S-Scheme System of MoS₂/Co₃O₄ Nanocomposites for Enhanced Photocatalytic Hydrogen Evolution and Methyl Violet Dye Removal under Visible Light Irradiation

Round 1

Reviewer 1 Report

Reviewer comments - Coatings-2117332

The authors of this manuscript reviewed the s-scheme system of MoS₂/Co3O₄ nanocomposites for enhanced photocatalytic hydrogen evolution and methyl violet dye removal under visible-light irradiation. The results reported in this manuscript deserve to be known by other researchers. But before the publication, several questions should be illustrated more clearly, to make the paper more readable and meaningful to readers. Detailed comments are as follows:

1.     Standardize value of 3,825 μmol/g/h, with a comma or without a comma

2.      None of the previously compared literature tabulated in Table 1 is MoS₂-composited photocatalysts. Kindly add related references (minimum 10) accordingly; they must be recent works. Include the type of lights (UV or visible lights) and compare the performance measurement in hydrogen production.

3.     Any specific reason why the XRD peak of 311 doesn’t appear in higher loading of Co₃O₄ in MoS₂/Co₃O₄ samples, especially MC-3 and MC-4

4.     Section 2.5 mentioned that solution was also stirred with the dark condition for 30 min to establish absorption-desorption equilibrium among photocatalysts and MV pollutants. However, Figures 6 (b) and (f) indicated differently. Kindly revise the graph according.

5.     “Electron paramagnetic resonance (EPR) spectra were recorded on a Bruker A300 at room temperature under atmosphere conditions”. Is this analytical contribution to the research work? If yes, kindly indicate the analysis clearly.

6.     It is recommended to indicate the values on top of each bar in the bar chart to ease the reader in understanding the research work

7.     How about the particle size after MoS2 was incorporated with Co₃O₄? Does the particle float or disperse well during the photocatalysis experiment?

8.     Improve the content in the abstract section to make it more comprehensive and add

Comments for author File: Comments.docx

Author Response

Dear Professor Sirawan Kaewsikoun (Editor) and Referees,

Thank you very much for your great efforts on handling our manuscript (coatings-2117332). We would like to express our deepest gratitude for the reviewers’ useful and constructive suggestions on our manuscript. We have modified and supplement the manuscript accordingly with the revised parts shown as red in the revised manuscript, respectively. A point by point response to the reviewers' comments is listed below.

Thanks again for your time and consideration.

We hope that the manuscript will be acceptable for publication after all these corrections.

Yours sincerely,

Edward L. Chen, PhD

Author Response File: Author Response.pdf

Reviewer 2 Report

The Manuscript "S-scheme system of MoS₂ /Co₃O₄ nanocomposites for enhanced photocatalytic hydrogen evolution and methyl violet dye re-moval under visible-light irradiation" by Tsung-Mo Tien, Edward L. Chen is devoted to the synthesis and study of the properties of MoS₂-Co₃O₄ nanocomposites with different content of Co₃O₄. In general, the topic of the study and the obtained results are interesting. However, there are a very large number of comments on the results and their presentation.

First, the level of English is very poor. Errors, omissions and inaccuracies already appear in the Abstract and the Title.

The Introduction is written in a very strange language, hard to read. It is necessary to rephrase some constructions in sentences. It is necessary to focus on the relevance and novelty of the proposed nanocomposite.

Materials and Methods

Row 106 - "dihydrate"

Row 110 – “Deionized water was used to make solutions to the examine.” – reformulate

Row 113 – “was adopted to” ?

Row 121 - Why authors use such a wide range of solvents - acetone, N-methyl-pyrrolidone, absolute ethyl alcohol and water. It would be enough to use acetone and water. It is also not clear from the description how the % ratio of cobalt oxide to molybdenum disulfide is calculated. Was this due to a change in the molar amount of the reactants? Then what ratio corresponds to the initial data - 1.2 mmol of Na₂MoO₄ 2H₂O and 2.6 mmol of CoCl₂ 6H₂O.

There is also no description of the preparation of pure Co₃O₄ and MoS₂, although they are mentioned in the text.

Scheme 1. Description of quantities of substances is made with errors (mmole). The Picture is very poor quality and blurry, needs to be improved.

Results

XRD. From the presented diffraction patterns in Fig. 1, the formation of a composite is completely unobvious. It is necessary to note in the Fig.1 the reflections corresponding to Co₃O₄ and MoS₂, because at first glance it seems that the cobalt oxide phase is absent in the material. The authors say that "peak intensity of Co₃O₄ became higher, which exhibited an extent in the amount of Co₃O₄ in the heterojunction", but in fact the only clear thing is a decrease of the reflection at 2θ = 14.4º. The Figure is also of very low quality.

SEM, TEM

Row 191. “It is declared that the dimension of MC-X was extremely decreased, the crystals phase of MoS₂ also keeps good crystallinity, as noted by the (002) primary peak recorded in the XRD analysis (Fig. 1).” X=?

Row 198 “During further testing, it could be found that the MoS₂ /Co₃O₄-4 nanocomposite is ultimately formed.” That is, the composite was first obtained, and then the % composition was determined?

Row 201. “The formation of the composite of MoS₂ /Co₃O₄ is broadly supposed to maintain an evident achievement on improving the charge carries separation capability of photocatalytic. The consistent dispersion of Mo, S, and Co elements can establish the functional construction of MoS₂ /Co₃O₄ nanocomposites”. It's not obvious!

Row 224. "Hence, the Co3O4 photocatalysts may be a valuable explanation to expand the visible light absorption of the MoS2 /Co3O4 nano-composites." This is an unsatisfactory explanation. The authors should completely rethink their approach to explaining the results

Row 232. Section 3.4 "XPS and N2 adsorption-desorption Analysis" is completely missing the description of N2 adsorption-desorption analysis.

All figures are of very low quality. The proposed illustrative material is very blurry. It is necessary to improve the quality of charts.

Sections 3.5 and 3.6 about the study of the properties of the resulting composite look interesting, but completely unreadable due to the large abundance of grammatical and stylistic errors in the text. The figures in the section are also difficult to understand.

The conclusions contain absolutely strange statements that do not correspond to the study: “It’s implying that Co₃O₄ acts as a critical factor in enhancing the photocatalytic capability of MoS₂/ Co₃O₄ nano-heterostructure.” The conclusions clearly need to be reformulated.

Author Response

Dear Professor Sirawan Kaewsikoun (Editor) and Referees,

Thank you very much for your great efforts on handling our manuscript (coatings-2117332). We would like to express our deepest gratitude for the reviewers’ useful and constructive suggestions on our manuscript. We have modified and supplement the manuscript accordingly with the revised parts shown as red in the revised manuscript, respectively. A point by point response to the reviewers' comments is listed below.

Thanks again for your time and consideration.

We hope that the manuscript will be acceptable for publication after all these corrections.

Yours sincerely,

Edward L. Chen, PhD

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

After the second review of the article "S-scheme system of MoS2 /Co3O4 nanocomposites for enhanced photocatalytic hydrogen evolution and methyl violet dye re-moval under visible-light irradiation" by Tsung-Mo Tien and Edward L. Chen, the most important remark still remains. This is a question of the level of English (see below)

Row 22. “H2” should use an index

Row 41. Space character in text

Row 57. Cobalt oxide should be written with a small letter. Here, maybe nanoparticles instead of nanomaterials?

Row 67. Space character in text

Row 69. “…catalysts displayed low photocatalytic capability due to their collection, insufficiency of surface active centers, and rapid photoexcited charge carriers recombination”. Collection?

Row 80. “Besides, Co3O4 receives the coordinated energy band gap energy potential coupled with MoS2 to improve a valid step-scheme (S-scheme) heterojunction due to the valence band (VB) of Co3O4 is close to the conduction band (CB) of MoS2 photocatalysts on previous studies [19].” The end of the sentence should be reformulated

Row 87. “sensibly” maybe, “well designed”?

Row 89. “Herein, sensibly designing and fabricating MoS2 /Co3O4 nanocomposites is proposed to reveal more surface active sites, shorten charge diffusion length and prompt numerous charge carriers redistribution, but it has not been reported.” It is not clear in the sentence what was not reported.

Row 102. “promarily”

Row 187 “Under the hydrothermal route” “arose”? The sentence should be reformulated

On Fig. 1 on the tab, the colors of the diffraction patterns of the samples do not match the colors of the main pattern. In addition, the estimated peak can only be determined with a very large assumption. It's at noise level.

Row 215. “As displayed in Fig. 2. a, b, obviously significant size pristine MoS2 and Co3O4 could be noted, respectively” Why respectively? Did the authors read their own text?

Row 253. The architecture for this system is that the less adding dosage of Co3O4 does not produce an apparent alteration during the light absorption capability of the MoS2/Co3O4 nanocomposites. Reformulate

Row 291. “As promote noted, MC-4 is particularly formed of Mo, S, O and Co elements, which include the entire elements of MoS2/Co3O4 nanocomposites.” It is very necessary to edit the language for a scientific text.

Very unsuccessful grammatical constructions in the text of the manuscript. The Article is real interesting and the authors corrected most of the comments. However, everything also needs to be revised in English. I leave this to the decision of the Editor.

Author Response

Dear Professor Sirawan Kaewsikoun (Editor),

Thank you very much for your great efforts on handling our manuscript (coatings-2117332). We would like to express our deepest gratitude for the reviewer useful and constructive suggestions on our manuscript. We have modified and supplement the manuscript accordingly with the revised parts shown as red in the revised manuscript.

Thanks again for your time and consideration.

Yours sincerely,

Edward L. Chen, PhD

Author Response File: Author Response.pdf