Enhanced Photocatalytic Performances of SnS2/TiO2 Composites via a Charge Separation Following Z-Scheme at the SnS2/TiO2{101} Facets
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors proposed enhanced photocatalytic performances via SnS2-TiO2 facets. The topic is critical regarding the application of TiO2-based photocatalyst. This work has well presented the results and can be accepted for publication. Some minor concerns should be addressed before moving forward.
1. Lots of Error info in the manuscript; those should be corrected.
2. Fig.6, it is not accurate to directly compare the Raman intensities; the Raman is used to identify the specific component while it is hard to compare the intensities among various datasets.
3. XPS data identified the existence of Ti-S; is there any other characterization that can further confirm this?
4. All figure resolution should be improved.
Comments on the Quality of English Language
Minor editing.
Author Response
Comments and Suggestions for Authors Review 1
The authors proposed enhanced photocatalytic performances via SnS2-TiO2 facets. The topic is critical regarding the application of TiO2-based photocatalyst. This work has well presented the results and can be accepted for publication. Some minor concerns should be addressed before moving forward.
Author Response:
We appreciate the reviewer’s positive suggestions and valuable comments. We added responses to the reviewer’s comments below.
- Lots of Error info in the manuscript; those should be corrected.
Author Response:
We appreciate the reviewer's comments on the formatting errors and apologize for that. The references previously indicated as "Error! Reference source not found" were due to formatting issues, which have now been rectified and updated.
- Fig.6, it is not accurate to directly compare the Raman intensities; the Raman is used to identify the specific component while it is hard to compare the intensities among various datasets.
Author Response:
In fact, what the review mentioned in Figure 6 must be for the photoluminescence spectra, not for Raman. The intensity changes in Fig. 6(c) are shown to explain the trend of the reduced PL intensities with increasing SnS2 ratios, which can be correlated with reduced recombination rates and charge separation across the SnS2/TiO2 heterojunction. The Raman spectra the reviewer mentioned are in Figure 5. We appreciate the reviewer’s comment.
- XPS data identified the existence of Ti-S; is there any other characterization that can further confirm this?
Author Response:
We appreciate the reviewer's comment on XPS. As the reviewer knows, XPS fitting can be quite arbitrary if the spectral feature is not pronounced. Thus, it may not be clear-cut evidence for the presence of the Ti-S bonds. Despite that, XPS is a unique tool that can probe the interfacial bonding state. We assume the structural heterogeneity of the real composite samples does not allow unambiguous evidence for that. Even though it’s not direct evidence for the Ti-S bonding, HRTEM images indicate a direct contact between SnS2 and TiO2, suggesting the possible existence of a chemical bonding between SnS2 nanoparticles at the edges of the TiO2 nanosheets. There is also a possibility of Sn-O bonding even though Sn 3d peak does not show any distinct feature. The following change was made to the manuscript.
Changes in the manuscript: (page 7, line 215).
“In addition, the broad Sn 3d spectral shape of the SnS2/TiO2 may suggest a possible contribution of Sn-O bonding even though it is not resolved.”
- All figure resolution should be improved.
Author Response:
Thank you for the reviewer’s comment. The manuscript now includes updated figures with improved resolution.
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors investigated the photocatalytic activity in the degradation of dyes of a heterojunction between SnS2 and TiO2. Despite high photoactivity of the composites (removal degree of about 100% within 1 h), there are several issues which should be solved before the acceptance:
1. There are several formatting and grammatical errors.
2. Some references are not shown in the text with the phrase "Error! Reference source not found" (see please p. 3-5, 8, etc.).
3. The authors studied the decomposition of methylene blue and Rhodamine B, which has already been overstudied. The photoactivity towards other emerging pollutants (e.g., antibiotics, phenolic compounds, etc.) should be elucidated.
4. The authors demonstrated that the composites exhbited high activity (removal degree of about 100% within 1 h). However, the concentration of dyes was very low (e.g., 3.75 ppm for Rhodamine B). It is necessary to study the photoactivity at higher pollutant concentrations.
5. Moreover, the authors did not indicate the adsorption capacity towards dyes.
6. The data in Table 1 indicate that there are more active materials in relation to higher concentrations of pollutants. What is the advantage of this work?
7. I would also recommend to determine the degradation products for at least one dye.
Comments on the Quality of English LanguageMinor editing is required.
Author Response
Comments and Suggestions for Authors Review 2
In this manuscript, the authors investigated the photocatalytic activity in the degradation of dyes of a heterojunction between SnS2 and TiO2. Despite the high photoactivity of the composites (removal degree of about 100% within 1 h), there are several issues which should be solved before the acceptance:
Author Response:
We appreciate the reviewer’s insightful and valuable comments. We added responses to the reviewer’s comments below.
- There are several formatting and grammatical errors.
Author Response:
We appreciate the reviewer's comments on the formatting errors and apologize for that. The references previously indicated as "Error! Reference source not found" were due to formatting issues, which have now been rectified and updated.
- Some references are not shown in the text with the phrase "Error! Reference source not found" (see please p. 3-5, 8, etc.).
Author Response:
We apologize for the formatting issue. The figures previously indicated as "Error! Reference source not found" were due to formatting errors, which have now been rectified and updated (Please see the highlighted version of the manuscript).
- The authors studied the decomposition of methylene blue and Rhodamine B, which has already been overstudied. The photoactivity towards other emerging pollutants (e.g., antibiotics, phenolic compounds, etc.) should be elucidated.
Author Response:
We appreciate the reviewer’s valuable suggestion. As the reviewer mentioned, MB and RhB are popular and overstudied dyes and that’s why they were selected in this study because the focus of this study is on the interface formation between SnS2 and TiO2 with increasing SnS2 in the composites. We would definitely move on to study the behavior of other dyes or organic contaminants such as phenol, but it is beyond the scope of the present study and the present level of understanding of the composites of SnS2 and TiO2. We would appreciate the reviewer’s kind understanding on this issue.
- The authors demonstrated that the composites exhibited high activity (removal degree of about 100% within 1 h). However, the concentration of dyes was very low (e.g., 3.75 ppm for Rhodamine B). It is necessary to study the photoactivity at higher pollutant concentrations.
Author Response:
We appreciate the reviewer’s suggestion. We understand the need to study at higher concentrations, but the main variable in this study is the SnS2 ratio in the composites and the concentration of RhB is optimized in a dilute range for the observation of a change in the performance of the composites with varying SnS2 ratios. For a fair enough evaluation of the high concentration performances, we believe it needs concentration-dependent performances of the composites which would require an extensive amount of work and analysis. Thus, we would appreciate the reviewer’s kind understanding regarding the reason for not extending the scope of the present study to the high concentrations.
- Moreover, the authors did not indicate the adsorption capacity towards dyes.
Author Response:
We appreciate the reviewer's comment. All the samples were kept stirring in the dark for 60 minutes to achieve adsorption-desorption equilibrium of the MB and RhB dyes. We added Figure S11 to illustrate the changes in the absorbance in the dark possibly due to the adsorption of dyes onto the catalyst. The absolute amount of changes in the dark was limited to about 10 % and was in accordance with the surface area shown in Figure S9.
Changes in the manuscript: (page 8. line 240)
“The changes in the concentration of both dye solutions with the catalyst present in the dark were limited to 3 – 14 % possibly due to the adsorption capacity of the catalysts (Figure S11).”
Figure S11. Photodegradation rates are shown as plots of C/Co vs time in the dark for (a) MB and (b) RhB.
- The data in Table 1 indicate that there are more active materials in relation to higher concentrations of pollutants. What is the advantage of this work?
Author Response:
We appreciate the reviewer's comment. Table 1 summarizes the composite systems with the heterojunctions of SnS2 and TiO2, particularly with the Z-scheme mechanism and definitely, there are reports on composites with higher performances. However, a direct comparison of the absolute performances is not easy since a detailed condition for photocatalytic evaluation (e.g., illumination condition, concentrations, and size of the system etc) can be quite different from each other. Instead of comparing the absolute performances, the table can be used to compare systems and conditions that can be explained with a similar charge separation mechanism, which is the main focus of the present manuscript.
Changes in the manuscript: (page 10, line 292)
“Composite systems with SnS2 and TiO2 heterojunctions listed in Table 1 were also proposed to follow either type II heterojunction or direct Z-scheme depending on the detailed preparation and evaluation conditions.”
- I would also recommend to determine the degradation products for at least one dye.
Author Response:
We appreciate the reviewer's suggestion regarding the determination of degradation products. Although the degradation products were not determined in this study due to the limitation of our experimental capability, RhB and MB degradation pathways were overstudied as the reviewer mentioned. Following changes were made to the revised manuscript to discuss the subsequent degradation pathways.
Changes in the manuscript: (page 10, line 323)
“Although the degradation products were not determined in this study, the subsequent degradation of both dyes was suggested to undergo the following pathways. The degradation of RhB was suggested to be initiated by the removal of ethyl groups, resulting in intermediate products such as phthalic acid, benzyloxyamine, and benzoic acid [54]. Similarly, the degradation of MB was suggested to begin with the removal of methyl groups, resulting in the formation of intermediates such as N-methyl formamide, azure A, B, and C, as well as thionine [55-57].”
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsAccept.
