Round 1

Reviewer 1 Report

This paper deals with the preparation of coatings, on several substrates, proposed for oil/water separation.
The topic of the paper is very interesting and the results can address a current issue. The context of the study is properly explained; the experimental plan is adequately structured; sufficient data have been reported and discussed.
I only have the following minor comments for the Authors:
- Line 43: avoid the terms “so on”.
- In the Introduction, mention how coatings can be classified as hydrophobic/suyperhydrophobic by WCA and sliding angle measurements; indicate the threshold values for these parameters.
- Section 2.4: describe the methodology for measuring the sliding angle.
- Section 3.3: please, rearrange this section, especially if the bullet point structure is necessary; I would suggest reporting the figure numbers and removing the bullet point.
- Section 3.3: add a comparison between these results and those reported (in the literature) for similar systems.
- In addition to Figure 7, videos (as Supplementary Materials) showing the separation would be appealing; did the Authors take into consideration this possibility?
- Section 3.4: replace “Error! … not found” with the number of the figures.

Carefully revise the text; there are some typos.

Author Response

Responses to Reviewer 1：

This paper deals with the preparation of coatings, on several substrates, proposed for oil/water separation.
The topic of the paper is very interesting and the results can address a current issue. The context of the study is properly explained; the experimental plan is adequately structured; sufficient data have been reported and discussed.
Point 1: Line 43: avoid the terms “so on”.

Response 1: The terms “so on” have been deleted in line 56.

 

Point 2: In the Introduction, mention how coatings can be classified as hydrophobic/suyperhydrophobic by WCA and sliding angle measurements; indicate the threshold values for these parameters.
Response 2: In the Introduction, the hydrophobic/suyperhydrophobic materials were defined by WCA measurements in line 37-45:

Surface wettability, the degree to which solid surface is wet by liquid, is one of most important properties of solid surface. Wettability is usually assessed by measurement of water contact angle (WCA) of a water droplet on a solid surface [7]. The WCA on solid surface depends on surface roughness and chemistry. In general, the surface is superhydrophilic when the solid-liquid WCA on the surface equals to 0º. The surface with WCA less than 90º is defined as hydrophilic. The surface with WCA higher than 90º is hydrophobic. When WCA is higher than 150º, the contact area between water and solid is very small, and the water droplet is easy to roll off solid surface with a sliding angle (SA) less than 10º. This surface is defined as superhydrophobic [8].

 

Point 3: Section 2.4: describe the methodology for measuring the sliding angle.

Response 3: The methodology for measuring the sliding angle was added in manuscript in line 147-150. The WCA and SA on the as-prepared sample was determined with a 5 μL droplet by a contact angle measurement instrument at room temperature (TST-200H, Shenzhen testing equipment CO., LTD, China). The SA was measured by inclining the rotating platform until the droplet is about to roll but has not rolled yet.

 

Point 4: Section 3.3: please, rearrange this section, especially if the bullet point structure is necessary; I would suggest reporting the figure numbers and removing the bullet point.

Response 4: Section 3.3 was rearranged, and the figure numbers were used.

 

Point 5: Section 3.3: add a comparison between these results and those reported (in the literature) for similar systems.

Response 5: In section 3.3, the comparison of fabrication and separation from this work and other superhydrophobic materials (Table 2) was added in line 302:

A comparison of preparation and separation performance from as-prepared sponge and other superhydrophobic materials was made to prove the superiority and significance of this work (Table 2). Compared with other preparation methods, the fabrication of superhydrophobic sponge in this work showed obvious advantages of low cost, easy to operate, and environmentally friendly without fluorinated reagent. Additionally, both heavy and light oils could be efficiently separated from oil/water mixtures by this method. Generally, the as-prepared sponge showed superior property in fabrication and separation performance compared with other superhydrophobic materials.

Table 2. Comparison of fabrication and separation from this work and other superhydrophobic materials

Substrate	Preparation	Coating	Oil	η(%)	Reference
carbon fibers	nickel electroplating	Ni/ fluoroalkylsilane	dichloromethane	99.1	[2]
fabric	in situ redox-oxidation polymerization	polypyrrole/Ag/hexane	chloroform	96.8	[40]
fabric	in situ polymerization	polydopamine/Fe/hexad-ecyltrimethoxysilane	tetrachloromethane	99.0	[41]
fabric	sol-gel method	polydopamine/SiO2/PDMS	dichloromethane	95.0	[42]
sponge	interfacial polymerization	halloysite nanotubes/SiO2/ODTMS	chloroform	99.9	[43]
sponge	sol-gel method	SiO2/PFDS	chloroform	98.7	[44]
sponge	liquid-phase deposition	TiO2/stearic acid	tetrachloromethane	99.1	This work

 

Point 6: In addition to Figure 7, videos (as Supplementary Materials) showing the separation would be appealing; did the Authors take into consideration this possibility?

Response 6: Videos showed the separation process of tetrachloromethane/water mixture, hexane/water mixture and water-in-tetrachloromethane emulsion were added in supplementary material.

 

Point 7: Section 3.4: replace “Error! … not found” with the number of the figures.

Response 7: In section 3.4, the figure 8 has been used to replace “Error! … not found”.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors present a mechanically durable superhydrophobic coating applied to different substrates for oil-water separation applications. This is a hot topic, especially taking into account the severe pollution of different aquatoria caused by oil spillage. The manuscript has many serious flaws that need to be addressed. 

1) According to the Introduction's content, the main novelty of their research is related to the fabrication of a mechanically robust superhydrophobic coating that can be used for oil-water separation ("However, the micro-/nanoscale roughness structure of superhydrophobic material is 52 a fragile nature, which can be destroyed by abrasion and erosion, resulting in limited ap-53 plications [25]. Besides, the long-term exposure to harsh conditions is necessary for com-54 plex oil/water separation. Therefore, finding a versatile and efficient approach to design 55 durable, high-efficient and low-cost superhydrophobic material for oil/water separation 56 is challenging but very useful." ; "This fabrication method was efficient and economical without special-64 ized reagents and equipment. The prepared coating showed remarkable durability 65 against severe abrasion, harsh environmental solutions and repeated usage for oil/water 66 separation."). While the mechanical durability is undoubtedly an important feature, the literature provides many instances for recent developments of highly-robust superhydrophobic coatings based on some and/or all of the materials listed in the manuscript (

On the Development of Ultradurable Extremely Water-Repellent and Oleophobic Soot-Based Fabrics with Direct Relevance to Sperm Cryopreservation ; Mechanically robust superhydrophobic coating from sawdust particles and carbon soot for oil/water separation ; Highly efficient and recyclable carbon soot sponge for oil cleanup ; Facile design of superhydrophobic and superoleophilic copper mesh assisted by candle soot for oil water separation ; One-Step Preparation of Robust Superhydrophobic Foam for Oil/Water Separation by Pulse Electrodeposition ; Superhydrophobic nanohybrid sponges for separation of oil/ water mixtures).  

Some of these coatings are used for oil-water separation, so from that point-of-view, the current manuscript is considered as incremental scientific advance. It is advisable to cite the mentioned literature and emphasize on the reusability of your superhydrophobic oil-water separators (number of working cycles), because most of the literature sources do not provide solid evidences for the lifespan of as-developed separators.

2) Mentioning that, the authors must provide clear evidences (videos, snap shots and/or lab book documentation) supporting the claim that "Moreover, the coated sponge still maintained a separation efficiency above 98.0% and stable reusability after 30 times of repeated separation". At the moment, there is only one Figure (Figure 8f) illustrating the separation efficiency, but this is not a proof, because obviously, the data in the figure can be manipulated (not saying they are, but could be). 

3) In section 2.2. is not clear how did you process the sponge with acetylamine, HDMTS, etc. More explanations are mandatory to be embedded in the text. Moreover, in the Introduction you mention sawdust and other substrates, but in the Materials & Methods it is not explained how exactly you modify them. Finally, why did you need to prepare so many samples? What is the rationale and why there is no comparison between the oil-water separation performance of individual samples?

4) The authors performed water-in-oil separation (i.e. a given amount of water in oily solution) - "The water-in-oil emulsion was acquired by mixing oil and water with the volume ratio of 50:1 using Span 80 (0.1 wt%) as emulsifier under stirring for 5 h until a stable milky solution was formed.". Why it is not studied the oil-in-water separation (i.e. small amounts of oil distributed in larger water volumes), which is the most common case during industrial pollution? Appropriate modifications of the text should be done and more experiments need to be shown. 

5) Section 3.1 - how did you define fs (solid fraction in contact with water), through which you then calculated 1-fs? It must be unambiguously shown in the text. 

6) The authors comment upon the sliding (roll-off) angle of superhydrophobic surfaces, but do not explain how it is measured. Please correct.

7) Figure 3 - please provide images with much higher magnification. The current versions are not legible. 

8) Figure 5 - the FTIR spectra have differences between the samples. For example, it is not true that "The characteristic peaks of C-H and C=O from stearic acid was observed in all superhydrophobic samples.". The sawdust and wheat straw do not have the characteristic C=O, so why? The same applies to the broad peak ranging within 1015-1141 cm^-1. 

9) The discussion in section 3.2, including the proposed reaction mechanism, is not supported by any scientific literature, which is unacceptable. 

10) Section 3.3 contains some weird sentences such as "error, reference source not found". In my opinion, this article has previous history. 

11) Lines 215-216 and others below do not indicate any figure, only a), b), etc. This needs to be corrected.

English language is fine, minor spell-check required.

Author Response

Responses to Reviewer 2：

The authors present a mechanically durable superhydrophobic coating applied to different substrates for oil-water separation applications. This is a hot topic, especially taking into account the severe pollution of different aquatoria caused by oil spillage. The manuscript has many serious flaws that need to be addressed.

Point 1: According to the Introduction's content, the main novelty of their research is related to the fabrication of a mechanically robust superhydrophobic coating that can be used for oil-water separation ("However, the micro-/nanoscale roughness structure of superhydrophobic material is 52 a fragile nature, which can be destroyed by abrasion and erosion, resulting in limited ap-53 plications [25]. Besides, the long-term exposure to harsh conditions is necessary for com-54 plex oil/water separation. Therefore, finding a versatile and efficient approach to design 55 durable, high-efficient and low-cost superhydrophobic material for oil/water separation 56 is challenging but very useful." ; "This fabrication method was efficient and economical without special-64 ized reagents and equipment. The prepared coating showed remarkable durability 65 against severe abrasion, harsh environmental solutions and repeated usage for oil/water 66 separation."). While the mechanical durability is undoubtedly an important feature, the literature provides many instances for recent developments of highly-robust superhydrophobic coatings based on some and/or all of the materials listed in the manuscript (On the Development of Ultradurable Extremely Water-Repellent and Oleophobic Soot-Based Fabrics with Direct Relevance to Sperm Cryopreservation ; Mechanically robust superhydrophobic coating from sawdust particles and carbon soot for oil/water separation ; Highly efficient and recyclable carbon soot sponge for oil cleanup ; Facile design of superhydrophobic and superoleophilic copper mesh assisted by candle soot for oil water separation ; One-Step Preparation of Robust Superhydrophobic Foam for Oil/Water Separation by Pulse Electrodeposition ; Superhydrophobic nanohybrid sponges for separation of oil/ water mixtures). 

Some of these coatings are used for oil-water separation, so from that point-of-view, the current manuscript is considered as incremental scientific advance. It is advisable to cite the mentioned literature and emphasize on the reusability of your superhydrophobic oil-water separators (number of working cycles), because most of the literature sources do not provide solid evidences for the lifespan of as-developed separators.

Response 1: The mentioned references have been cited in manuscript as reference 29-34. The reusability of the superhydrophobic material was emphasized in manuscript. This part was mentioned in line 70-77:

Therefore, finding a versatile and efficient approach to design durable, high-efficient and low-cost superhydrophobic material for oil/water separation is challenging but very useful [29-32]. Zulfiqar et al. [33] fabricated mechanically robust superhydropho-bic coating for oil/water separation. The coating could retain superhydrophobic prop-erties after severe mechanical abrasion. Zhang et al. [34] prepared robust superhy-drophobic foam for oil/water separation. The coating exhibited good performance with excellent chemical stability, anticorrosion and mechanical stability. In addition, the reusability of superhydrophobic materials was important for oil/water separation, which could greatly reduce the consumption of resources. However, most of the liter-ature sources did not provide solid evidences for the lifespan of superhydrophobic materials.

29. Esmeryan, K.D.; Fedchenko, Y.I.; Gyoshev, S.D.; Lazarov, Y.; Chaushev, T.A.; Grakov, T. On the development of ultradurable extremely water-repellent and oleophobic soot-based fabrics with direct relevance to sperm cryopreservation. ACS Appl. Bio Mater., 2022, 5, 3519-3529.
30. Gao, Y.; Zhou, Y.S.; Xiong, W.; Wang, M.; Fan, L.; Rabiee-Golgir, H.; Jiang, L.; Hou, W.; Huang, X.; Jiang L.; Silvain J.; Lu Y.F. Highly efficient and recyclable carbon soot sponge for oil cleanup. ACS Appl. Mater. Interfaces, 2014, 6, 5924-5929.
31. Cao, H.; Fu, J.; Liu, Y.; Chen, S. Facile design of superhydrophobic and superoleophilic copper mesh assisted by candle soot for oil water separation. Colloid Surface A, 2018, 537, 294-302.
32. Abu-Thabit, N.Y.; Uwaezuoke O.J.; Elella M.H.A. Superhydrophobic nanohybrid sponges for separation of oil/water mixtures. Chemosphere, 2022, 294, 133644.
33. Zulfiqar, U.; Hassain, S.Z.; Subhani, T.; Hussain, I.; Rehman, H. Mechanically robust superhydrophobic coating from sawdust particles and carbon soot for oil/water separation. Colloid Surface A, 2018, 539, 391-398.
34. Zhang, Y.; Liu, J.; Ouyang, L.; Li, J.; Xie, G.; Yan, Y.; Weng C. One-step preparation of robust superhydrophobic foam for oil/water separation by pulse electrodeposition. Langmuir, 2021, 37, 7043-7054.

 

Point 2: Mentioning that, the authors must provide clear evidences (videos, snap shots and/or lab book documentation) supporting the claim that "Moreover, the coated sponge still maintained a separation efficiency above 98.0% and stable reusability after 30 times of repeated separation". At the moment, there is only one Figure (Figure 8f) illustrating the separation efficiency, but this is not a proof, because obviously, the data in the figure can be manipulated (not saying they are, but could be).

Response 2: The separation process after 30 cycles was shown in Video S4 in supplementary material. The separation process of oil/water mixture was also shown in Video S1-S3.

 

Point 3: In section 2.2. is not clear how did you process the sponge with cetylamine, HDMTS, etc. More explanations are mandatory to be embedded in the text. Moreover, in the Introduction you mention sawdust and other substrates, but in the Materials & Methods it is not explained how exactly you modify them. Finally, why did you need to prepare so many samples? What is the rationale and why there is no comparison between the oil-water separation performance of individual samples?

Response 3: For modification of cetylamine, HDMTS, etc., the TiO₂ deposition process is same. Only the last step of immersion in stearic acid solution was changed. The modification process was as follows: in the last step, the dired sponge was immersed in an ethanol solution of n-cetylamine (3.5 wt.%) at 60 °C for 3 h of reaction. After drying, the sponge/TiO₂/cetylamine was finally prepared. Similarly, after immersed in HDTMS–ethanol solution at 60 °C for 4 h of reaction, sponge/TiO₂/HDTMS was prepared. The dried sponge was immersed in an ethanol solution of n-dodecanethiol (2.5 wt.%) for 5 h of reaction to obtain sponge/TiO₂/dodecanethiol. This part was added in manuscript in section 2.2 in line 108-116.

The sawdust (425-500µm), wheat straw (425-500µm), cotton (4×4 cm) and fabric (4×4 cm) were also washed in 2 % ethanol aqueous solution and dried in advance. The preparation of superhydrophobic coating on these substrates was same as that on sponge. This part was also added in section 2.2 in line 117-119.

We prepared the superhydrophobic coating on different substrates to prove that there are no limits on the type or shape of substrates. Cellulose-based materials, sponge, cotton and fabric could all be used without destroying their intrinsic appearance. Sponge was taken as an example to study the oil-water separation performance.

 

Point 4: The authors performed water-in-oil separation (i.e. a given amount of water in oily solution) - "The water-in-oil emulsion was acquired by mixing oil and water with the volume ratio of 50:1 using Span 80 (0.1 wt%) as emulsifier under stirring for 5 h until a stable milky solution was formed.". Why it is not studied the oil-in-water separation (i.e. small amounts of oil distributed in larger water volumes), which is the most common case during industrial pollution? Appropriate modifications of the text should be done and more experiments need to be shown.

Response 4: For oil-in-water emulsion, so much water existed. Water could not permeate the superhydrophobic sponge and oil could not contact with the superhydrophobic sponge. Thus, it is different to separate the oil-in-water emulsion using superhydrophobic sponge. However, the oil-in-water emulsion could be separated using superhydrophilic material. We will study the fabrication of superhydrophilic material and the transformation of them in our future research.

 

Point 5: Section 3.1 - how did you define fs (solid fraction in contact with water), through which you then calculated 1- f_s? It must be unambiguously shown in the text.

Response 5: In section 3.1, f_s is the fraction of solid contact area with water. f_s could be calculated through equation 3. Taking sponge coated with TiO₂/stearic acid as an example, θ is the WCA on sponge surface coated with a smooth film of stearic acid; θ_c is the WCA on sponge surface coated with TiO₂/stearic acid. Thus, f_s could be calculated by equation 3. Then 1- f_s could be obtained. The calculation was illustrated in manuscript in line 176-180.

 

Point 6: The authors comment upon the sliding (roll-off) angle of superhydrophobic surfaces, but do not explain how it is measured. Please correct.

Response 6: The measurement of sliding angle was explained in line 147-150 in manuscript.

 

Point 7: Figure 3 - please provide images with much higher magnification. The current versions are not legible.

Response 7: The SEM analysis was used to compare the differences before and after coating. From the SEM images, we could clearly see that all coated surfaces possess a rough structure characterized by a random distribution of particles having various sizes and shapes. Thus, the SEM image with higher magnification was not used.

 

Point 8: Figure 5 - the FTIR spectra have differences between the samples. For example, it is not true that "The characteristic peaks of C-H and C=O from stearic acid was observed in all superhydrophobic samples.". The sawdust and wheat straw do not have the characteristic C=O, so why? The same applies to the broad peak ranging within 1015-1141 cm^-1.

Response 8: The characteristic peak of C=O in sawdust and wheat straw overlaps with the characteristic peak of carboxy group (1700 cm^-1) in cellulose. Thus, it becomes a broad peak. The peak of Si-O-Si also overlaps with the characteristic peak of carbon skeleton (1250-800 cm^-1).

 

Point 9: The discussion in section 3.2, including the proposed reaction mechanism, is not supported by any scientific literature, which is unacceptable.

Response 9: The references have been added to support the proposed reaction mechanism in section 3.2 in line 234 and 236:

37. Feng, L.; Zhang, H.; Mao, P.; Wang, Y.; Ge, Y. Superhydrophobic alumina surface based on stearic acid modification. Appl. Surf. Sci., 2011, 257, 3959-3963.
38. Cai, Y.; Zhao, Q.; Quan X.; Feng, W.; Wang, Q. Fluorine-free and gydrophobic hexadecyltrimethoxysilane-TiO₂ coated mesh for gravity-driven oil/water separation. Colloid Surface A, 2020, 586, 124189.
39. Song, Y.; Liu, Y.; Zhan, B.; Kaya, C.; Stegmaier, T.; Han, Z.; Ren, L. Fabrication of bioinspired structured superhydrophobic and superoleophilic copper mesh for efficient oil-water separation. J. Bionic Eng., 2017, 14, 497-505.

 

Point 10: Section 3.3 contains some weird sentences such as "error, reference source not found". In my opinion, this article has previous history.

Response 10: The weird sentences have been deleted, and they were replaced with the figure number in section 3.3.

 

Point 11: Lines 215-216 and others below do not indicate any figure, only a), b), etc. This needs to be corrected.

Response 11: The “Figure 7” has been used section 3.3.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments to the Authors:
The authors of this paper propose an interesting method for durable superhydrophobic coating preparation. However, some details should be considered by the authors:

COMMENT: lines 31-32: More recent references could also be added.

COMMENT: line 36: Replace "has" with "have".

COMMENT: line 95: Some information about the Sudan III dye could be added.Further, why was this pigment chosen and what was its concentration? Also, what was the methylene blue concentration?

COMMENT: lines 112-113: More information about the FTIR technique should be added (for example, were the spectra shown obtained in reflectance or transmittance mode, what was the sampleholder (?) etc).

COMMENT: lines 168-174 and Fig. 4: The analysis of the XRD patterns is rather limited. More comments could be added about the assignment of peaks emerge in these patterns.

COMMENT: Add the correct references for the “Durability evaluation” section.

The paper is well written and the results support the authors conclusions. Thus, I think that this paper may be published.

By taking into account the interest of this work, in my opinion this paper deserves publishing, after minor revision.

Author Response

Responses to Reviewer 3：

The authors of this paper propose an interesting method for durable superhydrophobic coating preparation. However, some details should be considered by the authors:

Point 1: lines 31-32: More recent references could also be added.

Response 1: Recent references [3-5] have been added in line 31-32:

3. Haridharan, N.; Sundar D.; Kurrupasamy, L.; Anandan, S.; Liu, C.; Wu, J.J. Oil spills adsorption and cleanup by polymeric materials: a review. Polym. Advan. Technol., 2022, 33, 1353-1384.
4. Minh, T.D.; Ncibi, M.C.; Srivastava, V.; Doshi, B.; Sillanpaa, M. Micro/nano-machines for spilled-oil cleanup and recovery: a review. Chemosphere, 2021, 271, 129516.1-129516.12.
5. Wang, F.; Ma, R.; Zhan, J.; Tian, Y. Superhydrophobic modular cryogel with variable magnetic-actuated motion direction for discrete small-scale oil spill cleanup. J. Harzard. Mater., 2022, 430, 128448.

 

Point 2: line 36: Replace "has" with "have".

Response 2: The "have" have been used in line 36.

 

Point 3: line 95: Some information about the Sudan III dye could be added. Further, why was this pigment chosen and what was its concentration? Also, what was the methylene blue concentration?

Response 3: The oils were dyed with Sudan Ⅲ while water was dyed with methylene blue. Thus, the color of oils was changed to red and the water was blue in order that the separation process could be clearly investigated. The concentration of Sudan III and methylene blue was both 0.1%. During preparation of oil/water mixture, one drop of Sudan III solution was added to oil and one drop of methylene blue solution was added to water. The oil and water were mixed with different color.

The information of Sudan III and methylene blue was added in section “2.1 Materials” in line 94-95. The reason of choosing Sudan III and methylene blue was also added in manuscript in line 124-126.

 

Point 4: lines 112-113: More information about the FTIR technique should be added (for example, were the spectra shown obtained in reflectance or transmittance mode, what was the sampleholder (?) etc).

Response 4: The FTIR spectra was obtained in transmittance mode. The vertical axis of “Transmittance (%)” has been added in figure 4. The FTIR was recorded with KBr pressed pellets. The information about FTIR was added in manuscript in line 145.

 

Point 5: lines 168-174 and Fig. 4: The analysis of the XRD patterns is rather limited. More comments could be added about the assignment of peaks emerge in these patterns.

Response 5: More comments were added in XRD analysis in line 203-207 in manuscript.

 

Point 6: Add the correct references for the “Durability evaluation” section.

Response 6: The references have been added in “Durability evaluation” section in line 308:

41. Xie, A.; Wang, B.; Chen, X.; Wang, Y.; Wang, Y.; Zhu, X.; Xing, T.; Chen, G. Facile fabrication of superhydrophobic polyester fabric based on rapid oxidation polymerization of dopamine for oil–water separation. RSC Adv., 2021, 11, 26992-27002.
42. Gao, L.; Lu, Y.; Zhan, X.; Li, J.; Sun, Q. A robust, anti-acid, and high-temperature–humidity-resistant superhydrophobic sur-face of wood based on a modified TiO₂ film by fluoroalkyl silane. Surf. Coat. Tech., 2014, 262, 33-39.
43. Barthwal, S.; Barthwal S.; Singh, B.; Singh N.B. Multifunctional and fluorine-free superhydrophobic composite coating based on PDMS modified MWCNTs/ZnO with self-cleaning, oil-water separation, and flame retardant properties. Colloid Surface A, 2020, 597, 124776.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

It should be admitted that the authors have performed very serious revision and the manuscript's quality is much higher compared to the first draft. Therefore, it can be redirected for publication, but there are a few points that, whose explanation must appear in the text. 

1) I agree that for oil-in-water separation, the superhydrophobic coating will repel the water and likely the oil will not be able to reach the separation membrane. However, if using superhydrophilic materials, the water will be preferentially absorbed by the membrane, so the oil will remain in the ambience i.e., won't be able to be cleaned (extracted). As long as i consider the oil-water separation techniques using special-wettability-designed surfaces, the surface will need to preferentially adsorb/absorb the oil while repelling the water - this would be the perfect cleaning tool for oil spillages in water basins. So, there is obvious contradiction between the understanding of how a non-wettable membrane must operate and what is written in the text. Again, if the oil is too much in the water, in order to trigger the sorption process, a real case scenario would represent a environmental catastrophe. Please articulate clearly in the manuscript all of the aforementioned concerns. 

2) Video S4 (separation after 30 cycles) seems ok, but who guarantees that the membrane (sponge) on the video is the one used 30 times? I mean, there is no obvious and unambiguous evidence for the reusability of as-prepared oil-water separators. Perhaps showing a continuous video of a few consecutive experiments would be more convincing (without any stops, so the readers can see that indeed there is only one membrane used in all experiments). 

3) Figure 3, which is not legible does not show SEM images. It shows photos - so, please provide photos with higher magnification (i.e., make them by approaching the camera/smartphone closer to the samples and droplets). 

Author Response

Responses to Reviewer 2：

It should be admitted that the authors have performed very serious revision and the manuscript's quality is much higher compared to the first draft. Therefore, it can be redirected for publication, but there are a few points that, whose explanation must appear in the text. 

Point 1: I agree that for oil-in-water separation, the superhydrophobic coating will repel the water and likely the oil will not be able to reach the separation membrane. However, if using superhydrophilic materials, the water will be preferentially absorbed by the membrane, so the oil will remain in the ambience i.e., won't be able to be cleaned (extracted). As long as i consider the oil-water separation techniques using special-wettability-designed surfaces, the surface will need to preferentially adsorb/absorb the oil while repelling the water - this would be the perfect cleaning tool for oil spillages in water basins. So, there is obvious contradiction between the understanding of how a non-wettable membrane must operate and what is written in the text. Again, if the oil is too much in the water, in order to trigger the sorption process, a real case scenario would represent a environmental catastrophe. Please articulate clearly in the manuscript all of the aforementioned concerns. 

Response 1: Compared with superhydrophilic materials, the superhydrophobic materials are more suitable for oil collection from oil-water mixtures for oil absorption property. Increasing water pollution from frequent oil spills was usually caused by petroleum exploitation and transportation. In this case, the superhydrophobic absorbing materials could be used directly, which shows the great potential of application. The superhydrophobic filtrating materials also gained more popularity for simple operation and high separation efficiency. This part was discussed in manuscript in line 43-46 and 53-57. The superhydrophobic filtrating materials could be used for immiscible oil/water mixtures and water-in-oil emulsion, which has shortage in separation of oil-in-water emulsion.

 

Point 2: Video S4 (separation after 30 cycles) seems ok, but who guarantees that the membrane (sponge) on the video is the one used 30 times? I mean, there is no obvious and unambiguous evidence for the reusability of as-prepared oil-water separators. Perhaps showing a continuous video of a few consecutive experiments would be more convincing (without any stops, so the readers can see that indeed there is only one membrane used in all experiments). 

Response 2: If we make a continuous video of as-prepared sponge for separation after 30 cycles, the video is too long. Thus, the reusability of as-prepared sponge was deleted in manuscript.

 

Point 3: Figure 3, which is not legible does not show SEM images. It shows photos - so, please provide photos with higher magnification (i.e., make them by approaching the camera/smartphone closer to the samples and droplets). 

Response 3: The photos with higher magnification in Figure 3 were provided.

Round 3

Reviewer 2 Report

I support my positive opinion about this manuscript. It can be accepted for publication. The only thing i did not understand is why the authors have deleted the reusability part instead of enrich it (the video could be long, but there are ways to compress it). The latter will add a lot more scientific value to the published article. Plus, as commented in previous reports, a proof for reusable oil-water separation membrane is something that misses in the literature. Apart of that, good revision and interesting paper - congratulations.

Author Response

The video of continuous 30 cycles of oil-water separation is so long that its file size is still very big even if it is compressed.

The reviewer agreed the acceptance of the manuscript for publication. Thank you very much.