Hydrogenation of HOPG-Supported Gold Nanoparticles: Surface or Volume?
Round 1
Reviewer 1 Report
Please find my recommendations in the attached file.
Comments for author File: 
Comments.pdf
Author Response
To Reviewer #1
Many thanks for your valuable comments that helped us to improve the quality of the manuscript.
- The introduction can be improved by the main review articles on AuNPs organic reactions and hydrogenation processes (references…)
Answer: Thanks a lot for this amendment. References [17–24] were added.
- The figures 1c and 2b presented herein, were also exist in their previous paper (ref.23). I do not know if this is right! It is better to transfer into the SI.
Answer: Thanks a lot for your comment. We agree that these two figures were used in our previous work. We suppose that Fig. 1c can be excluded from the manuscript, indeed, as for our experiments Auger-spectroscopy is a standard method of elemental analysis. Relevant changes have been added to the manuscript. As for Fig. 2b, we would like it to remain. In “3.1 Measurements” we use this picture only to demonstrate qualitative changes in the local electronic structure in more explicit form for readers. We suppose that this figure is good enough to demonstrate such changes and in our opinion there is no need to change it.
- What does “an average height of the nanoparticles was approximately 1.5–2 nm” means? Did the authors mean the size of the nanoparticles?
Answer: As nanoparticles have oblate spheroidal form there is a difference between lateral size of nanoparticles (5-6 nm) and their height respectively to the HOPG surface (1.5-2 nm). In the manuscript we have to use both parameters to describe the form of the nanoparticles more accurately.
- The authors synthesized small sizes (1.5-2) of nanoparticles. What about of using different sizes of AuNPs (starting with higher initial concentration of HAuCl4 in the aqueous solution) and compare their activity with the present?
Answer: Thanks a lot for your amendment. This problem was elucidated in our previous work [Nanomaterials, 2019, 9(3), 344. DOI: 10.3390/nano9030344]. We have shown that an increase in the size of nanoparticles to up to 10 nm led to hydrogen chemisorption being inhibited and unable to be detected.
- Theoretical calculations on using different sizes of AuNPs will give additional support to their observation and conclusion on the surface dependence instead of volume.
Answer: Thank you for this amendment. In our previous work [Doklady Physical Chemistry, 2016, 470 (1), 125. DOI: 10.1134/S0012501616090013] we have shown that for clusters Aun (n=13, 20, 55, 100, 147) size effect has no noticeable influence on hydrogen adsorption. A bit later [Nanomaterials, 2019, 9(3), 344. DOI: 10.3390/nano9030344] we have proven experimentally that hydrogen chemisorption become inhibited only when the nanoparticle size increase up to 10 nm. In this case, quantum-chemical simulation of hydrogen adsorption for nanoparticles 5-10 nm in size can be of high value. Unfortunately, such calculations are extremely difficult, and we do not have enough resources to carry them out.
- How the authors exclude the possibility of the gold nanoparticles size change during the hydrogenation experiments? Did they check by STM experiment the size of the AuNPs after the hydrogenation process?
Answer: Thank you for this amendment. Of course, such a change in size could indicate the diffusion of hydrogen in the nanoparticle. The question of the size arose before us even in our very first works [Nanotechnologies in Russia, 2013, 8(1-2), 36. DOI: 10.1134/S1995078013010059]. We observed the selected particle indeed and compared its sizes before and after interaction with hydrogen. We found no size change. Unfortunately, the absence of changes in size does not allow us to declare unequivocally the absence of diffusion. So we just noted this fact without any interpretation.
- The manuscript needs extensive editing of English language.
Answer: Thank you for this amendment. We have added relevant changes to the manuscript according to recommendations of AJE (Certificate 2A26-BB42-6BB6-AAB9-56C4).
Author Response File: Author Response.pdf
Reviewer 2 Report
This manuscript sheds light on the nature of hydrogen species generated from H2 sorption on supported Au nanoparticles, concluding that that no hydrogen dissolution occurs, but all changes in their electronic structure are associated with surface processes, in contrast to other noble metals. The manuscript is nicely presented, the conclusions regarding the position of a H atom on Au cluster are useful, thus publication in Nanomaterials is recommended. In Figure 7 it is shown the metastable position of a hydrogen atom in the Au12H system (by the way, there is reference in the text regarding Figure 7). The authors should also add in the Figure the structure of the energetically more favorable state after displacement of the hydrogen atom from the equilibrium position.
Author Response
Reviewer #2
Many thanks for your valuable comments that helped us to improve the quality of the manuscript.
Amendment: In Figure 7 it is shown the metastable position of a hydrogen atom in the Au12H system (by the way, there is reference in the text regarding Figure 7). The authors should also add in the Figure the structure of the energetically more favorable state after displacement of the hydrogen atom from the equilibrium position.
Answer: Thank you very much for this amendment. The reference regarding Figure 7 was added to the text. As for H atom, we have calculated that its position over the surface of gold cluster is more stable in energy, but we did not watch the whole evolution of the system from initial to the final state. According to our previous works [Nanotechnologies in Russia, 2016, 11 (1-2), 7. DOI: 10.1134/S1995078016010031. and Doklady Physical Chemistry, 2016, 470 (1), 125. DOI: 10.1134/S0012501616090013 ] we can expect that H atom position “bridge” is a bit more favorable in comparison to “a top” and “hollow”.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors performed the proposed corrections and additions according to the reviewer comments. I recommend to be published.
