Green Zinc Oxide (ZnO) Nanoparticle Synthesis Using Mangrove Leaf Extract from Avicenna marina: Properties and Application for the Removal of Toxic Metal Ions (Cd2+ and Pb2+)
Round 1
Reviewer 1 Report
Reviewing report: water-2146077
In this work, the authors tried to extract zinc oxide from a type of plant and use it to absorb harmful elements in water. For this purpose, after extracting the oxide from the plant using chemical methods, the obtained inorganic product has been characterized structurally and morphologically. Then, with the use of element adsorption methods, it has been attempted to determine the appropriate kinetic model for this process. . Although the subject of this research can be interesting, but there are some issues that need to be answered accurately.
1. It is suggested to include some information about Avicenna marina in the Introduction of the article. Meantime, the reason why it is used should be included.
2. The relevance/novelty of the work needs to be highlighted.
3. Line 80: The term qe should be explained (presented for the first time in the article).
4. Line 111: What does “high quality” mean? Chemicals have a certain purity that should be noted.
5. Line 122: Is the extraction route done in an open flask or under reflux conditions? Please state it.
6. Line 124: What is the meaning of this statement:” The filter was utilized……
7. Line 135: According to the authors, why the obtained powder had a yellow color?
8. Line 139: How have the authors been able to characterize the surface area of the product using the stated techniques (XRD, SEM, FTIR)?
9. Line 153: Did the statement " basic circumstances" mean "basic condition"?
10. Line 173: What was meant: “the effect of Co…”?
11. Line 266: Do the authors believe that in the Debye–Scherer equation, the crystal size is the same as the particle size?
12. Line 284: From the explanation of the authors, it is deduced that the intensity of the peaks can be related to the change in the structure. If so, from what reference did they conceive this result?
13. Line Figure 4: In the spectrum, the presence of lead and cadmium elements is shown as an arrow, but there is no trace of them. It is suggested that the authors explain the absence of elements in the spectrum (Note: this method is not accurate for quantitative determination of elements and for qualitative detection of elements, the capability of this method depends on the element content.)
14. Line 252: If the authors prepared XRD from the sample containing adsorbed elements, it would be possible to determine whether they entered the crystal structure of zinc oxide or were surface adsorbed.
15. Line 323: The microscopic micrograph is not clear. In the image above this figure, it is not clear which element the MAP is related to.
16. It seems that the characterization techniques used in this work cannot accurately determine that the obtained zinc oxide particles are in the nano-scale.
17. Line 577: what does it mean: “composite structure of ZnO NPs”?
18. It is suggested that the authors clearly explain the practical importance of the model they have determined from the study of adsorption kinetics.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
The authors reported the properties of zinc oxide prepared using green synthesis. Overall, the text is well structured and written. The results appeared correct and interesting. Minor revisions are needed before acceptance :
1/ The title is general and should be more specified.
2 / A chart illustration for synthesis methods should be added.
3/All equations should be membered.
4/The unity of absorbance should be added in Fig.1
5/The unity degree should be addded for 2 theta in Fig.2
6/ The average particle size should be added for the prepared samples.
7/The discussions section 4 should be added and provided.
8/ The authors should compare their results with previous works.
9/The conclusions should be improved.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
In this work, the authors explored the elimination of cadmium and lead ions from aqueous solutions using the new biosynthesis of zinc oxide nanoparticles (ZnO-NPs) from mangrove leaf extract. The results and discussion of this manuscript are logical and reasonable. In my opinion, it could be accepted after a major revision. Some suggestions or concerns are as follows,
1. One figure/schematic diagram which describes the process used for the synthesis of ZnO nanoparticles should be provided in the manuscript.
2. Lots of methods/materials have already been reported synthesizing the ZnO nanoparticles, and the authors must further emphasize the main novelties of this work (especially for the introduction section). In addition, can this method also fit other plants to synthesize the ZnO nanoparticles?
3. How the authors desorbed the cadmium and lead adsorbed ZnO nanoparticles? How many times did the authors perform the adsorption experiments? The standard deviation should add to the corresponding figures.
4. The resolution of some figures in this manuscript (e.g., Figures 3-5) must be improved.
5. Many mistakes exist in the manuscript, and the author must correct them before resubmission. Such as the Cd2+, R2, Zn oxide, Cd2+ ions, etc.
6. One table that could summarize some of the other reported adsorbents used for removing Cd2+ or Pb2+ is strongly recommended to add to this manuscript. Such as Applied Surface Science 378 (2016): 196-206; Journal of colloid and interface science 477 (2016): 181-190; Chemical Engineering Journal 168 (2011): 737-745; Journal of colloid and interface science 477 (2016): 181-190.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The vast majority of recommended items in the referee report have addressed.
Reviewer 3 Report
I am happy with this version, and it can be accepted now.
