Recent Advances in Magnetic Nanoparticles and Nanocomposites for the Remediation of Water Resources
Round 1
Reviewer 1 Report
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Comments for author File: 
Comments.pdf
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript proposes a review of the most recent literature (about 150 references, mainly published in 2020) in the field of magnetic nanomaterials for water remediation. In particular, three classes of materials are described: (i) single magnetic nanoparticles; (ii) magnetic nanocomposites; (iii) magnetic nanocomposites containing a biomaterial. The review covers a wide theme as different water pollutants are studied in the reported literature. The central idea is the use of a material carrying a magnetic phase that can be exploited for the magnetic separation and the recovery/degradation of the water pollutants. Although other reviews, even recent ones (ref. 23-28 as stated by the author in the “Introduction” section), are available on the theme, the author reported the most recent literature for an update review, as many papers are published per year. Nevertheless, I have some doubts on the efficacy of the overall organization of the discussion, that seems to describe shortly each paper with no evident criteria of classification and connections between one paper and the others, and there is no clear evaluation of the research progress that the cited recent literature bring with. In particular, the following major issues might be solved:
- The introduction might be improved by briefly describing the different classes of water pollutants, stating also which are the most common or the most problematic ones and by indicating the legal limits (if known) in water and wastewater. By this information, a reader can be able to judge the impact of the single research examples presented after in the review and a wider readership can be reached.
- The cited references, in particular those reported in the single magnetic nanoparticles section, are presented without a clear criterium. The authors might organize the discussion and group the references according to a certain classification criterium as for instance (i) the kind of pollutant removed (inorganic vs. organic, or cations, anions, dyes, antibiotics, etc.), (ii) the chemical composition of the material with an increasing complexity (metal and metal alloys, iron oxide with only iron cations, substituted iron oxides, etc.), (iii) the role of the magnetic phase, i.e. in the phase separation or in the degradation catalysis, (iv) another feature of the particle such as the morphology, etc. To this end, maybe the presence of sub-paragraphs would help, and the review might serve better as key review for researchers working in the field but interested to a specific topic (e.g. inorganic pollutants, iron oxides-based removers, etc.). The logic followed in the presentation of the cases should be described too.
- Moreover, some studies from the literature, which are included in the description of the literature, are devoted to antibacterial activity, for instance ref. 37-39, or to soil (e.g. ref. 37, 58). If you are including bacteria as water pollutants, so then, dividing the discussion in different sub-paragraphs according to different classes of pollutants (e.g. inorganic cations, organic pollutants, bacteria) might be helpful (as suggested in point 2) together with the addition of a short description of the different pollutant classes in the introduction (as suggested in point 1).
- The “Key concepts for the Future” paragraph only presents positive aspects of the use of the magnetic nanomaterials for remediation of water resources. The advancement in this research field in the light of the very recent literature presented in the review is not clear. Additional conclusions can be defined according to a comparison in the efficacy in the removal/degradation process, efficacy of the magnetic separation, the time necessary for the removal process and the number of possible uses of the proposed material. Moreover, this paragraph should be completed by adding a discussion on the open issues of this research field, tracking the steps still needed to concretely apply those materials for the purpose they have been designed for. For instance, I would have added a short discussion regarding the issues associated with the regenerability of the materials proposed in the review after their usage (how the materials are regenerated (e.g. ref. 71)? How the solutions used to regenerate the materials are recovered in the optic of a zero-waste process? Have these solutions any environmental concerns?) and with the nanotoxicity or secondary pollution (e.g. possible secondary pollution due to ions or nanoparticles released from the nanoremovers or reaction products (ref. 96), manipulation of nanomaterials itself), as also cited by the author in the “Introduction” section (page 2, lines 50-51).
- Another aspect that I would have inserted in the discussion of the literature is the magnetic particle size and the surface area (if known) for each system, as these two parameters strongly affect the removal capacity, the chemical and colloidal stability and the magnetic properties.
- Some important details might be made explicit in the description of the studies (e.g. for ref.29 the porous structure is not described and the expression “high degree of reusability” is too vague; for ref. 30 it is written “multiple cycles” but the number should be specified; for ref.65 the author referred to metalloid oxyanions without specifying the metalloids).
- Additionally, schemes or figures representing the best materials described in the review would be precious to emphasise the take-home message (e.g. panel with the TEM/SEM images of the most significative materials, or of the differently shaped particles, etc.). A table/scheme summing up the requirements of a well-designed water pollutant remover and which ones have been reached so far by the proposed systems might be also useful.
Additional minor issues are:
Page 1, line 2: Because one section of the review is devoted to “single magnetic nanoparticles”, I suggest changing the title as follows: “Recent advances in magnetic nanoparticles and nanocomposites for the remediation of water resources”.
Page 1, lines 25-26: Please, delete “from this resource is extracted for use”: the sentence will be much more readable.
Page 1, line 33: I would delete the adjective “new” in the definition of nanomaterials as class of materials, as nanomaterials are used by decades.
Page 1, lines 34-35: You might include “biomedicine” as a potential application field of nanomaterials.
Page 2, line 62: Superparamagnetism is not a property of nanomaterials in general, so please rephrase the sentence to clarify it.
Page 2, line 68: Please, rephrase the sentence “has been promoted in use for use” to avoid repetition.
Page 2, line 72: Please, check the correct spelling of “never the less”.
Page 2, line 78: Please, substitute “single material nanoparticle materials” with “single nanoparticle materials” or “single phase nanoparticles”.
Page 2, line 93-94: Please, rephrase the sentence to make it more understandable.
Page 3, lines 97-98: Please, substitute the adjective “singular” with “single”, as I guess the author refers to single phase material.
Page 3, line 98: what does the author mean with the expression “straight-forward nanomaterial”? Does he refer to that single magnetic nanoparticles are the simplest class of nanomaterials presented in the review?
Page 3, line 102: Please, substitute “single particles” with “single magnetic nanoparticles” in order to use every time the same definition and avoid any confusion in the reader.
Page 3, Table 1: Please, substitute “structure” with “morphology” as “structure” usually refers to the crystalline structure and not to the shape of the particles. Also, substitute “particles” (listed in the “structure” column) with the description of the shape, for example “spherical” or “spheroidal”, if this is the case. Insert a comma between Cu2+ and Ni2+.
Page 4, line 105: Please, remove the space between “super” and “paramagnetic”.
Page 4, line 105: I would delete the adjective “magnetic” before the name of the crystalline phase or the chemical formula. It is clear that all the presented phases in the “single magnetic nanoparticles” are magnetic, and the readability would be improved.
Page 4, line 120: in all the manuscript, sometimes the names of the crystalline phases and the elements have capital letters and sometimes have not: please, make the text uniform, accordingly.
Page 5, line 151: Please, add “and” between “green” and “Pb2+”.
Page 5, lines 159-160: Please, delete the space between “un” and “modified”.
Page 6, lines 176: Please, delete the space between “de” and “coupled”.
Page 6, lines 186-187: what does the author mean with the expression “biferrites”?
Page 6, line 207: Please, add a space between “pH” and “5”. Make this correction in all the manuscript.
Page 6, line 213: Why does the author define the material with formula MnxZn(1-x)Fe2O4 a “composite” material? This seems to be a single-phase material.
Page 6, line 215: Please, check the space between digits and units and delete the full stop in the units (1g.L-1). Make this correction in all the manuscript.
Page 7, line 264: Please, check the sentences “for the x is equal to 0.25 sample” and “This same sample”.
Page 7, line 266-267: Please, remember to fully express the name of the bacteria or acronyms the first time thy are cited in the text (S. aureus, C. tropicalis). Check all the manuscript.
Page 9, lines 333: what does the author mean with the expression “state of the art levels”?
Page 9, line 335: Please, delete the space between “nano” and “adsorbent”. Check also the spelling of adsorbent.
Page 9, lines 374-376: Please, rephrase the sentence to make it clearer.
Page 10, line 387: Please, check if you refer to absorption or adsoption and correct, accordingly.
Page 12, line 446: Please, substitute “an” with “a”.
Page 12, line 482: Please correct “hi adsorption” with “high adsorption”.
Page 13, line 496: The comment “This nanocomposite may be a useful material for the treatment of water resources.” should be better explained.
Page 14, line 514: Please, check if “affects” should be substituted by “effects”.
Page 14, line 518: Maybe, the term “ultrasound” can be substituted by “sonication”.
Page 15, line 537-538: Please, check the sentence “compared to other heavy metals compared to Cd, Ni and Hg”.
Page 16, line 572: Change in italic style all the Latin names. Check all the manuscript.
Page 17, line 603: Please, add a comma between “chloramphenicol” and “an antibiotic”.
Page 19, line 669: Please, substitute “these” with “there”.
Page 22, line 765: Please, check the sentence for repetitions.
Page 22, line 772: Which “magnetic nanoparticles” is the author referring to?
Page 22, line 802: Add a full stop after “GO”.
Page 23, line 824: Add a full stop at the end of the sentence.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
The author presents a well described and detailed review on nanomaterials as water treatment agents. Here, an extensive bibliographic search has been performed and the author successfully merge together all the recent information on the subject. I believe this review will be of great significance to the scientific community as it does not fail to consider all the current work in the field. English check is required as there are a lot of typos, misleading sentences and repetitive phrases. These makes this review a little bit difficult to read. Besides the English revision I would consider to accept this manuscript after consideration of the following comments:
- As the manuscript tends to be hard to read I suggest the author to distinct it in different sections and subsections.
- Even though, the author gives his opinion at the end of the manuscript It is necessary for him to interact with the manuscript. I suggest the author to add some conclusions after each section where he can summarize the information given and highlight the most interesting facts. Otherwise, the review is too boring and the only thing done is the collection of different abstracts. I emphasize the need of sections and subsections to facilitate the manuscript reading.
- Tittle: I suggest to change magnetic nanocomposites to magnetic nanomaterials as here are considered more than just nanocomposites.
- L25-27: Unclear sentence.
- L39: Nanomaterials can not only be used as adsorbents and for catalytic degradation. There are other water and wastewater treatment that involves this kind of materials. It would be better to say something like: Two of the main forms of processes are: ……
- L68: In use for use is confusing.
- L72: Nevertheless should be one word.
- L138: grammar attention “in at pH" remove “in”
- L139: grammar attention: parabens was should be parabens were.
- L212: I believe the term nanocomposite is not well-defined.
- L443-442: high degree of degradation should be mentioned just once.
- L482: grammar check “hi”… should be high
- L487: It would be interesting to include surface area value.
- Table 6, include this article https://doi.org/10.1016/j.scitotenv.2019.134644 (Superparamagnetic nanosorbent for water purification: Assessment of the adsorptive removal of lead and methyl orange from aqueous solutions) as they compare a similar material for heavy metals and organic dyes adsorption. This comparison would be interesting for the review.
- L996; there is a missing comma after pH 6.5
- L1169: grammar attention: it is possible to not only reduce
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The author has answered to the many points raised by the reviewer.
After that the manuscript is improved, clearer and can be read more easily. Anyway other points emerged as not clear enough. These are marked in the manuscript I send back.
The English is improved, but to my advise it must be still improved. Sentences present repetitions of the concepts. I marked the more evident. This is not my duty, anyway, I guess.
So, before acceptance, I ask again for revisions, especially aimed at the language, sentences and so on.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.docx
Reviewer 2 Report
Though some of the suggestions have not been completely taken into account (e.g. point 7), the overall organization and readability of the manuscript have been improved by the changes adopted by the author. Moreover, the examples are more critically discussed, and some issues related to the use of the different class of pollutant removers clearly highlighted in the “Key concepts for the Future” paragraph. However, concerning the point 5 of the first step review (magnetic nanoparticle size), being the size an extremely important parameter in defining the magnetic nanoparticle’s features, I furtherly suggest adding at least a sentence at the beginning of the paragraphs to define the size range of the particles discussed in the examples. Indeed, I experienced that often the terms “nanoparticle” and “nanomaterial” are not used properly. Other minor issues are:
Page 2, Table 1: please modify “NO3-(10 mgL-1)” in agreement with the other polyatomic anions, i.e. nitrate (NO3-).
Page 4, Table 2: still the term “particles” is present in the Morphology column, but it does not refer to any kind of shape. So, please specify it.
Author Response
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Author Response File: Author Response.docx
