Photocatalytic Degradation of Methylene Blue from Aqueous Solutions by Using Nano-ZnO/Kaolin-Clay-Based Nanocomposite

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The present manuscript entitled “Photocatalytic Degradation of Methylene Blue from Aqueous Solutions by Using nano-ZnO/Kaolin Clay based Nanocomposite” by Shreya et al., describes the synthesis of zinc oxide nanoparticles (ZnONPs) were using Allium sativa peel (garlic skin) extract which was further processed to develop ZnO/Kaolin clay nanocomposite. Furthermore, as-synthesized zinc-based nanocomposite has been fabricated for the elimination of the dye (methylene blue). The authors report an interesting work. The objective and justification of the work are partially clear and the performed characterization techniques of the as-synthesized nanocomposites are presented in a better way. Therefore, I recommend it for publication. However, some issues are detailed below which need to be addressed before its final acceptance in Water.

I advise the authors to take the following points into account while revising their manuscript.

Comment 1: There are some typographical, grammatical, superscript, and subscript errors in the manuscript text, so the authors need to correct them in the revised manuscript. For. e.g. Line 21, “the dye: methylene blue” should be “the dye (methylene blue)”; line 24, “clay nanocomposite” should be “clay (NC)”; In Figure 1, ZnO2 should be ZnO₂; line 26, MBD is first time introduced in the manuscript, so include the full form of MBD as methylene blue dye (MBD); in the manuscript text, some places NC mentioned clay NC mentioned as short form, so I suggest the authors make consistency of using short forms throughout the manuscript.

Comment 2: The whole manuscript must be cross-checked thoroughly for English editing, grammatical, spelling mistakes, and syntax errors. So, I suggest the author's English language should be polished.

Comment 3: The Abstract needs to be revised, let the author focus main points, and explain the research question clearly also include the performed characterization techniques of the as-synthesized nanocomposites in the abstract such as XRD, TEM, FT-IR, and FESEM, etc., a slight revision of the abstract is required to attract a broad readership.

Comment 4: Lines 52-55, required suitable references. So include the references for the mentioned lines.

Comment 5: Figure 1 is not required, so insert the synthesis details (Figure 1) in section 2.2. as text.

Comment 6: In lines 181-182, the authors mentioned the statement (Khan and Fulekar 2018 also obtained a similar result for the chemically synthesized ZnONPs), however, they forgot to include reference number 30 for this statement, so include it in the revised version.

Comment 7: In Figure 4, the authors mentioned ZnO2, I think mistakenly they wrote ZnO2 so correct it in Figure 4. Also include the miller indices of peak positions and discuss the peak positions properly.

Comment 8: Revise the Figure 5 caption as suggested, Figure 5. TEM images at different scale bars (a-d), SAED pattern (e) & PSD (f) of NC. Also, include the details of PSD drawn using Image  J software or any other software, which need to be clearly mentioned in the manuscript text. Also, the average particle size mentioned in the PSD figure is 50.42 nm, it can not be exact. It should be like 50.42 ±… So revise it in the PSD Figure

Comment 9: Include the EDS peak positions of all elements in the manuscript text. Also, revise the Figure 6 caption as suggested. Figure 6. FESEM images at different scale bars (a &b) and EDS spectra of NC.

Comment 10: Conclusions: This section is quite too general. Include in this section the most important findings to highlight the importance of this study.

Comment 11: The homogeneity of the reference section needs to be maintained. In some references, journal names are abbreviated, and some are in full form. So please check and revise the references according to the journal's instructions.

Comments on the Quality of English Language

 Moderate editing of English language required.

Author Response

Comment 1: There are some typographical, grammatical, superscript, and subscript errors in the manuscript text, so the authors need to correct them in the revised manuscript. For. e.g. Line 21, “the dye: methylene blue” should be “the dye (methylene blue)”; line 24, “clay nanocomposite” should be “clay (NC)”; In Figure 1, ZnO2 should be ZnO₂; line 26, MBD is first time introduced in the manuscript, so include the full form of MBD as methylene blue dye (MBD); in the manuscript text, some places NC mentioned clay NC mentioned as short form, so I suggest the authors make consistency of using short forms throughout the manuscript.

A/R: Thank you for your comment. The manuscript has been revised as per the suggestion (changes highlighted in yellow).

Comment 2: The whole manuscript must be cross-checked thoroughly for English editing, grammatical, spelling mistakes, and syntax errors. So, I suggest the author's English language should be polished.

A/R: Thank you for your comment. The manuscript has been thoroughly revised for errors (changes highlighted in yellow).

Comment 3: The Abstract needs to be revised, let the author focus main points, and explain the research question clearly also include the performed characterization techniques of the as-synthesized nanocomposites in the abstract such as XRD, TEM, FT-IR, and FESEM, etc., a slight revision of the abstract is required to attract a broad readership.

A/R: Thank you for your comment. The abstract has been re-written in the revised manuscript a suggested by the reviewer.

Comment 4: Lines 52-55, required suitable references. So include the references for the mentioned lines.

A/R: Thank you for this comment. The authors have now provided the latest reference for the said line no in the revised manuscript as suggested by the reviewer.

Comment 5: Figure 1 is not required, so insert the synthesis details (Figure 1) in section 2.2. as text.

A/R: Thank you for your comment. Figure 1 is removed and the related synthesis details have been provided in text in section 2.2.

Comment 6: In lines 181-182, the authors mentioned the statement (Khan and Fulekar 2018 also obtained a similar result for the chemically synthesized ZnONPs), however, they forgot to include reference number 30 for this statement, so include it in the revised version.

A/R: Thank you for pointing out this mistake. The authors have now added the missing reference in the revised version of the manuscript as suggested by the reviewer.

Comment 7: In Figure 4, the authors mentioned ZnO2, I think mistakenly they wrote ZnO2 so correct it in Figure 4. Also include the miller indices of peak positions and discuss the peak positions properly.

A/R: Thank you for your comment. The authors have now rectified the mistake in the revised manuscript as suggested by the reviewer.

 

Comment 8: Revise the Figure 5 caption as suggested, Figure 5. TEM images at different scale bars (a-d), SAED pattern (e) & PSD (f) of NC. Also, include the details of PSD drawn using Image  J software or any other software, which need to be clearly mentioned in the manuscript text. Also, the average particle size mentioned in the PSD figure is 50.42 nm, it cannot be exact. It should be like 50.42 ±… So revise it in the PSD Figure

A/R: Thank you for this suggestion. Suggested changes have been incorporated in the revised manuscript.

Comment 9: Include the EDS peak positions of all elements in the manuscript text. Also, revise the Figure 6 caption as suggested. Figure 6. FESEM images at different scale bars (a &b) and EDS spectra of NC.

A/R: Thank you for your comment. Suggested changes have been incorporated in the revised manuscript.

Comment 10: Conclusions: This section is quite too general. Include in this section the most important findings to highlight the importance of this study.

A/R: Thank you for this valuable comment and suggestion. The authors have now rewritten the conclusion section along with highlighting the major findings in the revised manuscript as suggested by the reviewer.

Comment 11: The homogeneity of the reference section needs to be maintained. In some references, journal names are abbreviated, and some are in full form. So please check and revise the references according to the journal's instructions.

A/R: Thank you for your comment. Now the authors have kept a similarity in the references in the revised manuscript as suggested by the reviewer.

Comment 12: Moderate editing of English language required.

A/R: Thank you for your comment. The authors have now thoroughly edited the manuscript in terms of English editing.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript submitted by Modi et al. aims to describe the photocatalytic degradation of Methylene Blue from aqueous solutions using a nanocomposite ZnO/Kaolin clay as catalyst.   The subject could be interesting for researchers working in the field of environmental protection. However, the manuscript lacks in clarity, and the authors should carefully revise their statements.

In the abstract it is claimed that: "zinc oxide nanoparticles (ZnONPs) were prepared to utilize Allium sativa peel (garlic skin) extract". However, in the text of the manuscript there is no description of how these nanoparticles were obtained from garlic skin, not even a reference to a previously published work. 

The first part of the introduction section is too long.

In lines 35-76 the authors gave numerous references (14) commenting the general advantages of nanotechnology without emphasizing its use in water treatment. Among these 14 references, ref. 5 is the same as ref 7; ref 9 is the same as ref 12. Half of the remaining 12 references are authored by Yadav S.K (one of the authors of this manuscript). This paragraph should be shortened.

The next paragraph of the introduction lines 77-94 (references 14-22) is dedicated to the natural clays and their utilization in wastewater treatment. 

In the next paragraph lines 95-106 (ref 23-32) the authors made an inadequate statement at line 102 -"nanocomposite material is non-toxic eco-friendly and biodegradable". It cannot be stated that clays, TiO₂ or ZnO are biodegradable.... ! Again half of the references belong to author Yadav S.K.   

At lines 107-119 the authors summarize their previous publications concerning the photodegradation of MB using different nanocomposite catalysts.  " Modi 2019 developed ZnONPs/kaolin [ref?], Choudhary et al., 2021 (Montmorillonite/Ag) [ref?], and Gnanamoorthy et al., developed CuNiO₂ and their rGO nanocomposite [ref?] which have been applied for the remediation or photocatalytic degradation (PD) of methylene blue."

At line 121 the authors state: "Another objective was to characterize the organic material kaolin as an adsorbent." Since when is kaolin Al₂Si₂O₅(OH)₄ an organic material ?

Comments on the experimental section

The obtaining of ZnO from Allium sativa peel (garlic skin) extract should be described in detail. The extraction procedure should be described and the chemical composition of the extract should also be given.

Line 132 -50-micron mess- may be mesh

The text in Figure 1 should be carefully revised what is the meaning of

(ZnO 2) ?

the most used abbreviation for grams is g not gm

Line 138 -"The photodegradation of MBD was calculated in a simple reactor under exposure to 138 solar light."

Using the term calculated is not correct - it would be better to use "determined"

Lines 146-147 "Gas chromatography-mass Spectroscopy investigation (GC-MS) to find out the degradation pathway and formation of metabolites at each step." What are the metabolites considered taking into account that tests are not made in a biological system ? !

Section 3. Characterization of nanoparticles and nanocomposites

The authors should carefully revise the text. the expression "was done by using" should be replaced by "was performed by"+the name of the tehnique. at line 160 "at a resolution of 1 nm." - the resolution cannot be 1 nm for FTIR.

Lines 165-166: The phase identification of the samples was done by using an X-ray diffraction pattern.

Section 4.1. UV-visible spectroscopy

 Lines 173-174 "A typical Uv-vis spectrum of the developed nanocomposite is shown in Figure 2, which was dispersed in ddw prior to analysis" - rephrase

"A typical Uv-vis spectrum of the developed nanocomposite dispersed in ddw prior to analysis is shown in Figure 2 " 

Line 175 - 379 and 423 add nm after 423

Use always the abbreviations mentioned at line 170 ZnONPs and ZnO/Clay NC instead of ZnO and ZnO/Clay NC used in the figure and at line 175

Figure 2. UV-vis measurement of zinc oxide NPs ZnONPs (a) and ZnO NC ZnO/Clay NC (b). 

4.2. FTIR analysis of ZnONPs and NC ZnO/Clay NC

Figure 3. FTIR analysis of zinc oxide ZnONPs (a) and ZnO NC ZnO/Clay NC (b).

4.3. Phase identification by using XRD

characteristic peaks - characteristic diffraction lines

line 205: The peak at 34 and 370 indicates the iron oxide phase i.e., hematite and magnetite [49–51].???  Kaolin Al₂Si₂O₅(OH)₄ does not contain iron in the composition 

Figure 4. XRD pattern of ZnONPs, Kaolin, and nanocomposite - the green line is attributed to ZnO 2???

The discussion of the results obtained by XRD analysis should be significantly improved. The characteristic reflections of the phases should be noted on the figure.

4.4. Morphological analysis of NC by TEM

lines 213-214 rephrase: "The layered structure could be clearly observed by TEM which is the property of clay. " "The layered structure of the clay could be clearly observed by TEM . "

lines 215-216 "Fig.5e exhibits the SAED pattern of the developed NC, which indicates the amorphous or partially crystalline in nature. " It is not clear why the authors state that the structure is amorphous or partially crystalline? The XRD pattern in figure 4 red line showed well defined diffraction lines hence it is not appropriate to say that the sample is amorphous. 

4.5. Morphological analysis of NC by FESEM

Lines 228-229 "A normal kaolin particle will have O, C, Al, and Si along with H. but here H will not be detected by the EDS analyzer."

and lines 230- 232-"Among all the elements O is the highest i.e., 36.81%, followed by Zn i.e., 25.92% followed by Si and C i.e., 18.98% and 17 25% respectively. It has also Al which was about 1.06%. "

Why should Kaolin Al₂Si₂O₅(OH)₄ and ZnO contain carbon?

4.6. Photocatalytic degradation of dye

4.6.2. Effect of catalyst dose

The catalyst dose utilized was ten up to sixty folds the amount of MB. What is the reason to employ a catalyst dose higher than the pollutant amount?

lines 252-255: "A graph plotted for the percentage (%) degradation of MB dye for various catalyst dosages v/s time was plotted. It was observed that with the increase in photocatalyst dosage, the % degradation of MB dye increased and it reaches the optimum value of catalyst dosage (300 ppm) at which the % degradation of MB dye was maximum (95.84 %) for the duration of 120 min. " This graph is not present in the manuscript. The phrase should be reformulated.  

4.6.3. Effect of initial concentration of dye

line 267 - stock solution of 10 pm.?? may be 100 ppm

line 304-305 The authors state that: "The degradation percentage of MBD at various pH was almost the same i.e., 86-96%, but at 5 pH degradation was marginally highest. " However, looking at figure 8 it is obvious that at pH 9 the degradation of MBD was higher at 60 minutes and at 120 minutes it was almost equal to that obtained at pH 5. How do the authors comment on this aspect?

Table 1. PD of MBD by several investigators using nanocomposite under UV-light.

third line Hyallosite/ZnO NPs is probably Halloysite

lines 8,9,10 of the table should be removed if the authors cannot calculate the removal percentage and the initial concentration of dye.

4.6.5. Photocatalytic Activity and Mechanism

The mechanism depicted in figure 9 is incomplete, and the comments are insufficient. 

lines 332-333: The statement:  "Electrophilic attack by hydroxyl radical (·OH) at the free doublet of the S heteroatom changes its oxidation state from -2 to 0." is not supported by the formulas presented in the figure. 

The Conclusions of the manuscript should be reformulated. Especially the last sentence "Such approaches not only minimize the solid waste arising from the disposal of vegetable waste rather also suggest an efficient and economical approach for dye remediation from wastewater treatment." - The authors failed to give the evidence that they synthesized ZnONPs from garlic leafs extract...

Comments on the Quality of English Language

There are many mistakes in orthography all along the manuscript.

Please pay attention to the plural and singular forms of the verbs in accordance with the subject of the sentence.

Several phrases should be reformulated (I made some suggestions in the first commentary):

lines 252-255 "A graph plotted for the percentage (%) degradation of MB dye for various catalyst dosages v/s time was plotted. It was observed that with the increase in photocatalyst dosage, the % degradation of MB dye increased and it reaches the optimum value of catalyst dosage (300 ppm) at which the % degradation of MB dye was maximum (95.84 %) for the duration of 120 min. "

lines 260-263 Consequently, there is an increase in the turbidity of the MB dye solution which will decrease the light penetration into the solution will decrease as a result of the increased effect of scattering.

line 267 - Obtained data during the experiment were plotted as the % degradation versus time is shown in Figure 7.

Author Response

The manuscript submitted by Modi et al. aims to describe the photocatalytic degradation of Methylene Blue from aqueous solutions using a nanocomposite ZnO/Kaolin clay as catalyst.  The subject could be interesting for researchers working in the field of environmental protection. However, the manuscript lacks in clarity, and the authors should carefully revise their statements.

1. In the abstract it is claimed that: "zinc oxide nanoparticles (ZnONPs) were prepared to utilize Allium sativa peel (garlic skin) extract". However, in the text of the manuscript there is no description of how these nanoparticles were obtained from garlic skin, not even a reference to a previously published work. 

A/R: Thank you for this valuable comment and suggestion. The authors have now provided the synthesis procedure of ZnONPs in the revised manuscript. The authors have already synthesized previously, and now a reference has been provided in the revised manuscript.

2. The first part of the introduction section is too long.

A/R: Thank you for this valuable comment and suggestion. The authors have now removed the irrelevant section text from the introduction section as suggested by the reviewer in the revised manuscript.

3. In lines 35-76 the authors gave numerous references (14) commenting the general advantages of nanotechnology without emphasizing its use in water treatment. Among these 14 references, ref. 5 is the same as ref 7; ref 9 is the same as ref 12. Half of the remaining 12 references are authored by Yadav S.K (one of the authors of this manuscript). This paragraph should be shortened.

A/R: Thank you for this valuable comment and suggestion. The authors have now provided only relevant references in the said section as suggested by the reviewer.

4. The next paragraph of the introduction lines 77-94 (references 14-22) is dedicated to the natural clays and their utilization in wastewater treatment. In the next paragraph lines 95-106 (ref 23-32) the authors made an inadequate statement at line 102 -"nanocomposite material is non-toxic eco-friendly and biodegradable". It cannot be stated that clays, TiO₂or ZnO are biodegradable.... ! Again half of the references belong to author Yadav S.K.   

A/R: Thank you for this valuable comment and suggestion. The authors have now provided only relevant references in the said section as suggested by the reviewer.

 

5. At lines 107-119 the authors summarize their previous publications concerning the photodegradation of MB using different nanocomposite catalysts.  " Modi 2019 developed ZnONPs/kaolin [ref?], Choudhary et al., 2021 (Montmorillonite/Ag) [ref?], and Gnanamoorthy et al., developed CuNiO₂and their rGO nanocomposite [ref?] which have been applied for the remediation or photocatalytic degradation (PD) of methylene blue."

A/R: Thank you for pointing out this mistake. The authors have now provided references in the said section as suggested by the reviewer.

6. At line 121 the authors state: "Another objective was to characterize the organic material kaolin as an adsorbent." Since when is kaolin Al₂Si₂O₅(OH)₄ an organic material ?

A/R: Thank you for pointing out this mistake. The authors have now rectified the sentence as suggested by the reviewer in the revised manuscript.

Comments on the experimental section

7. The obtaining of ZnO from Allium sativa peel (garlic skin) extract should be described in detail. The extraction procedure should be described and the chemical composition of the extract should also be given.

A/R: Thank you for this valuable comment and suggestion. The authors have now provided a detailed procedure for the synthesis of ZnO NPs by using Allium sativa peel in the revised manuscript as suggested by the reviewer.

8. Line 132 -50-micron mess- may be mesh

A/R: Thank you for pointing out this mistake. The authors have now rectified the mistake.

9. The text in Figure 1 should be carefully revised what is the meaning of (ZnO 2) ?

A/R: Thank you for your comment. The flow chart has now been converted into text paragraph in section 2.2.

10. the most used abbreviation for grams is g not gm

A/R: Thank you for your comment. Correction has been made.

11. Line 138 -"The photodegradation of MBD was calculatedin a simple reactor under exposure to 138 solar light."Using the term calculated is not correct - it would be better to use "determined"

A/R: Thank you for your comment. The correction has been made.

 

12. Lines 146-147 "Gas chromatography-mass Spectroscopy investigation (GC-MS) to find out the degradation pathway and formation of metabolites at each step." What are the metabolites considered taking into account that tests are not made in a biological system ? !

 A/R: Thank you for your valuable comment and suggestion. The authors have already provided the metabolites and their pathways in the last section of the manuscript.

 

Section 3. Characterization of nanoparticles and nanocomposites

13. The authors should carefully revise the text. the expression "was done by using" should be replaced by "was performed by"+the name of the tehnique. at line 160 "at a resolution of 1 nm." - the resolution cannot be 1 nm for FTIR.

A/R: Thank you for pointing out this mistake. The mistake has been corrected.

14. Lines 165-166: The phase identification of the samples was done by using anX-ray diffraction pattern.

A/R: Thank you for your comment. The statement has been corrected.

 

Section 4.1. UV-visible spectroscopy

15. Lines 173-174 "A typical Uv-vis spectrum of the developed nanocomposite is shown in Figure 2, which was dispersed in ddw prior to analysis" – rephrase

"A typical Uv-vis spectrum of the developed nanocomposite dispersed in ddw prior to analysis is shown in Figure 2 " 

A/R: Thank you for your comment. Changes have been made as per suggestion.

16. Line 175 - 379 and 423 add nm after 423

A/R: Thank you for pointing out this mistake. Corrections have been incorporated.

17. Use always the abbreviations mentioned at line 170 ZnONPs and ZnO/Clay NC instead of ZnO and ZnO/Clay NC used in the figure and at line 175

A/R: Thank you for your comment. Changes have been made as per suggestion.

18. Figure 2. UV-vis measurement of zinc oxide NPsZnONPs (a) and ZnO NC ZnO/Clay NC (b). 

A/R: Thank you for your comment. Corrections have been incorporated.

19. 2. FTIR analysis of ZnONPs and NC ZnO/Clay NC

A/R: Thank you for your comment. Changes have been made as per suggestion.

20. Figure 3. FTIR analysis of zinc oxideZnONPs (a) and ZnO NC ZnO/Clay NC (b).

A/R: Thank you for your comment. Correct abbreviations are placed in the figure caption.

21. 3. Phase identification by usingXRD
22. characteristic peaks- characteristic diffraction lines

A/R: Thank you for your comment. Changes have been made as per suggestion.

23. line 205: The peak at 34 and 370 indicates the iron oxide phase i.e., hematite and magnetite [49–51].???Kaolin Al₂Si₂O₅(OH)₄ does not contain iron in the composition 

A/R: Thank you for your comment. Changes have been made as per suggestion.But in sevrral cases small amount of Fe is there.

24. Figure 4. XRD pattern of ZnONPs, Kaolin, and nanocomposite - the green line is attributed to ZnO 2???

A/R: Thank you for your comment. It is ZnO only. The correction has been applied in the figure 4 (highlighted in turquoise color)

25. The discussion of the results obtained by XRD analysis should be significantly improved. The characteristic reflections of the phases should be noted in the figure.

A/R: Thank you for your comment. The authors have improved the discussion section of XRD in the revised manuscript. Since the authors have got the PDF form of the pattern (from the outsourced institute) so unable to edit it.

4.4. Morphological analysis of NC by TEM

26. lines 213-214 rephrase: "The layered structure could be clearly observed by TEM which is the property of clay. " "The layered structure of the clay could be clearly observed by TEM. "

A/R: Thank you for your comment. The sentence has been rephrased as per suggestion.

27. lines 215-216 "Fig.5e exhibits the SAED pattern of the developed NC, which indicates the amorphous or partially crystalline in nature. " It is not clear why the authors state that the structure is amorphous or partially crystalline? The XRD pattern in figure 4 red line showed well defined diffraction lines hence it is not appropriate to say that the sample is amorphous. 

A/R: Thank you for your comment. Corrections have been employed.

4.5. Morphological analysis of NC by FESEM

28. Lines 228-229 "A normal kaolin particle will have O, C, Al, and Si along with H. but here H will not be detected by the EDS analyzer." and lines 230- 232-"Among all the elements O is the highest i.e., 36.81%, followed by Zn i.e., 25.92% followed by Si and Ce., 18.98% and 17 25%respectively. It has also Al which was about 1.06%. "Why should Kaolin Al₂Si₂O₅(OH)₄ and ZnO contain carbon?

A/R: Thank you for your comment. The possible reason behind the carbon peak in the EDS spectrum of the sample might be the environmental CO₂ attached to the sample. Another reason could be the attached biomolecules, as ZnONPs were synthesized using garlic peel which contains several carbon-containing phytochemicals.

4.6. Photocatalytic degradation of dye

4.6.2. Effect of catalyst dose

29. The catalyst dose utilized was ten up to sixty folds the amount of MB. What is the reason to employ a catalyst dose higher than the pollutant amount?

A/R: Thank you for your valuable comment and suggestion. The authors have used this conc. after going through previous literature so tried to keep the dose of photocatalyst near to those only.

30. lines 252-255: "A graph plotted for the percentage (%) degradation of MB dye for various catalyst dosages v/s time was plotted. It was observed that with the increase in photocatalyst dosage, the % degradation of MB dye increased and it reaches the optimum value of catalyst dosage (300 ppm) at which the % degradation of MB dye was maximum (95.84 %) for the duration of 120 min. " This graph is not present in the manuscript. The phrase should be reformulated.  

A/R: Thank you for pointing out this mistake. The authors have now rephrased the sentence in the revised manuscript.

4.6.3. Effect of initial concentration of dye

31. line 267 - stock solution of 10 pm.?? may be 100 ppm

A/R: Thank you for pointing out this mistake. Corrections have been applied.

32. line 304-305 The authors state that: "The degradation percentage of MBD at various pH was almost the same i.e., 86-96%, but at 5 pH degradation was marginally highest. " However, looking at figure 8 it is obvious that at pH 9 the degradation of MBD was higher at 60 minutes and at 120 minutes it was almost equal to that obtained at pH 5. How do the authors comment on this aspect?

A/R: Thank you for pointing out this mistake. The authors have now rectified the sentences in the revised manuscript as suggested by the reviewer.

33. Table 1. PD of MBD by several investigators using nanocomposite under UV-light. third line Hyallosite/ZnO NPs is probably Halloysite

A/R: Thank you for pointing out this mistake. The authors have now rectified the mistake.

 

34. lines 8,9,10 of the table should be removed if the authors cannot calculate the removal percentage and the initial concentration of dye.

A/R: Thank you for your valuable comment and suggestion. Actually, the authors didn't get the complete paper as it was published recently.

4.6.5. Photocatalytic Activity and Mechanism

35. The mechanism depicted in figure 9 is incomplete, and the comments are insufficient. 

A/R: Thank you for pointing out this mistake. The authors have now rectified the figure in the revised manuscript as suggested by the reviewer.

36. lines 332-333: The statement:  "Electrophilic attack by hydroxyl radical (·OH) at the free doublet of the S heteroatom changes its oxidation state from -2 to 0." is not supported by the formulas presented in the figure.

A/R: Thank you for pointing out this mistake. The authors have now rectified the formula in the figure.

37. The Conclusions of the manuscript should be reformulated. Especially the last sentence "Such approaches not only minimize the solid waste arising from the disposal of vegetable waste rather also suggest an efficient and economical approach for dye remediation from wastewater treatment." - The authors failed to give the evidence that they synthesized ZnONPs from garlic leafs extract...

A/R: Thank you for your valuable comment and suggestion. The authors have now rewritten the conclusion section in the revised manuscript as suggested by the reviewer.

38. There are many mistakes in orthography all along the manuscript.

A/R: Thank you for pointing out this mistake. The authors have now rectified all such orthography-related mistakes in the revised manuscript as suggested by the reviewer.

39. Please pay attention to the plural and singular forms of the verbs in accordance with the subject of the sentence.

A/R: Thank you for pointing out this mistake. The authors have now rectified all such English-related issues in the revised manuscript as suggested by the reviewer.

40. Several phrases should be reformulated (I made some suggestions in the first commentary):

lines 252-255 "A graph plotted for the percentage (%) degradation of MB dye for various catalyst dosages v/s time was plotted. It was observed that with the increase in photocatalyst dosage, the % degradation of MB dye increased and it reaches the optimum value of catalyst dosage (300 ppm) at which the % degradation of MB dye was maximum (95.84 %) for the duration of 120 min. "

lines 260-263 Consequently, there is an increase in the turbidity of the MB dye solution which will decrease the light penetration into the solution will decrease as a result of the increased effect of scattering.

line 267 - Obtained data during the experiment were plotted as the % degradation versus time is shown in Figure 7.

A/R: Thank you for your comment. Corrections have been applied.

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

In the revised manuscript the authors took into consideration some of my comments and disregarded others. Therefore I cannot accept the publication of the manuscript in its current state.

Here are some more comments that may be usefull for the next revision.

The synthesis of ZnO nanoparticles described in the text needs to be improved. The authors shoud state in what stage of the preparation they performed the pH adjustment with NaOH. In the current version of the text the pH adjustment appears somewhere at the end. In order to obain ZnO a calcination step is required otherwise you obtain Zn(OH)₂. The chemical composition of the garlic peel extract should be given (I checked the previous publication of Moti and Fulekar J Nanostruct 10(1): 20-27, Winter 2020- and they also did not give the composition), and the role of its components in the synthesis should be explained. 

Line 170-171 In the revised version you still have the phrase:

"The sample was also examined by the Gas chromatography-mass Spectroscopy investigation (GC-MS) to find out the degradation pathway and formation of metabolites at each step" - Since the experiments are not performed wih living organisms you do not have metabolites 

In Table 1 -remove the lines corresponding to

GO- Fe3O4

MnFe2O4/rGO magnetic NPs

Fe3O4 NPs

 

Polyacrylic acid-bound iron oxide NPs 

I could not notice significant revisions in the text and figure related to the reaction mechanism.

Lines 58-70 - Try to improve this paragraph

 

Conventionally, composite materials add reinforcements in most of the matrix that  enhance the material’s properties such as thermal–electrical conductivity, ductility, hardness, tensile strength, and durability [13,14]. Nanocomposites, by definition, are a class of materials that are made up of either one or more than one phase at nanoscale dimensions such as 0-dimension, 1-dimension, and 2-dimension [15,16]. Nanocomposites consist of two phases’ i.e., nano-crystalline phase and matrix phase [17]. Nanocomposites overcome the problems and limitations of metals or composites that are micron-scale reinforcements [18,19]. Thus, the nanocomposite material is an innovative advanced material that consists of nanofillers dispersed in different matrices [20]. The two phases may be inorganic-inorganic, organic-organic, or inorganic-organic [21–23]. Adding a small quantity of nanomaterials in a matrix or polymer enhances the physical, chemical, mechanical, and electrical properties of the materials [24,25]. Moreover, the nano additives in nanocomposites can improve properties such as heat distortion temperature, modulus, barrier properties, and flexural strength of the composite [26–29].

There are still many aspects related to the English language usage.

Comments on the Quality of English Language

There are still many aspects related to the English language usage.

The most important one is the inappropriate use of the word remediation which signifies the improvement of a parameter (purity, aspect whatever you want)

Line 75 - for the remediation of pollutants  - so you do not remediate the pollutants but you want to eliminate the pollutants

Line 94

for the remediation of cationic dyes - the removal of cationic dyes

line 95-96 for the remediation of methylene blue dye from wastewater - removal

line 97 for the remediation or photocatalytic degradation (PD) of methylene blue

line 99 have also remediated methylene blue dye (MBD) from the aqueous solution - removed

line 112 which was used for the remediation of MBD efficiently - efficient removal/elimination

lines 361-362 for the remediation of MBD from the liquid solutions -removal/elimination

line 366 efficiently remediated the MBD - removed

line 368 remediated the methyl orange and rhodamine B -removed/eliminated

line 374 for the remediation of acridine orange 7 - removal/elimination

lines 378-379 for the remediation of biological oxygen demand, chemical oxygen demand, Cr and Fe ions at - here you may remediate only the biological oxygen demand, chemical oxygen demand, wheareas in the case of Cr and Fe ions you should use the term removal

line 405 the MBD remediation - removal/elimination

In the section related to XRD discussion - mention diffraction lines / reflexions instead of peaks  

Author Response

In the revised manuscript the authors took into consideration some of my comments and disregarded others. Therefore I cannot accept the publication of the manuscript in its current state.

Here are some more comments that may be usefull for the next revision.

1. The synthesis of ZnO nanoparticles described in the text needs to be improved. The authors shoud state in what stage of the preparation they performed the pH adjustment with NaOH. In the current version of the text the pH adjustment appears somewhere at the end. In order to obain ZnO a calcination step is required otherwise you obtain Zn(OH)₂. The chemical composition of the garlic peel extract should be given (I checked the previous publication of Moti and Fulekar J Nanostruct 10(1): 20-27, Winter 2020- and they also did not give the composition), and the role of its components in the synthesis should be explained. 

A/R: Thank you for this valuable comment and suggestion. The authors have now added the phytochemicals of the garlic peel extract from the previously reported work in the revised manuscript as suggested by the reviewer.

Line 170-171 In the revised version you still have the phrase:

2. "The sample was also examined by the Gas chromatography-mass Spectroscopy investigation (GC-MS) to find out the degradation pathway and formation of metabolites at each step" - Since the experiments are not performed wih living organisms you do not have metabolites 

A/R: Thank you for pointing out this mistake. The authors have now corrected the mistake.

3. In Table 1 -remove the lines corresponding to

GO- Fe3O4

MnFe2O4/rGO magnetic NPs

Fe3O4 NPs

 

Polyacrylic acid-bound iron oxide NPs 

A/R: Thank you. The authors have removed lines corresponding to the above-said words.

4. I could not notice significant revisions in the text and figure related to the reaction mechanism.

A/R: Na

5. Lines 58-70 - Try to improve this paragraph

Conventionally, composite materials add reinforcements in most of the matrix that  enhance the material’s properties such as thermal–electrical conductivity, ductility, hardness, tensile strength, and durability [13,14]. Nanocomposites, by definition, are a class of materials that are made up of either one or more than one phase at nanoscale dimensions such as 0-dimension, 1-dimension, and 2-dimension [15,16]. Nanocomposites consist of two phases’ i.e., nano-crystalline phase and matrix phase [17]. Nanocomposites overcome the problems and limitations of metals or composites that are micron-scale reinforcements [18,19]. Thus, the nanocomposite material is an innovative advanced material that consists of nanofillers dispersed in different matrices [20]. The two phases may be inorganic-inorganic, organic-organic, or inorganic-organic [21–23]. Adding a small quantity of nanomaterials in a matrix or polymer enhances the physical, chemical, mechanical, and electrical properties of the materials [24,25]. Moreover, the nano additives in nanocomposites can improve properties such as heat distortion temperature, modulus, barrier properties, and flexural strength of the composite [26–29].

A/R: Thank you for this valuable comment and suggestion. The authors have now completely rewritten the said paragraph in the revised manuscript as suggested by the reviewer.

There are still many aspects related to the English language usage.

Comments on the Quality of English Language

There are still many aspects related to the English language usage.

6. The most important one is the inappropriate use of the word remediation which signifies the improvement of a parameter (purity, aspect whatever you want)
7. Line 75 - for the remediationof pollutants  - so you do not remediate the pollutants but you want to eliminate the pollutants
8. Line 94
9. for the remediationof cationic dyes - the removal of cationic dyes
10. line 95-96 for the remediationof methylene blue dye from wastewater - removal
11. line 97 for the remediation or photocatalytic degradation (PD) of methylene blue
12. line 99 have also remediated methylene blue dye (MBD) from the aqueous solution - removed
13. line 112 which was used for the remediationof MBD efficiently - efficient removal/elimination
14. lines 361-362 for the remediationof MBD from the liquid solutions -removal/elimination
15. line 366 efficiently remediatedthe MBD - removed
16. line 368 remediated the methyl orange and rhodamine B -removed/eliminated
17. line 374 for the remediationof acridine orange 7 - removal/elimination
18. lines 378-379 for the remediation of biological oxygen demand, chemical oxygen demand, Cr and Fe ions at - here you may remediate only the biological oxygen demand, chemical oxygen demand, wheareas in the case of Cr and Fe ions you should use the term removal
19. line 405 the MBD remediation- removal/elimination

A/R: Thank you for pointing out this mistake. The authors have now rectified the mistake in the revised manuscript as suggested by the reviewer. The authors have replaced the remediation either with the removal or with the elimination in the revised manuscript.

 

20. In the section related to XRD discussion - mention diffraction lines / reflexions instead of peaks  

A/R: Thank you for your valuable comment and suggestion. The authors have now replaced the peaks with the diffraction lines in the XRD sections in the revised manuscript a suggested by the reviewer.

 

 

Author Response File: Author Response.pdf