Behavior of C₇₀ Fullerene in a Binary Mixture of Xylene and Tetrahydrofuran

Round 1

Reviewer 1 Report

Comments from Reviewer

Manuscript ID: liquids-2478626-peer-review-v1.pdf

Title: Behavior of C70 fullerene in a binary mixture of xylene and tetrahydrofuran

The current form's presentation of methods and scientific results is unsatisfactory for publication in the Liquids journal. The minor and significant drawbacks to be addressed can be specified as follows:
1.    Has a similar study been carried out for the C60? If so, what results were obtained?
2.    Tab. 1. What is included in this table? The refractive index? The concentration of C70? Please enter instead of C, C70 (then the following text "The C70 concentration in a solution." will not be necessary). Unclear to me…
3.    Fig. 1. Please, add the legend.
4.    The authors write “a range of "~185-900 nm" (line 84). However, Figure 1 shows a different one. Why?
5.    Fig. 1. For which concentration was the measurement performed? Were similar results obtained for the second concentration? Please provide a corresponding figure.
6.    Fig. 2. Storage time ( days) - Storage time, days
7.    The conclusion presented in this manuscript is not in the format of a conclusion for a scientific article. According to the literature: "The Conclusion section presents the outcome of the work by interpreting the findings at a higher level of abstraction than the Discussion and by relating these findings to the motivation stated in the Introduction." The conclusions are too long.
8.    The authors have not convinced me that they are dealing with a significant degree of self-organization in these solutions

Sincerely,
    The reviewer.

Author Response

Dear Reviewer,

We have made the corrections which you requested and accepted your suggestions. Thank you indeed for putting these forward.

We have carefully considered your proposals and given the answers below in the attached file. Please see the attachment.

Sincerely yours,

Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript reports the behavior of C70 fullerene in a binary mixture of xylene and THF. The results are interesting. However, there are several comments have to address:

1.      The length of article is short. It should be a communication or letter.

2.      In Figures, the legends are missing.

3.      Pictures or images of C70 fullerene in different initial concentration are required.

4.      Only two kinds of initial concentrations, in this work. May need more initial concentrations to support the conclusion.

Therefore, I recommend it as major revision to publish.

Author Response

Dear Reviewer,

We have made the corrections which you requested and accepted your suggestions. Thank you indeed for putting these forward.

We have carefully considered your proposals and given the answers below in the attached file. Please see the attachment.

Sincerely yours,

Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments for author File: Comments.pdf

Minor editing of English language might be useful

Author Response

Dear Reviewer,

We have made the corrections which you requested and accepted your suggestions. Thank you indeed for putting these forward.

We have carefully considered your proposals and given the answers below in the attached file. Please see the attachment.

Sincerely yours,

Authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I believe that there is surely an improvement in the quality of the manuscript. This work is likely to be interesting to the readers of the journal. It may now be considered for possible publication.

Author Response

Dear Reviewer,

First of all, thank you for the deep study of our manuscript and good comments. This, as you noted, undoubtedly led to an increase in the quality of the article and interest in the journal's readers. We wish you success in your future endeavors.

Sincerely,
Authors

Reviewer 2 Report

The manuscript has revised well according to the comments. Therefore, in my opinion, the article could be accepted to publish in present form.

Author Response

Dear Reviewer,

First of all, thank you for the deep study of our manuscript and good comments. We respect your opinion. We wish you success in your future endeavors.

Sincerely,
Authors

Reviewer 3 Report

In the revised version of the manuscript entitled »Behavior of C70 fullerene in a binary mixture of xylene and tetrahydrofuran« the authors (Makhmanov et al.) have indeed satisfactorily replied to my comments expressed in the first round of the reviewal process.

 

Unfortunately, neither I nor the other reviewers during the first reviewal process noticed an important failure in reporting spectrophotometric results. The methodological error in the interpreting spectrophotometric results is so crucial that the second revision round is indispensable.

Namely, the authors are using in the interpretation of the experimental results obtained with the use of spectrophotometer the term “absorbance”. Such a use would be appropriate in case when the sample would be homogeneous (only solution with the solute having the size of the molecule would be present – see e.g. definition of absorbance in the IUPAC’s Gold Book). Due to rather small size of C70, the scattering of the molecular solution of C70 can be probably neglected, however, when C70 molecules are assembled, the size of such clusters is much larger and such particles then become a a notable source of scattering (and such solution cannot be called homogeneous; haziness occurs). Said more directly, when such particles are present in the cuvette inserted into the spectrophotometer, a notable fraction of light beam is scattered and does not reach the detector. So, while a fraction of light is really absorbed by C70 molecules forming molecular solution (and may therefore contribute to real absorbance), another fraction of light is scattered on particles (and not absorbed) but also not reaching the detector. Considering that in the regular use of spectrophotometers it is presumed that only absorption of light is the reason why some fraction of light does not reach the detector, the spectrophotometers erroneously report absorbance when the cuvette is filled with the hazy solution. This is testified in Figure 1 when “absorbance” is e.g. increased during elapsed time also at 700 nm although the absorbance of the original solution is very low at that wavelength.

 

Therefore, I ask author, to consider also this my remark/comment and change the manuscript accordingly. They should be aware that in such a case they should be very careful with the use of words “absorbance”, “absorbed”, “absorption” etc. They should also inspect if the red shift they are reporting is a real red shift or it is just an artefact due to combination of diminished absorbance (as a consequence of diminished concentration of the solute present in the real solution) and increased “absorbance” due to diminished intensity of the light beam being scattered (this may happen in case of unsymmetrical absorption peaks).

 

I ask the authors to check also possible effect of haziness of the solution on the measured refractive indices.

Author Response

Dear Reviewer,

We have made the corrections you requested and have accepted your suggestions. We sincerely thank you for your suggestions.

We have carefully considered your proposals and have responded below in the attached file. Please see the attachment.

Yours sincerely,

Authors

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

In the second revised version of the manuscript entitled »Behavior of C70 fullerene in a binary mixture of xylene and tetrahydrofuran« the authors (Makhmanov et al.) have tried to respond to my comment that the “absorbance” spectrum they are reporting is actually a hybrid between the real absorbance spectrum and outcome of the scattering process occurring on the nanoclusters present in the solution.  In this revised manuscript the authors are also presenting the result of the repeated experiment where the “absorbance” was monitored during the time frame of 12 days.

 

I merit a lot the initiative of authors to repeat the above-mentioned experiment, however, this does not resolve the issue. Moreover, the repetition of the experiment has shown that the concentration of molecularly dissolved C70 is not well controlled parameter. Namely, in the case of molecularly dissolved solutes Beer-Lambert law should be valid and the initial spectra (of fresh solution) recorded in both runs of the experiment should be (ideally) equally intensive (showing the same absorbances at the chosen wavelengths). This is not the case and the spectrum shown in the last version is characterized by higher absorbances hinting that this time the initial concentration of C70 in the solution was higher (approximately 25 %) than it was in the first experiment (see Point 4 in my review of the first version of the manuscript and also the response of the authors). But this is just my marginal comment during this revision round.

 

What worries me more is that the authors have not responded to my comment that the signal recorded on the spectrophotometer is not pure absorbance but an outcome of several physical processes:

i) absorption of the light in electronic systems of solutes (what the absorbance in UV-Vis region should be about)

ii) depletion of light (increased “absorbance”) due to scattering on the nanoclusters (it is not only the light at 632.8 nm from the Zetasizer Nano ZEN3600 instrument that is scattered on the nanoclusters in the solution but it is also the light at 632.8 nm [and also at other wavelengths in UV/Vis spectrum] from Shimadzu UV-2700 spectrophotometer that is scattered and therefore not reaches the detector of the spectrophotometer thus contributing to the apparent “absorbance”). Again, nanoclusters in solutions are the reason why “absorbance” is increased because nanoclusters prevent some photons (due to scattering of the light on nanoclusters) to reach the detector of the spectrophotometer.

 

Sadly, I needed to repeat again above this explanation why “absorbance” is increased due to occurrence of nanoclusters in the solution. On the other hand, inclusion of molecularly dissolved C70 molecules into nanoclusters diminishes the concentration of molecularly dissolved C70 and the absorbance (this time without quotation marks) can be diminished. So, it is difficult to predict whether the “absorbance” would be increased or decreased upon formation of nanoclusters in solution where molecularly dissolved solutes absorb light. And there is still the size of nanoclusters that matters. The same quantity of the solute can be incorporated into many small nanoclusters or in less numbered larger nanoclusters. DLS would distinguish the sizes while spectrophotometer would not (and it is also difficult to say in which case of the above two the “absorbance” would be higher).

 

To conclude: the authors haven’t fulfilled my expectations related to objective discussion of their results (in fact, they failed completely in this part) and from that perspective I should recommend rejection of the manuscript. Nevertheless, I merit a lot that the authors have repeated the experiment and I hope that they have got at least a bit of taste how tricky their experiments are.

Considering the repeated experiment, I would give to the authors the last chance to prepare the paper properly and

-        present in the new version both “absorbance” diagrams (the first one and the new one), pointing out that it is difficult to say what the concentration of C70 in fresh solution is

-        comment the difference in both diagrams (in my opinion, formation of the nanoclusters is not very well-defined process and sizes of nanoclusters may be also different in both cases). It would be beneficial to also show the size distribution of C70 nanoclusters in the second experiment if this measurement was done.

-        avoid use of the word absorbance and other terms related to absorbance as seen by spectrophotometer when other effects also contribute to lowering of intensity of the light beam being measured by the spectrophotometer.

 

My recommendation is major revision of the paper.

Author Response

Dear Reviewer,

We have carefully considered your proposals and have responded below. Please see the attachment.

Yours sincerely,

Authors

Author Response File: Author Response.pdf