and adequate answers and for taking my comments into account and pointing out the required changes in their manuscript.

 

best regards

Author Response

Point 1: I thank the authors for their detailed and adequate answers and for taking my comments into account and pointing out the required changes in their manuscript.

 

Response 1: Thank you very much for your kindest help and precious comments.

 

Author Response File: Author Response.pdf