β-Cyclodextrin-Silica Hybrid: A Spatially Controllable Anchoring Strategy for Cu(II)/Cu(I) Complex Immobilization
, Katia Martina 1,*, Elisa Borfecchia 2, Fernando Chávez-Rivas 2,3, Giancarlo Cravotto 1 and Gloria Berlier 2,*Round 1
Reviewer 1 Report
Present manuscript demonstrated the production of a stable and efficiently grafted silica-beta-CD hybrid catalysts in to two-step process and tested their activity by using different flexible amino groups as bearing spacers. Cu was used as an active site for performing click azide-alkyne cycloaddition reaction and correlation were deduced between catalytic activity and amino spacer-beta-CD ligand. Authors did an interesting study by extending their previously published work. Major part of the catalyst characterization was nicely explained by using sophisticated techniques. But still there are some experimental data missing for logical conclusions in this manuscript. Authors can find my below comments.
Final product analysis including dimers formation was done by using GC-MAS only. But I strongly recommend doing proton-NMR for further supporting the dimers products formation.
Authors observed nearly 50% yield loss with Si-TriAm-CD-Cu at 5th recycle. Why the catalyst is not stable?. And the quantitative data of Cu is missing in the present manuscript. I strongly believe, both qualitative and quantitative data of Cu is needed for reasonable conclusion for catalyst stability. So I would prefer to do ICP-OES prior finalizing the data.
Line 303: In EXAFS data, authors observed "certain modifications in the signal at higher R values, expected due to structural rearrangement of the system, while still containing highly dispersed Cu-species." EXAFS and TEM data doesn't provide accurate values of Cu dispersions so I would recommend doing N2O chemisorption experiments for fresh and used catalysts.
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Author Response
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Reviewer 2 Report
Review of the manuscript Catalysts-928318 – to Authors
This article presents a study were Cu-based multi-structured organic-inorganic silica catalyst was prepared and characterized. The used multi-technique analysis all demonstrated the successful incorporation and stability of modifiers, presence of Cu(II) and formation of Cu(I), with good reusability of the synthesised catalysts. The paper offers interesting design and characterization of the catalyst, Throughout the manuscript English language and style need to be heavily upgraded.
Abstract could benefit in clarity upon upgrades in English writing and style.
The introduction is very extensive, but jumps from one topic to another, one ligand to another, and should be more concisely and orderly written.
“The demand of functional materials” – not of, yes for.
“make them tuneable to produce smart materials” – different choice of word instead of produce?
“Literature research in organic-inorganic hybrid systems for catalysis indeed revealed that in general not-innocent ligands have not received much attention to date.” – references?
“nevertheless the evidence that Cu(I) is generated in the medium and that CD-Cu(II) is able to release Cu(I) species has still to be described” – the mechanism has still to be described?
“The selection of grafting procedure was proved to” – has proved
The last paragraph of the introduction is suggesting results in advance and is completely unnecessary, please remove.
Results and discussion – “Based on our previous experience on silica surface modification, amine-bearing silica materials were prepared.” – Reference to previous work.
“Spacers showed an increasing number of amino moieties, β-CD was directly bound to the silica (Si-NH-CD), it was grafted through a diethylenetriamine spacer(Si-DETA-CD) or it was grafted through different monoamino, diamino and triamino alkoxy silyl spacers to obtain Si-MonoAm-CD, Si-DiAm-CD and Si-TriAm-CD respectively. Finally, an amino alcohol spacer (Si-Gly-CD) was also studied.” – should be written more clearly.
“On the basis of our experience, as depicted in Scheme 1” – again reference.
“is recorded on a UV spectrophotometer” – was recorded.
“We supposed that the use of condensation reaction between silanol groups of the surface and alkoxy silane generates more stable amine-bearing silica materials, therefore it was discarded” TGA section is a bit chaotic. I don’t agree with cut off at 150°C. You should show the spectra from RT and maybe use the 150°C for calculation. Also water may easily remain until 200°C, so 150°C can’t ensure dry samples.
“Scope of the reaction with Si-TriAm-CD-Cu was to investigate” – Aim of the reaction
“moderate excess of catalyst was employed” – moderate?
“indicating the stability of the grafted functionalities” – some other word for functionalities?
“the result points to a decrease in the amount of Cu(II) in the catalyst, which can be related to a partial reduction to Cu(I),” – speculative
“represents an ideal counterpart of the IR and UV-Vis results discussed before.” – Is complementary, offers more insight, or something like that maybe better
“as-prepared and exhaust catalyst” – exhaust vs reused catalyst?
“which may lead to partial antiphase effects and ultimately dampen the amplitude of the EXAFS signal which respect to what is observed in CuIIO.” + “Certain modifications are however observed in the EXAFS signal structure at higher R values, underpinning a long-range structural rearrangement of the system, while still containing highly dispersed Cu-species.” – chaotic again, thoroughly upgrade please, only then the understanding may be clear.
“suggest the presence of very small (few nanometers) Cu nanoparticles, which can be seen as dark spots in both materials.” – TEM was not sufficiently utilized, I guess you should be able to do point electron diffraction. Maybe you have instrument limitations, but what you can most definitely do if average the electron diffraction. Instead of points you will obtain circles, but that would be interesting to see because it will bring more information. Please provide that.
Materials and Methods describe the experiment sufficiently.
“The synthesis of 6I-O-p-Toluenesulfonyl-β-CD was performed following published synthetic procedure” – reference? And it is necessary to describe the procedure
“the device has been designed” – was designed
Conclusions summarise the results quite nicely, minor English check could be beneficial.
“the synergic activity” – synergistic
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Authors made enough changes to the revised manuscript, and the experimental and discussion part looking reasonable to me. Therefore I would recommend publishing the revised version in "Catalysts" journal.
Author Response
We are happy the reviewer has acknowledged our efforts to improve the manuscript
Reviewer 2 Report
Review of the manuscript Catalysts-928318R2 – to Authors
The manuscript was upgraded in terms of language and clarity. The authors devoted considerable effort, still 2 issues remain:
I understand technical limitations of TEM may limit point spectra, but it should be easily possible to obtain average spectra, in line with my previous suggestion. Please provide something otherwise the discussion is not really up to the point.
EXAFS section is described better, still the difference between the results is not super convincing.
Other than that the manuscript can be accepted after minor revision.
Author Response
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The comments by the reviewer are in grey, our reply in black and the modifications to the manuscript are reported in blue.
Author Response File: Author Response.pdf
