Film Growth of Tetragonal SnO2 on Glass Substrate by Dip-Coating Technique for Ethanol Sensing Applications
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The authors report a thin-film sensor based on tetragonal SnO2 nanoparticles fabricated by a sol-gel method and a dip-coating technique on a glass substrate. They study the sensing material produced through a cycling annealing process at 400 °C and 600 °C by using tin chloride (IV) pentahydrate as a precursor in polyethylene glycol (PEG) solution as a surfactant. The fabricated sensor was able to detect low ethanol ppm-levels at lower temperatures in comparison to the commercial one and with a conductivity similar to those reported in previous studies.
Several Figures are difficult to read.
Line 87: (NH4OH) should be rewritten to (NH4OH).
Line 89: Wrong section edit.
Figure 3: Draw squares representing (b), (c), and (d) the enlarged picture.
Line 172: What is the sensor MQ3?
Line 15, 131: "Sensor response" or "gas response"? The “gas response” is also used, for example, in line 288.
Line 131: “gas response (7.21)” should be rewritten. Such as, The sensor response to 40 ppm of ethanol at 120 °C was 7.21.
Figure 8 (b): Without the Villarreal model, can a mathematical model be proposed?
Author Response
Point 1: Several Figures are difficult to read.
Response 1: All the Figures have been changed to High-Definition quality. Also, in Figure 7 the image’s size was re-size, and in Figure 3 a square inside the image indicates in which part the zoom was made.
-----------------------------------------------------------------------------------------------Point 2:Line 87: (NH4OH) should be rewritten to (NH4OH).
Response 2:The miswritten subindex is already corrected.
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Point 3:Line 89: Wrong section edit.
Response 3:The wrong section edit is already corrected.
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Point 4:Figure 3: Draw squares representing (b), (c), and (d) the enlarged picture.
Response 4:The draw squares were added to the images. Thank you very much for that suggestion. -----------------------------------------------------------------------------------------------Point 5:Line 172: What is the sensor MQ3?
Response 5:MQ3 is a suitable gas sensor for detecting Alcohol, Benzene, CH4, among others, but be more sensitive to alcohol than the other gases. It has commercial applications with the disadvantage that it needs 200 °C as operating temperature for detecting alcohol and simply it has been used as a reference for ethanol gas.
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Point 6:Line 15, 131: "Sensor response" or "gas response"? The “gas response” is also used, for example, in line 288.
Response 6:The word Gas Response has been updated in the whole document for Sensor Response.
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Point 7:Line 131: “gas response (7.21)” should be rewritten. Such as, the sensor response to 40 ppm of ethanol at 120 °C was 7.21.
Response 7:The Phrase was edited and now it appears on the document your suggestion.
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Point 8:Figure 8 (b): Without the Villarreal model, can a mathematical model be proposed?
Response 8:The phenomena of the chemical reaction inside the sensor are still under study for now. The changing variables must be determined with deep analysis and, by this, the mathematical model is out of scope for this research paper. We only are using a published mathematical model apply for this kind of experiment, and in the present work, we established that the mathematical model did not fix accordingly to our signal. Nevertheless, a mathematical model will be proposed in future works.
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Sotelo et al. discuss development of an ethanol gas sensors using simple and low cost fabrication of thin SnO2 films. The work is interesting, the study was nicely conducted and the manuscript is well-written. This work should of interest in the community. Therefore I suggest publication in Coatings pending responses to my comments below:
Title: I think using "gas" in the title might be misleading as the only gas studied is ethanol. Therefore it is more appropriate to use "ethanol" instead.
Line 90: This is the first mention of S241 sensor. Here it should be described what this S241 is. Until the end there is no explanation of this naming.
Line 117: reheated at what temperatures?
Line 174: 0 to 1023. What are these numbers? Units?
Figure 7a: Why after 120 the signal decreases? Is it the thermal diffusion mentioned in the text? In any case this discussion should be expanded.
Figure 9: What happened at day 30? It suddenly drops and therefore needs further discussion.
Author Response
Point 1: Title: I think using "gas" in the title might be misleading as the only gas studied is ethanol. Therefore, it is more appropriate to use "ethanol" instead.
Response 1: The word “Gas” was changed for the word “Ethanol” in the main title.
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Point 2: Line 90: This is the first mention of the S241 sensor. Here it should be described what this S241 is. Until the end, there is no explanation of this naming.
Response 2: In order to avoid confusion, the word S241 was changed to “fabricated sensor” in the whole document.
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Point 3: Line 117: reheated at what temperatures?
Response 3: The mistake was corrected, and now on line 117 the document indicates that it was reheated at 120 °C for one month to observe its signal behavior.
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Point 4: Line 174: 0 to 1023. What are these numbers? Units?
Response 4: The range 0 - 1023 comes from the analog-to-digital converters (ADC) built-in to Arduino. What they do is take a voltage reading (e.g., from your sensor) and compare it to the analog reference voltage (which is typically 5 volts, although it can be changed).
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Point 5: Figure 7a: Why after 120 °C the signal decreases? Is it the thermal diffusion mentioned in the text? In any case, this discussion should be expanded.
Response 5: The Scope of this research is to design a new sensor capable of detecting ethanol gas at low temperatures. The sensor in charge to monitor the operation temperature starts to give noisy data above the 130 °C. In order to avoid confusion with the data, the temperatures above 120 °C were taking out of Figure 7a. Higher temperatures are out of the scope of this research for now.
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Point 6: Figure 9: What happened on day 30? It suddenly drops and therefore needs further discussion.
Response 6: It is possible that the sensor starts to fail after 25 days because the sensor was under monitoring every day with excessive tests proves to find every bad aspect or variation in the signal. The information after 30 days of testing could help us to extend the average life of the sensor in future developments.
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Author Response File: Author Response.pdf
Reviewer 3 Report
There are some weaknesses through the manuscript which need improvement. Therefore, the submitted manuscript cannot be accepted for publication in this form, but it has a chance of acceptance after a major revision. My comments and suggestions are as follows:
1- Abstract gives information on the main feature of the performed review, but some details about fabricated sensor must be added.
2- Authors must clarify necessity of the performed research. Objectives of this study must be clearly mentioned in introduction.
3- Introduction is short and the literature study must be enriched. In this respect, authors must refer to: (a) https://0-doi-org.brum.beds.ac.uk/10.1016/j.sna.2020.112105 (b) https://0-doi-org.brum.beds.ac.uk/10.1115/DSCC2020-3280
4- Since the manuscript deals with an experimental study, authors must present some real figures to show fabricated sensor and fabrication process.
5- The main reference of each formula must be cited and all parameters must be introduced.
6- Figures must be illustrated in high quality (e.g., Fig. 7).
7- In its language layer, the manuscript should be considered for English language editing. There are sentences which have to be rewritten.
8- The conclusion must be more than just a summary of the manuscript. List of references must be updated based on the proposed papers. Please provide all changes by red color in the revised version.
Author Response
Point 1: Abstract gives information on the main feature of the performed review, but some details about the fabricated sensor must be added.
Response 1: More information about the fabricated sensor was added to the abstract in order to give more details about it. (Starting in Line 13).
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Point 2: Authors must clarify the necessity of the performed research. The objectives of this study must be clearly mentioned in the introduction.
Response 2: The necessity of the performed research is now with a broader perspective in the introduction starting in line 62. Thank you very much for that suggestion.
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Point 3: Introduction is short, and the literature study must be enriched. In this respect, authors must refer to (a) https://0-doi-org.brum.beds.ac.uk/10.1016/j.sna.2020.112105 (b) https://0-doi-org.brum.beds.ac.uk/10.1115/DSCC2020-3280
Response 3: The suggested literature was added into the introduction starting in Line 74 and in Line 298, which also has been enriched with information to enlarge it with updated data.
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Point 4: Since the manuscript deals with an experimental study, the authors must present some real figures to show fabricated sensors and fabrication processes.
Response 4: New Figures have been added to the article with the main objective to show the fabricated sensors and the fabrication process.
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Point 5: The main reference of each formula must be cited, and all parameters must be introduced.
Response 5: Each formula is now cited, and all the parameters in each formula have been added to the main text.
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Point 6: Figures must be illustrated in high quality (e.g., Fig. 7).
Response 6: Figures have already changed to high-definition quality starting from Figure 1 to the last one. Also, the images are re-size a little bigger.
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Point 7: In its language layer, the manuscript should be considered for English language editing. There are sentences that have to be rewritten.
Response 7: Thank you very much for the suggestion, and we will definitely do that. We will send the manuscript to English language editing.
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Point 8: The conclusion must be more than just a summary of the manuscript. The list of references must be updated based on the proposed papers. Please provide all changes by red color in the revised version.
Response 8: The conclusion has already updated with a little more discussion and the references have already updated with the suggested papers. Finally, all the revised changes have already with red color.
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Thanks a lot for your thorough revision, All changes were made.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The author revised the manuscript with reference to all suggestions.
Reviewer 3 Report
The paper has been improved and corresponding modifications have been conducted. In my opinion, the current version can be considered for publication in Coatings.
