Synthesis of Multiwalled Carbon Nanotubes on Stainless Steel by Atmospheric Pressure Microwave Plasma Chemical Vapor Deposition

Round 1

Reviewer 1 Report

This paper presents an atmospheric pressure microwave plasma synthesis of carbon nanotubes on a 304 stainless steel substrate. The novel feature of this method is the demonstration of an efficient production of carbon radicals from ethanol precursor at atmospheric pressure. The experimental setup and synthesis conditions are adequately described so that it can be reproduced by other laboratories. The carbon nanotube characterization by XPS, SEM, TEM, and Raman is adequate.

There is phrase which is repeated in the paper at several locations "The mess of CNTs.." The authors should clarify the meaning of this phrase whether they mean total mass of CNTs produced under a given condition. The CNTs yield should be quantified in some way and reported in the paper.

Since the paper summary emphasizes growth at 500 degree Celsius. Figure 5 HRTEM should show comparison between quality at 500 degree Celsius and 800 degree Celsius if such data is available.

Overall, I recommend publication after these revisions are carried out.

Author Response

Dear Reviewer,

Thank you very much for your review. Your revise advice is very helpful to me, and I have revised my article according to your suggestions.

 

1. There is phrase which is repeated in the paper at several locations "The mess of CNTs.." The authors should clarify the meaning of this phrase whether they mean total mass of CNTs produced under a given condition. The CNTs yield should be quantified in some way and reported in the paper.

 

Answer: “the mess of CNTs” is a mistake I have changed it to “the total mass of CNTs is 300mg”, which was shown in line 225. Because the precursor has been completely decomposed by plasma, we introduced the conversion efficiency of precursor and CNTs to characterize the effect of temperature on the growth of CNTs (line 222-228).

 

2. Since the paper summary emphasizes growth at 500 degree Celsius. Figure 5 HRTEM should show comparison between quality at 500 degree Celsius and 800 degree Celsius if such data is available.

 

Answer: It was my negligence not to provide HRTEM results at 500 °C in Figure 5. Therefore, I have added the HRTEM results of 500, 600, 700 in Figure 5. By comparing the microstructures of CNTs at different temperatures, we found that the CNTs prepared at 700 and 800 °C consist of hollow compartments which is not obvious at 500 and 600 °C, and the carbon layers of CNTs grown at high temperatures are neater than that grown at low temperatures. The causes of this phenomenon are given.(line 246-253, and line 255-258).

 

Thank you for your review once more.

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China

Reviewer 2 Report

The manuscript applsci-798254 deals with the preparation of carbon nanotubes by atmospheric pressure microwave plasma CVD using 304 stainless steel as the catalyst and ethanol as the carbon source. The authors prepared CNT at different temperatures (400°C-1000°C) and diverse content of ethanol at 600°C. The samples have been compared based on SEM observations. But only the sample obtained at 800°C have been deeply characterized. 

 

The authors can find my three significant comments below. 

- the title is not enough specific, and the reader can expect that it is a review about the synthesis of CNT by atmospheric pressure microwave plasma CVD. 

- the authors claimed that this study is the first dealing with the synthesis of CNTs from ethanol on the 304 stainless steel substrate at 500°C by atmospheric pressure microwave plasma CVD. But as the full characterization of the sample obtained at 500°C is not presented, we can not conclude about the type and quality of the deposited carbonaceous materials. 

- there is no comparison with the literature (only 13 references). 

 

Hence, the authors need to do more experiments and analysis and to rewrite several parts of the manuscript. Those are the reasons why I reject this manuscript for publication in Applied Sciences.

Author Response

Dear Reviewer,

Thank you very much for your review. Your revise advice is very helpful to me, and I have revised my article according to your suggestions.

 

1. the title is not enough specific, and the reader can expect that it is a review about the synthesis of CNT by atmospheric pressure microwave plasma CVD.

 

Answer: I will ask the editor if I can change my title to “Synthesis of Multi-walled Carbon Nanotubes on the Stainless Steel by Atmospheric Pressure Microwave Plasma Chemical Vapor Deposition”.

 

 

2. the authors claimed that this study is the first dealing with the synthesis of CNTs from ethanol on the 304 stainless steel substrate at 500°C by atmospheric pressure microwave plasma CVD. But as the full characterization of the sample obtained at 500°C is not presented, we can not conclude about the type and quality of the deposited carbonaceous materials.

 

Answer: It was my negligence not to provide the characterization results of the sample obtained at 500 °C. I have added the HRTEM results of 500, 600, 700 in Figure 5. By comparing the microstructures of CNTs at different temperatures, we found that the CNTs prepared at 700 and 800 °C consist of hollow compartments which is not obvious at 500 and 600 °C, and the carbon layers of CNTs grown at high temperatures are neater than that grown at low temperatures. The causes of this phenomenon are given.(line 246-253, and line 255-258).

 

 

3. there is no comparison with the literature (only 13 references).

 

Answer: I added 9 references(3 CVD, 1 DC-PECVD, 2 RF-PECVD, and 3 MPCVD) to my article, and list the parameters needed by different kinds of PECVDs in the synthesis of nanomaterials in detail (line 39-57). The advantages of AMPCVD compared to other techniques used for the synthesis of CNTs was shown in line 90-95.

 

Thank you for your review once more.

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China

Reviewer 3 Report

The manuscript has interesting results for the readers, who intend to apply the CNT and stainless steel composite system into various industrial fields. However, the present manuscript has a room for improvements as follows:

In Introduction: There are less relevant references on CVD growth method using normal (low pressure) PECVD. Although the author insists that the CVD growth temperature is normally beyond 1200 C, I consider that the minimum growth temperature by CVD is limited to the growth of single-walled not but multi-walled CNTs. I recommend that the author explain the difference in the minimum growth temperature  among different CNT structures by presenting the relevant references. In addition, the author may present the importance and research history of the direct CNT growth on stainless steels.

In lines 174 and 184: The author should explain the word "the mess of CNT" quantitatively. If the "mess" should be replaced by "mass", I recommend that the author describe the temperature dependence of the growth mass per unit surface in more detail or quantitatively.

Author Response

Dear Reviewer,

 

Thank you very much for your review. Your revise advice is very helpful to me, and I have revised my article according to your suggestions.

 

1. In Introduction: There are less relevant references on CNTs growth method using normal (low pressure) PECVD. Although the author insists that the CVD growth temperature is normally beyond 1200 C, I consider that the minimum growth temperature by CVD is limited to the growth of single-walled not but multi-walled CNTs. I recommend that the author explain the difference in the minimum growth temperature among different CNT structures by presenting the relevant references.

 

Answer: I provide another 9 references (include 3 CVD, 1 DC-PECVD, 2 RF-PECVD and 3 MPCVD, all the CNTs mentioned in the references are multi-walled) in the article and list the parameters needed by different kinds of PECVDs in the synthesis of CNTs in detail (line 39-57). The advantages of AMPCVD compared to other techniques used for the synthesis of CNTs was shown in line 90-95.

 

 

2. In addition, the author may present the importance and research history of the direct CNT growth on stainless steels.

 

Answer: We chose stainless steel as the substrate because it is cheap and easy to access. In addition, small metal droplets can be formed on the surface at high temperature as catalyst for the growth of CNTs. In fact, it is not an ideal substrate, because the catalyst particles formed by stainless steel contain many impurities and are uneven in size, there is rarely study of the direct CNT growth on stainless steels. The main purpose of this experiment is to study the feasibility of AMPCVD in the synthesis of nanomaterials, and more research is needed to make it play a greater role in the synthesis of nanomaterials.

 

 

3. In lines 174 and 184: The author should explain the word "the mess of CNT" quantitatively. If the "mess" should be replaced by "mass", I recommend that the author describe the temperature dependence of the growth mass per unit surface in more detail or quantitatively.

 

Answer: “The mess of CNTs” is a mistake, I have changed it to “the total mass of CNTs is 300mg”, which was shown in line 225. Because the precursor has been completely decomposed by plasma, we introduced the conversion efficiency of precursor and CNTs to characterize the effect of temperature on the growth of CNTs (line 222-228).

 

 

Thank you for your review once more.

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China

Reviewer 4 Report

The manuscript by Dashuai Li et al. entitled: "Synthesis of Carbon Nanotubes by Atmospheric Pressure Microwave Plasma Chemical Vapor Deposition" is an interesting research work of interest to the scientific community involved in CNTs research and in general involved in composite materials with various forms of carbon (in this case CNTs). Unfortunately the authors despite of the interesting work the manuscript as it is written is very difficult to understand at once due to the poor quality in English. I would strongly suggest and recommend that prior to resubmitting the authors should check thoroughly the English language and style in order to thoroughly improve their work. I recommend publication after major revision. The authors should also answer the following questions/remarks:

1. In the Introduction the authors mention: “But it has not been widely used in the field of nanomaterial synthesis due to the characteristics of the excitation difficulty, open space, and stability of atmospheric pressure microwave plasma.” What exactly due they mean with this phrase? What is open space, which characteristics of the excitation difficulty are they referring to? I strongly believe that in order for this work to be accepted not only for publication but from the scientific community the authors should in detail explain why there is so scarce use of the atmospheric pressure microwave plasma and how their work will lead to enhanced improvement on the application of the technique.
2. Also in the Introduction the authors mention: “The present experiment is focused on the decomposition ability of the microwave plasma for precursor and the nanomaterial growth influenced by temperature of the tube furnace. In this study, we have synthesized CNTs on the stainless steel substrate using AMPCVD technology with the ethanol as carbon source at the temperature of 500 °C. We also remind the reader that there is no earlier study of nanomaterial synthesis by AMPCVD.” This is an example of the poor English used to elaborate major statements of the research work. The last sentence is very important (“We also remind the reader that there is no earlier study of nanomaterial synthesis by AMPCVD”) but it is lost within the text and is not strengthened as it should. Actually I strongly suggest the authors to consider rewriting the Introduction part showing prominent attention on the importance of their work compared to what has been mentioned in the literature. They should provide a straightforward part in the Introduction of the advantages of AMPCVD compared to other techniques used for the synthesis of CNTs and in general carbon related materials.
3. In Materials and Methods the AMPCVD schematic diagram in Figure 1 should be very thoroughly explained. Why the used source is ethanol and not any other alcohol? How is the set-up of the coaxial plasma generator? Why the gas control system includes three mass flowmeter?
4. In general how did the authors conclude for the specific decomposition rates of ethanol precursor at the specific different temperatures? Was their decision based on any literature already reported for CNTs synthesis or it was based on their knowledge and experience on the specific subject?
5. In the Results and Discussion part the authors mention: “the decomposition of ethanol is all about 99% when the microwave plasma is turned on, no matter what the temperature of tubular furnace is”. Therefore even at 400 °C or 1000 °C the decomposition is similar and up to 99%. Why not 100% decomposition of the ethanol? Is that possible and under which conditions and circumstances?
6. According to the above comment and question the sentence the authors use: “So we can prove that the atmospheric pressure microwave plasma indeed does decompose the precursor completely” is not correct since they do not mention 100% decomposition.
7. The analysis of Figure 4 (SEM results) is very weak and does not convince the reader of what the authors are trying to prove. Actually they mention that: “the most suitable temperature for the growth of CNTs on the stainless steel substrate is 800 °C” and then in Figure 4 (g-i) they give SEM images of substrates with the growth situation of carrier gas for the precursor of 100, 200, and 300 sccm at the temperature of 600 °C instead of 800 °C as one should expect. The authors should reconsider changing the specific part of Figure 4 and the respective analysis.
8. The images given at Figure 5 [especially those at Figure 5(d), (e) and (f)] from HRTEM are of excellent quality and prove that the resulted CNTs are MWCNTs with layers’ average number of 10-20 (as the authors mention).
9. The phrase: “tightly aligned with a high density of graphite sheets with a thickness of 6.4 nm, and the distance between layers is 0.35 nm” is not something seen for the first time but is what should be expected for MWCNTs characterization. Actually did the authors make any thorough study whether or not the number of layers is reproducible in all temperatures above 600 °C and up to 800°C? The HRTEM results in Figure 5 correspond to the 800 °C which, according to the authors’ comments, is the most suitable temperature for the growth of CNTs (without any further explanation and strengthening of their comment).

Author Response

Dear Reviewer,

Thank you very much for your review. Your revise advice is very helpful to me, and I have revised my article according to your suggestions.

 

1. The authors despite of the interesting work the manuscript as it is written is very difficult to understand at once due to the poor quality in English.

 

Answer: I tried my best to revise the writing of the article and asked my teachers for help.

 

 

2. In the Introduction the authors mention: “But it has not been widely used in the field of nanomaterial synthesis due to the characteristics of the excitation difficulty, open space, and stability of atmospheric pressure microwave plasma.” What exactly due they mean with this phrase? What is open space, which characteristics of the excitation difficulty are they referring to? I strongly believe that in order for this work to be accepted not only for publication but from the scientific community the authors should in detail explain why there is so scarce use of the atmospheric pressure microwave plasma and how their work will lead to enhanced improvement on the application of the technique.

 

Answer: I detailed explain the difficulties of atmospheric pressure microwave plasma technology in line 70-78. The commonly used atmospheric pressure microwave plasma generator is based on waveguide structure, which is bulky(1-2 m³ and 200 kg ), high-power (>900 W, the magnetron voltage up to 30 kV), noisy and difficult to control. It's difficult for people who don't know microwave to use atmospheric pressure microwave plasma correctly. We use solid-state microwave source and coaxial plasma generator instead of magnetron and waveguide plasma generator. Our microwave plasma equipment can be packed in a 40 * 30 * 30 cm box, and its weight does not exceed 5 kg, no need for high voltage in the equipment, quiet at runtime and easy to excite.

 

 

3. Also in the Introduction the authors mention: “The present experiment is focused on the decomposition ability of the microwave plasma for precursor and the nanomaterial growth influenced by temperature of the tube furnace. In this study, we have synthesized CNTs on the stainless steel substrate using AMPCVD technology with the ethanol as carbon source at the temperature of 500 °C. We also remind the reader that there is no earlier study of nanomaterial synthesis by AMPCVD.” This is an example of the poor English used to elaborate major statements of the research work. The last sentence is very important (“We also remind the reader that there is no earlier study of nanomaterial synthesis by AMPCVD”) but it is lost within the text and is not strengthened as it should. Actually I strongly suggest the authors to consider rewriting the Introduction part showing prominent attention on the importance of their work compared to what has been mentioned in the literature. They should provide a straightforward part in the Introduction of the advantages of AMPCVD compared to other techniques used for the synthesis of CNTs and in general carbon related materials.

 

Answer: I added 9 references(3 CVD, 1 DC-PECVD, 2 RF-PECVD, and 3 MPCVD) to my article, and list the parameters needed by different kinds of PECVDs in the synthesis of CNTs in detail (line 39-57). The advantages of AMPCVD compared to other techniques used for the synthesis of CNTs was shown in line 90-95.

 

 

4. In Materials and Methods the AMPCVD schematic diagram in Figure 1 should be very thoroughly explained. Why the used source is ethanol and not any other alcohol? How is the set-up of the coaxial plasma generator? Why the gas control system includes three mass flowmeter?

 

Answer: The ethanol were used as the carbon source, because they are cheap, easy to access, safe, and the concentration of ethanol vapor can be easily controlled by temperature (line 118-119) . The set-up of the coaxial plasma generator was briefly described (line 111-115). And the reason why the gas control system includes three mass flowmeter is that “The central two-way airflow is used to control the precursor concentration, and the side hydrogen is used to stabilize the plasma and works as the deoxidizer.”(line 123-125).

 

 

5. In general how did the authors conclude for the specific decomposition rates of ethanol precursor at the specific different temperatures? Was their decision based on any literature already reported for CNTs synthesis or it was based on their knowledge and experience on the specific subject?

 

Answer: The specific decomposition rates of ethanol precursor at the specific different temperatures is based on the knowledge on the subject of atmospheric pressure microwave plasma waste gas treatment, it is generally necessary to calculate the waste treatment rate. I introduced this concept into CNTs synthesis to emphasize the decomposition ability of 200W atmospheric pressure microwave plasma.

 

 

6. In the Results and Discussion part the authors mention: “the decomposition of ethanol is all about 99% when the microwave plasma is turned on, no matter what the temperature of tubular furnace is”. Therefore even at 400 °C or 1000 °C the decomposition is similar and up to 99%. Why not 100% decomposition of the ethanol? Is that possible and under which conditions and circumstances?

 

Answer: The remaining 1% ethanol may be due to the turbulence on the top of the inside copper tube, make a small amount of ethanol escaped from the plasma, and the decomposition effect of high temperature on ultra-low concentration ethanol is not obvious. Moreover, 1% of precursor residues are acceptable in engineering (Line 195-198). I think it’s not possible to achieve 100% decomposition. We can improve the power for microwave plasma to increase the volume of the plasma, and optimize the structure of the top of the inside copper tube to reduce the ethanol escaped, but can’t reduce the remaining to 0.

 

 

7. According to the above comment and question the sentence the authors use: “So we can prove that the atmospheric pressure microwave plasma indeed does decompose the precursor completely” is not correct since they do not mention 100% decomposition.

 

Answer: I have change this sentence into “Therefore, we can conclude that the 200 W atmospheric pressure microwave plasma almost completely decompose the precursor.”(line 201)

 

 

8. The analysis of Figure 4 (SEM results) is very weak and does not convince the reader of what the authors are trying to prove. Actually they mention that: “the most suitable temperature for the growth of CNTs on the stainless steel substrate is 800 °C” and then in Figure 4 (g-i) they give SEM images of substrates with the growth situation of carrier gas for the precursor of 100, 200, and 300 sccm at the temperature of 600 °C instead of 800 °C as one should expect. The authors should reconsider changing the specific part of Figure 4 and the respective analysis.

 

Answer: I have deleted the original Figure 4. The new Figure 4 (line 211) shows the SEM images of CNTs grown at 500, 600, 700, 800 ℃ with high resolution and low resolution, and the diameter distribution of CNTs at specific temperatures. I have rewritten the analysis of new Figure 4, and laid special stress on analyzing the growth rate and diameter distribution of CNTs at different temperatures. “the most suitable temperature for the growth of CNTs on the stainless steel substrate is 800 °C” have been revised, “In the temperature range of 700-800 °C, the conversion efficiency of precursor increases greatly, indicating that the most suitable temperature for the growth of CNTs should be in the range of 700-800 °C and need further research.”(line 228-230) The effect of precursor concentration on the growth of CNTs is deleted in this paper, because the precursor concentration limit of the AMPCVD is far more than 300 sccm, which needs a lots of experimental researches.

 

 

9. The phrase: “tightly aligned with a high density of graphite sheets with a thickness of 6.4 nm, and the distance between layers is 0.35 nm” is not something seen for the first time but is what should be expected for MWCNTs characterization. Actually did the authors make any thorough study whether or not the number of layers is reproducible in all temperatures above 600 °C and up to 800°C? The HRTEM results in Figure 5 correspond to the 800 °C which, according to the authors’ comments, is the most suitable temperature for the growth of CNTs (without any further explanation and strengthening of their comment).

 

Answer: I have added the HRTEM results of 500, 600, 700 in Figure 5. By comparing the microstructures of CNTs at different temperatures, we found that the CNTs prepared at 700 and 800 °C consist of hollow compartments which is not obvious at 500 and 600 °C, and the carbon layers of CNTs grown at high temperatures are neater than that grown at low temperatures. The causes of this phenomenon are given.(line 246-253, and line 255-258).

 

 

Thank you for your review once more.

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China

Round 2

Reviewer 2 Report

The modifications performed by the authors bring some elements of the answer to my three significant comments. However, the title is, in my opinion, always to general, the characterization of the sample obtained at 500°C is not complete (e.g., Raman spectroscopy), and there is no real comparison of the CNT quality with the literature. 

Thus, I think that the authors still need to perform more analysis and to rewrite some parts of the manuscript. Those are the reasons why I decided not to change my decision about the manuscript applsci-798254.

 

 

My comments are summarised below, and I hope that they will help the authors to improve the quality of their manuscript: 

 

Introduction:

• lines 41-42: it is possible to synthesize CNT at lower temperatures (e.g., 10.3390/nano9030473). The authors should use reviews and (hand)books as references for this sentence. 
• Lines 53-56“Compared with normal CVD, the growth rate of DC-plasma CVD, RF PECVD and MPCVD have different degrees increase while the temperature did not change much, indicating that the influence of plasma on the synthesis of nanomaterials is significant.” For more clarity, I think that the authors should rewrite this sentence or split it into two ones. 
• Lines 86-87: where are the references associated with the AMPCVD?

 

Materials and Methods: 

• The authors have to mention the range of temperatures used, at least for CNTs Growth. 

 

Results and discussion:

• Part 3.2 Exhaust Gas Detection: Why did the authors define C0 and Cx, and the ethanol content as they did not use those parameters is the following text. 
• Part 3.3 CNTs: This part has to be constructed like a demonstration. Hence, the authors have to rewrite it, to modify the order of the ideas. For instance, SEM does not allow us to know if they obtained CNTs; so instead of CNTs, it will be better to use carbonaceous nanostructures. Another example, “The total mass of CNTs increased with the increase of the temperature at the range of 500-800 °C.” (lines 223-224) has to be replaced by: The total mass of deposited carbon increased with the increase of the temperature at the range of 500-800 °C. 
• Fig. 4 (c), (f), (i), and lines 231-233: the authors have to use the same axis scale to allow a direct comparison by the readers. 
• The TEM micrographs have to be described in detail, and the samples' observations have to be compared. For instance, the thickness and distance between layers have to be measured in different areas and for different CNTs of the same sample. And the CNTs morphology also has to be described.
• What is the quality of CNTs (i.e., Raman spectrum) of the different samples?
• The ID/IG ratio will have to be discussed.
• Etc.

 

- I also think that the help of an English native speaker will help improve the quality of the manuscript. 

Author Response

Dear Reviewer,

 

Thank you very much for your review. Your revised advice is very helpful to me, and I have revised my article according to your suggestions.

 

1. lines 41-42: it is possible to synthesize CNT at lower temperatures (e.g., 10.3390/nano9030473). The authors should use reviews and (hand)books as references for this sentence.

 

Answer: I quoted the references you recommended to me in the article (lines 53-54), which did greatly reduce the temperature of PECVD synthesis of CNTs, thank you very much.

 

 

2. Lines 53-56“Compared with normal CVD, the growth rate of DC-plasma CVD, RF PECVD and MPCVD have different degrees increase while the temperature did not change much, indicating that the influence of plasma on the synthesis of nanomaterials is significant.” For more clarity, I think that the authors should rewrite this sentence or split it into two ones.

 

Answer: I have changed this sentence to “Compared with normal CVD, the nanomaterials growth rate of DC-plasma CVD, RF-PECVD, and MPCVD are increased by 2-5 times at the same temperatures. The plasma is very significant for the improvement of the growth rate of nanomaterials.”(lines 54-57)

 

 

3. Lines 86-87: where are the references associated with the AMPCVD?

 

Answer: In fact, there was no precedent for the preparation of nanomaterials by AMPCVD, and no relevant literature can be retrieved. So, I have changed the sentence to “We remind readers that there is no earlier study of nanomaterial synthesis by AMPCVD.”(lines 86-87)

 

 

4. The authors have to mention the range of temperatures used, at least for CNTs Growth.

 

Answer: Your suggestion is very valuable. I have revised the article (line 138).

 

 

5. Part 3.2 Exhaust Gas Detection: Why did the authors define C0 and Cx, and the ethanol content as they did not use those parameters is the following text.

 

Answer: I thought it would be more intuitive, but your suggestion is very correct. I have deleted C0 and CX and described them in the language (lines 177-182).

 

 

6. Part 3.3 CNTs: This part has to be constructed like a demonstration. Hence, the authors have to rewrite it, to modify the order of the ideas. For instance, SEM does not allow us to know if they obtained CNTs; so instead of CNTs, it will be better to use carbonaceous nanostructures. Another example, “The total mass of CNTs increased with the increase of the temperature at the range of 500-800 °C.” (lines 223-224) has to be replaced by: The total mass of deposited carbon increased with the increase of the temperature at the range of 500-800 °C.

 

Answer: Your suggestion is really valuable, I adjusted the description order of Part 3.3 CNTs, put the Raman characterization analysis of samples in the front, and combined with the TEM characterization results, it was proved that the samples were CNTs (lines 197-211).

 

 

7. 4 (c), (f), (i), and lines 231-233: the authors have to use the same axis scale to allow a direct comparison by the readers.

 

Answer: According to your suggestion, I have changed their axis scale to the same (lines 229, Figure 5(c),(f),(i)).

 

 

8. The TEM micrographs have to be described in detail, and the samples' observations have to be compared. For instance, the thickness and distance between layers have to be measured in different areas and for different CNTs of the same sample. And the CNTs morphology also has to be described.

 

Answer: I tried my best to describe the TEM micrographs in detail, and compared different samples (lines 250-258, 265-266). The thickness and distance between layers are measured and marked in Figure 6, as well as the amorphous carbon layer is marked by red arrows (lines 244, Figure 6).

 

 

9. What is the quality of CNTs (i.e., Raman spectrum) of the different samples? The ID/IG ratio will have to be discussed.

 

Answer: I have added the Raman spectrums of the CNTs prepared at 500, 600, 700 °C in Figure 4. the ID/IG ratio of CNTs at different temperatures were calculated and discussed (lines 197-211)

 

 

10. I also think that the help of an English native speaker will help improve the quality of the manuscript.

 

Answer: I have found a teacher from an English speaking country to help me modify the language of the article, hoping that the article can meet the publishing requirements.

 

Thank you for your review once more.

 

Best wishes!!

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China

Reviewer 4 Report

The authors have tried really hard to answer the questions raised in my initial review. Still, substantial editing in English is needed throughout the manuscript. The manuscript may be accepted now after minor revision.

The answer to my comments:

In general how did the authors conclude for the specific decomposition rates of ethanol precursor at the specific different temperatures? Was their decision based on any literature already reported for CNTs synthesis or it was based on their knowledge and experience on the specific subject?

In the Results and Discussion part the authors mention: “the decomposition of ethanol is all about 99% when the microwave plasma is turned on, no matter what the temperature of tubular furnace is”. Therefore even at 400 °C or 1000 °C the decomposition is similar and up to 99%. Why not 100% decomposition of the ethanol? Is that possible and under which conditions and circumstances?

is not satisfactory enough and the authors should try harder to convince me.

Author Response

Dear Reviewer,

 

Thank you very much for your review. Your revised advice is very helpful to me, and I have tried my best to answer your question.

 

1. Still, substantial editing in English is needed throughout the manuscript.

 

Answer: I have found a teacher from an English speaking country to help me modify the language of the article, hoping that the article can meet the publishing requirements.

 

2. In the Results and Discussion part, the authors mention: “the decomposition of ethanol is all about 99% when the microwave plasma is turned on, no matter what the temperature of the tubular furnace is”. Therefore even at 400 °C or 1000 °C the decomposition is similar and up to 99%. Why not 100% decomposition of the ethanol? Is that possible and under which conditions and circumstances?

 

Answer: According to our previous experience of using atmospheric pressure microwave plasma to treat VOCs, the decomposition rate of VOCs has a great relationship with its concentration. When the concentration drops to a certain extent, the decomposition effect of plasma on it disappears. The experimental results show that the ethanol decomposition rate before and after plasma treatment is 99% and 1%, respectively, indicating that the ethanol decomposition rate at the current concentration is about 99%. So we think that the ethanol decomposition rate by plasma is 99% at 1000 °C. The reason why the remaining 1% ethanol does not decompose at 1000 °C is that the ethanol concentration represented by residual 1% is too low to be decomposed by 1000 °C, The decomposition capacity of 200 W microwave plasma is higher than that of 1000 °C. If the plasma does not decompose such a low concentration of ethanol, it is even more impossible to decompose it at 1000 °C. Thus, I think it is not possible to achieve 100% decomposition.

 

 

Thank you for your review once more.

 

Best wishes!!

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China

Round 3

Reviewer 2 Report

The authors did a lot of modifications to their manuscript, which improves its quality. However, this manuscript still misses comparisons of the results with ones from the literature (i.e., CNTs growth over stain steel; CNTs growth using MPCVD; thermal CVD CNTs synthesis; etc.). The reader needs to know if this approach (AMPCVD) is beneficial or not for CNTs growth and in which conditions and for which purposes. That is why I recommend "major revision".

• L 41-42: "750 to 1000°C" It is possible to synthesis CNTs by thermal CVD at temperatures ranging from 600 to 1050°C at 0.6-760 Torr (e.g., in Aligned Carbon Nanotubes: Physics, Concepts, Fabrication and Devices by Zhifeng Ren, Yucheng Lan, Yang Wang)
• L 180-181: ethanol contents rate is mentioned only one time in the text. So, why? What is the conclusion about it?
• Check the numbers of the figures.
• L 202-206: There is no comparison with literature results from the reported ratios of D peak and G peak (even if the CNTs have been obtained using another process)

Hence, the authors have to check their manuscript carefully and to rewrite some parts by adding a comparison with the corresponding scientific literature. The conclusion part should also conclude about these comparisons of the results.

Author Response

Dear Reviewer,

Thank you very much for your review. Your revise advice is very helpful to me, and I have revised my article according to your suggestions.

1. lines 41-42: "750 to 1000°C" It is possible to synthesis CNTs by thermal CVD at temperatures ranging from 600 to 1050°C at 0.6-760 Torr (e.g., in Aligned Carbon Nanotubes: Physics, Concepts, Fabrication and Devices by Zhifeng Ren, Yucheng Lan, Yang Wang)

Answer: I studied the book you recommended. The summary of CVD synthesis CNTs in the book is very comprehensive. According to section 4.1 “Thermal Chemical Vapor Deposition” at pp 67, I correct my description (line 41-42), and added this book to my references.

2. Lines 180-181: ethanol contents rate is mentioned only one time in the text. So, why? What is the conclusion about it?

Answer: I propose this concept to describe the decomposition efficiency of atmospheric pressure microwave plasma for ethanol. However, in the later description, the concept of ethanol decomposition rate is used for discussion, which is a mistake. Thank you very much for your careful discovery of this problem. I have changed the description from “ethanol decomposition rates” to “ethanol contents rate” (lines 187-191). The conclusion is that the ethanol decomposition capacity of atmospheric pressure microwave plasma is higher than 1000 °C high temperature, and 200 W atmospheric pressure microwave plasma could almost completely decompose the precursor.

3. Check the numbers of the figures.

Answer: I have checked my article very carefully and revised the number and caption of Figure 4. Thank you very much for pointing out this problem.

4. Lines 202-206: There is no comparison with literature results from the reported ratios of D peak and G peak (even if the CNTs have been obtained using another process).

Answer: According to your suggestion, I have added the results comparison of different synthesis methods of CNTs, including CVD, DC-PECVD, RF-PECVD, and MPCVD (lines 207-210). The results comparisons of CNTs grown on stainless steel substrate by RF-PECVD and CVD with AMPCVD can be seen in lines 210-212. By comparison, we come to the conclusion of that stainless steel substrate is not suitable for growing high quality aligned CNTs (lines 212-215). The morphology of the CNTs synthesized by AMPCVD have compared with the CNTs synthesized by CVD and PECVD (lines 229-233, 248-249). The comparison of CNTs by AMPCVD with other processes have added in the Conclusion section (lines 301-302, 305-308).

 

Thank you for your review once more.

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China

Round 4

Reviewer 2 Report

Dear Authors, 

I reread your manuscript, and even if the quality of your paper increased since the first version, I could not accept it for publication in the present form. 

I stayed for a long time in the introduction section. Because you mainly treated the different kinds of CVD processes for CNTs synthesis (Lines 29 to 86 ). And you finished the paragraph by “We remind readers that there is no earlier study of nanomaterial synthesis by AMPCVD.” However, Varanda et al. (Smart Mater. Struct. 11 (2002) 610–616) indicated: “The microwave CVD process presented in this paper does not require this vacuum, and thus it is amenable for large-scale production of CNTs with a high yield.” So, there is a precedent for your use of AMPCVD. 

Then, you continued by writing (Lines 88-89:)  “we studied the decomposition ability of the microwave plasma for precursor and the nanomaterial growth influenced by the tube furnace temperature.” These two aspects are not discussed in detail before. If I check the literature, I will probably find other studies about the “decomposition ability of microwave plasma for carbon precursor” and “material growth influenced by the tube furnace temperature.” Moreover, ethanol and stainless steel appear inline 90, but their use in CNTs synthesis is not discussed before in the introduction, etc.

So, that I try to tell you is that in my opinion, you should be clear about your main finding (e.g., AMPCVD or stainless steel or ethanol, etc.). And this aspect has to be discussed in the introduction, and the more significant articles dealing with the same subject have to be presented, allowing the reader to know how meaningful is your finding. Afterward, your results should be discussed regarding the existing literature (for instance, for the part dealing with Raman spectra, you should look at Nanomaterials 2017, 7, 284; doi:10.3390/nano7100284). You also need to pay attention is the information you give to the reader when you discuss your results (e.g., you mentioned that ethanol decomposition is about 99%. However, the yield of CNT is ranging from 2 to 42% for 500°C <T<700°C, but what is about 800°C?). 

To conclude, I think that you have enough results for a publication. However, you need to focus your attention only on one point and to rewrite it following your main idea. 

Best regards,

Reviewer 

Author Response

Dear Reviewer,

 

Thank you very much for your review. Your revise advice is very helpful to me, and I have revised my article according to your suggestions.

 

1. I stayed for a long time in the introduction section. Because you mainly treated the different kinds of CVD processes for CNTs synthesis (Lines 29 to 86 ). And you finished the paragraph by “We remind readers that there is no earlier study of nanomaterial synthesis by AMPCVD.” However, Varanda et al. (Smart Mater. Struct. 11 (2002) 610–616) indicated: “The microwave CVD process presented in this paper does not require this vacuum, and thus it is amenable for large-scale production of CNTs with a high yield.” So, there is a precedent for your use of AMPCVD.

 

Answer: I have studied the reference you recommended carefully. The microwave CVD uses microwave to heat the substrate instead of the thermal filament. The reaction mechanism of the microwave CVD is to activate the precursor by microwave heating , it’s a kind of thermal CVD. And the reaction mechanism of AMPCVD is to decompose the precursor by microwave plasma and recombine into materials, it’s a kind of PECVD. So I think they are not same synthesis mechanism.

 

2. Then, you continued by writing (Lines 88-89:) “we studied the decomposition ability of the microwave plasma for precursor and the nanomaterial growth influenced by the tube furnace temperature.” These two aspects are not discussed in detail before. If I check the literature, I will probably find other studies about the “decomposition ability of microwave plasma for carbon precursor” and “material growth influenced by the tube furnace temperature.” Moreover, ethanol and stainless steel appear in line 90, but their use in CNTs synthesis is not discussed before in the introduction, etc. So, that I try to tell you is that in my opinion, you should be clear about your main finding (e.g., AMPCVD or stainless steel or ethanol, etc.). And this aspect has to be discussed in the introduction, and the more significant articles dealing with the same subject have to be presented, allowing the reader to know how meaningful is your finding.

 

Answer: Your suggestion is really beneficial for me, I have realized my introduction is confused and disordered. I have rewritten the introduction section, deleted the description of CVD development at first, and started the introduction of CNTs synthesis methods directly, include CVD, DC-PECVD, RF-PECVD, MPCVD, and atmospheric pressure microwave plasma direct synthesis, which can be seen in lines 30-49. PECVD cannot work under atmospheric pressure (lines 44), and atmospheric pressure microwave plasma have its disadvantages in synthesis nanomaterials (lines 52-55). Thus, we combined an atmospheric pressure microwave plasma generator and tube furnace to setup the atmospheric pressure PECVD, which overcome the pressure limits of PECVD, and achieved accurate control of the nanomaterials synthesis process (lines 58-63). At the end of the introduction, I compared the AMPCVD with CVD, PECVD and atmospheric pressure microwave plasma direct synthesis process (lines 65-69).

 

3. Afterward, your results should be discussed regarding the existing literature (for instance, for the part dealing with Raman spectra, you should look at Nanomaterials 2017, 7, 284; doi:10.3390/nano7100284). You also need to pay attention is the information you give to the reader when you discuss your results (e.g., you mentioned that ethanol decomposition is about 99%. However, the yield of CNT is ranging from 2 to 42% for 500°C <T<700°C, but what is about 800°C?).

 

Answer: I have revised my Raman spectra results discussion (lines 170-1175) regarding the literature you recommended, and added this literature into my references list as [16]. The I_D/I_G ratio of the CNTs grown on the stainless steel comparison between AMPCVD and PECVDs can be seen in lines 179-183. The CNTs grown on the substrate without oxidation processes are similar with our results, and the quality of CNTs grown on oxidized substrate is better. For the results discussion of the yield of CNTs, I have added the results of 800°C into the sentence (lines 204-205).

 

Thank you for your review once more.

 

Best wishes!

 

Sincerely,

Dashuai Li.

University of Electronic Science and Technology of China