Template-Free Synthesis of One-Dimensional SnO2 Nanostructures Using Highly Efficient Hydrothermal Method
Round 1
Reviewer 1 Report
The present manuscript is focused on the synthesis of 1D tin oxide nanostructures. It can be noted that a detailed study of the produced nanostructures from various parameters such as synthesis time, temperature and chemical parameters was carried out. The synthesized structures have been examined in detail by advanced methods. Although I believe that some details are not sufficiently explained and some aspects need to be improved in order to accept the manuscript. Below are the questions and comments.
- The introduction provides a relatively detailed overview of the hydrothermal method of synthesis that the authors utilized in their work. However, it is a bit redundant. On the other hand, alternative synthesis methods that can be used are not given. It would be appropriate to make a comparative evaluation of available techniques, as well as the cited works, where the hydrothermal method was used;
- Also, in the section of the introduction, where potential applications are given, there are no references to actual works confirming the actuality of such a study;
- The manuscript demonstrate how the influence of various parameters leads to the formation of structures with different shape and morphology. Apart from the asbstract and next it says about the use of PVP, as a surfactant. What was the reasoning supporting the choice of this compound? Have any comparisons been done with other surfactants (at least in the literature). At what concentrations (ratios) does PVP work best and what is the reason?
- The manuscript provides a study of the synthesized structures from various parameters. It is recommended to add in the introduction or further - which shape and morphology of the nanostructures are promising for further applications;
- There is an omission in the text about some figures. For example, Fig. 1 and Fig. 7, however, there is no description or reference to these pictures in the text.
Author Response
Response to Reviewer 1 Comments
Point 1: The manuscript demonstrate how the influence of various parameters leads to the formation of structures with different shape and morphology. Apart from the asbstract and next it says about the use of PVP, as a surfactant. What was the reasoning supporting the choice of this compound? Have any comparisons been done with other surfactants (at least in the literature). At what concentrations (ratios) does PVP work best and what is the reason?
Response 1: The PEG[1] and CTAB[2] were used as surfactants, the hydrothermal time was too long for 24h. However, the addition of PVP can inhibit the precipitation of solute on the particles, thereby inhibiting the growth of crystals and yielding smaller particles. So We chose to use PVP as the surfactant. When the amount of PVP added was too low, the stability performance of small particles was poor[3]. But the addition of too much PVP[4] (100mg) had little effect on the morphology of 1DSnO2. Therefore, we chose to add 50mg of PVP.
[1] Zhou X, Fu W, Yang H, et al. Synthesis and ethanol-sensing properties of flowerlike SnO2 nanorods bundles by poly (ethylene glycol)-assisted hydrothermal process. Mater. Chem. Phys, 2010, 124(1): 614-618; DIO:10.1016/j.matchemphys.2010.07.022
[2] Chen D, Gao L. Facile synthesis of single-crystal tin oxide nanorods with tunable dimensions via hydrothermal process. Chem. Phy. Lett, 2004, 398(1-3): 201-206; DIO:10.1016/j.cplett.2004.09.055
[3] Shen X S. Shape-controlled synthesis, self-assembly and SERS properties of noble metal nanoparticles. Doctor’s Thesis, University of Science and Technology of China, Hefei, China, 2010.
[4] Lin Z J. Microstructure control and properties of Ag-SnO2 and Ag-Ni electrical contact materials. Doctor’s Thesis, Northeastern University, Shenyang, China, 2016.
Point 2:The manuscript provides a study of the synthesized structures from various parameters. It is recommended to add in the introduction or further - which shape and morphology of the nanostructures are promising for further applications;
Response 2: At present, 1DSnO2 are used for preparing gas-sensitive components, which can improve the sensitivity and accuracy of gas detection. In the follow-up study, we intend to prepare silver-based electrical contact material (AgSnO2(1D)) by combining the as-prepared 1DSnO2 with silver for comparing the mechanical and electrical properties with the traditional AgSnO2(0D). The present findings provide research direction for the development of high-performance silver-based electrical contact materials.
Point 3:There is an omission in the text about some figures. For example, Fig. 1 and Fig. 7, however, there is no description or reference to these pictures in the text.
Response 3: Fig.1 is intended to illustrate that 1DSnO2 is not available in an anhydrous ethanol system. In Fig. 7, we observed a different nanostructure from FIG. 6, which was shown to be a nanostructure with a larger aspect ratio in the high-resolution scanning electron microscope image. Due to the instrument, the nanostructure could only be observed at 400,000 times, and a higher magnification could only get a fuzzy picture.
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Reviewer 2 Report
In this work, the author introduced a synthesis method of SnO2 with one-dimensional structure. The effects of reaction time, solvent ratio and surface activity on the synthesis of the materials were investigated. In my opinion, there are some unclear representations and explanations of the work. Therefore, I believe this work need a major revision before its possible publication.
Here are some suggestions for the author to improve this article:
1. The author mentioned in the abstract that "The 1DSnO2 nanostructures were effectively observed 25 without a template". In fact, among the preparation methods mentioned in the article, PVP was introduced into the synthesis system as a structure directing agent.
2. In SEM images, many SnO2 nanostructures are not parallel to the observation plane, so the material aspect ratio measured by SEM images is inaccurate.
3. The SnO2 material introduced by the author has a clear shape. What are the main exposed crystal faces of SnO2?
4. This paper focuses on the preparation method of a material, and touts the possibility of industrialization of this method. How high is the yield of this preparation method and how long does it take? Are there clear advantages compared with existing preparation methods?
5. The author introduces a synthetic method of SnO2 with one-dimensional structure. Then what is the use of obtained materials? It is also suggested that the author briefly discuss.
Author Response
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Reviewer 3 Report
Dear Author:
In my viewpoint, the manuscript number applsci-2120746 titled "Template-free synthesis of one-dimensional SnO2 nanostructures using highly efficient hydrothermal method" can be accepted after minor revision. In this sense, I suggest to cut off the reference 17, since such authors (ref 17) developed a great number of materials based on the equilibrium idea of crystals.
In this sense, the development of multiple geminate crystals is a condition out of equilibrium.
Continuing, I suggest strongly that the approach of authors be based on set of acicular crystals, a kind of druse of crystals.
Also, the very high aspect ratio of crystals should be shown in the specific diffraction line that should turn explicit the preferential grain growth via increasing of intensity of a hkl diffraction line.
Author Response
Response to Reviewer 3 Comments
In my viewpoint, the manuscript number applsci-2120746 titled "Template-free synthesis of one-dimensional SnO2 nanostructures using highly efficient hydrothermal method" can be accepted after minor revision. In this sense, I suggest to cut off the reference 17, since such authors (ref 17) developed a great number of materials based on the equilibrium idea of crystals.
In this sense, the development of multiple geminate crystals is a condition out of equilibrium.
Continuing, I suggest strongly that the approach of authors be based on set of acicular crystals, a kind of druse of crystals.
Also, the very high aspect ratio of crystals should be shown in the specific diffraction line that should turn explicit the preferential grain growth via increasing of intensity of a hkl diffraction line.
Response: Thank you very much for your advice. We have deleted Ref. [17] and Figure 5(b) has been revised according to your suggestion.
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Reviewer 4 Report
In the manuscript, the author represents about: “Template-free synthesis of one-dimensional SnO2 2 nanostructures using highly efficient hydrothermal method”. The manuscript is too simple with the list of the experimental results of SEM images but without explanation and discussion. Moreover, the author needs to measure more properties of the material as optical, electrical, thermal properties, and chemical activity. Besides, the author needs to clearly answer some issues:
21. What is the name of the sample in Fig. 5b.
32. The SEM images in Fig. 3 should be on the same scale to compare all samples.
43. The references are too old. The author needs to find the new reference.
14. The caption of Fig. 7a and b need to be clear because they are zoom images.
Author Response
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Round 2
Reviewer 1 Report
The authors have revised the manuscript considerably, but some of the questions and comments have been ignored.
First of all, it relates to the comments about the existing ALTERNATIVE methods of synthesis. A detailed description of the present techniques of the hydrothermal method is quite sufficient.
- The introduction provides a relatively detailed overview of the hydrothermal method of synthesis that the authors utilized in their work. However, it is a bit redundant. On the other hand, alternative synthesis methods that can be used are not given. It would be appropriate to make a comparative evaluation of available techniques, as well as the cited works, where the hydrothermal method was used;
- As for the comment about Fig. 1 and Fig. 7.
In the case of Fig. 1: these images appear in section 3.1, but the description only in section 3.2 and on another page. This location is extremely inconvenient. In the case of Fig. 7. There is no mention of this figure in the TEXT. So it is either not important to the manuscript, or there is a mistake in the text.
- In response to question #2, the authors do not explain the shape and morphology of the synthesized samples, although such studies are provided in the manuscript. Since the major application in the future is gas sensing, size and porosity will play a key role. This issue should be clarified.
Author Response
Response to Reviewer 1 Comments
The authors have revised the manuscript considerably, but some of the questions and comments have been ignored.
First of all, it relates to the comments about the existing ALTERNATIVE methods of synthesis. A detailed description of the present techniques of the hydrothermal method is quite sufficient.
Point 1:- The introduction provides a relatively detailed overview of the hydrothermal method of synthesis that the authors utilized in their work. However, it is a bit redundant. On the other hand, alternative synthesis methods that can be used are not given. It would be appropriate to make a comparative evaluation of available techniques, as well as the cited works, where the hydrothermal method was used;
Thank you very much for your advice, and the response to your suggestion is stated as follows:
Response 1: The introduction provides that the current hydrothermal preparation of 1DSnO2 nanostructures required more than 12h hydrothermal time, which can be reduced to 12h by the experiment in this paper. So we believe that this paper made a contribution to the reduction of hydrothermal time.
Point 2:-As for the comment about Fig. 1 and Fig. 7.
In the case of Fig. 1: these images appear in section 3.1, but the description only in section 3.2 and on another page. This location is extremely inconvenient. In the case of Fig. 7. There is no mention of this figure in the TEXT. So it is either not important to the manuscript, or there is a mistake in the text.
Response 2:We simply explained that 1DSnO2 nanostructures could not be obtained by hydrothermal method in pure anhydrous ethanol system in section 3.1. We discussed that 1DSnO2 nanostructures were obtained by hydrothermal method from the mixed solution of anhydrous ethanol and deionized water in specific volumes in section 3.2. The results showed the experimental process that the author prepared 1DSnO2 nanostructures in Fig.1. So we thought this process was important. We observed nanorods with small aspect ratio and nanowire with large aspect ratio through the product of the same experiment in Figure 6 and Figure 7 respectively. So We thought that the results were two different nanostructures in Fig.6 and Fig.7. We should present the results of the experiment through the paper.
Point 3:-In response to question #2, the authors do not explain the shape and morphology of the synthesized samples, although such studies are provided in the manuscript. Since the major application in the future is gas sensing, size and porosity will play a key role. This issue should be clarified.
Response 3: One cause for instability in powdered and polycrystalline SnO2 sensors is growth and conglomeration of grains, but if the 1DSnO2 morphology is single crystalline, this origin for instability should not be relevant. The high surfaceto-volume ratio of nanomaterials can provide more positions for absorbing gas molecules.
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Author Response File: Author Response.docx
Reviewer 2 Report
The revised manuscript could be published in Applied Sciences.
Author Response
Thank you very much for your advice.
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 4 Report
After reading a revised version, I have some suggestions as follows:
1 1. The author needs to format the paragraph Justify (not Align Left).
2. The SEM images in Fig. 1, 2, and 4 should be on the same scale to compare all samples.
Author Response
Response to Reviewer 4 Comments
Thank you very much for your advice, and the response to your suggestion is stated as follows:
Point 1:The author needs to format the paragraph Justify (not Align Left).
Response 1: We revised the paragraph format.
Point 2:The SEM images in Fig. 1, 2, and 4 should be on the same scale to compare all samples.
Response 2: We have basically completed the unification of scales in Figure 1, 2 and 4. Figure 4(a) uses 10μm because the one-dimensional structure cannot be observed under a 20μm scale.
Point 3: What is the name of the sample in Fig. 6, 7?
Response 3: The nanorods with a small length-diameter ratio, it were observed in Fig. 6 , the nanowires with a large length-diameter ratio were observed in Fig. 7 through FSEM. We have named the sample in Fig. 6 as nanorods and the sample in Fig. 7 as nanowires.
Point 4: You don’t change the caption of Fig. 7.
Response 4: We have completed the revision as required.
Point 5:In line 289 on page 8, the author needs to measure the specific surface energy. The author shouldn’t use the results from other references due to the condition differences.
Response 5: Although the synthetic parameters are different, the products are all rutile phase SnO2. For rutile phase SnO2, computer simulation studies have demonstrated that the sequence of surface energy in different crystallographic orientations is (001)>(101)>(100)>(110), that is, the (001) crystal face has the highest surface energy. References([5]、[8]、[10]) cited the calculation results of [23-24]. So we cited the calculation results of [23-24] in the paper.
Point 6: In conclusion, the author said: “after reaction for 8-48h” (in line 315), but the experiment is 12-48h in the manuscript.
Response 6: It is mentioned here that 8-48h is the reaction time in Figure 1, and the experimental conditions were: with absolute alcohol, without the addition of PVP, and after reaction for (8,12,48)h at a temperature of 200 ℃, lamelliform SnO2 was observed in the products, but 1DSnO2 was not detected.
Point 7: Finally, I don’t know which is the best condition for the synthesis SnO2 in your research.
Response 7: Only 1DSnO2 was observed in Fig4(a). So the optimum experimental conditions were at the reaction temperature of 200 ℃, reaction time of 12h, and V = 1:1, with the addition of 50 mg PVP, the product morphology exhibited microsphere structures of 1DSnO2.
Author Response File: Author Response.docx
