Doped Tin Dioxide (d-SnO₂) and Its Nanostructures: Review of the Theoretical Aspects, Photocatalytic and Biomedical Applications

Round 1

Reviewer 1 Report

In this manuscript, the authors present a review on doped SnO2, its structure and applications. In my opinion, there are some points that should be elucidated /improved and the study requires a major revision before the publication.

- In Figure 2 energy gap and acceptor and donor levels should be labeled and the proportion between the size of the bandgap and the position of the bands and acceptor and donor levels should be maintained.  New energy levels appearing after doping should be also described in the text of the manuscript.

- Figure 4 presents the electronic bands' scheme of SnO2 and valence and conduction bands labeled as Sn states and O states, which is not consistent with solid-state theory. I recommend removing the Figure because Figures 1,5, 6, and 7 present the bandgap scheme of tin oxide. The text of the manuscript (lines 170-173, ”A detailed evaluation of the bands generated….) should be modified.

- Figure 14 should be removed. The structural formula of sulfur-containing compounds is not necessary for the SnO2 review.

- Part 3 should be summarized with an explanation of the doping effect and surface oxygen vacancies on the photocatalytic performance of d-SnO2 in comparison to pure tin oxide

- The authors present many reports that show increasing doping levels resulted in decreases of energy bandgap and also high photocatalytic efficiency. The photocatalytic mechanism influenced by the bandgap value of  SnO2 should be described and the process of pollutant decomposition should be elucidated.

- Part 4 presents also heterostructures of SnO2 and other materials as a valuable system for CO2 reduction – the working mechanism and phenomena of the interface should be described in the text of the manuscript. It is worth mentioning that also the heterojunctions of SnO2 with metal nanostructures are efficient photocatalytic systems.

- The part on 3D hierarchical structures indicates their high photocatalytic activity as a result of oxygen vacancies and doping ions. It should be elucidated with regard to dimensionality.

- The biological application of d-SnO2 should be compared to pure SnO2 and its antimicrobial activity. The doping process's influence on antimicrobial properties should be considered.

- The bacteria and fungi species names should be presented without the abbreviations when they appear for the first time in the text of the manuscript and should be written using the italic font (Figure 17 caption).

- Line 657 and 706 indicate that there is a different antibacterial mechanism of d-SnO2NPs, in fact, it is not a different mechanism but different material – heterostructure with AgNPs or Ag ions. Silver is a material with well-known antimicrobial properties.  In these kinds of structures, the antibacterial properties of both components are combined.

- The text should be carefully read to remove informality, colloquialisms, and not clear enough parts, e.g.:

- “more positive conduction bands” – line 53

- “many-electron problem” - line 140

- “electron promotion” - line 226

- “favorable formation energy” – line 238

-    “for nanostructures, the control of the length and …”  - why only the length, probably it should be “size”.

Author Response

Please see the file attached

Author Response File: Author Response.pdf

Reviewer 2 Report

This review manuscript presents some modifications to tin dioxide (SnO₂), mainly through the doping process. And introduced the SnO₂ structural features and the computational models used to explain the role of the doping process on these features. Moreover, it also summarizes some examples related to SnO₂ composites with other nanomaterials. Some applications of SnO₂ and SnO₂ composites with other nanomaterials are also summarized. This review manuscript was systematical. However, some serious issues should be addressed before publication as follows:

1. At the end of abstract, a general conclusion for the work should be given for making paper more scientific. It is suggested that the abstract should be polished or re-edited to highlight the classification logic of the summary topic, so that readers can understand this article more quickly.
2. Some papers are useful for support and explaination, such as Chem Eng J 443 (2022) 136341, J Electrochem Soc, 2020,167: 020550, Electrochim Acta, 2018, 265: 577.
3. The manuscript should be clearer about the classification logic of the summarized topic, and merely summarized the structural characteristics and applications of SnO₂ may not meet the publication requirements of this journal.
4. As for the aesthetics of some figures in the manuscript, such as Figure 9, when combined and re-edited, letter numbers on each small figure should be appropriately small, so that the overall look is better.
5. Now that the structure characteristics and application of SnO₂ have been summarized in the manuscript, the authors should have some understanding of the bottleneck of the current research direction. And the conclusion of the paper should provide some tentative answers and forward-looking predictions to these questions，this could brighten the manuscript.
6. The figures in the manuscript are only placed in a single figure, such as Fig. 1-Fig. 8. From the point of view of rich content, it is difficult to give readers a comprehensive summary feeling. It is suggested to refer to the figure combination of high-level review articles. If the figures in the cited manuscript can be flexibly combined, the level of the article will be improved obviously.

Author Response

Please see the file attached

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript should be accepted in its present form. The authors elucidated all raised issues and answered the questions, some parts not in English. I have coped with it. Best regards and I wish you many citations.

Reviewer 2 Report

I suggest the publication of this paper after the modifications.