N- and S-Doped Carbons Derived from Polyacrylonitrile for Gases Separation

Round 1

Reviewer 1 Report

The report is written in the attached file.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This paper describes the synthesis of activated and nonactivated carbon materials for CO2 capturing using PAN as a precursor. The overall work is suitable for this journal after a major revision and addressing the following points:

1. The author submitted this work to Sustainability based on the CO2 capturing story. However,  the Authors used carbonization to prepare their materials in which CO2 is one of the major gases that will be produced upon carbonization. So authors need to elaborate on this point.
2. CO2 diameter is smaller than N2 and thus in BET calculation we always see the BET generated from N2 has smaller values than the one generated from CO2. However, in this work, they showed that the BET from CO2 is way less than the BET from N2 for PAN-C-Act and PAN-S-C-act as shown in Table 1. This is unusual and uncommon. The authors need to recheck the BET calculation and elaborate more.
3. The tile is addressing the effect of S- and N-doped on separation performance. However, I don't see that the effect of these two groups has been addressed properly in this work. Extra work needs to be done to prove that the S-doped and N-doped are really working. I recommend changing the title as it is not conveying the message of the work. 
4. The effect of Nitrogen atom presence has been discussed before by one of the pioneers in gas separation and authors are recommended to cite it and involve it in the discussion: https://doi.org/10.1016/j.polymer.2017.10.017
5. Figure 4 needs to be generated with better resolution as the axis label is not clear at all. 
6. Authors should report at least three to five cycles of sorption and desorption of CO2 to evaluate its performance.
7.  IAST calculation models should be stated clearly in the manuscript 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The present work studied the effect of nitrogen and sulphur doping in carbons derived from polyacrylonitrile as carbon precursor. The structural properties of synthesized materials were confirmed and the influence of pressure and temperature on CO₂ separation were studied. The experimental data obtained fit well with Toth isotherm. This work offered a new material for gas separation with high CO2 uptake. The suggestions are listed as below:

Suggestions:

1. There are a few similar works reported on nitrogen and sulfur doping on carbons and or activated carbons. It is suggested to highlight the novelty of this work in Introduction.
2. The quality of the written English is modest and in certain parts of the manuscript renders comprehension difficult. A thorough review of the text is required before it can be considered for publication.
3. Figure 6 (right figure): Please explain the influence of temperature on the CO2 uptake at low pressure range.
4. It is mentioned that the type of adsorption produced with low interactions reduces the energy penalty (Line 57). May the authors provide explanations on this mechanism?
5. The presence of sulphur entails an enhancement of interactions with higher values of isosteric heat compared with sorbents of similar nature (Line 80). May the authors clarify the benefit given by high value of isosteric heat for adsorbent?
6. Please include the XPS spectra is Section 3.1.3.
7. Please clarify and elaborate ‘non significance of surface chemistry’ (Line 424).
8. There are a number of spelling error in the text, e.g., “emiosion” (Line 37) and “atractive” (Line 60). May the authors please do revision accordingly.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The report of me has been partly improved, The the quantitative emphasis of the most important results, e.g. in the conclusion, was not carried out. 

But independently of this deficiency, considering  the overall scientific level of the renewed paper, I accept this paper as it is.   

Reviewer 2 Report

The responses were sufficient 

Reviewer 3 Report

The authors have addressed all the comments.