Covalent Organic Frameworks for Simultaneous CO₂ Capture and Selective Catalytic Transformation

Round 1

Reviewer 1 Report

Very nice, concise, clear, well-writen and well-presented paper. Congratulations. I extremely advise for publication.

I would only increase size/resolution of Fig. S11 (difficult to see as it is now). Also, Fig. 5 legend it should start as "FT-IR" and not "FI-IR".

Author Response

please kindly see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This article by Gao and co-workers describes the synthesis of a Co-porphyrin-based COF, and, as a consequence, the material presents open metal sites suitable for catalytic transformations. In this study, the authors explored the catalytic cycloaddition of CO₂ and epoxides under mild conditions, an interesting avenue to decrease CO₂ emissions while forming value-added products, cyclic carbonates. I kindly recommend the authors address the following comments before the publication of their findings.

• The state-of-the-art of utilization of porous materials (COFs and MOFs) for cycloaddition of CO₂ and epoxides has to be improved in the introduction section. For example, recent studies in the field (including the work of the authors of the present article) were not cited such as 0.1021/acs.inorgchem.1c00053, doi.org/10.1039/D1GC00267H, doi.org/10.1016/j.mcat.2020.111253, oi.org/10.1016/S1872-2067(19)63487-X. The catalytic performances of this catalyst should be compared to the present study. What are the advances in the field? I suggest the authors add a table in the manuscript showing the comparison/ advancements/ advantages to better sell the new catalyst presented. In this sense, the conclusion of the study can also be improved.
• The last paragraph of the introduction shows methodology and results, please move it to the results and discussion. Also, the order in which the figures are presented in the main manuscript has to be reorganized to allow a better reading flow. For example, Figures 1 and 2 are stacked together as well as Figures 4 and 5. If they need to be close, they can be merged and presented as Figures 1a-b and 4a-b, otherwise, they have to be placed properly. As for Figure 3, it appears before the discussion in the text. Please revise the whole manuscript carefully.
• The elemental analysis for Co(II)@TF-TA COF presented at the end of the synthetic procedure in the SI is different from that presented in Table S1. Moreover, the formulas are different, and the cobalt content presented in the SI differs from that mentioned in the main manuscript (2.7% vs 4.2%). In the discussion, the authors mentioned that 91% of the porphyrin is metallated based on the ICP-OES analysis for the COF. However, this sounds strange. Did the authors conduct an ICP-OES analysis for the Co-TAPP starting material? This analysis has to be done to prove that the Co(II) ions are not leaving the porphyrin sites, which I believe is less likely to occur than the utilization of a mixture of metallated and non-metallated TAPP.
• In the instrumentation section in the SI, the brand and model of the surface area analyzer were not described as well as the conditions used for the activation of the COF. Moreover, it is mentioned that the morphology of the COF sample was observed by transmission electron microscopy, which is not presented in the main manuscript nor in the SI.
• Is the SEM image presented in Figure S10 representative of the whole sample? To answer this question, more images have to be shown in the SI including some with lower magnification allowing the visualization of more particle aggregates. Moreover, EDS has to be shown to prove the homogeneity of the Co in the COF particles as well as a graph showing the size particle
• The scale of the weight axis has to be changed allowing for better visualization of the weight loss. As presented, the TGA curve seems to show a plateau before thermal decomposition, but it is not necessarily true considering the presence of solvents and moisture in the pores of the COF. Change the scale (105-90%), one will be able to assess the curve accurately.
• The stability tests shown by the powerful PXRD analyses for the COF submitted to different solvents, basic and acidic conditions seem to confirm the retention of crystallinity of the material. However, further experiments need to be performed to assure there is no Co(II) leaching or irreversible OH^- binding occurring in harsh acidic and basic media, respectively, which can compromise the catalyst site. For this, ICP-OES has to be performed in the samples after the stability test. Moreover, the BET surface area has to be assessed for the materials after the stability test to prove pore availability for CO₂ capture, which is crucial for the study presented. The authors need to clarify the following points: 1) they mentioned in the main manuscript that the concentration of NaOH solution used in the stability test is 12 M while in the SI, Figure S9 shows 14 M, and 2) they mentioned in the main manuscript that the stability tests lasted 24 hours while in the caption of Figure S9 they affirm to be one week.
• The authors affirm that the N₂ sorption isotherm is a type I. It seems to be type II. A must reference is the IUPAC technical report (DOI 10.1515/pac-2014-1117) that affirms: “Reversible Type II isotherms are given by the physisorption of most gases on nonporous or microporous adsorbents. The shape is the result of unrestricted monolayer-multilayer adsorption up to high p/p⁰ If the knee is sharp, Point B – the beginning of the middle almost linear section – usually corresponds to the completion of monolayer coverage. A more gradual curvature (i.e., a less distinctive Point B) is an indication of a significant amount of overlap of monolayer coverage and the onset of multilayer adsorption. The thickness of the adsorbed multilayer generally appears to increase without limit when p/p⁰ = 1”. This seems to be exactly what is shown in Figure 3a, and the authors need to revise it. Moreover, the pore distribution shown in the inset of Figure 3a seems to show mostly a micropore (1.6 nm), but also the presence of bigger pores that can explain the type II isotherm shape.
• The authors described in the main manuscript (line 185) that the co-catalyst was TBI. However, it has also to be showing in the footnotes of Table 1 in the reaction conditions (^a).
• The authors discussed close to Figure S11 in the SI the role of the co-catalyst in the proposed mechanism. However, they do not discuss why Cl^- and Br^- are less effective species than I^-. Figure S11 representing the mechanism is unclear. Therefore, a better figure has to be presented for clarity.
• Although explained in the text, the caption of Figure 5 has to be improved to explain which bands are highlighted by the dashed circles and what they show.
• The catalytic activity of the Co(II)@TAPP was investigated for comparison purposes as discussed in lines 204-209 although the results for varied pressures are not shown in Table 1.
• Please present the ICP-OES results for the Co leaching test in the SI.

Author Response

please kindly see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Major comments:

The study is focused on Covalent Organic Frameworks for Simultaneous CO2 Capture and Catalytic Transformation. The research is very limited in the aspects of the study and covers only a few points of the whole study. The literature study is very weak and outdated, and there is no proper linkage between different sections of the papers. The language of the paper also needs further improvements as it contains several mistakes. The equations should be written using equation writer instead of the same word format and references should be divided properly and should not be generic. The headings also need changes as they should be based on obtained results instead of the equipment used. The English language used in the manuscript needs improvements, as there are some punctuation and grammatical mistakes throughout the manuscript. Sentences need more clarity and better construction. Some figures need more transparency; special focus is required in labelling the axis and titles. Overall, the paper needs some structural and literature revisions to meet the requirements of the journal. It is obvious the quality of the manuscript does not meet the standards of the catalysts journal, therefore should be rejected in its present form or needs major revisions.

Introduction:

The introduction is very short and too general, therefore need more specific information related to the present research. It should be more focused on the topic of interest. The literature in the introduction needs more updates and the latest literature should be used for the studies. The introduction needs to be more emphasized on the research work with a detailed explanation of the whole process considering past, present, and future scope. The conventional materials and technologies need to be explained well to indicate the relevance of the research work. It needs to be strengthened in terms of recent research and updated literature review in this area with possible research gaps. It is strongly recommended to add a recent literature survey about novel materials, catalysts renewable fuels, climate change, recent global warming trends and the role along with the wide range of applications. How these sustainable fuels affect the current levels of CO₂ and alarming global warming issues? Research gaps should be highlighted more clearly and future applications of this study should be added.

 Materials and methods:

This section is missing, please add this section after the introduction. The methodology section also needs detailed information and specifications. The source of chemicals is missing, and the conditions used for the preparation also need to be mentioned. The synthesis process should be explained step by step instead of going back and forth and referring to other sources.

 Specific comments:

1. Abstract: It is suggested to add some background with few objectives and possible applications of this study and highlight the novelty of this work clearly. The abstract only contains some parameters without any process conditions or key values from results, which is insufficient to delineate the whole pictures of contribution and possible application of this study.
2. Revise keywords add more specific and novel keywords with broader meanings (5-7 words).
3. Most of the information presented in the introduction is too general and very common. Therefore, should be omitted and replaced by some latest research and their findings.
4. Please add the materials and methods section after the introduction because this section is missing.
5. Please add subsection as Textural characterizations in materials and methods: Authors have not mentioned what standard methods have been followed, please compare SEM/XRD techniques with the following recent studies: Saudi Pharmaceutical Journal, 2019; 27(8):1164-73. Crystal Growth & Design, 2020; 20(4):2406-14.
6. Please combine results and discussion under on heading as “Results and Discussion” for a better understanding of the readers.
7. Major formatting changes including proper paragraphing is required throughout the manuscript.
8. The figures and tables numberings must consistent, you have used Fig. and Figure at different places?
9. Most of the headings and subheadings need to be revised in a professional way and for better understating.
10. Some figures/graphs are very dim and low quality, need to be revised. You can use Origin Lab software if you like.
11. Most of the information presented in the discussion is refereed to your own findings/values, please discuss this critically with the literature and other published word.
12. The tables/ figures inserted are not explained or discussed well in the text please discuss critically/explain all tables/figures in the text wherever possible.
13. The graphs throughout the manuscript are not consistent, some coloured, some black and white with blurry resolution. Revise all graphs with high-quality images and keep all figures as coloured with consistent fonts. The units stated in the graphs axis need to be double-checked.
14. Please round off all numbers up to two decimal places throughout the text in the entire manuscript.
15. The obtained values in the results are just stated in the text without explaining them. Explain the reasons behind your trends/values and discuss them critically with literature.
16. Revise figures in the manuscript. Draw all figures in high-quality figures should be coloured and attractive.
17. More recent research about types of novel materials, nanocatalysts, CO₂ reduction methods and sustainable development is suggested to be added to make the background and discussion more strong: Industrial & Engineering Chemistry Research, 2020; 59: 22092–22106. Energy, 2020; 209:118444. ACS Sustainable Chemistry& Engineering, 2020;8(34):12877-90. TrAC Trends in Analytical Chemistry, 2020;132:116066. Environmental Research, 2021;195:110839. International Journal of Chemical Reactor Engineering, 2019;17(11).
18. All figures numbering needs to be carefully checked and revised.
19. All figures captions should be revised in a more meaningful way.
20. Avoid an abundance of references do not cite more than 2 references in a single place. Correct all these types of references throughout the manuscript.
21. The conclusions only talk about some studied parameters, which is insufficient to depict the whole picture of the contribution of this study. The authors are advised to write the conclusions in a comprehensive way and should contain key values, suitability of the applied method, the major findings, contributions and possible future outcomes.
22. References: The authors are advised to revise this section, including the latest reference. Please see some suggestions in the specific comments and in the ‘introduction’ section.

Author Response

please kindly see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors revised the manuscript carefully and addressed all the points raised. Therefore, now it has adequate quality for publication in Catalysts.

Please check the following minor issues:

 

• The title of the manuscript was changed. Please change it in the ESI accordingly.
• In the main manuscript, please add the letters a) and b) in the figure, not only in the caption.
• In Figure S9, there is a square in the label of the red curve.
• The authors added, as suggested, the EDS in the ESI. However, they should provide a label in the figure showing the mapping refers to Co. Please provide a better caption for the figure as well.

After these small modifications, I am happy to recommend the publication without the need for further revision by myself.

Author Response

Reviewer 2:

Question 1: The title of the manuscript was changed. Please change it in the ESI accordingly.

Answer: We thank the referee for the valuable comments. The title in the ESI was also changed accordingly.

Question 2: In the main manuscript, please add the letters a) and b) in the figure, not only in the caption.

Answer: We have added this in the figure in the revised manuscript.

Question 3: In Figure S9, there is a square in the label of the red curve.

Answer: We have remade this Figure and removed the square.

Question 4: The authors added, as suggested, the EDS in the ESI. However, they should provide a label in the figure showing the mapping refers to Co. Please provide a better caption for the figure as well.

Answer: We have done this in the revised manuscript.

After these small modifications, I am happy to recommend the publication without the need for further revision by myself.

 

Reviewer 3 Report

The authors have responsed well to those proposed questions by reviewers and carefully revised the whole paper according to the suggestions of reviewers step by step. Therefore, the quality of this paper has elevated greatly, hence I agree to publish the current version of the paper without any further changes.

Author Response

We thank the referee again!