Electrospun Nanofibrous Membranes for Air Filtration: A Critical Review
Round 1
Reviewer 1 Report (Previous Reviewer 2)
After the initially rejected manuscript (2251551), the author now also addresses potential risks of released nanoscale fibres.
The manuscript thus appears fit for publication.
I recommend to use "DeepL Write" to detect incorrect use of the English language.
Author Response
Point 1: After the initially rejected manscript (2251551), the author now also addresses potential risks of nanoscales fibres.
The manuscript thus appears fit for publication.
I recommend to use “DeepL Write” to detect incorrect use of the English language.
Response 1: The reviewer’s suggestion was followed and the text was revised by “DeepL Write”.
Reviewer 2 Report (New Reviewer)
This review explores the use of electrospinning to improve nanofibre membranes for air filtration, including the latest advancements and layered structures for innovative solutions. The authors need to address some concerns before it is considered for publication:
1) There is only one reference in the first three paragraphs, which is absolutely not enough. More references are necessarily added.
2) Please add the axis titles in Figure 1.
3) More references are needed in Part 2 as well. Most of the sentences in this manuscript lack references.
4) There are two Figure 3 in this manuscript. Please re-order all the figures.
5) Uppercase the first letter of Figure 5 title.
6) Please make Figure 9c clearer.
Author Response
Point 1: There is only one reference in the first three paragraphs, which is absolutely not enough. More references are necessarily added.
Response 1: Some references have been added as requested.
Point 2: Please add the axis titles in Figure 1.
Response 2: The axis titles in Figure 1 have been added.
Point 3: More references are needed in Part 2 as well. Most of the sentences in this manuscript lack references.
Response 3: Some references have been added as requested.
Point 4: There are two Figure 3 in this manuscript. Please re-order all the figures.
Response 4: The numeration of the figures has been corrected.
Point 5: Uppercase the first letter of Figure 5 title.
Response 5: The captions of the figures have been corrected and capitalised.
Point 6 Please make Figure 9c clearer.
Response 6: Figure 9c has been enlarged and the relative caption made clearer.
Reviewer 3 Report (New Reviewer)
Comments to the Author:
In this manuscript, the authors reported the review on electrospun nanofibrous membranes for air filtration. The theme and schematic diagram in the article are very good. The author has carefully and diligently written the research content, which is worth publishing. But there are several questions that need to be revised.
1. The scope of the topic is too large and should be narrowed.
2. The content of the two tables is too rough, suggest refinement.
3. The article framework needs to be revised, some first level headings and second level headings are not designed properly.
4. Lack of comparative data on the air filtration efficiency of different materials.
5. Many references are too old and do not reflect the progress of research in recent years, such as Refs. 3,6,19,21,24,25,27,28,29 …
6. There is also the issue of incorrect citation formatting.
7. The content of parts 1-5 is too much, and it seems that the research progress on various materials is too little. This makes the article seem top-heavy.
English Language is OK. Just need to be minor editing.
Author Response
Point 1. The scope of the topic is too large and should be narrowed.
Response 1: The author agrees with the reviewer, but believes that the aspects addressed (process parameters, materials and structures of nanofibrous electrospun filters) are of great importance and have a relevant impact on filtration performance. The aim of the manuscript is to give general indications to the reader approaching the subject, and it does not claim to be exhaustive, nor does it have the intention of selectively presenting the results reported in the literature, precisely because there are many published studies, and the experiments and data often are not complete, clear and contradictory. However, the author hopes to have written an interesting and useful manuscript.
Point 2. The content of the two tables is too rough, suggest refinement.
Response 2: see Response 1
Point 3. The article framework needs to be revised, some first level headings and second level headings are not designed properly.
Response 3: The framework of the manuscript has been revised.
Point 4. Lack of comparative data on the air filtration efficiency of different materials.
Response 4: A comparison table for some materials has been added.
Point 5. Many references are too old and do not reflect the progress of research in recent years, such as Refs. 3,6,19,21,24,25,27,28,29 …
Response 5:
The references to studies on filtration membranes are dated from 2017 onwards. The earlier ones refer to important papers published on filtration theory or on early fundamental studies.
Point 6. There is also the issue of incorrect citation formatting.
Response 6: The format of the citations has been adhered to as required.
Point 7. The content of parts 1-5 is too much, and it seems that the research progress on various materials is too little. This makes the article seem top-heavy.
Response 7: Some parts of paragraphs 1-5 have been deleted to make the manuscript more readable.
Round 2
Reviewer 2 Report (New Reviewer)
The revised version has been sufficiently improved to warrant publication in Compounds.
Author Response
I am grateful to the reviewer for the time and attention he has given to the reading of the manuscript.
Reviewer 3 Report (New Reviewer)
I still feel that the scope of the topic is too large. Additionally, there are two Tables 2 in the manuscript.
Author Response
Reviewer's comment: I still feel that the scope of the topic is too large.
Response:
I am grateful to the reviewer for the time and attention he has given to the reading of the manuscript. His suggestions will help me to improve it. This manuscript aims to describe the problems associated with air filtration using specific membranes (nanofibrous) produced by a specific technique (electrospinning). To achieve this aim, I believe that the scope should include some aspects to provide the reader (even if unfamiliar with the subject) with the minimum information necessary to frame the problem accurately and to examine the literature (both the literature cited and others dealing with the same subject) in a careful and informed manner.
The examples of membranes discussed in this manuscript, which mainly refer to materials and macroscopic structures, show how the typical problems of nanofibre membranes (typically caused by their poor mechanical properties) can be solved with appreciable results. As has been pointed out both in the text of the manuscript and in the responses to the reviewers, the solution to the problems of poor effectiveness or poor mechanical strength is not unique and the results described in the literature are sometimes inconsistent.
For the sake of clarity, I have included in the introduction what I consider to be fundamental aspects of the scope, with the addition of the following sentence.
“After considering the nature and characteristics of the physical pollutants, this review has focused on (i) the filtration properties to be assessed, (ii) the technology used to produce nanofibres and its operating principle, (iii) the elements that influence the effectiveness of electrospun membranes for air filtration, namely process parameters, materials used, the macroscopic structure of the membranes.
The membrane examples discussed in this manuscript, mainly related to materials and macroscopic structures, show how the typical problems of nanofibrous membranes, caused by their poor mechanical properties, can be solved with significant results.”
Reviewer's comment: Additionally, there are two Tables 2 in the manuscript.
Response:
The numbering of the tables has been corrected.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
1. More comparison and analysis should be given rather than just state “important”, “different”, “more efficient”. How does each factor of the electrospinning process and material influence the filtration efficiency? How much are the factors favorable or unfavorable to the efficiency?
2. Please give some subtitles in Sec. 6.
3. Could you point out the future research directions?
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript reviews a wide range of different approaches to the formation of pure and composite nanofibres by electrospinning. However, it lacks a systematisation of the reported material properties to show their potential benefits for filtration applications. The reader asks: What are the general trends? Is thinner better? For example, what is the range of tensile strengths achieved? What is the strongest nanofibre material? What is the optimum between diameter, strength and filtration efficiency? What is the most promising material? What are the potential drawbacks? Tables or viewgraphs of the data could help to identify trends and learn about property ranges.
For example, the section "Dependence of filtration efficiency from fibre and filter structure" gives many examples, but does not identify trends in the dependence of filtration efficiency or filter stability on material properties such as tensile strength or filter structure.
The manuscript is "critical" in the sense that it addresses a number of critical issues of nanofibres in filtration applications.
- Recycling and disposal issues for nanofibre products
- Potential release of harmful VOCs during re-use
- Limited mechanical stability for the intended filtration application.
However, although the manuscript motivates the use of nanofibres for filtration applications with airborne particulate pollutants and toxic substances, it completely neglects the central issue of the respirability and therefore potential toxicity of biopersistent nanofibre fragments. This is surprising because, as the author points out, the requirement that "filters must maintain structural integrity" and the fact that "most electrospun nanofibre membranes are either too thin or too fragile to meet this requirement" lead directly to the problem of the release of respirable fibre fragments.
Such release may imply potential health risks that are not addressed, although such aspects have been extensively studied, e.g. for carbon nanofibres, and have led to a harmonized European CLP classification for carbon nanofibres thicker than 30 nm (Carc. 1B). Only environmental risks of synthetic polymers are mentioned in the section on 'green' nanofibres that considers the aspect of biodegradability of fibres for environmental protection purposes after disposal. However, the production of nanofibres that are biodegradable on sufficiently short timescale could also lead to sustainable fibres that are free of potential fibre-related health hazards. The mentioning of PVA to be “nontoxic to the human body” misses the main point: Practically all chemically inert polymers are nontoxic. However, for biodurable materials, fibre-related toxicity is a morphology-, not composition-dependent property.
It is imperative that experts in the field of fibre production are aware of the fibre pathogenicity paradigm and consider its potential implications for their work. The work of Cogliano et al. cited by the authors refers to the IARC Monographs 100. Volume 100C deals with fibre carcinogens.
The death toll from asbestos exposure is too high to praise the potential benefits of filters containing fibres thin enough to be inhaled for the purpose of removing toxic particles from the air without considering and discussing the potential release of fibre fragments into the air and balancing the inhalation benefits and risks. A practical example could be FFP2 face masks using (biodurable) PVDF nanofibres, commercially available from a Korean company (Air Queen).
Some details to improve
· Line 10: “inhalable suspended particles in the air […] irreversible damage to human health.” What purpose serves the phrase “in many countries and regions”?
· Line 11: Is “nanotechnology” able to “propose” anything?
· Line 189: The physics behind the Taylor cone and filament formation is not well described, nor further literature cited.
· Line 21: Particles may exhibit not only different size but also different shape
· Line 54: “human health” effects are solely discussed for PM, not for fibres
· Line 105: “Filters prepared with electrospun nanofibres have outstanding properties, …” Suggestion: “may have outstanding …”
· Line 107: “excellent performance”. Why “a critical review” if praised as excellent here? Excellent with respect to which property?
· Line 128: What are “main filters”?
· Line 139-145: “Particle penetration, P” etc. Formula symbols are to be typeset in italics
· Line 156: “SARS COVID-19”? The official term is “SARS-CoV-2”
· Line 161: What is meant by “mobile surface”?
· Line 164: What stands the acronym “TNT” for?
· Line 191: “movement toward the collector, the solvent evaporates” – starts to evaporate. It depends on the vapour pressure of the solvent and the flight distance whether it can fully evaporate
· Line 211: “cost-effective” is claimed but considering the small amount of fibre mass spun per time and the costs for the high-voltage equipment and the high ratio of solvents evaporated per fibre mass, this claim requires additional arguments.
· Line 415: “However, it should be mentioned that when using a magnetized filter, it is necessary to consider a balance between energy consumption and improving filter efficiency.” What about permanent magnets?
· Line 448: “This implies the use of large amounts of organic solvents 448 that could be toxic, flammable, and environmentally unfriendly.” – DMF and DMAc are indeed toxic. No “could” necessary.
· The “efficiency” of electrospinning is claimed multiple times, to what aspects the term “efficiency” actually refers is not always clear and should be added. E.g., “efficiency with respect to …”
Some examples of sub-optimal use of the English language
· Line 103: “opportune combination of polymer and solvent” – Reconsider the use of the word “opportune”
· Line 111: “Definitions of filtration” – Why plural?
· Line 113: “It is important to avoid that the matter removed from the fluid forms a cake on the surface of the porous medium because the service life of the filter will end in a brief time due to the high pressure drop across the filter.”
· Line 152: “Nanofibres production” – Why plural?
· Line 172: “through a splitting”? … process?
· Line 177: “gaining an increasing interest”? “an”? Can we count interest?
· Line 183: “In substance,”?
· Line 187: “surface, that results” Comma? “that”?
· Line 188: “At an opportune voltage” – Reconsider the use of the word “opportune”
· Line 189: “syringe apex”? – “syringe’s needle tip” meant? It could be worth mentioning that the tip is generally metallic and forms one of the two electrically contacted electrodes.
· Line 190: “tiny wire”? – Is “tiny wire” appropriate? Suggestion: “thin filament”
· Consider using “DeepL Write” or a human expert to improve the use of the English language.
· Line 210: “even in a combination of them” – " even in combination”
· Line 220: “Significantly, electrospun nanofibre non-wovens have the filtration efficiency is up to 90–99 %, particularly when filters are designed with multi-component, porous or core-shell structures, or superficial nanostructures on the fibres [21-23].” – Check this sentence.
· Line 224: “used in electrospinning process” – “the” missing or plural (processes)?
· Line 231: “Dependence of the filtration efficiency from electrospinning process” – “… on electrospinning process parameters”?
· Line 233: “rapid removal” – Is “rapid” appropriate here?
· Line 269: “Dependence of the filtration efficiency from electrospun material” – “…on the electrospun material”#
· Line 318: “exhibit high particulate removal efficiency” – “particle”?
· Line 715: “resistance 714 to temperature, chemicals or mechanical stress is not so exciting” – “exciting”? Colloquial English!
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Despite a focus on hazardous particle dusts, the author, describing the fragility of electrospun fibres in filtration applications, failed to comply with the reviewer's request to address potential inhalation risks of fibre dusts. This review articles also lacks a systematic and at least semiquantative analysis of the benefit of electrospun fibres in such applications. The selected references therefore appear to be anecdotal and of litte value to the community.
Author Response
As suggested, some parts have been added and/or revised mainly concerning a discussion of the nature and sources of airborne particulate and microplastics, a summary of the main effects of process parameters on the characteristics of electrospun nanofibrous membranes, and a recap of the effects of the characteristics of electrospun nanofibrous membranes on filtration efficiency.
The author has selected the references for the recent publication date and for the interesting suggestions on the materials and structure of the membranes.
