Robust Super-Amphiphobic Titanium Surface for Liquid/Liquid Mini Separations
Round 1
Reviewer 1 Report
In the current work, the authors have claimed an in-site synthesis of nanoscale flower-like TiO2 on the surface of a titanium mesh via a hydrothermal method. The authors have also claimed the fabrication of a super-amphiphobic coating with excellent chemical and mechanical durability which after irradiation for 8 h with ultraviolet light, was used for oil/water and oil/oil mini-separations. Overall, the authors have performed a systematic study but failed to demonstrate any novelty in this work. There are some serious flaws in the work and some comments must be addressed by the authors:
Comment 1: Abstract must be rewritten. There is no need for discussing the fabrication methodology in the abstract. The abstract must be the summary of the research article which must discuss what, why, how and result very briefly.
Comment 2: Introduction is not sufficient. Authors must discuss various types of ampiphobic coating other than TiO2 and emphasize the importance of this subject.
Comment 3: In the methodology section, the authors have etched the TiO2 mesh with HCl followed by hydrothermal treatment, HF treatment and FOTS treatment. Is this method earlier reported? If yes, why the literature has not been cited? If not, how did the authors optimize the methodology parameters? Explain.
Comment 4: In the abstract, the author claimed the synthesis of flower-like TiO2, however, in the methodology section the authors are only modifying the already fabricated titania mesh. Can the author comment on these contradictory claims?
Comment 5: What is the source of Titania mesh? Write in detail the purity of all materials along with the source of procurement.
Comment 6: In the abstract authors claim nanoscale flower, however, the FESEM images does not validate their claims, since the structure is in the micron range rather than the nano range. Can the author explain this anomaly?
Comment 7: In section 3.2, fig. 2a, which etched mesh author is referring to ? 4h, 6h, 7h, 8h, or 10 h treated mesh?
Comment 8: Authors have discussed "Fabrication of unidirectional oil-transport Ti mesh", " Self-cleaning, chemical and mechanical stability of super-amphiphobic Ti mesh", and " Liquid/liquid mini separations of Ti mesh". However, the authors have not given any mechanism for these results. The results are not supported by proper justifications. The authors must explain the tentative mechanism for all these results for a better understanding of the reader
Author Response
Comment 1: Abstract must be rewritten. There is no need for discussing the fabrication methodology in the abstract. The abstract must be the summary of the research article which must discuss what, why, how and result very briefly.
Answer: We have rewritten the abstract as follows:
Super-amphiphobic surface with low robustness is not suitable for practical application due to its weak mechanical strength. In this work, an in-site growth of micro-/nanoscale flower-like TiO2 on the surface of a titanium mesh was successfully fabricated through hydrothermal synthesis, followed by chemical modification with low-surface-energy heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane. The resultant super-amphiphobic coating was highly repellent to all of the ethanol-water mixtures with surface tensions ranging over 26.0–72.8 mN/m, as well as excellent chemical and mechanical durability. After it was irradiated for 8 h with ultraviolet light, it was used for oil/water and oil/oil mini-separation with the help of its Janus characteristic. This was attributed to its unidirectional penetration for liquid droplets having different surface tensions. This kind of smart super-amphiphobic mesh with photochemical activity could potentially gate and sort liquids via surface tensions.
Comment 2: Introduction is not sufficient. Authors must discuss various types of ampiphobic coating other than TiO2 and emphasize the importance of this subject.
Answer: we have added some descriptions about various types of amphiphobic coatings other than TiO2 and emphasized the importance of this subject (see line 37-39). Moreover, another two papers were cited for the description involved in this part as follows.
- Liu, K.F.; Li, P.P.; Zhang, Y.P.; Liu, P.F.; Cui, C.X.; Wang, J.C.; Qu, L.B. Laboratory filter paper from superhydrophobic to quasi-superamphiphobicity: facile fabrication, simplified patterning and smart application. Cellulose 2019, 26:3859–3872.
- Li, D.; Guo, Z. Versatile superamphiphobic cotton fabrics fabricated by coating with SiO2 /FOTS. Appl.Sur. Sci. 2017, 426, 271–278.
Comment 3: In the methodology section, the authors have etched the TiO2 mesh with HCl followed by hydrothermal treatment, HF treatment and FOTS treatment. Is this method earlier reported? If yes, why the literature has not been cited? If not, how did the authors optimize the methodology parameters? Explain.
Answer: Actually, in line 53, we have cited the previous papers for the in-situ growth of TiO2 nanoparticle on the surface of Ti substrate. Here, we report in situ synthesis of TiO2 nanoparticles on a Ti substrate based on previous reports [15,16]. Now, we also cited the papers in the methodology section in our revised manuscript (see line 69). Many thanks for the reviewer’s kind suggestion!
Comment 4: In the abstract, the author claimed the synthesis of flower-like TiO2, however, in the methodology section the authors are only modifying the already fabricated titania mesh. Can the author comment on these contradictory claims?
Answer: Many thanks for the reviewer’s comment ! We have changed it to “an in-site growth of micro-/nanoscale flower-like TiO2 on the surface of a titanium mesh……”. Based on the previous study, we have immersed the etched mesh in the FOTS solution in order to obtain a superamiphiphobic surface. Moreover, a Janus mesh fabricated after UV irradiation was successfully used for new application of mini-separation of liquid/liquid droplets.
Comment 5: What is the source of Titania mesh? Write in detail the purity of all materials along with the source of procurement.
Answer: Actually, in line 62, we have ever given the purity of Ti mesh (99.5%), herein, we added the source of Ti mesh. A Ti mesh (Hebei Kangwei Wire Mesh Co., Ltd, Hengshui City, China with the thickness of 0.60 mm or so and an aperture of 300 mesh was used in our experiments.
Comment 6: In the abstract authors claim nanoscale flower, however, the FESEM images does not validate their claims, since the structure is in the micron range rather than the nano range. Can the author explain this anomaly?
Answer: Anyway, the clusters with micron range on the surface of Ti mesh are formed from many small in-site growth nano-size TiO2 particles. The micro-/nanoscale flower in our abstract was replaced in our revised manuscript.
Comment 7: In section 3.2, fig. 2a, which etched mesh author is referring to ? 4h, 6h, 7h, 8h, or 10 h treated mesh?
Answer: Here, meshes in Fig.2a are referring to the pristine mesh, the etched mesh and modified mesh by FOTS, all samples are not irradiated. The resulted mesh is super-amphiphobic and photosensitive.
Comment 8: Authors have discussed "Fabrication of unidirectional oil-transport Ti mesh", " Self-cleaning, chemical and mechanical stability of super-amphiphobic Ti mesh", and " Liquid/liquid mini separations of Ti mesh". However, the authors have not given any mechanism for these results. The results are not supported by proper justifications. The authors must explain the tentative mechanism for all these results for a better understanding of the reader
Answer: In our revised manuscript, we have added some sentences to discuss the mechanism of superamphiphobic surface and the mini separation as follows:
These results are in good agreement with the Cassie and Baxter model. The re-entrant geometries allowed air to be trapped in the crevices and gaps of the microstructures under the liquid droplets, resulting in the formation of a rough surface. Air and the FOTS film on this surface provided low surface energy, thus widening the contact angles of the re-entrant geometries and reducing the contact area of the liquid droplets with the surface. Therefore, superoleophobicity and superhydrophobicity depend on the synergistic effects of both surface structures and chemistry. (see line 110-114 )
The oleophilicity-to-oleophobicity gradient profile could be well tailored by the UV-irradiation time, which led to the selectivity of the unidirectional liquid transport property. (see line 213-215)
Reviewer 2 Report
The designed materials are impressive, having amphiphobic properties as well as excellent chemical and mechanical properties. The authors modified a Ti mesh and clearly demonstrated the newly formed material's ability to separate both oil/water and oil/oil mixtures. I only have some minor inquiries/revisions:
- line 72 – close parentheses after describing the equipment
- Figure 1S, image e shows smaller TiO2 particles after treatment with FOTS, compared with the size of the TiO2 particles after etching (Figure 1 e) – can the authors try to explain why the immersion in FOTS led to a change in the patricle size only for this sample (8h etching time)?
Author Response
- Comment 1: line 72 – close parentheses after describing the equipment
- Answer: we have added close parentheses in our revised manuscript
- Comment 2: Figure 1S, image e shows smaller TiO2 particles after treatment with FOTS, compared with the size of the TiO2 particles after etching (Figure 1 e) – can the authors try to explain why the immersion in FOTS led to a change in the patricle size only for this sample (8h etching time)?
- Answer: In principle, FOTS immersion will not lead to the size change for the in-site growth TiO2 particles. It is probably attributed to the different position of the UV irradiated (8h) mesh when they were characterized by SEM. Another possibility resulted from two different samples, one etched mesh and another etched mesh after FOTS modification were used for SEM, respectively. So It looks like there are some nuances for their SEM images.
Reviewer 3 Report
The study deals with the detailed development of synthetic and fine-tuning procedures for producing flower-like TiO2 nanostructures. The basic outcome is the achievement of experimental evidences for the onset of super-amphiphobic material, with well-expressed self-cleaning properties, and enhanced chemical stability with respect to corrosive liquids (acidic, basic, and salt solutions). Particularly important is the key result that the Ti substrate (modified Ti mesh) has a finely tunable and switchable wettability following ultraviolet (UV) irradiation. This property signals about high potential for broader application options, e.g. in liquid/liquid separation processes.
The manuscript is well-focused; the materials processing details are clearly and convincingly presented. The MS will be of considerable interest to the readers of MDPI Coatings and might be published in the present form.
Round 2
Reviewer 1 Report
The authors have addressed the commnets. The manuscript can now be accepted for publication.
