This paper presents an interesting work on synthesis of COF membranes using a stoichiometric layer-by-layer spraying technique. For that, authors have used a substrate to form their membranes on top of it, leading the membranes not to be self-standing. It can further enable synthesis of other similar COF materials on different substrates. Also, the mentioned envisaged application i.e. water-treatment applications sound interesting; though its feasibility might be still questioned due to problems about the scale-up, possible contamination and so on. In overall, I believe the work has been carried out well and is well-written, though there are still some rooms for improvement and some more measurements/evidences can be added to better support the presented claims. Here are some suggestions/questions:

1. The authors claim that they have synthesized this COF membrane (made of 1,3,5-benzenetricarboxaldehyde (TFB) and p-phenylenediamine (PDA)) for the first time; however, looking into the literature one realizes that this COF has been used by other researchers too; though the author’s technique for preparation of this technique is novel and I believe the focus of their claim is regarding their preparation technique. For example, these papers have also used the same monomers to produce COF materials:

2. Yang, Y., Xiong, X., Fan, Y., Lai, Z., Xu, Z., & Luo, F. (2019). Insight into volatile iodine uptake properties of covalent organic frameworks with different conjugated structures. Journal of Solid State Chemistry, 279, 120979.

3. Fan, H., Gu, J., Meng, H., Knebel, A., & Caro, J. (2018). High‐flux membranes based on the covalent organic framework COF‐LZU1 for selective dye separation by nanofiltration. Angewandte Chemie International Edition, 57(15), 4083-4087.

4. Reference #5 is missing the last page details.

5. It is claimed that the reported method is easy to scale-up, while no evidence or experimental results have been reported to support this claim.

6. “The effect of the concentration of reactants (PDA of 0.069, 0.035, 0.023, 0.017 and 0.014 mol L-1, TFB/PDA concentration ratio of 2/3) was also explored”. What is the justification to take this range (from 0.069 to 0.014 mol L-1)? Why did not go below the lower limit nor above the upper limit?

7. In the SEM images presented in Figure S7 for the cross sections, it is difficult to see the membrane layer (and estimate the thickness accurately) at this magnification. Perhaps images at higher magnification can help to provide more accurate values.

8. It would be nice to add a real photograph of the membrane to give a better idea about how this membrane looks like, as I am not sure whether the image in Fig. 2a is a real or schematic image.

9. Do the author have any idea or plan to make the membrane self-standing? Have they tried to proceed to several layers, up to where it would be possible to peel of the membrane from the substrate?

10. Regarding the EDXS mapping of N element (Figure S1c), it is not clear from this figure that that more N elements have been distributed in the COF-LZU1 layer, than in the PAN layer! The amount of N elements in both COF-LZU1 layer and PAN membrane seems to be similar. How do the authors explain this?

11. Following the previous comment, it would be perhaps better to perform the mapping of another element, where the difference between its distribution in the two layers would be more distinct, and add that into the Supplementary information.

In summary, I believe the length of the manuscript is rational and the number of figures/tables is sufficient to show the achieved results. I also believe the authors have sufficiently cited the previous works, but they can still add a couple of more references to make sure they cover different methodologies reported for synthesis of these materials (i.e. COFs). More measurements, for instance to support the scalability of the approach (possibility to scale-up) might be incorporated to better support the presented results.