Visible-Light-Driven CO2 Reduction into Methanol Utilizing Sol-Gel-Prepared CeO2-Coupled Bi2O3 Nanocomposite Heterojunctions
, Ahmed Shawky 2,*, Sharif Fakhruz Zaman 3, Katabathini Narasimharao 1, Mohamed Abdel Salam 1, Abdulmohsen Ali Alshehri 1, Nezar H. Khdary 4, Sulaiman Al-Faifi 1 and Abhishek Dutta Chowdhury 5
Round 1
Reviewer 1 Report
MANUSCRIPT – CATALYSTS - 1937603
In this manuscript, Visible-light-driven CO2 reduction into methanol utilizing sol-gel prepared CeO2-coupled Bi2O3 nanocomposite heterojunctions, the authors have synthesized visible-light photocatalysts composed of bismuth oxide (Bi2O3) and cerium oxide (CeO2) nanocomposite of different wt. % ratios and studied its impact on photocatalytic reduction of CO2 to CH3OH.
General comments
1. The language must be checked with the native English speaker.
2. The whole manuscript comprises concise sentences. Better to rewrite some to a proper sentence format.
Significant comments that should be addressed
Introduction
1. This section is very crisp and simple. I feel it could be enhanced with other metals/metal oxides/semiconductors etc., to provide much more information to the readers.
2. Schematic illustration could be provided, if possible.
Experiments
1. 5 wt% corresponds to 50 mg or 52mg. Can you explain this for other wt% too?
2. Better to provide a photo of a homemade photoreactor
3. Line 312-spread should be replaced with dispersed
4. Reusability of photocatalyst is without any treatment?
Results and discussion
1. Fig 1 – mentioned sample a is for CeO2, but it is labelled in RED, change the font to black
2. Provide standard JCPDS for Bi2O3 in figure 1.
3. Considering 5 wt%, even though it is a minimum, I believe it is better to redo the XRD and double-check it.
4. Peaks c, d, and e do not show the hkl of CeO2; why are other peaks not indexed?
5. Fig 2c contradicts the result of XRD, where the change is observed. So, in this case, a better explanation is necessary.
6. Increasing the wt% of Bi2O3 results in elongated structures. Please explain what favours this growth mechanism.
7. Also, in the case of Bi2O3, the ratio of nanoparticles is higher when compared to elongated structures. Please explain why?
8. Images show too much aggregation even after using a surfactant. Explain why?
9. Why is the 15 wt% TEM image missing? As you mentioned, is it an optimal % with high efficiency? It is necessary to provide it.
10. Also, provide EDAX for the pristine and heterostructures to have numerical data for wt%.
11. Provide BET graph representation for other wt% also
12. What is the pore size for other wt%?
13. Provide XPS scan survey for 15 wt%
14. Fig 5 – interpretation for 20 wt% is missing for absorption edge and bandgap in the paragraph
15. Fig 5 – represent in vice versa manner, Tauc plot as Figure and inset as absorption spectra to have better bandgap visibility.
16. Bandgap numbers in the Tauc plot are not visible; change the colour for better visibility
17. Production rate of CH3OH for 15 & 20 wt% compared to CeO2 is 15.4 & 15.7 times, it is not 17.5 fold; please verify it
18. If the production rate of CH3OH is higher than 20 wt%, then why is 15 wt% considered optimal?
19. PL spectra – 20wt% interpretation is missing in the paragraph
20. In PL spectra, both for 15 & 20 wt% intensity is almost overlapping
21. What is the quenching % for 20 wt%?
22. Fig 7b – Photocurrent value is higher for 20wt% than 15wt%, better check it
23. Line 209-210 – it should be replaced for 2.8 g L-1 rather than explaining for 3.5 g L-1
24. Why is the recyclability study limited to 5 cycles even though it exhibited 98% of efficiency?
Conclusion
Not sure how did you conclude 18.5% CH3OH generation? be specific.
Author Response
We appreciate your kind revision. The responses to the comments are given one-by one in the attached file
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Authors have synthesized CeO2-coupled Bi2O3 nanocomposite heterojunctions by using sol-gel technique and then they have done visible-light-driven CO2 reduction into methanol medium. Significant amount of work has been done however, they can incorporate following comments:
1) The Introduction part is too short and needs some improvements. Author should use cite more related articles from literature to improve the introduction part.
2) The portion of XRD could be improved and author could add some parameters of XRD (Like lattice parameters, particle size, dislocation density packing factor etc.) and explain the effects of these parameters for photocatalytic activity.
3) In the TEM results authors may add the effect of heterojunction for improved photocatalytic activity.
Author Response
We appreciate your kind revision. The responses to your valuable comments are given in the attached file
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear authors,
Still, i feel the introduction section can be improved.
Schematic illustration could be provided, if possible.
For this question, you have mentioned only the review article needs an illustration, but my suggestion is to provide a kind of graphical abstract for the whole work.
Author Response
Dear authors,
Still, i feel the introduction section can be improved.
Response: We thank the reviewer for his comment. We have tried our best this time to improve the introduction part. We hope it is okay this time
Schematic illustration could be provided, if possible.For this question, you have mentioned only the review article needs an illustration, but my suggestion is to provide a kind of graphical abstract for the whole work.
Response: We thank the reviewer for his comment. We have made the graphical abstract as follows (attachment)
Author Response File: Author Response.pdf
