Transition Metal Dichalcogenides [MX2] in Photocatalytic Water Splitting
Round 1
Reviewer 1 Report
There is increasing interest in technologies for water splitting since it has some inherent advantages over conventional H2 production. This is an unnecessarily lengthy manuscript that summarizes literature information on materials for water-splitting photocatalysts. It also purports to provide information on the fundamentals of water splitting and "advanced photocatalysts." After closely reading the manuscript, I cannot recommend its publication in its current form as it lacks several important characteristics underlying an authoritative review. My comments are given below.The biggest flaw with the manuscript is that it does not provide any new insights into the theory or applications of materials for water-splitting photocatalysts. Any authoritative review should critically consider previous publications and provide deeper understanding of underlying phenomena. Through the critical review, it should identify gaps in our current understanding thereby providing directions for future research. Unfortunately, this manuscript largely fails in this aspect. The authors for most part just collect previously published statements/results without figuring out underlying unifying phenomena. They do not even discuss whether earlier results are correct or not! No comparisons on H2 production have been done and energy requirement estimations were not calculated and compared.A closely second flaw is that there is no discussion of H2 production efficiency depending on materials for water-splitting photocatalysts.Section 2 is probably the only meritorious section in the manuscript. I would encourage them to focus on important aspects of the ways in which materials for water-splitting photocatalysts has been coupled with other technologies to improve its efficiency or increase its application. For example, electrochemistry. This is a cutting-edge application of this technology, which has been inexplicably left out of their discussions. I should emphasize that the major portion of this manuscript i.e. section 2 but is a non-critical compilation of information from numerous papers that can be pulled from any database. They largely summarize removal data without providing mechanistic understanding of underlying photocatalytic or sorption phenomena. Clearly, the authors have put in considerable effort in tabulating previous publications in Table 1, but a table is not equivalent to a critical distillation of available information.
A useful review should focus on good publications and criticize the bad ones giving detailed explanations. Non-numerical results have been critically discussed in the review, then, it is not a support for the begginers or experts in the field, then, lower citations metrics will be obtained.
Author Response
Comments and Suggestions for Authors
There is increasing interest in technologies for water splitting since it has some inherent advantages over conventional H2 production.
This is an unnecessarily lengthy manuscript that summarizes literature information on materials for water-splitting photocatalysts. It also purports to provide information on the fundamentals of water splitting and "advanced photocatalysts." After closely reading the manuscript, I cannot recommend its publication in its current form as it lacks several important characteristics underlying an authoritative review. My comments are given below.
The biggest flaw with the manuscript is that it does not provide any new insights into the theory or applications of materials for water-splitting photocatalysts. Any authoritative review should critically consider previous publications and provide deeper understanding of underlying phenomena. Through the critical review, it should identify gaps in our current understanding thereby providing directions for future research. Unfortunately, this manuscript largely fails in this aspect. The authors for most part just collect previously published statements/results without figuring out underlying unifying phenomena. They do not even discuss whether earlier results are correct or not! No comparisons on H2 production have been done and energy requirement estimations were not calculated and compared.
RESPONSE
We appreciate the reviewer’s views on this aspect of the manuscript. We believe that within the intended scope of the manuscript, we have brought together and analysed relevant literature on the subject and have identified existing gaps that could be explore for future research. Particularly, we have shown that group IVB TMDCs have only been demonstrated in theory for their potential application in water splitting reactions and that there is potential for them to be investigated practically just as the group VIB TMDCs have been. We do not think that it is within the rights of the manuscript to judge published literature results on their correctness but to rather bring these together and compare them, which we have done.
A closely second flaw is that there is no discussion of H2 production efficiency depending on materials for water-splitting photocatalysts.
RESPONSE
We believe that Table 1 in the manuscript has summarized literature data on the H2 production efficiency for various catalysts for water-splitting photocatalysts under various experimental conditions. In section 3 of the manuscript, we have also compared and discussed the activities of some of the catalysts and shown reasons for the observed activities, especially in cases where there is activity enhancement as a result of the formation of composite catalysts with TMDCs.
Section 2 is probably the only meritorious section in the manuscript. I would encourage them to focus on important aspects of the ways in which materials for water-splitting photocatalysts has been coupled with other technologies to improve its efficiency or increase its application. For example, electrochemistry. This is a cutting-edge application of this technology, which has been inexplicably left out of their discussions.
RESPONSE
We thank the reviewer for providing this insight to the manuscript. We have included a paragraph under section 2.1 where we have discussed the coupling of water splitting technology with electrocatalysis, thermal catalysis and photovoltaic electrochemical cells to improve the hydrogen production in the photocatalytic process.
I should emphasize that the major portion of this manuscript i.e. section 2 but is a non-critical compilation of information from numerous papers that can be pulled from any database. They largely summarize removal data without providing mechanistic understanding of underlying photocatalytic or sorption phenomena. Clearly, the authors have put in considerable effort in tabulating previous publications in Table 1, but a table is not equivalent to a critical distillation of available information.
RESPONSE:
We believe that in section 3 of the manuscript, we have compared and discussed the activities of some catalysts for photocatalytic water splitting and shown reasons for the observed activities, especially in cases where there is activity enhancement as a result of the formation of composite catalysts with TMDCs.
A useful review should focus on good publications and criticize the bad ones giving detailed explanations. Non-numerical results have been critically discussed in the review, then, it is not a support for the begginers or experts in the field, then, lower citations metrics will be obtained.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Overall, this review collets a piece of good information about Transition metal-based dichalcogenides for photocatalytic water splitting.
However, the authors have not mentioned much about water splitting. The authors should provide more literature and examples in section 2.1.
Specific examples with their structures and significance should be presented for all three reported methods (2.2.1. Exfoliation, 2.2.2. Chemical vapour deposition, 2.2.3. Wet chemical synthesis)
Author Response
Comments and Suggestions for Authors
Overall, this review collets a piece of good information about Transition metal-based dichalcogenides for photocatalytic water splitting.
However, the authors have not mentioned much about water splitting. The authors should provide more literature and examples in section 2.1.
RESPONSE:
Section 2.1 discusses the general underlying principle and mechanism of photocatalytic water splitting. Specific examples as related to transition metal dichalcogenides have been provided and discussed in Section 3 of the
Specific examples with their structures and significance should be presented for all three reported methods (2.2.1. Exfoliation, 2.2.2. Chemical vapour deposition, 2.2.3. Wet chemical synthesis)
RESPONSE: We have revised the section and included Figures 4 – 8 to give schematic representations and examples of the various methods of synthesis of transition metals dichalcogenides.
Author Response File: Author Response.pdf
Reviewer 3 Report
The work deals with reviewing a family of catalysts for photocatalytic water splitting. The production of H2 from this reaction may interest readers of "Catalysts."
Only one Figure and one Table are presented in the manuscript, which seems very little to be a review. Therefore, the authors must include more Figures and Tables with the structure of the catalysts, how they act, the experimental results obtained, etc.
The paper's title could be slightly modified to include the type of catalyst: "Transition metal dichalcogenides MX2 in photocatalytic water splitting".
Author Response
Comments and Suggestions for Authors
The work deals with reviewing a family of catalysts for photocatalytic water splitting. The production of H2 from this reaction may interest readers of "Catalysts."
Only one Figure and one Table are presented in the manuscript, which seems very little to be a review. Therefore, the authors must include more Figures and Tables with the structure of the catalysts, how they act, the experimental results obtained, etc.
RESPONSE
We thank the reviewer for this observation. We have revised the manuscript and included Figures 2 – 8 which give further details on the preparation of TMDCs and their structures. Table 1 gives comprehensive information about the activities of the class of materials under various experimental conditions.
The paper's title could be slightly modified to include the type of catalyst: "Transition metal dichalcogenides MX2 in photocatalytic water splitting".
RESPONSE:
We have modified the title of the manuscript as suggested.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
All concerns have been carefully addressed, and it is suitable for publication in its present form.
Reviewer 3 Report
Accept in present form.
