The Effect of Additives on the Hydrothermal Synthesis and Thermochromic Performance of Monoclinic Vanadium Dioxide Powder

Round 1

Reviewer 1 Report

The present study is focused on the monoclinic VO2 via hydrothermal synthesis and following calcination treatment and its thermochromic performance. In spite of several novel and original findings, it cannot be accepted for the publication, unless it will be revised. See the following comments.

1.    Why did the authors choose the calcination condition, 700 C for 2 hours? How to focus on it? They should describe the reason and the determination process. If not, the discussion on VO2 crystallization seems non-sense.

2.    In table 1, the word, “amorphous” seems wrong, because Figure 1a shows many crystalline peaks. What did the authors mean? In addition to this, one cannot identify “amorphous” structure judging from only XRD patterns. The authors show us the evidence of “amorphous” structure.

3.    In table 2, values of 2theta(deg) are in the range from27.74 to 27.76. Since the XRD facility used in the study is laboratory one with 0.2degree step scan. Such an accuracy could not be obtained. If the authors use the synchrotron radiation facility, it can be.

4.    On line 203 in the text, what did the authors mean “2theta = 28.7”?

5.    Crystallite sizes in table 2 are in the range from 36.5 to 47.7 nm. These values must be wrong, judging from SEM observation. From the latter, they seem single crystalline materials. If Crystallite sizes are correct, the authors should discuss it.

6.    The authors should the mechanistic discussion of VO2(M) formation by the calcination at 700 C. How was VO2 formed?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This work, at a first glance, looks quite interesting. However, the hydrothermal synthesis that the authors use has been already reported: Journal of Crystal Growth, Vol 590, 126702 (2022). In that paper, the authors use also V2O5 as a precursor, they use also oxalic acid, they use water and heat their autoclave at 220 C (like the current manuscript). Also, they do post-synthesis annealing, for 2h (like the current manuscript). I think that it would be better if the authors cited the works which inspired their research endeavor. Then, they used also succinic acid, urea and thiourea, which is nice, but it would be nice also to cite any works that might have inspired their protocol, I believe. To say it simply: please, cite previous works.

More comments are below:

1)      Line 106: The furnace was preheated at 220 C before putting your vessel inside or you put it first and then you heated the furnace up to 220 C? Also, could you explain better the non-dynamic vacuum conditions that you state at line 107? I can understand that the oven may have non-dynamic vacuum but the vessel of the reaction is sealed so it has air inside. How can you degass a sealed vessel? I think you cannot do it. Please explain better about vacuum.

2)      Line 178: The presence of additives led to amorphous products only in the case of succinic acid or also for the oxalic acid? See what you write at Table 1, please. Do you mean that they are ‘more’ amorphous than in the case of oxalic acid? By the way when I see Figure 1a, I would not call those as-prepared samples as ‘amorphous’. OK, the oxalic acid-thiourea sample is kind of amorphous in a large extent, but several peaks are observed for the other samples, even before their annealing at high temperature.

3)      Line 81, you writing that introducing promoters is beneficial….(to meet some demands) but also previously at line 77 you write that the introduction of promoters helps to regulate resulting materials. Check if you can compile the role of promoters in one phrase of possible. But again, at line 83 you write that there is a lack in the literature for the approach of adding promoters. So the references 5, and 34-36 on the role of promoters (line 78) are just ‘scarce examples’?

4)      Line 210: When you speak about sizes like 46.7, 44.3 and 47.7, it is not safe to write the word ‘increasing the crystallite size’. I mean, increasing, compared to what? From 44.3 nm, to go to 47.7, this is a rather marginal increase, it might be in the limit of statistical error. Or to ‘decrease’ from 46.7 to 44.3, it also seems to be a quite small decrease to speak ‘seriously’ about it.

 

More comments are below:

Line 78: Isn’t what you write there a kind of repetition with what is written at line 67? In both occasions you write that higher temperatures favor higher crystallinity for the produced materials.

Line 103: Why don’t you disclose this ‘specific amount’? At least give a range.

Line 109: Please write centrifugation conditions (time in minutes, speed in rpm).

Line 154: What might be responsible for this difference in the yield? Oxalic acid has fairly strong reducing properties while succinic acid has relatively low acidity. Might these properties affect the yield? They affect the particle size in some cases, for example for the magnetite system. You can check a book chapter on acids used as reducing agents, which also discusses about those two acids:

https://pubs.rsc.org/en/content/chapter/9781839163623-00157/978-1-83916-362-3

Line 169: It is not the pattern 80-0690, it should be 42-0876. Check also Figure 1a.

Line 203: It is not 28.7, it is 27.8 (or 27.77) that you write at Table 2.

Line 225: In which way urea and thiourea prevent the formation of ‘larger and bulkier particles’? Do they act as some type of ligands, surfactants? What do you think? Also, how do you explain that the heating treatment of the structures at 700 C did not ‘break’ their morphology? Wouldn’t this temperature be possible to lead to a more widespread aggregation?

Lines 271-272: Do you have any photo of the vials to show this change of colour with the passing of time?

 At the discussion of FTIR measurements of Page 7, do you notice any peak related to urea or thiourea? If not, is this because of the high temperature of annealing that might have degraded these molecules? If you carried out TGA measurements, this would maybe give some insight on the ‘fate’ of urea and thiourea after annealing, wouldn’t it?

Line 308: Not easy to call the particles as ‘low-dimension’ when their size reaches several microns, right? They are not nanoparticles. They are quite bigger than ‘nano’.

Do you think that the decomposition of thiourea might have led to the decomposition of sulfur atoms into the vanadium oxide lattice?

Line 329: ‘slowly’ or ‘slow’?

Line 347: correct ‘will be take place’ to ‘will take place’.

Line 368: Please do not confuse the crystalline grain size (measured by Scherrer - XRD) with the ‘real’ overall particle size measured by SEM imaging.

References list:

Ref 23: Page number is missing.

Ref 55: Volume and page numbers are missing.

I don’t think it is suitable to write ‘et al.’ in the list of references. Please write all author names. Only in specific cases, some publishers allow to write ‘et al.’ if there are more than 10 authors in some papers. But in general, it is not a good practice. Imagine, for example, a corresponding author having 25 self-citations. The reviewer should download one by one all these papers to check the amount of self-citations. Not practical, I would say.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The revision was fine, but still some minor revisions are needed:

You replied that the novelty of your work lies in the use and resulting effects of the presence of specific additives. You cite the suggested reference at Journal of Crystal Growth that the reviewer suggested, but you need to cite it also at the Experimental Part. There is strong evidence (as explained in my first reviewer report) that the presented synthetic protocol is inspired by the literature so please add the relevant citation(s) that inspired your work also at the experimental part, not only at the Introduction.

For the role of succinic acid you replied that an explanatory phrase was added near line 154 regarding the effect of additives on yield according to the proposed literature by the reviewer. Still, this book chapter is not cited at the revised version. If the change was done according to this proposed literature, you need to cite that chapter, too.

Line 104: the 1:4 is urea/V2O5 molar ratio or V2O5/urea?

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf