Reduction and Degradation of Paraoxon in Water Using Zero-Valent Iron Nanoparticles

Round 1

Reviewer 1 Report

Abstract: Line 12: Replace "... Kenya and many countries of the world." Line 13-14: Paraoxon is very 13 toxic with LD50 ... (Mention the value of LD50) Line 19: 75.9 %, 63.78%... 2 %.. make sure to use one uniform style throughout the manuscript Line 19: 3 hours' treatment or 3 hour treatment? Line 30: Remove . before introduction 2 Methodology 1. A section on QA/QC should be included 2. A section on data analysis should be included 3. Results and Discussion Line 210: EDXS spectrum or EDXA spectrum clarify. Line 260: Equation is not visible Figure 10: in the figure revise retension time as Retention time. The arrow of metabolite often overlaps with the words. Indicate properly.

Author Response

Abstract: Line 12: Replace "... Kenya and many countries of the world.": This has been rewritten

Line 13-14: Paraoxon is very 13 toxic with LD50 ... (Mention the value of LD50): The specific LD50 value has been added

Line 19: 75.9 %, 63.78%... 2 %.. make sure to use one uniform style throughout the manuscript: This has been revised throughout the document.

Line 19: 3 hours' treatment or 3 hour treatment?: This has been changed to 3 hour treatment.

Line 30: Remove . before introduction: Removed.

2 Methodology 1. A section on QA/QC should be included 2. A section for data analysis should be included: A section on Quality Control has been included and Microsoft Excel and OriginPro 9.0 softwares  indicated as the method used for data analysis.

3. Results and Discussion Line 210: EDXS spectrum or EDXA spectrum clarify: This has been changed to EDXA

Line 260: Equation is not visible: Revised to be visible

Figure 10: in the figure revise retension time as Retention time: This has been revised to retention.

The arrow of metabolite often overlaps with the words. Indicate properly: This has been revised to remove the overlap for clarity

Author Response File: Author Response.docx

Reviewer 2 Report

The paper Okello et al. discussed the degradation of Paraoxon using iron nanoparticle. The discussed topic is interesting with some suggestions to improve the paper are listed below:

1. Please provide function of the presented result in the last sentence of introduction

2. Section 2 needs more reference

3. Statement stating the function of chain like structure in Section 3.1.1 need to be sourced

4. Same goes to the SEM result

5. Author should compare the obtained result with previous finding and discuss in the matter of similarities, differences, supporting the theory or even different with the theoritical standard

6. Section 3.2.4 some sentences here need to be moved to section 2 since it more appropriate as Materials and method

7. Statement of: and confirmed to follow first order kinetics is so weak. How author confirm? If only one kinetics being used? Why author only check first order? How about the zero and second order? Author should also explain what the order means to the degaradtion. Once again please compare with previous findings

8. Figure 10 is a bit useless for me. The author fails to present the Figure well. The metabolite compound should be written by the iupac name, not only mention as metabolite. Discussion on this particular matter is also not enough for publication in the current form. Please refer to the previous comments.

9. The used reference is too low in number. While also old. For me, this topic is new and interesting, but authors present old references. Like year 2000 is already 20 years behind. Please consider using only latest 10 years publication.

10. While providing an interesting topic, the presentation of this paper is not satisfactory. Great improvement is needed before the manuscript can be accepted. 

Author Response

REVIEWER 2

The paper Okello et al. discussed the degradation of Paraoxon using iron nanoparticle. The discussed topic is interesting with some suggestions to improve the paper are listed below:

1. Please provide function of the presented result in the last sentence of introduction

Conclusion edited accordingly

2. Section 2 needs more reference

Relevant references added

2. Statement stating the function of chain like structure in Section 3.1.1 need to be sourced

Relevant references added

4. Same goes to the SEM result

Relevant references added

5. Author should compare the obtained result with previous finding and discuss in the matter of similarities, differences, supporting the theory or even different with the theoritical standard

Relevant references added

6. Section 3.2.4 some sentences here need to be moved to section 2 since it more appropriate as Materials and method

Corrected

7. Statement of: and confirmed to follow first order kinetics is so weak. How author confirm? If only one kinetics being used? Why author only check first order? How about the zero and second order? Author should also explain what the order means to the degaradtion. Once again please compare with previous findings

Degradation processes, like radioactive decay, are typical first order reactions monitoring the rate of disappearance of a molecule

8. Figure 10 is a bit useless for me. The author fails to present the Figure well. The metabolite compound should be written by the iupac name, not only mention as metabolite. Discussion on this particular matter is also not enough for publication in the current form. Please refer to the previous comments.

Figure 10 has been revised and adequately discussed. The name is given in the figure caption

9. The used reference is too low in number. While also old. For me, this topic is new and interesting, but authors present old references. Like year 2000 is already 20 years behind. Please consider using only latest 10 years publication.

Recent references have been added.

Author Response File: Author Response.docx

Reviewer 3 Report

In this work, the authors have provided clearly results concerning the degradation of Paraoxon in water in the presence of nanoparticles based on zero-valent Fe. Some comments should be addressed in order to be accepted for publication:

1- Please, check the gramatical wording since some expresions are rare, for example in line 13 change "It's" for "Its"

2- There are Figures which can be moved to the Supporting information. For example, Figure 3 and Figure 4.

3- Please, Figure 10 must be improved. Authors can collected all chromatograms in one Figure in order to clearly observe the trend. 

4- Other important thing for this reviewer is that there is no any figure depicting the molecular structure of the compounds, paraoxon and metabolites.  

5- Finally, what is the mechanism of the paraoxon degradation?? It should be convenient to show the reactions involved...

Author Response

1- Please, check the gramatical wording since some expresions are rare, for example in line 13 change "It's" for "Its": This has been changed

2- There are Figures which can be moved to the Supporting information. For example, Figure 3 and Figure 4: We have moved Figure 3 and maintained Figure 4 in the main text but superimposed all the figures in 10 to be as one figure

3- Please, Figure 10 must be improved. Authors can collected all chromatograms in one Figure in order to clearly observe the trend.: This has been improved into one figure 

4- Other important thing for this reviewer is that there is no any figure depicting the molecular structure of the compounds, paraoxon and metabolites: The molecular structure of paraoxon has been included  and the degradation of paraoxon (1) by the hydroxyl radicals to form p-nitrophenol (2) and O,O-diethyl phosphate (3) shown in scheme 1.  

5- Finally, what is the mechanism of the paraoxon degradation?? It should be convenient to show the reactions involved: This has been shown in scheme one and the degradation mechanism discussed under Section 3.3

Author Response File: Author Response.docx

Reviewer 4 Report

The paper described a route to treat special organics with metal Fe and is interesting to the journal readership. Even though the phrase of “zero-valent iron” and “emerging organophosphate pollutant” are of hot spot, the paper needs a major revision to emphasize its highlights. Here are the comments.

1. In the batch experiment, the organic concentration approached to 10-20 mg/L, so that the related circumstance should be clear. I am interesting that which wastewater or surface water contained such a highly concentrated organic.
2. The introduction should be revised, especially more concise, to introduce the related the question why the related organics should be concentrated and why zero-valent iron was used for the contaminant’s removal?
3. Some references should be indexed in the paper to show the preparation method of zero-valent iron. If you want to do some extra experiment in this field, the preparation of metal iron should be upgraded without the use of costly reagents, e.g., NaBH₄.
4. It is noted that zero-valent iron was easily aggregated. Thus, which method do you use to disperse effectively the metal iron into water?
5. A illustration graph should be given to interpretate the mechanism for the degradation of contaminants by metal Fe.

Author Response

1. In the batch experiment, the organic concentration approached to 10-20 mg/L, so that the related circumstance should be clear. I am interesting that which wastewater or surface water contained such a highly concentrated organic: Agreed. However these were standard solutions.
2. The introduction should be revised, especially more concise, to introduce the related the question why the related organics should be concentrated and why zero-valent iron was used for the contaminant’s removal?: This has been done. The introduction starts from general to specific. A brief review on paraoxon has been given, followed by existing degradation methods in literature. The introduction then ends with giving the reasons as to why ZVI NPs was chosen for this particular study (see the last paragraph).
3. Some references should be indexed in the paper to show the preparation method of zero-valent iron. If you want to do some extra experiment in this field, the preparation of metal iron should be upgraded without the use of costly reagents, e.g., NaBH_4.  El-Shafei et al., 2018 has been cited and other recent articles added.
4. It is noted that zero-valent iron was easily aggregated. Thus, which method do you use to disperse effectively the metal iron into water?: Agreed. In our study we did not use stabilizers hence the aggregation.
5. A illustration graph should be given to interpret the mechanism for the degradation of contaminants by metal Fe: This has been done (See scheme 1). Relevant discussion has been provided in section 3.3.

Author Response File: Author Response.docx

Reviewer 5 Report

Review for “Reduction and Degradation of Paraoxon in Water using Zero-2 valent iron Nanoparticles ” by V.A. Okello et. al.

The authors performed experiments to study the degradation of paraoxon in water using Zero-valent iron Nanoparticles (ZVI NPs). The effect of ZVI NPs to degrade paraoxon was evaluated in terms of paraoxon initial concentration, ZVI dosage, solution pH, and contact time. The topic is suitable for consideration of publication in Sustainability. However, there are some minor and major comments to be addressed before being considered for publication. Especially there are many format issues that the authors should be more careful about, including but not limited to the items pointed out below.

Minor:

1. Some percentages have a gap between the number and the percentage sign (e.g., “75.9 %” in the abstract), but some others don’t (e.g., 63.78% in the abstract). Please check all and keep consistent. The same issue is found for somewhere else, e.g., 0Hrs in Figure. 10a. Please read though the paper and make sure this is not occurring.
2. The caption of Figure 4b says EDXA image. Is this SEM image instead?
3. In Figure 5, the first datapoint (red dot) is only showing half of the point. Please modify the figure to show a complete point.
4. Figure 7, the “time” in title of x-axis should be capitalized.
5. In Figure 9, “ppm” is used for the three concentrations but “mg L^-1” is used in the text. Please make sure the units are consistently used to avoid confusion.
6. Figure 2 and Figure 3 are showing the same kind of data but using very different format. Please make sure the plots are consistently presented. Besides, Figure 3 is not showing the y-axis.
7. The arrows and labels in Figure 10 are not pointing towards the correct positions. Please check and update them.

Major:

1. Did the authors repeat the experiments? None of the figures contains error bars. Without error bars, it is hard to tell the trends observed.
2. Although as pointed out by the authors, that the Energy Dispersive X-ray Analysis (EDXA) images in Figure 3 and Figure 4a are different, however, as indicated in Figure 4b, those two EDXA images were taken from different locations on the sample. Can the authors be confident in the difference was caused by incubation with paraoxon instead of unevenly distribution of samples?
3. I don’t see the model of paraoxon degradation kinetics in 3.2.4 on Page 9. The image shows an empty box with error. Please check and make sure the figure is included to the manuscript properly.
4. In Figure 8, could the authors comment on why the second data point (0 hours) of the 4% w/v ZVI NPs is higher than the first data point instead of following a decreasing trend as shown by other data points in 2% and 6%?
5. It seems that each experiment was only performed for three hours. I was wondering what will happen after three hours. Do the authors have the data for over three hours? For example, in Figure 5, when the time is longer, do we observe a higher percentage of degradation and when will it reach a steady state? Will it be possible to reach 100%, etc..
6. Generally, the authors presented sufficient experimental data, but there is a lack of in-depth thoughts and explanations on the data. For many of the subsections, the author should provide some more content than just simply showing and describing the data.

Author Response

Minor:

1. Some percentages have a gap between the number and the percentage sign (e.g., “75.9 %” in the abstract), but some others don’t (e.g., 63.78% in the abstract). Please check all and keep consistent. The same issue is found for somewhere else, e.g., 0Hrs in Figure. 10a. Please read though the paper and make sure this is not occurring.

This has been adequately addressed.

2. The caption of Figure 4b says EDXA image. Is this SEM image instead?

This has been corrected to SEM image

3. In Figure 5, the first datapoint (red dot) is only showing half of the point. Please modify the figure to show a complete point.

This was included however still not very visible since the axis starts at point zero.

4. Figure 7, the “time” in title of x-axis should be capitalized.

This has been corrected

5. In Figure 9, “ppm” is used for the three concentrations but “mg L^-1” is used in the text. Please make sure the units are consistently used to avoid confusion.

This has been corrected.

6. Figure 2 and Figure 3 are showing the same kind of data but using very different format. Please make sure the plots are consistently presented. Besides, Figure 3 is not showing the y-axis.

Figure 3 has been moved to supplementary information now as Figure S1.

7. The arrows and labels in Figure 10 are not pointing towards the correct positions. Please check and update them.

This has been corrected.

Major:

1. Did the authors repeat the experiments? None of the figures contains error bars. Without error bars, it is hard to tell the trends observed.

The experiments were done in triplicate. This has been corrected and error bars included where applicable.

2. Although as pointed out by the authors, that the Energy Dispersive X-ray Analysis (EDXA) images in Figure 3 and Figure 4a are different, however, as indicated in Figure 4b, those two EDXA images were taken from different locations on the sample. Can the authors be confident in the difference was caused by incubation with paraoxon instead of unevenly distribution of samples?

Figure 3 has been moved to supplementary information and numbering of the remaining figures reorganized. This has been necessitated by the fact that we were unable to access the original data since the samples were analyzed in South Africa.

3. I don’t see the model of paraoxon degradation kinetics in 3.2.4 on Page 9. The image shows an empty box with error. Please check and make sure the figure is included to the manuscript properly.

This has been revised.

4. In Figure 8, could the authors comment on why the second data point (0 hours) of the 4% w/v ZVI NPs is higher than the first data point instead of following a decreasing trend as shown by other data points in 2% and 6%?

This was an error and it has been corrected

5. It seems that each experiment was only performed for three hours. I was wondering what will happen after three hours. Do the authors have the data for over three hours? For example, in Figure 5, when the time is longer, do we observe a higher percentage of degradation and when will it reach a steady state? Will it be possible to reach 100%, etc..

After three hours the data points remained more or less constant therefore 100% efficiency was not achieved

6. Generally, the authors presented sufficient experimental data, but there is a lack of in-depth thoughts and explanations on the data. For many of the subsections, the author should provide some more content than just simply showing and describing the data.

This has been adequately addressed. Figure S2 under supplementary added to further show degradation of paraoxon

Author Response File: Author Response.docx

Reviewer 6 Report

Comments and Suggestions for Authors

Manuscript review report "Reduction and Degradation of Paraoxon in Water using Zero-2 valent iron Nanoparticles" by  V.A. Okello, I.O. K’Owino, K. Masika, V.O. Shikuku.

The present work is devoted to describe the reduction and degradation of paraoxon by zero-2-valent iron nanoparticles, which are currently one of the promising materials for water purification. I believe that the material presented can be applied in many fields where there is a great need for clean drinking water. This is very important, especially in countries where water is a scarce product or is contaminated Therefore, the work is quite promising and can be recommended for publication after clarifying a few issues that will undoubtedly only improve it.

Line 3. Please change – iron to Iron

Line 9. Please change font size

Line 10. Please change font size

Line 30. Please remove the period before the word Introduction

Line 119. I would suggest not writing the word "nano" because it says "nanoparticles".
                 Same   in the name:  nZVI

Line 143. Please change: FeCl₃.6H₂O to FeCl₃·6H₂O

Line 145. Please change: FeCl₃.6H₂O to FeCl₃·6H₂O

Line 151. Please chence: electron microscopy to Electron Microscopy

Line 193. Please reduce the space

Line 214. I suggest making Figures 4a and 4b more readable. Especially the graph and   description in the figure.

Line 238. Please change paraoxon to Paraoxon

Line 248. Please change paraoxon to Paraoxon

Line 260. The equation is not shown

Line 271. Please change paraoxon to Paraoxon

Line 296. Please change: p-Nitrophenol to p-nitrophenol

Line 308. Please change: p-Nitrophenol to p-nitrophenol

Figure 10. Probably the arrows showing the corresponding peaks have moved on the chart

Line 320. In the word " Acknowledgement " I would suggest using a bolder font

Line 324. In the word „Conflict of Interest” I would suggest using a bolder font

Line 326. In the word „Compliance with Ethical Standards” I would suggest using a bolder font

Line 328. In References please remove the period after [ ]

Comments for author File: Comments.docx

Author Response

Line 3. Please change – iron to Iron: Agreed and changed.

Line 9. Please change font size: Agreed and changed.

Line 10. Please change font size: Agreed and changed.

Line 30. Please remove the period before the word Introduction: Agreed and removed.

Line 119. I would suggest not writing the word "nano" because it says "nanoparticles".
                 Same   in the name:  nZVI: Agreed and done

Line 143. Please change: FeCl₃.6H₂O to FeCl₃·6H₂O: Agreed and changed.

Line 145. Please change: FeCl₃.6H₂O to FeCl₃·6H₂O: Agreed and changed.

Line 151. Please chence: electron microscopy to Electron Microscopy: Agreed and changed.

Line 193. Please reduce the space: Agreed and reduced

Line 214. I suggest making Figures 4a and 4b more readable. Especially the graph and   description in the figure.: This has been revised

Line 238. Please change paraoxon to Paraoxon: paraoxon changed to Paraoxon throughout the document.

Line 248. Please change paraoxon to Paraoxon: paraoxon changed to Paraoxon throughout the document.

Line 260. The equation is not shown: Equation is now clearly shown as equation 4

Line 271. Please change paraoxon to Paraoxon: paraoxon changed to Paraoxon throughout the document

Line 296. Please change: p-Nitrophenol to p-nitrophenol: This has been changed

Line 308. Please change: p-Nitrophenol to p-nitrophenol: This has been changed

Figure 10. Probably the arrows showing the corresponding peaks have moved on the chart: The graphs in this figure have been superimposed into one graph and corresponding peaks clearly described within the text. 

Line 320. In the word " Acknowledgement " I would suggest using a bolder font: The word has been bolded

Line 324. In the word „Conflict of Interest” I would suggest using a bolder font: The words have been bolded

Line 326. In the word „Compliance with Ethical Standards” I would suggest using a bolder font: The words have been bolded

Line 328. In References please remove the period after [ ]: All the periods have been removed

Questions for Authors

1. What is the specific surface area of the obtained iron nanoparticles ? This was not determined.

2. What is the density of the obtained iron nanoparticles ? This was not determined.

3. What is the average grain size of the obtained iron nanoparticles ? This was not determined.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

This current version is now acceptable

Author Response

No new review comments from the reviewer.

Reviewer 3 Report

The authors have already addressed all the comments so I feel that this manuscript can be now ready for publication.

Author Response

No new review comments from the reviewer.

Reviewer 4 Report

Suggested an acceptance in the consideration of the revised manuscript.

Author Response

No comments from reviewer

Reviewer 5 Report

Line 179: “Microsoft excel” should be “Microsoft Excel”.

Figure 5: I see error bars have been added, however, the authors should mention in the caption how the error bars were calculated, e.g., “error bars reflect the standard deviation of three repeat experiments”.

Line 367: “270 nm nm” should be “270 nm”.

The figures should be generated more properly. For example, in Figure S2, the figure is distorted, and the text was stretched.

The caption of Figure S2 still uses “nZVI” instead of “ZVI” as elsewhere in the manuscript. Also, “Figure S2.” Should be “Figure S2:”.

Figure 8: there is an empty line below the label ”20 ml”, please delete it.

Figure 8: there are three data points falling on top of the y-axis, which is quite ugly. Please adjust the lower limit of x-axis range to about -0.25.

Figure 9: I am not sure if the current version of the figure is better, because the curves are stacked on top of each other, and it is hard to tell the difference between different colors. Although from the label, there are 7 curves (0, 0.5, …, 3 Hrs), I can only see four colors from the curves. Also, the title of the x-axis is missing a space between “Retention time” and “(Min)”, where "Min" I believe should be “min”.

The unit “hour” should be consistent in the manuscript, e.g., in Figure 4 “hours” is used but in Figure 9 it is “Hrs” and sometimes it is “h” in the text.

Figure 3b is clearly SEM image but the caption says it is EDXA image.

The supporting information document should have title of the paper (Supporting Information of “Reduction and Degradation of Paraoxon in Water using Zero-valent Iron Nanoparticles”) and the list of authors and affiliations.

The supporting information figures should be “Figure S1” instead of “Figure 1S”. Please also change accordingly in the manuscript when referring to those figures.

Overall, the authors should be more careful when revising the manuscript. Please pay attention to the formatting, figure rendering, and consistency of the choice of words. Also, more the manuscript still lacks in-depth analysis and the conclusion is too short and too simple. Before this manuscript can be considered to be publishable, more careful work has to be put into the revision.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 3

Reviewer 5 Report

1.    Figure 9 is missing. I can only see a blank square and the caption.

2.    A period is missing for the sentence “Data was obtained from triplicate analyses and processed using Microsoft Eexcel and OriginPro 9.0 softwares”

3.    Figure 3 is over-stretched in the y-axis direction. It would be easier to read if the figure is slightly compressed in the y-axis. Generally, when changing the size of a figure, the aspect ratio should be fixed to avoid such issue.

4.    The graphical abstract image is very fuzzy. The words are not clear. Please render this image again with a higher resolution.

Author Response

Figure 9 is missing. I can only see a blank square and the caption.

Figure 9 is present in the word document. In addition, see PDF document and the attachment with List of Figures too.

2. A period is missing for the sentence “Data was obtained from triplicate analyses and processed using Microsoft Excel and OriginPro 9.0 softwares” The period has been added.
3. Figure 3 is over-stretched in the y-axis direction. It would be easier to read if the figure is slightly compressed in the y-axis. Generally, when changing the size of a figure, the aspect ratio should be fixed to avoid such issue. This has been corrected.
4. The graphical abstract image is very fuzzy. The words are not clear. Please render this image again with a higher resolution. This has been revised.

Author Response File: Author Response.docx