Nano-Sheet-like Morphology of Nitrogen-Doped Graphene-Oxide-Grafted Manganese Oxide and Polypyrrole Composite for Chemical Warfare Agent Simulant Detection
Round 1
Reviewer 1 Report
In this manuscript, the authors study the Nano Sheet Like Morphology of Nitrogen Doped Graphene Oxide Grafted Manganese Oxide and Polypyrrole Composite for Gas Sensor Applications.This work sounds very interesting and meaningful, and the analysis is reasonably clear, but there are still a few concerns regarding this article, therefore, I suggest it for publication in this journal after the following major revisions:
1. The long-term stability of the material needs to be measured.
2. The concentration of doping is also an important index affecting the sensing performance, and the influence of concentration should be studied.
3. Some grammatical errors are found. A proof-reading of the article will enhance the quality of the paper.
4. A list of acronyms is needed.
5. The diagram and illustration should be on one page.
Author Response
Reviewers' comments:1
Q1-1: The long-term stability of the material needs to be measured.
- Response to reviewer’s: The authors would like to extend our thanks to the potential reviewer for valuable comments on this presented work. Long term stability is a crucial indicator used for the practical applications in gas monitoring. Under the normal room temperature, it has been reported that the graphene oxide exhibited only a small declination of 1.34% in the response for the detection of DMMP which was monitored for 30 days [related refrence: Wang, Y.; Yang, M.; Liu, W.; Dong, L.; Chen, D.; Peng, C. Gas Sensors Based on Assembled Porous Graphene Multilayer Frameworks for DMMP Detection. J. Mater. Chem. C 2019, 7, 9248–9256].
In addition, manganese oxide-based composites were investigated for the long-term stability of 6 months. The composites revealed satisfying repeatability and stability with slight declination in frequency shift of ~18 Hz [related reference: Thomas, G.; Spitzer, D. 3D Core–Shell TiO2@MnO2 Nanorod Arrays on Microcantilevers for Enhancing the Detection Sensitivity of Chemical Warfare Agents. ACS Appl. Mater. Interfaces 2021. 13(39) 47185-47197].
Furthermore, it has been reported that the polypyrrole based composites showed more than 95% retention of the initial sensitivity during the monitoring period of 21 days [related reference: Kwon, O.S.; Park, C.S.; Park, S.J.; Noh, S.; Kim, S.; Kong, H.J.; Bae, J.; Lee, C.-S.; Yoon, H. Carboxylic Acid-Functionalized Conducting-Polymer Nanotubes as Highly Sensitive Nerve-Agent Chemiresistors. Sci. Rep. 2016, 6, 1–7].
The potential reviewers suggested that the long-term stability needs to be measured. Given the time frame of 7 days to upload the revised manuscript, we conducted the stability test of the composite materials for 5 consecutive days. The results suggest that the composite materials showed satisfying stability for DMMP detection during the monitoring period. The results (diagram and explanation) can be found in the supplementary information and revised manuscript.
Figure. Stability test of the NGO@MnO2/PPy for detection of 150 ppm DMMP for five consecutive days.
Q1-2. The concentration of doping is also an important index affecting the sensing performance, and the influence of concentration should be studied.
- Response to reviewer’s: Thank you very much for your comments on our manuscript. Generally, there are two ways to dope the graphene chemically: 1) organic molecules, metals, or gas adsorbed onto the surface of graphene; 2) substitutional doping which infuse the nitrogen atoms inside the lattice structure of graphene. When a nitrogen atom is introduced or doped into the graphene lattice structure, there occurs three different types of bonding configurations such as pyrrolic N, Pyridinic N, and graphitic N. The N doped graphene exhibits the distinct behavior than the graphene. The neighboring nitrogen dopants influences the spin density and carbon atoms charge distribution, that induces the activation region onto the surface of the graphene. After the nitrogen is doped onto the graphene monolayer, the Fermi level moves above the Dirac point, which results in the opening of the bandgap between the conduction and valence band. This bandgap makes nitrogen doped graphene to be used as a sensor.
It has been reported that increase in the nitrogen concentration into the graphene materials lead to the improvement in the sensing performance for dopamine, ascorbic acid, and uric acid [related reference: Megawati, M.; Chua, C.K.; Sofer, Z.; Klímová, K.; Pumera, M. Nitrogen-Doped Graphene: Effect of Graphite Oxide Precursors and Nitrogen Content on the Electrochemical Sensing Properties. Phys. Chem. Chem. Phys. 2017, 19, 15914–15923].
However, for the NADH, the sensitivity was decreased compared to the bare graphene surface. Also, the N-doped graphene oxide nanosheet greatly enhances the sensitivity towards the NO at the room temperature, indicating excellent potential as a gas sensor [related reference: Chang, Y.-S.; Chen, F.-K.; Tsai, D.-C.; Kuo, B.-H.; Shieu, F.-S. N-Doped Reduced Graphene Oxide for Room-Temperature NO Gas Sensors. Sci. Rep. 2021, 11, 1–12].
In case of the glucose biosensing, the concentration of nitrogen percentage achieved in the N-GO was from 0.11 to 1.35%, which showed excellent sensitivity and selectivity [Related refrence: Wang, Y.; Shao, Y.; Matson, D.W.; Li, J.; Lin, Y. Nitrogen-Doped Graphene and Its Application in Electrochemical Biosensing. ACS Nano 2010, 4, 1790–1798].
For sensing NO2, the composites constituting N-GO (6% concentration) showed optimum response and recovery times depicting suitable sensitivity and selectivity [Related reference: Badiezadeh, F.; Kimiagar, S. Modified WO3 Nanosheets by N-GO Nanocomposites to Form NO2 Sensor. J. Exp. Nanosci. 2021, 16, 144–158]. For the selective detection of CO, nitrogen doped graphene showed excellent response which would lead to the covalent bond between the lone pair electron and thus leading to vanishing of defective graphene system [Related reference: Ma, C.; Shao, X.; Cao, D. Nitrogen-Doped Graphene as an Excellent Candidate for Selective Gas Sensing. Sci. China Chem. 2014, 57, 911–917].
It was found that the doping temperature has huge impact on the concentration of nitrogen in the graphene oxide. The increase in doping temperature leads to the lower content of nitrogen and vice versa [Related reference: Song, J.; Kim, C.-M.; Yang, E.; Ham, M.-H.; Kim, I.S. The Effect of Doping Temperature on the Nitrogen-Bonding Configuration of Nitrogen-Doped Graphene by Hydrothermal Treatment. RSC Adv. 2017, 7, 20738–20741]. The electrical conductivity increases with the increase in the concentration of nitrogen in the graphene oxide [Related reference: Ngidi, N.P.D.; Ollengo, M.A.; Nyamori, V.O. Effect of Doping Temperatures and Nitrogen Precursors on the Physicochemical, Optical, and Electrical Conductivity Properties of Nitrogen-Doped Reduced Graphene Oxide. Materials (Basel). 2019, 12, 3376].
Q1-3: Some grammatical errors are found. A proof-reading of the article will enhance the quality of the paper.
- Response to reviewer’s: We would like to thank the potential reviewer for the comments on our manuscript. The potential reviewers suggested to check the grammatical errors in the manuscript which has been revised to our best efforts. We hope that the revised manuscript is enhanced to publish in the nanomaterials journal.
Q1-4: A list of acronyms is needed.
- Response to reviewer’s: Thank you very much for your comments on our manuscript. The potential reviewers suggested to add a list of acronyms which has been added to the supplementary information (Table S1). The list of acronyms can also be found below:
Table. List of acronyms.
Acronyms |
Definition |
Acronyms |
Definition |
CWAs |
Chemical warfare agents |
IPA |
Isopropyl alcohol |
QCM |
Quartz Crystal Microbalance |
sccm |
standard cubic centimeters per minute |
SAW |
Surface Acoustic Wave |
MFCs |
Mass Flow Controllers |
DMMP |
Dimethyl methyl phosphonate |
ppm |
parts per million |
NGO |
Nitrogen doped Graphene Oxide |
Fc |
Carrier gas flow rate |
MnO2 |
Manganese dioxide |
Po |
Outlet pressure |
PPy |
Polypyrrole |
Pth |
Thermodynamic pressure |
VOCs |
Volatile Organic Compounds |
Ps |
Saturated vapor pressure |
MEMS |
Micro-electromechanical system |
Fd |
dilution gas flow rate |
Co3O4 |
Cobalt oxide |
SRS |
Stanford Research System |
R.H. |
Relative Humidity |
VNA |
Vector Network Analyzer |
ZnO |
Zinc Oxide |
SMA |
SubMiniature Version A Connector |
M.W. |
Molecular weight |
∆f |
Resonant frequency |
FTIR |
Fourier Transform Infrared Spectroscopy |
Cf |
Sensitivity factor |
XRD |
X-Ray Diffraction |
∆m |
mass change |
XPS |
X-ray Photoelectron Spectroscopy |
IDTs |
Interdigital Transducers |
SEM |
Scanning Electron Microscopy |
Fc |
Central frequency |
TEM |
Transmission Electron Microscopy |
v |
Velocity |
H2O2 |
Hydrogen peroxide |
λ |
Wavelength |
DD |
Double distilled water |
FE-SEM |
Field Emission Scanning Electron Microscopy |
NaNO3 |
Sodium Nitrate |
FE-TEM |
Field Emission Transmission Electron Microscopy |
H2SO4 |
Sulfuric acid |
EDX |
Energy Dispersive X-Ray Analysis |
KOH |
Potassium hydroxide |
R2 |
Coefficient of determination |
FeCl3 |
Ferric chloride |
D |
Coefficient of variation |
KMnO4 |
Potassium permanganate |
δ |
Standard deviation (δ) |
NH4OH |
Ammonium hydroxide |
k |
Average |
PTFE |
PTFE = Polytetrafluorethylene |
T90 |
response time to attain 90 % of the equilibrium |
Q1-5: The diagram and illustration should be on one page.
- Response to reviewer’s: The authors would like to extend our thanks to the potential reviewer for valuable comments on this presented work. The potential reviewers suggested to include the diagram and the illustration on one page which has been updated in the revised manuscript as per the reviewer’s suggestions.
Author Response File: Author Response.pdf
Reviewer 2 Report
The ms reports a work on nitrogen doped graphene oxide grafted MnO2 and Polypyrrole Composite for Gas Sensor Applications. Overall, the ms is interesting, however, a thorough revision is needed before reconsideration.
1) the title could be made a bit more catchy and gives the idea of the molecules being detected. For example the title should contain the word "chemical warfare agents".
2) The ms is far too long with an excessive number of references. I suggest to place some of the figures in the supporting info section;
3) Figs 11, 12, 16, 17, and 20 should report the error bars. How many times the experiments have been repeated?
4) Tabs 3 and 6 could go into the supporting info section;
5) 161 references are far too many. They should be reduced to less than 100;
6) The values of R2 in Figs 12 and 17 is quite low. is this acceptable? Wouldn't this mean that the as proposed sensors are not so good, or not enough reliable?
Author Response
Reviewers' comments:2
Q2-1 : the title could be made a bit more catchy and gives the idea of the molecules being detected. For example the title should contain the word "chemical warfare agents".
- Response to reviewer’s: The authors would like to thank the potential reviewer for the valuable comments on this presented work. The potential reviewers suggested to change the title to make it catchier. So, we have changed the title to “Nano sheet like morphology of nitrogen doped graphene oxide grafted manganese oxide and polypyrrole composite for chemical warfare agent’s simulant detection”. We hope that the revised title would best fit for our manuscript.
Q2-2. The ms is far too long with an excessive number of references. I suggest to place some of the figures in the supporting info section;
- Response to reviewer’s: Thank you very much for your valuable comments on our manuscript. The potential reviewers suggested to place some figures into the supporting information. We have transferred the Figures like chemical structure of CWAs and simulant, FTIR and XRD pattern analysis of composite materials, FE-TEM images of composite materials, effect of mass accumulation of the composite materials, repeatability of composite materials in QCM sensor, response and recovery times of composite materials in QCM sensor, repeatability of composite materials in SAW sensor, response and recovery times of composite materials in SAW sensor, and effect of relative humidity on the sensing performance, to the supporting information section as per reviewer’s suggestions.
Q2-3. Figs 11, 12, 16, 17, and 20 should report the error bars. How many times the experiments have been repeated?
Response to reviewer’s: First of all, we would like to thank the potential reviewer for the comments on our manuscript. The potential reviewers suggested to report the error bars in Figure 11, 12, 16, 17, and 20. We have updated the error bars in the mentioned figure as per reviewer’s suggestion. The experiments have been repeated for four times.
Figure. Selectivity of (a) NGO@MnO2, and (b) NGO@MnO2/PPy in QCM sensor, (c) the polar plot of response ratio (R1/R2) between the NGO@MnO2/PPy coated and NGO@MnO2 coated QCM (T = 20 °C, R.H. = 25-30%).Figure. Linearity of (a) NGO@MnO2, and (b) NGO@MnO2/PPy in QCM sensor (T = 20 °C, R.H. = 25-30%).
Figure. Selectivity of (a) NGO@MnO2, and (b) NGO@MnO2/PPy in SAW sensor, (c) the polar plot of response ratios (R3/R4) between the NGO@MnO2/PPy coated and NGO@MnO2 coated SAW (T = 20 °C, R.H. = 25-30%).
Figure. Linearity of (a) NGO@MnO2, and (b) NGO@MnO2/PPy in SAW sensor (T = 20 °C, R.H. = 25-30%).
Figure. The effect of different R.H. conditions on the SAW sensor coated with NGO@MnO2/PPy under 25-30, 60-65, and 85-90% R.H. conditions at 20 °C for 75 and 150 ppm DMMP.
Q2-4. Tabs 3 and 6 could go into the supporting info section;
- Response to reviewer’s: Thank you very much for your comments on our manuscript. The potential reviewers suggested to move Tables 3 and 6 to the supporting information section which has been transferred to the supporting information as per reviewer’s suggestion.
Q2-5. 161 references are far too many. They should be reduced to less than 100;
- Response to reviewer’s: We would like to thank the potential reviewer for the valuable comment on our manuscript. The potential reviewers suggested to reduce the number of references to less than 100 which has been reduced to 98 in the revised manuscripts as per reviewer’s suggestion.
Q2-6. The values of R2 in Figs 12 and 17 is quite low. is this acceptable? Wouldn't this mean that the as proposed sensors are not so good, or not enough reliable?
- Response to reviewer’s: The authors would like to thank the potential reviewer for the valuable comments on this presented work. Generally, the sensitivity of sensor for specific gases is complicated and challenging. Sensitivity is dependent on various parameters, such as gas adsorption and co-adsorption mechanisms, surface reaction kinetics, and electron transfer to or from the conduction band of the semiconductor. In this present study, which is focused on the DMMP sensor, linearity results seem to be low which may be due to the chemical properties of the composite materials, catalytic, and electronic effects on the dopants and surface modification of carbon nanomaterials. The conducting polymers such as polypyrrole (PPy), polyaniline, and polythiophene polymers have been widely used for the development of highly sensitive DMMP sensors. Many conducting polymers have demonstrated the changes in sensitivity on exposure to various gases and humidity. Amongst conducting polymers, PPy has been one of the most studied due to the easy deposition from aqueous and non-aqueous conditions using either chemical or electrochemical oxidation reactions. Another approach of PPy films have been used as a sensitive layer which is a p-type semiconductor whose main carriers are holes. Based on the properties, the PPy has been used as active layer for gas sensing and it has been proved that PPy is a promising material for gas sensor applications at room temperature conditions. Hence, the composite materials may have showed the different trend in linearity results. It is important to note that reported literatures [The related references are listed as below] whose R2 is relatively similar or lower than R2 obtained in our presented manuscript has been successfully applied to detect the DMMP and chemical warfare agents.
Related references
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The manuscript can be accepted in its present form.
Author Response
Response to Reviewer's and Academic Editor’s comment
Manuscript no.: nanomaterials-1851425
Title: Nano sheet like morphology of nitrogen doped graphene oxide grafted manganese oxide and polypyrrole composite for chemical warfare agent’s simulant detection
Dear Reviewers and Editor and Editorial office,
First of all, the authors appreciate the reviewers and academic editor for the most valuable comments. We have modified the manuscript according to the editor’s comment. Please find the detailed answers in the revised manuscript. We hope that the manuscript is now acceptable for publication in the nanomaterials (MDPI).
Reviewer’s and Editor' comments:
- I agree with the Reviewer 2 that the reference list is too long. There are 98 refs even after revision. The authors should list the most related literature as reference. In addition, the information of some refs is incomplete, such as Ref. 94 and 98.
Response to Academic editor: The authors would like to extend our thanks to the editor for valuable comments on this presented work. We have only listed the most related literature as reference which has been reduced to 78 in the revised manuscript. The incomplete reference has been modified and completed in the revised manuscript. The modifications of references in 2nd revision are shown as below.
[Ref. No in the 1st rev] è [ New Ref. No in the 2nd rev.]
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Author Response File: Author Response.pdf
Reviewer 2 Report
The authors have revised the ms taking into account the referees' suggestions. I think the ms is now suitable for publication.
Author Response
Response to the Reviewer’s and Academic Editor’s comment
Manuscript no.: nanomaterials-1851425
Title: Nano sheet like morphology of nitrogen doped graphene oxide grafted manganese oxide and polypyrrole composite for chemical warfare agent’s simulant detection
Dear Reviewers and Editor and Editorial office,
First of all, the authors appreciate the reviewers and the academic editor for the most valuable comments. We have modified the manuscript according to the editor’s comment. Please find the detailed answers in the revised manuscript. We hope that the manuscript is now acceptable for publication in the nanomaterials (MDPI).
Reviewer’s and Editor' comments:
- I agree with the Reviewer 2 that the reference list is too long. There are 98 refs even after revision. The authors should list the most related literature as reference. In addition, the information of some refs is incomplete, such as Ref. 94 and 98.
Response to Academic editor: The authors would like to extend our thanks to the editor for valuable comments on this presented work. We have only listed the most related literature as reference which has been reduced to 78 in the revised manuscript. The incomplete reference has been modified and completed in the revised manuscript. The modifications of references in 2nd revision are shown as below.
[Ref. No in the 1st rev] è [ New Ref. No in the 2nd rev.]
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