Graphene Oxide Decorated with Ag and CeO2 Nanoparticles as a Catalyst for Room-Temperature 4-Nitrophenol Reduction
Round 1
Reviewer 1 Report
This manuscript reports Graphene Oxide Decorated with Ag and CeO2 Nanoparticles as Catalyst for Room-Temperature 4-Nitrophenol Reduction. The authors fully characterized GO, Ag and Ag-CeO2/GO nano catalysts, and compared the catalytic performance of Ag/GO, with other Ag-CeO2/GO to prove the role of metal center of Ag-CeO2/GO in the reduction reaction.
Some specific suggestions are as follows:
1. Other catalysts like Metal-organic Frameworks also used for the reduction of Nitroarens. The authors should include the literatures.
2. The authors have mentioned the Nano sized Ag and CeO2 particles with sizes up to 30 and 5 nm, respectively. The authors should provide an experimental evidence for the size by SEM and TEM images.
3. In p3 line 142 “certain mass of GO was introduced into 50 ml of water and subjected to ultrasonic” Clarify the mass of GO used in the experiment.
- UV spectra Fig S3 of 4-NP and 4-AP are not enough to prove the reduction product is 4-AP, HPLC characterizations or mass spectra are needed.
5. Provide a complete progressive decrease of the reactant signal UV spectra of the one set of complete reduction reaction to know the proper formation of respective aminophenol by reduction of Nitro phenol.
- PXRD patterns after reduction should be checked to confirm the integrity of the catalysts structure.
7. Provide a schematic of mechanism of catalytic conversation reaction using the catalyst.
8. Provide the AFM images of the formation of layer formation on the GO surface.
9. Conclusion should be in one paragraph not in bullet points.
Author Response
Dear Reviewer, hereby we submit our manuscript entitled “Graphene oxide decorated with Ag and CeO2 nanoparticles as catalyst for room-temperature 4‑nitrophenol reduction” written by Aleksey Taratayko and Dr. Grigory Mamontov after correction for publication as a full paper in the Catalysts.
Thank you for your interest to our manuscript and helpful questions and remarks. We improved the manuscript according to your recommendations. Please, find responses on questions below.
Reviewer:
This manuscript reports Graphene Oxide Decorated with Ag and CeO2 Nanoparticles as Catalyst for Room-Temperature 4-Nitrophenol Reduction. The authors fully characterized GO, Ag and Ag-CeO2/GO nano catalysts, and compared the catalytic performance of Ag/GO, with other Ag-CeO2/GO to prove the role of metal center of Ag-CeO2/GO in the reduction reaction.
Some specific suggestions are as follows:
- Other catalysts like Metal-organic Frameworks also used for the reduction of Nitroarens. The authors should include the literatures.
Response: We added references [70-72] about the application of MOFs for reduction of nitroarenes.
- The authors have mentioned the Nano sized Ag and CeO2particles with sizes up to 30 and 5 nm, respectively. The authors should provide experimental evidence for the size by SEM and TEM images.
Response: Thank you for comment. Yes, electron microscopy (both SEM and TEM) is informative method for analysis of catalysts. Unfortunately, we don’t have possibility to carry out SEM and TEM studies quickly.
- In p3 line 142 “certain mass of GO was introduced into 50 ml of water and subjected to ultrasonic” Clarify the mass of GO used in the experiment.
Response: We mentioned that one synthesis run implies obtaining 1 g of catalyst. In addition, we indicated the calculated amount of active components in the catalysts (5 wt.% for Ag and 10 wt.% for CeO2), hence the rest of mass is the amount of GO used for synthesis.
- UV spectra Fig S3 of 4-NP and 4-AP are not enough to prove the reduction product is 4-AP, HPLC characterizations or mass spectra are needed.
Response: Employment of UV-vis spectra for monitoring of the 4-nitrophenol reduction is widespread technique approved in a large number of corresponding papers. The formation of other products was not observed because high selectivity of this reaction over Ag catalysts [15. Liao G. et. al. Unlocking the door to highly efficient Ag-based nanoparticles catalysts for NaBH4-assisted nitrophenol reduction. Nano Res. 2019, 12, 2407–2436.] in comparison with Au, Cu, etc.
- Provide a complete progressive decrease of the reactant signal UV spectra of the one set of complete reduction reaction to know the proper formation of respective aminophenol by reduction of Nitro phenol.
Response: In our previous work devoted to the 4-NP reduction over Ag-CeO2/SBA-15 catalysts [A. Taratayko, Yu. Larichev, V. Zaikovskii, N. Mikheeva, G. Mamontov, Catal. Today 375 (2021) 576–584. DOI: 10.1016/j.cattod.2020.05.001], we demonstrated the evolution of UV-vis spectra during the reaction. The data indicate the decrease of 4-nitrophenol signal (absorption band with maximum at 400 nm) and simultaneous increase of 4-aminophenol signal (absorption band with maximum at 300 nm).
- PXRD patterns after reduction should be checked to confirm the integrity of the catalysts structure.
Response: We agree that structure of catalysts may be changed after catalytic reaction of nitrophenol reduction and XRD and other methods are necessary to study the transformation of structure. Unfortunately, we cannot study the structure of catalysts after catalytic tests because few milligrams (3-12 mg) of sample are used in experiment. However, the stability test (Fig. 9) shows the relatively high stability of catalyst during 6 catalytic cycles. Thus, we conclude that the changes in catalysts structure are insignificant.
- Provide a schematic of mechanism of catalytic conversation reaction using the catalyst.
Response: Scheme of the reaction mechanism over Ag-containing catalysts is described in other papers, for example, [M. Kohantorabi, M.R. Gholami, New J. Chem. 41 (2017) 10948–10958. DOI: 10.1039/C7NJ03009F]
or in [S. Karuppusamy, F. Marken, M.A. Kulandainathan, New J. Chem. 44 (2020) 17780–17790. DOI: 10.1039/D0NJ03713C]
Thus, we will not include the mechanism of reaction because it is known and described in the literature.
- Provide the AFM images of the formation of layer formation on the GO surface.
Response: Unfortunately, we don’t have possibility to carry out AFM studies quickly.
- Conclusion should be in one paragraph not in bullet points.
Response: It was corrected.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The development of a catalyst and its efficiency for the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride in aqueous medium at laboratory temperature and atmospheric pressure is described in the reviewed work. The catalyst used, based on graphene oxide coated with silver and CeO2 nanoparticles, is characterized using basic methods, and the influence of reaction conditions on the course of the catalysed reaction is thoroughly described. The presented results showed that the synthesized catalysts have high catalytic efficiencies comparable to and in some cases exceeding those of highly active catalysts for the reduction of 4-NP, thus they are promising efficient systems in the reduction of aromatic nitro compounds to the corresponding amino compounds. The catalyst is chemically and mechanically stable under reduction conditions and stable activity was achieved under repeated cycles without significant deactivation. The work is of interest to readers involved in the study of catalysts and provides new insights. It is written in a clear and sufficiently concise manner, and the graphical presentations of the results are easy to understand. I did not notice any errors or ambiguities. I recommend to publish.
In addition, the evaluated manuscript deals with the development and characterization of a catalyst based on graphene oxide modified with silver nanoparticles and CeO2 The joint deposition of Ag and CeO2 on graphene oxide stabilizes silver nanoparticles in the catalyst. Testing of the catalyst properties on the model reduction of nitrophenol to aminophenol by sodium borohydride in aqueous medium confirmed its good catalytic properties and stability. The use of CeO2 to stabilize Ag particles on graphene oxide may be important for improving the properties of catalysts of this type of reactions and is, to my knowledge, original and not yet described in the literature. In my opinion, the authors' conclusions are consistent with the evidence and arguments presented and confirm the stabilising effect of CeO2. I consider the cited references relevant, self-citations are used in an acceptable number.
Author Response
Dear Reviewer, hereby we submit our manuscript entitled “Graphene oxide decorated with Ag and CeO2 nanoparticles as catalyst for room-temperature 4‑nitrophenol reduction” written by Aleksey Taratayko and Dr. Grigory Mamontov after correction for publication as a full paper in the Catalysts.
Thank you for your interest to our manuscript and helpful questions and remarks. We improved the manuscript according to your recommendations. Please, find responses on questions below.
Reviewer:
The development of a catalyst and its efficiency for the reduction of 4-nitrophenol to 4‑aminophenol by sodium borohydride in aqueous medium at laboratory temperature and atmospheric pressure is described in the reviewed work. The catalyst used, based on graphene oxide coated with silver and CeO2 nanoparticles, is characterized using basic methods, and the influence of reaction conditions on the course of the catalysed reaction is thoroughly described. The presented results showed that the synthesized catalysts have high catalytic efficiencies comparable to and in some cases exceeding those of highly active catalysts for the reduction of 4‑NP, thus they are promising efficient systems in the reduction of aromatic nitro compounds to the corresponding amino compounds. The catalyst is chemically and mechanically stable under reduction conditions and stable activity was achieved under repeated cycles without significant deactivation. The work is of interest to readers involved in the study of catalysts and provides new insights. It is written in a clear and sufficiently concise manner, and the graphical presentations of the results are easy to understand. I did not notice any errors or ambiguities. I recommend to publish.
Response: Thank you for interest to our work and high evaluation of the results obtained.
Reviewer 3 Report
This work deals with the reduction of 4-nitrophenol into 4-aminophenol using Ag and CeO2 nanoparticles immobilized on graphene oxide (GO) support. The authors have carried out a thorough characterization of the catalytic materials.
Experimental par: for the synthesis of GO, the authors should mention if the reduction was total and how it was determined. In section 2.3 Characterization of samples, the authors should add ICP data in order to determine the content of silver and ceria in the catalysts.
Taking into account the plausible presence of small Ag particles, a Transmission Electron Microscopy analysis of the catalytic materials Ag/GO and Ag-CeO2/GO will help to evidence them. For determining the surface state, XPS analyses can give information on the oxidation state of the silver particles.
The catalytic study is rigorous and appropriately discussed. The authors should add the reactivity with some other nitro-arenes in order to check the catalytic ability of the Ag/GO and Ag-CeO2/GO.
Based on these comments, this paper can be considered for the publication in Catalysts after adding the suggested experimental data.
Author Response
Dear Reviewer, hereby we submit our manuscript entitled “Graphene oxide decorated with Ag and CeO2 nanoparticles as catalyst for room-temperature 4‑nitrophenol reduction” written by Aleksey Taratayko and Dr. Grigory Mamontov after correction for publication as a full paper in the Catalysts.
Thank you for your interest to our manuscript and helpful questions and remarks. We improved the manuscript according to your recommendations. Please, find responses on questions below.
Reviewer:
This work deals with the reduction of 4-nitrophenol into 4-aminophenol using Ag and CeO2 nanoparticles immobilized on graphene oxide (GO) support. The authors have carried out a thorough characterization of the catalytic materials.
Experimental par: for the synthesis of GO, the authors should mention if the reduction was total and how it was determined.
Response: The conversion of 4-NP was total that was confirmed by the UV-vis spectroscopy (adsorption band at 400 nm). Only 4-aminophenol was observed as product of reaction that is associated with high selectivity of Ag catalysts in this reaction [15. Liao G. et. al. Unlocking the door to highly efficient Ag-based nanoparticles catalysts for NaBH4-assisted nitrophenol reduction. Nano Res. 2019, 12, 2407–2436.].
In section 2.3 Characterization of samples, the authors should add ICP data in order to determine the content of silver and ceria in the catalysts.
Response:
The nominal loading of active components in the catalysts was 5 wt.% for Ag and 10 wt.% for CeO2. The measurement of real loading of components by XRF analysis is difficult because C is light element in comparison with Ag and Ce. The element analysis of GO-based materials is difficult due to non-stoichiometry of carbon oxide (COx) and we observe the reduction of GO during catalysts preparation and in catalytic process. We can see that in many articles authors don’t show the real loading of components in GO-based materials because of difficulty of this analysis, even if ICP method is used.
Taking into account the plausible presence of small Ag particles, a Transmission Electron Microscopy analysis of the catalytic materials Ag/GO and Ag-CeO2/GO will help to evidence them. For determining the surface state, XPS analyses can give information on the oxidation state of the silver particles.
Response: We agree that both TEM and XPS analysis are informative methods for analysis of catalysts. We take our attention in present study on the catalytic reaction, and results of different conditions on the catalytic properties are presented. Both TEM and XPS gives important information about the structure and chemical state of materials, however these methods are destructive for Ag/GO composites because the action of vacuum and electron bean leads to the reduction of AgOx species and possible reduction of GO (due to decarboxylation process that was shown be DTG-DSC analysis).
The catalytic study is rigorous and appropriately discussed. The authors should add the reactivity with some other nitro-arenes in order to check the catalytic ability of the Ag/GO and Ag-CeO2/GO.
Response: We start this work using 4-NP as model molecule which can easy detected by UV-vis spectroscopy. The substrate diversity, different reductive reagents, etc. could be considered in the further work. For example, now we study the photoreduction of 4-NP over same GO-based composites and these results will be published in our next article.
Based on these comments, this paper can be considered for the publication in Catalysts after adding the suggested experimental data.
Response: We agree with reviewer that addition of suggested experimental data improve the understanding of the catalysts structure and increase quality of the manuscript. At the same time, we include many experimental results in the manuscript and in supplementary which give us the main understanding of the catalysts structure, its properties, stability, and catalytic properties in the 4‑nitrophenol reduction under different conditions. We focused our attention on the catalytic properties of materials because it has high scientific novelty, while the structure of GO and same GO-based composites is well studied and described in other publications.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have declared that they do not have SEM and TEM facilities. Hence, without that the paper ma be accepted
Author Response
Dear Reviewer, thank you for your interest to our work.
also, we carried out XPS studies and added the XPS data to improve the quality of presented manuscript.
Reviewer 3 Report
I cannot accept this version. The authors did not include any of my suggestions. I therefore do not agree that the article may be published in this form.
Author Response
Dear Reviewer, thank you for your intest to our study and helphul remarks and questions.
Unfortunately, we don't have posibility to carried out TEM studies fast, however we carried out XPS studies with our colleques from Tomsk State University and added these results in manuscript.
XPS data show the loading of elements and these results are in good agreemnet with XRD and TGA.
Also, we described the chemical state of GO support and supported silver. These results are also with good agreement with results of other methods.
Thus, we improved the quality of presented results and understanding the both structure of materilas and increased catalytic activity of Ag-CeO2/GO material in the p-nitrophenole reduction.
