Chemical Recycling of Consumer-Grade Black Plastic into Electrically Conductive Carbon Nanotubes

Round  1

Reviewer 1 Report

In this manuscript, the authors claim that the PS contributes to the growth of MWCNT. This research is interesting and encouraged to be continued.  However, considering  scientific rigorousness, I would like to raise some questions on the 'role of polystyrene'. The main conclusion of this manuscript- chemical recycling- is not convincing. What is the role of polystyrene is not clear and the difference between control samples and samples with plastics is very small. Though this can be left for the future research, at least, coversion of polystyrene to MWCNT should be clarified here.(or does it only act as catalyst?) This manuscript can be accepted if these questions are well addressed. 

1) Because PS is dissolved in toluene for injection and toluene can provide carbons for growth of MWCNT, it might be the case that toluene contributes to the majority of MWCNT synthesized and the PS just thermally decompose. In this scenario, the conversion of plastics to MWCNT can not be claimed and the authors should exclude this possibility. To verify this, questions such as 'What portions of the synthesized MWCNT come from PS?' and 'Does the yield of MWCNT increase after dissolving PS?' could be relevant. 

2) It suggests the possibility of improving the quality of MWCNT. However, in my opinion, the contribution of PS to the formation of MWCNT is not supported clearly.  In Fig. 1, the MWCNT diameter distribution looks similar in all cases and the average diameters are almost the same. The increase is very small. Improved homogeneity in diameter distribution can be supported better by standard deviation. In Fig. 2, the difference of Raman spectra between samples is small. It looks clear that the PS does not degrade the MWCNT quality at least. However, whether it improves is not clear. 

Considering the small differences, the diameter distributions in SEM images and Raman spectra might depend on positions where the SEM and Raman are taken. Are these dependencies reproducible in other positions of the samples?

3) In Fig. 3a, the two probe resistance measurement of each individual MWCNT is demonstrated. However, the individual CNT that is contacted by STM is electrically shorted to the bulk of CNT net. The measurement of individual CNT can be justified only when the resistance of the bulk CNT net is extremely small compared with the single MWCNT. Importantly, average resistances of control samples are omitted in Fig 3b for comparison.

Is the current-voltage measurement linear? If not, current-voltage curves should be presented because definition of resistance is not trivial in this case. 

These are other issues that need to be considered before publication.

4) The necessity of recycling PS is well described. However, it is recommended to introduce MWCNT fabrication from plastics more. The authors are recommended to cite previous reports on using plastics for MWCNT growth, for example, after 'plastics' in line 54.

2) Among many other plastics, why polystyrene? Is it because it is the source of the most of black plastics or are there other reasons?

3) The authors raised questions in the last paragraph of introduction (line 57 to 71). Are they completely open questions? Short introduction on this research line, at least experimental facts, are required.

4) The method can be described in more detail. For example, in line 75, which solution and which gas are they?

5) In Fig. 1b, what are white dots on the MWCNT? Can it be iron-related in the catalyst? They are not visible in Fig 1 e, h. Ideally, elemental analysis should be presented for samples especially samples with PS.

Author Response

Thank you for your valuable input. Please find word document showing point-by-point all responses to your thoughtful review. We hope that your point have been raised appropriately, and that our response is appropriate to your liking.


Sincerely,

Alvin Orbaek White

Author Response File: Author Response.docx

Reviewer 2 Report

I was asked to review this manuscript It is written very good, however, I would recommend to add several sentences concerning state of art of plastics recycling/upscaling into CNT or other carbon nano materials. Examples can be found in literature.

In Abstract authors wrote "...using novel injection method (LIR)..." LIR is either a ratio or reactor of liquid injection. This has to be modified.

Line 44: Is data concerning PS production global or US? Do Authors sure that citation 2 in this context is proper?

Line 75: "...under gas flow..." please specify the gas

Line 78: "...dissolved" What was the type of solvent?

Line 93: "..effects of the shank.."???

Line 139: G peak in fact is a mesure of ordering, it can be also combined with graphitic domains or graphitic structure not with a graphite.

Line 212: "...opens op possibility.."

Author Response

Thank you for your valuable input. Please find word document showing point-by-point all responses to your thoughtful review. We hope that your point have been raised appropriately, and that our response is appropriate to your liking.


Sincerely,

Alvin Orbaek White

Author Response File: Author Response.docx

Round  2

Reviewer 1 Report

This article don't have flaws but additional experiments are actually needed. However, as the response letter, the contribution of polystyrene to CNT is backed up in other works submitted in other journals. If these are already published, they should be cited in this manuscript. In my opinion, if the authors revise the manuscript as in the cover letter, the raised points will be addressed in the boundary that this submission is a small subset of a larger body of work and the hypothesis will be confirmed in future. The reliability of data in this manuscript is improved. With authors response, it is more convincing. The points of the authors comments should be delivered clearly for the readers in the revised manuscript.

Author Response

Since receiving your previous request I have attended the Rice/NASA Guadalupe Carbon Nanotube growth conference, where I had the opportunity to discuss this work with several colleagues - hence the delay in my response to you.

In short, you requested that we make reference to the two other articles that are in press. Please see the comments below:
Article 1: The RSC article is now cited as reference 13 in the text. The article is still being finalised, but the title and authors have been defined. The article will be submitted in the next 5 days.

Article2: This was planned for Nanoscale Horizons, to deal with the question of how large can a carbon molecule be, in order to be considered viable for CNT growth. Since the Rice/NASA Guadalupe conference I have now begun discussions with Prof Alister Page (University of Newcastle, Australia) about this matter. And since this event I have chosen to work more on this paper, so this means it is not ready for submission at this time, and so we cannot cite it as you had requested.


I hope that you can accept the article in it's current form. I look forwards to hearing from you.


Sincerely,
Alvin