Methane Hydrate Formation in Hollow ZIF-8 Nanoparticles for Improved Methane Storage Capacity
Round 1
Reviewer 1 Report
The manuscript deals with preparation of hollow ZIF-8 nanoparticles and their application for methane hydrate storage. The preparation of hollow ZIF-8 nanoparticles is well known approach based on etching of polystyrene core from PS@ZIF-8 core -shell nanoparticles. There are a few issues that should be clarified. Authors strictly follow the solvothermal approach for hollow ZIF-8 nanoparticles described in Chem. Commun., 2012,48, 221-223 by Hee Jung Lee without any modifications. However, the thickness of ZIF-8 shell in the current manuscript and in citated paper differs significantly. According to the Chem. Commun., 2012,48, 221-223 the thin shell achieved after first solvothermal cycle is not sufficient to form a secure spherical shape after removal PS core and the second coating is required to get reliable hollow ZIF-8 nanoparticles. For this, a thickness of the shell should be around 50 nm. However, authors present the TEM images of hollow particles with ideal spherical shape and shell thickness of 20 nm after the first solvothermal cycle. The additional discussion is needed on such differences. Besides, authors skipped the procedure of separation of pure nanosized ZIF-8 nanoparticles from the core-shell NPs during the preparation process.
The second issue is BET data. For a reliable comparison, BET data for PS@ZIF-8 core-shell nanoparticles are required. The adsorption-desorption isotherms look strange. According to literature ( for examples see: Proc. Nat. Acad. Sci. USA, 103 (2006), pp. 10186-10191; https://doi.org/10.1016/j.memsci.2015.01.038) the type I nitrogen sorption isotherm should be typical for ZIF-8 which reveals its microporous nature. In the manuscript authors observed a mesoporous structure of the ZIF-8. Please, clarify.
The paper should be improved substantially to be published.
Author Response
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Author Response.pdf
Reviewer 2 Report
the present paper with the results is excellent and I hope to make a feasibility study to transfer into a large scale
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Reviewer 3 Report
The manuscript is about the methane storage in Hollow ZIF-8 Nanoparticles. The manuscript is very well written and can be accepted after a revision based on my (and other reviewers’) comments.
- Regarding the formatting of the manuscript, I am afraid if this according to the rules of the journal to put the Materials and Methods after the Results and Discussion. Please check and modify if necessary.
- Figure 1, is there any possibility to present the EDX/mapping analysis of the sample to be able to distinguish the position of the elements clearly?
- JCPDS cards have not been used for the characterization of the materials (XRD)? Please include those results.
- Figures 4 and 6, Y-axis should start from 0.
- The authors are encouraged to include the real applicability of the materials developed in this manuscript somewhere in the introduction and in the conclusion of the manuscript.
- Also, the authors are asked to emphasize the novelty aspects of the manuscript in the introduction of the manuscript.
Author Response
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Round 2
Reviewer 1 Report
In my first round review, I noticed that " According to literature, the thin shell of 20 nm achieved after the first solvothermal cycle is not sufficient to form a secure spherical shape after removal PS core and the second coating is required to get reliable hollow ZIF-8 nanoparticles." And more discussion is required to explain this phenomenon observed by the authors. I did not find any additional discussion on this subject in the revised manuscript. Moreover, in their responses, the authors did not clarify the main question WHY a 20 nm thick shell is sufficient to ensure a reliable spherical shape , while according to the cited literature, this requires a thicker shell.
As for my second comment on the BET experiments, I strongly believe that to relaible evidence and refinement the mesoporous structure that appears after template etching, a comparison with the parent PS@ZIF-8 nanoparticles is mandatory. The explanation proposed by the authors on mesoporosity origin is only speculative. I really hope , that authors will found an opportunity to conduct this experiment.
Author Response
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Author Response File: Author Response.pdf
Round 3
Reviewer 1 Report
The manuscript has been improved sufficiently and I believe it can be accepted for publication
