Continuous flow vortex fluidic-mediated exfoliation and fragmentation of two-dimensional MXene

MXene (Ti2CTx) is exfoliated in a vortex fluidic device (VFD), as a thin film microfluidic platform, under continuous flow conditions, down to ca 3 nm thin multi-layered two-dimensional (2D) material, as determined using AFM. The optimized process, under an inert atmosphere of nitrogen to avoid oxidation of the material, was established by systematically exploring the operating parameters of the VFD, along with the concentration of the dispersed starting material and the choice of solvent, which was a 1 : 1 mixture of isopropyl alcohol and water. There is also some fragmentation of the 2D material into nanoparticles ca 68 nm in diameter.


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compares spectra of three types of MXene samples -collected, retained, and as prepared. This figure can be improved at several fronts: (a) From the corresponding text on Page 3, It is not being clear what the phrases collected, retained, and as prepared refer to. Should the readers expect a difference in these spectra.
(b) The features of these spectra can be explained at the right places in the manuscript. At present, the spectra are being explained after the discussion for Figure 4.For example, the Rama spectra can be explained further, the absorbance peaks can also be explained, and if there are some differences, these can be commented upon. The manuscript can be reorganized to make it in sync with the order in which figures are appearing.
(c) The y-axis of XRD spectra doesn't have a corresponding axis title. The spectra for collected/retained is different from as prepared. What could be some reasons behind this? 6. The FESEM images g-i shown in Figure 4 are not clear. The nanoparticulate formation is observed more clearly in the TEM images, and hence the authors can use this for supporting their claims. The authors should also acknowledge the formation of nanoparticulate matter in their title as these are not necessarily 2D. 8. The title of the paper states exfoliation of 2D Mxene. The title should be revised as exfoliation happens of a layered material, which is Ti2AlC in this case. Also, in addition to nanosheets, there are also nanoparticulate matter being formed. This should also be incorporated in the title. The editor assigned to your manuscript has now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Subject Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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2) The effects of various process parameters on the exfoliation efficiencies of mxene nanosheets should be quantitatively discussed.
3) Please provide results on lateral sizes and distribution of resulting mxene sheets. 4) Please give explanation on the significant influence from the tilte angle?
Reviewer: 2 Comments to the Author(s) The manuscript is presenting a useful and scalable approac to exfoliated a MAX phase compound. However, there are several places where the manuscript can be improved. These are listed below: 1. It would be helpful if the authors can further explain the statement that sonication can result in different shaped material. Fig 1b and Fig 1c can be improved for their clarity, and their associated message.

The insets shown in the
3. The manuscript would benefit if some statements are made shorter and rewritten as 2-3 shorter statements. For example, the statements at the end of the introduction section are very long. The authors are requested to revisit the manuscript and see if this correction can be made at other places as well within the manuscript.
4. The authors have tested co-solvent approach in addition to using single solvents. It would be helpful if the authors can include the thought process of testing co-solvents and by citing the relevant literature. Figure 3 compares spectra of three types of MXene samples -collected, retained, and as prepared. This figure can be improved at several fronts:

5.
(a) From the corresponding text on Page 3, It is not being clear what the phrases collected, retained, and as prepared refer to. Should the readers expect a difference in these spectra.
(b) The features of these spectra can be explained at the right places in the manuscript. At present, the spectra are being explained after the discussion for Figure 4.For example, the Rama spectra can be explained further, the absorbance peaks can also be explained, and if there are some differences, these can be commented upon. The manuscript can be reorganized to make it in sync with the order in which figures are appearing.
(c) The y-axis of XRD spectra doesn't have a corresponding axis title. The spectra for collected/retained is different from as prepared. What could be some reasons behind this? 6. The FESEM images g-i shown in Figure 4 are not clear. The nanoparticulate formation is observed more clearly in the TEM images, and hence the authors can use this for supporting their claims. The authors should also acknowledge the formation of nanoparticulate matter in their title as these are not necessarily 2D. Figure 6a and 6b can be made more clear, these are not legible in the present form. Similarly Fig 6e and Fig 8e can be improved as well. 8. The title of the paper states exfoliation of 2D Mxene. The title should be revised as exfoliation happens of a layered material, which is Ti2AlC in this case. Also, in addition to nanosheets, there are also nanoparticulate matter being formed. This should also be incorporated in the title.

Author's Response to Decision Letter for (RSOS-192255.R0)
See Appendix A.

Recommendation?
Accept as is

Comments to the Author(s)
The revision has been made carefully according to the comments from reviewers. So I am glad to recommendate its publication in the present state. Comments to the Author(s) The revision has been made carefully according to the comments from reviewers. So I am glad to recommendate its publication in the present state.

Cover letter Dear Editor,
Thank you for your positive feedback. The manuscript has been revised accordingly. Please refer to our responses below, in addressing all issues raised by the referee, as well as your comments. We look forward to hearing from you.

4-Please give explanation on the significant influence from the tilt angle?
Answer: A following has been added to the revised manuscript (page 3) to clarify the tilt angle "Varying the different operating parameters of the VFD led to determining the optimal conditions for exfoliation of MXene and the highest yield of material exiting (collected) the tube under continuous flow. This was for a tilt angle of 45 o , which is consistent with most optimised processes in the VFD."