Au@CdS Nanocomposites as a Visible-Light Photocatalyst for Hydrogen Generation from Tap Water
Marija Prekajski-Djordjevic
Round 1
Reviewer 1 Report
The manuscript titled “Au@CdS nanocomposites as a visible-light photocatalyst for 2 hydrogen generation from tap water” written by Ying-Ru Lin et al, is an interesting article that investigates the Au@CdS nano-composites that can have significant applications in photocatalytic tap water splitting under blue-LED light excitation. The authors synthesized the Au@CdS nanocomposites via the wet chemical and hydrothermal approaches at the lower reaction temperature and made an effort to fully characterized obtained materials with numerous methods. Nevertheless, I have a few comments, suggestions, and scientific questions, that I wish the authors to address.
I marked in yellow and red all the parts in the manuscript where I have some questions or comments. Comments and questions are given in PDF as “comment”.
I recommend publication of the manuscript in the Catalysts after the authors give the answers to questions and correct the errors.
Comments for author File: 
Comments.pdf
Author Response
Reviewers' comments:
The manuscript titled “Au@CdS nanocomposites as a visible-light photocatalyst for 2 hydrogen generation from tap water” written by Ying-Ru Lin et al, is an interesting article that investigates the Au@CdS nano-composites that can have significant applications in photocatalytic tap water splitting under blue-LED light excitation. The authors synthesized the Au@CdS nanocomposites via the wet chemical and hydrothermal approaches at the lower reaction temperature and made an effort to fully characterized obtained materials with numerous methods. Nevertheless, I have a few comments, suggestions, and scientific questions, that I wish the authors to address.
I marked in yellow and red all the parts in the manuscript where I have some questions or comments. Comments and questions are given in PDF as “comment”.
Comments and questions
This sentence should be written better (at least if it doesn't start with this "in additon").
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
HAVE or MAY HAVE??
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
This sentence is related to my question from the abstract, whether it is "HAVE" or "MAY HAVE"!
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
"blue-LED ligh excitation" shoud be explained (is it the simulation of visible light?!)
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
The begining of the results and the discussion section is not good!
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
The authors should make some kind of introduction at the beginning of this section, and not start immediately with the results without explaining exactly which synthesized samples they are talking about.
Response: Thanks for your reminder. We have amended this description in the revised manuscript. Figure 1 reveals the fabrication processes of Au@CdS nanocomposites by com-bining wet chemical and hydrothermal methods. First, Au nanoparticles were synthe-sized by a facile wet chemical method. Second, tween 20 can stabilize Au nanoparticles by vigorous stirring for 1 h. Third, Au nanoparticles were decorated with CdS to form Au@CdS nanocomposites under different CdS precursor concentrations and reaction temperatures for 3 h.
For example: first, describe which samples were synthesized - under which different conditions of concentration and temperature, and explaine why you do that, and then start with the results, and maybe it's better to start with the XRD + SEM results first, and then these HRTEM results, etc.
Response: Thanks for your reminder. We have re-ordered the figures in the revised manuscript.
Moreover, it is mandatory to describe exactly which sample or samples the HRTEM analysis was performed on (is it a sample synthesized with 5mM CdS at 100 C or some another?)
Response: Thanks for your reminder. We have re-ordered this description in the revised manuscript.
As mentioned before, it is mandatory to describe exactly which sample or samples the HRTEM analysis was performed on (is it a sample synthesized with 5 mM CdS at 100 C or some another?)
Response: Thanks for your reminder. We have added this description in the revised manuscript.
Is the subtraction of the instrument width taken into account? If it is not, it shod be!
Response: Yes, it is
CHANGE the symbols on all XRD images that indicate the phases, because in this scaled-down image both symbols look like triangles and are difficult to distinguish.
Response: Thanks for your reminder. We have changed the symbols in the revised manuscript.
Why was the sample with concentration 5 mM of the CdS chosen for further detail analysis ?Please explain.
Response: Thanks for your reminder. Due to the maximum HER of of Au@CdS nanocomposites has been obtained at CdS precursors of 5 mM.
Why was the sample with concentration 5 mM of the CdS synthesized at 100 C chosen for further XPS analysis ?Please explain.
Response: Thanks for your reminder. Due to the maximum HER of Au@CdS nanocomposites has been obtained at 5 mM CdS precursors and 100 °C.
And in the following please specify which are the appropriate reaction condition with the highest HER ?
Response: Thanks for your reminder. Therefore, based on the above results, the appropriate reaction conditions of 5 mM CdS precursors and 100 °C can grow Au@CdS nanocomposites with the highest HER under blue-LED light excitation.
Why was the sample with concentration 5 mM of the CdS synthesized at 100 C chosen for further analysis ?Please explain.
Response: Thanks for your reminder. Due to the maximum HER of Au@CdS nanocomposites has been obtained at 5 mM CdS precursors and 100 °C.
This is an incomplete sentence?? Maybe it should have been joined with the following sentence?
Response: Thanks for your reminder. To demonstrate that Au@CdS nanocomposites can also use for photocatalytic tap water splitting, herein, we use CdS NPs (without Au NPs) and Au@CdS nanocomposites (5 mM CdS precursors and 100 °C) to disperse in 50 mL tap water with 0.1 M sodium sulfide as a scavenger at pH = 12 under blue-LED light excitation (5 W, λmax = 420 nm), as shown in Figure 7d.
It shoud be mentioned in the conclusion that the influence of different synthesis conditions (concentration and temperature) was examined and to state in the conclusion which synthesis conditions proved to be the best?!
Response: Thanks for your reminder. The optimal Au@CdS nanocomposites at 5 mM CdS precursors and 100 °C achieve 1.041 (de-ionized water) and 1.204 mmolh−1g−1 (tap water) under blue-LED light exci-tation, up to 175.3 and 512.3 times over CdS NPs, respectively.
Are both synthesis methods together or just one of those methods? Specify.
Response: Thanks for your reminder. Au@CdS nanocomposites have been successfully synthesized by the combination of feasible wet chemical and hydrothermal approaches at lower reaction temperatures.
I recommend publication of the manuscript in the Catalysts after the authors give the answers to questions and correct the errors.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments to the authors
The present manuscript reports the synthesis of Au@CdS nanocomposites for the generation of hydrogen from tap water under visible light. Designing effective and economical photocatalysts for water splitting to generate hydrogen has received increased attention in the last decades due to energy crises in the near future. The manuscript contain is well written and the research work is supported with scientific references. The manuscript contain major flaws, therefore I suggest major revision for quality enhancement, which are given bellow.
1. The manuscript contains a large number of grammatical and typing mistakes which should be carefully read and remove and the language need sufficient improvement.
2. Mention the scientific results obtained in the abstract.
3. Explain the novelty of your work as a lot of work are published on Au@CdS materials for water splitting in the introduction.
4. Page 1, line 44-45, modify the sentence as “De-ionized water refers to pure water that has obtained by removing ionic impurities from tap water”
5. Discuss some catalytic applications of Au and CdS in the introduction section. Also discuss the advantages of water splitting and hydrogen gas.
6. The authors should properly correlate the XRD data with the results presented in the manuscript.
7. Modify the sentence on page 7, line 201-202 as “The UV-vis absorption spectra of CdS NPs and Au@CdS nanocomposites (5 mM CdS precursors and 100 °C) are shown in the figure 6a”. Follow such modifications in the whole manuscript.
8. The characterization of the materials should be discussed before describing their catalytic activity. Therefore Figure 6 and their discussion should be kept after figure 4 and before figure5.
9. Discuss the mechanism of photocatalyst by using and citing this article “Journal of Environmental Chemical Engineering 8 (2020) 104364”.
10. Keep all the figures after their discussion.
11. Insert pH on the x-axis of Figure 8a and 8b.
Author Response
Reviewers' comments:
The present manuscript reports the synthesis of Au@CdS nanocomposites for the generation of hydrogen from tap water under visible light. Designing effective and economical photocatalysts for water splitting to generate hydrogen has received increased attention in the last decades due to energy crises in the near future. The manuscript contain is well written and the research work is supported with scientific references. The manuscript contain major flaws, therefore I suggest major revision for quality enhancement, which are given bellow.
Response: Thanks for the pertinent and positive comments.
- The manuscript contains a large number of grammatical and typing mistakes which should be carefully read and remove and the language need sufficient improvement.
Response: Thanks for your reminder. We have amended grammatical and typing mistakes in the revised manuscript.
- Mention the scientific results obtained in the abstract.
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
- Explain the novelty of your work as a lot of work are published on Au@CdS materials for water splitting in the introduction.
Response: Thanks for your reminder. There are no reports about using Au@CdS nanocomposites for photocatalytic tap water splitting under blue-LED light (as the visible light) excitation. De-ionized water refers to pure water that has been obtained by removing ionic impurities from tap water [1]. Therefore, if hydrogen can be generated by directly decomposing tap water through photocatalysts, the cost and time of purifying tap water into de-ionized water can be effectively reduced, thereby contributing to the practical application of photocatalysts.
- Page 1, line 44-45, modify the sentence as “De-ionized water refers to pure water that has obtained by removing ionic impurities from tap water”
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
- Discuss some catalytic applications of Au and CdS in the introduction section. Also discuss the advantages of water splitting and hydrogen gas.
Response: Thanks for your reminder. We have added some descriptions in the revised manuscript.
- The authors should properly correlate the XRD data with the results presented in the manuscript.
Response: Thanks for your reminder. This variation of HER of Au@CdS nanocomposites is consistent with the observation of average crystalline sizes. The maximum average crystalline sizes and HER have been obtained at CdS precursors of 5 mM. This result is ascribed to self-nucleation becoming more and more evident under high concentrations of CdS precursors, leading to an increase in the recombination rate of electron-hole pairs for decreasing photocatalytic hydrogen production by increasing the amount of CdS NPs. This variation of HER of Au@CdS nanocomposites is also consistent with the observa-tion of average crystalline sizes. However, the maximum average crystalline sizes and HER are obtained at the reaction temperature of 100 °C. This result shall be attributed to the accelerated self-nucleation growth becoming more and more evident at higher reaction temperatures, leading to an increase in the recombination rate of electron-hole pairs for decreasing photocatalytic hydrogen production by increasing the amount of CdS NPs.
- Modify the sentence on page 7, line 201-202 as “The UV-vis absorption spectra of CdS NPs and Au@CdS nanocomposites (5 mM CdS precursors and 100 °C) are shown in the figure 6a”. Follow such modifications in the whole manuscript.
Response: Thanks for your reminder. We have amended this description in the revised manuscript.
- The characterization of the materials should be discussed before describing their catalytic activity. Therefore Figure 6 and their discussion should be kept after figure 4 and before figure5.
Response: Thanks for your reminder. We have amended these figures in the revised manuscript.
- Discuss the mechanism of photocatalyst by using and citing this article “Journal of Environmental Chemical Engineering 8 (2020) 104364”.
Response: Thanks for your reminder. We have updated this reference in the revised manuscript.
- Keep all the figures after their discussion.
Response: Thanks for your reminder. We have amended these figures in the revised manuscript.
- Insert pH on the x-axis of Figure 8a and 8b.
Response: Thanks for your reminder. We have inserted pH on the x-axis of Figures 8a and 8b.
- Zhang, M.; Gu, P.; Yan, S.; Pan, S.; Dong, L.; Zhang, G. A novel nanomaterial and its new application for efficient radioactive strontium removal from tap water: KZTS-NS metal sulfide adsorbent versus CTA-F-MF process. Chem. Eng. J. 2020, 391, 123486, doi:https://doi.org/10.1016/j.cej.2019.123486.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Sufficient medifications were made but some changes/modifications suggested were not proporly incorporated e.g point 6, 9 and 11.
6. XRD is not prperly correlated,
7. Mechanism is not clearly explained in the ligh of mentioned article
11. pH of the medium in not inserted in figure 9.
Author Response
Sufficient medifications were made but some changes/modifications suggested were not proporly incorporated e.g point 6, 9 and 11.
- XRD is not prperly correlated,
Response: Thanks for your reminder. This variation of HER of Au@CdS nanocomposites is consistent with the observation of average crystalline sizes. The maximum average crystalline sizes and HER have been obtained at CdS precursors of 5 mM. This result is attributed to the self-nucleation to form CdS NPs becomes more and more evident under the high concentration of CdS precursor, resulting in more CdS NPs in the photocatalyst per unit mass, which makes the photocorrosion phenomenon more obvious, thereby reducing the photocatalytic hydrogen production. This variation of HER of Au@CdS nanocomposites is also consistent with the observation of average crystalline sizes. However, the maximum average crystalline sizes and HER are obtained at the reaction temperature of 100 °C. This result shall be attributed to the accelerated self-nucleation to form CdS NPs becoming more and more evident at higher reaction temperatures, resulting in more CdS NPs in the photocatalyst per unit mass, which makes the photocorrosion phenomenon more obvious, thereby reducing the photocatalytic hydrogen production. Therefore, based on the above results, the appropriate reaction conditions of 5 mM CdS precursors and 100 °C can grow Au@CdS nanocomposites with the highest HER under blue-LED light excitation.
- Mechanism is not clearly explained in the ligh of mentioned article
Response: Thanks for your reminder. We have amended this description and Fig. 8 in the revised manuscript.
- pH of the medium in not inserted in figure 9.
Response: Thanks for your reminder. We have inserted the medium in Fig. 9.
Author Response File: Author Response.docx
