Deposition of Size-Selected Gold Nanoclusters onto Strontium Titanate Crystals for Water Splitting under Visible Light

Round 1

Reviewer 1 Report

In order for the article to become suitable for publication, it is necessary to take into account the following comments:

1. The size distribution of gold clusters, shown in Fig.2, is very wide. It is necessary to clearly write  how exactly the author carried out the deposition of gold clusters of a certain size. It is also necessary to provide experimental evidence that the author actually obtained samples with gold clusters with a narrow size distribution (with a size other than Au₂₀)
2. The title of the article is "Deposition of Size-Selected Gold Nanoclusters onto Strontium Titanate Crystal for Efficient Water Splitting Under Visible Light" . However, the article does not provide any experimental data confirming the efficient water splitting. Such results should be presented in the revised version.

Author Response

Catalysts - 1620314 

                                                         March. 19, 2022

                                      

RESPONSES TO THE COMMENTS

 

 

(Answered by Chuhang Zhang)

 

 

 

First of all, it is our pleasure to offer sincere thanks to the referees, who have reviewed our manuscript (Catalysts - 1620314), for their time, attention and comments. All the comments are very helpful for improving the quality of the manuscript. After a careful consideration, we now give a brief response to the comments and detail the changes in the revised manuscript.

 

 

 

COMMENTS FROM REF 1

 

COMMENT 1:

1. The size distribution of gold clusters, shown in Fig.2, is very wide. It is necessary to clearly write how exactly the author carried out the deposition of gold clusters of a certain size. It is also necessary to provide experimental evidence that the author actually obtained samples with gold clusters with a narrow size distribution (with a size other than Au₂₀)

 

ANSWER 1:

Thanks for this comment. In the condensation cell after sputtering, the sputtered materials including gold atoms, anions and cations are cooled down by collisions with buffer gas of helium. In this case, gold clusters (neutral, negatively and positively charged) with various of size are self-assembled in gas phase. After that, the clusters are guided by an OPIG to an ion deflector, and then charged species are deflected to a quadruple mass spectrometer (Q-MS), where size distribution of gold clusters are analyzed and displayed in terms of a mass-spectrum. Before deposition, proper parameters are set for Q-MS so that clusters with a specific mass-charge ratio are allowed to pass through the outlet of the Q-MS and deposit on the sample surface. Before deposition, there is a movable shield mounted between the Q-MS outlet and the sample platform to ensure no other clusters are deposited before selection. When deposition starts, the shield is opened so that selected clusters are deposited on the sample. We have detailed the description for this size-selection process in revised manuscript (see lines 73 - 75, 98 - 104 and lines 116 - 120). In order to present a comparable study to Au₂₀, we also present a SEM image for Au₃₀ on STO and corresponding size distribution in figure 3 in the revised manuscript (see figure 3(c) and (d)).

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COMMENT 2:

-----2.The title of the article is "Deposition of Size-Selected Gold Nanoclusters onto Strontium Titanate Crystal for Efficient Water Splitting Under Visible Light" . However, the article does not provide any experimental data confirming the efficient water splitting. Such results should be presented in the revised version.

 

ANSWER 2:

The author appreciate this comment. The maximum photo-current under the visible light reaches 20 μA/cm², which is comparable with the reported value on the Ref. 11, under the fact that the deposition amount of the gold atoms in Ref. 11 is a lot more than in this manuscript. However, the main target for this research is the size-specific water splitting efficiency under visible light and therefore author agree that the word ‘efficient’ may not proper. We have changed the title of the manuscript as ‘Deposition of Size-Selected Gold Nanoclusters onto Strontium Titanate Crystal for Water Splitting Under Visible Light’ (see title).

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Author Response File: Author Response.doc

Reviewer 2 Report

The paper submitted to Catalysts by Zhang regards the realization of size-selected gold nanoclusters grown on strontium-titanate crystal substrates to be used as co-catalysts (more precisely as photoanode) for photocatalytic water-splitting reaction. Nanoclusters are grown with a  pulsed power magnetron sputtering device coupled with quadrupole mass spectrometer that allows the size selection of the deposited clusters. The size-selected deposition appears to be confirmed by Scanning Electron Microscopy measurements and photocatalytic performance of the Au₁₆ photoanode results to be convincing and interesting for other researchers working in the same field. Nevertheless, beside the complete description of the deposition apparatus and the photocurrent measurements, the paper results still not very well presented and requires still some work before publication in this Journal; in particular:

• Extensive English revision is required; numerous sentences results not clear and not in the right English form, such as in lines 22-26 in the Introduction section, line 83 and 84 in the Materials and Methods section, lines from 110 to 112 in Results and Discussion and so on.
• Lines 37-38 require a reference
• The acronym IPCE (line 39) is not previously introduced in the text
• Line 45 also requires a reference: is not obvious that high power pulses in the magnetron sputtering conduct to high densities in the deposited material.
• Au_n nanoclusters are grown on STO Crystals: no mention about the orientation of the crystal is done;
• Referring to the previous point: there is no structural characterization of the investigated samples: have XRD measurements been performed? Au nanoclusters are oriented or randomly oriented? If the Au orientation is influenced by the substrate’s orientation does this orientation of the substrate play a role in the enhancement of the photocatalytic performance or it is not influent?   
• The photocatalytic activity of the Au/STO mechanism is only hinted and not extensively explained: maybe adding a sketch of the process can make this explanation more clear and complete.
• There are not enough data point at low n to determine that an oscillating behavior of the photocurrent is observed, though it could be possible that this is the case. The statement needs to be softened.
• It would be useful to state how many samples were measured for each NC size n.
• How were the error bars calculated in figure 5(a)?

Author Response

Catalysts - 1620314 

                                                         March. 19, 2022

                                      

RESPONSES TO THE COMMENTS

 

 

(Answered by Chuhang Zhang)

 

 

 

First of all, it is our pleasure to offer sincere thanks to the referees, who have reviewed our manuscript (Catalysts - 1620314), for their time, attention and comments. All the comments are very helpful for improving the quality of the manuscript. After a careful consideration, we now give a brief response to the comments and detail the changes in the revised manuscript.

 

 

 

 

 

COMMENTS FROM REF 2

 

COMMENT 1:

----- •Extensive English revision is required; numerous sentences results not clear and not in the right English form, such as in lines 22-26 in the Introduction section, line 83 and 84 in the Materials and Methods section, lines from 110 to 112 in Results and Discussion and so on.  

 

ANSWER1:

Thanks for this comment and the paper has been carefully edited by a native English speaker.

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COMMENT 2

-----Lines 37-38 require a reference. 

 

ANSWER 2:

Following this useful comment, a reference has been cited.

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COMMENT 3

----- The acronym IPCE (line 39) is not previously introduced in the text 

 

ANSWER 3:

The author appreciate this kind comment and the full name (incident photo-current efficiency) for the IPCE has been added in the manuscript (see line 40).

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COMMENT 4

----- Line 45 also requires a reference: is not obvious that high power pulses in the magnetron sputtering conduct to high densities in the deposited material.

 

ANSWER 4:

Following this useful suggestion, a new reference (ref. 12, line 47) supporting the statement that high power pulses in the magnetron sputtering conduct to high densities in the deposited material has been added in the revised manuscript.The index of the reference has been updated accordingly in the revised manuscript.

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COMMENT 5

----- Au_n nanoclusters are grown on STO Crystals: no mention about the orientation of the crystal is done.

 

ANSWER 5:

The STO used in this research has a <110> orientation and this information has been added in the revised manuscript (see line 49).

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COMMENT 6

----- Referring to the previous point: there is no structural characterization of the investigated samples: have XRD measurements been performed? Au nanoclusters are oriented or randomly oriented? If the Au orientation is influenced by the substrate’s orientation does this orientation of the substrate play a role in the enhancement of the photocatalytic performance or it is not influent?

 

ANSWER 6:

This is an excellent suggestion. The findings in this manuscript has indicated a strong contact between the STO and the Au_n. Therefore, it is quite reasonable to consider the orientation and the geometrical structure may be influenced by the crystal structure of the STO, which may in turn impact the photocatalytic performance. Actually, the author is now investigating the geometrical structure effect of the gold nanocluster on the photo-current. Relevant reports will be submitted soon.

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COMMENT 7

----- The photocatalytic activity of the Au/STO mechanism is only hinted and not extensively explained: maybe adding a sketch of the process can make this explanation more clear and complete.

 

ANSWER 7:

Following this suggestion, a sketch showing the scheme of the water splitting process on Au/STO has been added in the revised manuscript (see Fig. 6).

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COMMENT 8

----- There are not enough data point at low n to determine that an oscillating behavior of the photocurrent is observed, though it could be possible that this is the case. The statement needs to be softened.

 

ANSWER 8:

It is true that the data points are not enough to fully support the oscillation behavior. Therefore we have revised the sentence accordingly (see lines 190-192)

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COMMENT 9

----- It would be useful to state how many samples were measured for each NC size n.

 

ANSWER 9:

In this research, we performed the measurement 5 times for each NC size n and this information has been added in the revised manuscript (see line 160).

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COMMENT 10

----- How were the error bars calculated in figure 5(a)?

 

ANSWER 10:

As mentioned in comment 9, we have performed the PEC measurement 5 time for each NC size and calculate the average photo-current under 0.4 V vs. Ag/AgCl reference electrode. The error bar is calculated by taking the difference between maximum measured value and average value. We have added this information in the revised manuscript accordingly (see lines 163 - 165).

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Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

The article can be accepted in its present form.