Facile Synthesis of Dual Modal Pore Structure Aerogel with Enhanced Thermal Stability
, Chongfei Tian 1, Xinsheng Zhang 3 and Zhongtao Luo 1,*Round 1
Reviewer 1 Report
This paper presents a study of aerogel which was prepared with atmospheric drying. This paper is well written and suggested for publication after some minor changes:
- Fig. 3 shows a drop in contact angle between a volume ratio of 0.8 and 0.6, without a discussed explanation. The microstructure (Fig. 4) is comparable in both cases and a better explanation for the results in Fig. 3 is necessary.
- Larger magnifications in Fig 4 (a) - (d) for better comparison of micro-structure
- Table 2 - could you please describe what the typ of pore size you are presenting in this table (mean or median pore size and standard deviation)
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Under atmospheric drying conditions (APD), the author created vinyl-functionalized silica aerogel using vinyl-triethoxysilane (VTES) and water glass (W) as co-precursors. The primary issue with the co-precursor approach of making aerogel is skeletal collapse. The author employed vinyl-triethoxysilane (VTES) to solve this problem by fortifying the 3D network. A substance with a high degree of cross-linking reaction, low toxicity, and high hydrophobicity is vinyltriethoxysilane (VTES). The co-precursors' components had an impact on how well aerogels performed. The prepared aerogel has exceptional properties such as low thermal conductivity (0.0254 W/(mK)), super hydrophobic (hydrophobic angle of 160°), high specific surface area (890.76 m2/g), high porosity (96.82%), and low density (0.087 g/cm3) when the VTES:W ratio was 0.8. SEM and BET test findings revealed that the VTES: W ratio had an impact on the pore structure. The aerogel had a dual modal pore structure consisted of both small (6–8 nm) and large (20–30 nm) mesopores when the VTES: W ratio was approximately 0.8, which may have helped to increase the aerogel's skeletal strength. However, by lowering the capillary force, the addition of vinyltriethoxysilane improved the skeleton's stability. The unique co-precursor combinations of vinyltriethoxysilane and water glass can offer direction for the production of aerogels under APD circumstances. So, the work is interesting and well-written with proper explanation.
So, the work can be published as it is.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript ” Facile synthesis of dual modal pore structure aerogel with enhanced thermal stability” addresses the current problem of preparing mechanically stable and superinsulating aerogels without using supercritical drying. The ideas are interesting and the most of the measurements seem to be carried out with care. However, the technical quality of the manuscript needs to be substantially improved before publication.
General issues:
Materials and Methods:
1.) The synthesis conditions and the preparation steps are not given in full details. The absolute amounts (volume, mass, molar amount) and the relative ratios of the reagents are not given. The physical and chemical steps and conditions are not given in details. Without these, the procedures cannot be reproduced.
2.) The description of the characterization methods is almost completely missing or very incomplete. There is nothing on the delicate thermal conductivity measurements. Water contact angle determination is only mentioned, and the full process is not given, which could validate the results.
Results and Discussion:
3.) There are no error bars or ±SD values given anywhere, neither in Figures, nor in Tables. This flaws makes it impossible to assess the validity of the experimental data.
Specific Issues:
4.) The IR technique alone is not sufficient for identifying and contrasting the structures of the different aerogels to one another. Preferably, solid-state NMR, or maybe XPS should be used to validate the assumptions phrased on the chemical structures in Sections 3.5 and 3.6.
5.) In order to support the discussion on the morphological evolution of the aerogels, much higher magnification SEM images should be presented.
6.) The formation of the gel structure, i.e. the mechanisms of the concerted hydrolysis and polycondensation reactions have been investigated, both by experimental and by theoretical methods for a long time. Please find the appropriate models in the literature, cite the appropriate references, and build the discussion in Section 3.6.
7.) Figures 9, 10, 11, 12 are instructive for demonstration, but they are only presentation quality. Additional information should be added both in the graphical content and in the captions to focus their meaning and purpose.
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
1. The novelty of the presented work remains insufficiently justified. Is VTES and water glass (W) selected as the co-precursor combinations to prepare vinyl-functionalized silica (VF-SiO2) aerogel under APD first time ever? If not, and there were other authors' attempts to use this or similar technological paths, it should be discussed in the Introduction showing the novelty and added value of the presented work.
2. How thermal conductivity was measured?
3. In „3.5. Chemical structure“ it is written, „According to previous reports...“. Would be useful to show references.
4. There are lots of presumptions in “3.6. Synthesis mechanism”: for example “…the particle surfaces are, thereafter, adequately covered by silanol groups (Si-OH)…”, “…There are only a few Si-O-Si bond connections in these defects…”, “…under the combined action of W sol and V sol, a large number of Si-O-Si bonds (as derived from W) increases the cross-linking degree…”. If all these presumptions were related to the FT-IR spectra of the samples, it should be interrelated and properly discussed, because of the synthesis mechanism as presented looks speculative and insufficiently justified.
5. It is written in the conclusions “…the strength of surface free energy…”. Consider changing it to simple “…the surface energy…”.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
My original comment No. 4 was rebutted in the authors' response. I find this piece of chemical information substantial to prove the reasoning on the structure of the gels. Thus, the manuscript is still not ready for publication.
"4.) The IR technique alone is not sufficient for identifying and contrasting the structures of the different aerogels to one another. Preferably, solid-state NMR, or maybe XPS should be used to validate the assumptions phrased on the chemical structures in Sections 3.5 and 3.6."
Author Response
Response to Reviewer 3 Comments
The manuscript ” Facile synthesis of dual modal pore structure aerogel with enhanced thermal stability” addresses the current problem of preparing mechanically stable and superinsulating aerogels without using supercritical drying. The ideas are interesting and the most of the measurements seem to be carried out with care. However, the technical quality of the manuscript needs to be substantially improved before publication.
The IR technique alone is not sufficient for identifying and contrasting the structures of the different aerogels to one another. Preferably, solid-state NMR, or maybe XPS should be used to validate the assumptions phrased on the chemical structures in Sections 3.5 and 3.6.
Response: Thank you very much for your suggestion. In accordance with your suggestion, we perfected this part, and the revised results are as follows:
Modification: The peaks at -58ppm and -67ppm are T2 and T3 peaks of Si respectively, which correspond to C2H3Si(-O)2(-OH)1 and C2H3Si(-O)3 in aerogel, and the latter (T3) peak is stronger, indicating that most of the Si-OH in VTES and water glass have been completely hydrolyzed. VTES and water glass condense together into C2H3Si(-O)3, and the weak T2 peak is mainly due to the small amount of silicon hydroxyl group remaining. On the left side of the spectrum, there are two relatively small peaks at -105ppm and -113ppm, corresponding to Q3 and Q4 peaks, which can be regarded as Si(-O)3(-OH)1 and Si(-O)4, which are structural fragments formed by self-polymerization of sodium silicate. Q4 peak is stronger than Q3, mainly because of the high degree of hydrolysis of water glass, and only a small amount of silicon hydroxyl is unhydrolyzed.
Author Response File: Author Response.docx
Reviewer 4 Report
The manuscript was properly improved following most of the reviewers comments.
Author Response
Thank you for your suggestions, and we have supplemented and improved the manuscript again according to the second review suggestions. The reviewer comments make the content of the article more substantial.
