Nanostructured metal oxide semiconductor-based sensors for greenhouse gas detection: progress and challenges

Climate change and global warming have been two massive concerns for the scientific community during the last few decades. Anthropogenic emissions of greenhouse gases (GHGs) have greatly amplified the level of greenhouse gases in the Earth's atmosphere which results in the gradual heating of the atmosphere. The precise measurement and reliable quantification of GHGs emission in the environment are of the utmost priority for the study of climate change. The detection of GHGs such as carbon dioxide, methane, nitrous oxide and ozone is the first and foremost step in finding the solution to manage and reduce the concentration of these gases in the Earth's atmosphere. The nanostructured metal oxide semiconductor (NMOS) based technologies for sensing GHGs emission have been found most reliable and accurate. Owing to their fascinating structural and morphological properties metal oxide semiconductors become an important class of materials for GHGs emission sensing technology. In this review article, the current concentration of GHGs in the Earth's environment, dominant sources of anthropogenic emissions of these gases and consequently their possible impacts on human life have been described briefly. Further, the different available technologies for GHG sensors along with their principle of operation have been largely discussed. The advantages and disadvantages of each sensor technology have also been highlighted. In particular, this article presents a comprehensive study on the development of various NMOS-based GHGs sensors and their performance analysis in order to establish a strong detection technology for the anthropogenic GHGs. In the last, the scope for improved sensitivity, selectivity and response time for these sensors, their future trends and outlook for researchers are suggested in the conclusion of this article.

2) When only the title of the article is read, we have the impression of a review on greenhouse gas sensors based on metallic oxide semiconductor (MOS). But the article has lost its focus, and makes further revisions on the achievements of climate change and its solutions (renewable energies). These themes could be approached as a justification and motivation for the article. But it has an excess of pages, sometimes in a simple language but more suitable for a book than for a scientific text (article). The review (MOS) does not mention other gas detection techniques such as photoacoustic spectroscopy and chemiluminency etc ... There could be a comparison of the advantages and disadvantages with other techniques. The NO2 gas sensors (which is not a greenhouse) are widely discussed, so it is beyond the scope of the article. The greenhouse gas that is (N2O), has no comment in the text, nor reference !! .And the article still lacked comments on the part of the sensors (MOS).
3)"The article needs a new writing that defines its objectives well" 4)Nothing is said about other GHC sensors, only satellite sensing. Why ? there are many gas detection techniques . (The introduction) 5)Let's see the statements in the abstract a) "GHGs sensors and their sensing mechanism have been discussed briefly" This should be better discussed, rather than discussing details of climate change. b)'The status of global GHGs emissions during the COVID-19 pandemic lockdown has also been discussed'.
Why discuss this topic in the article? I don't see this essential topic for a sensor review.

The introduction
1)This topic is about environmental sustainability, this topic is really important, but it will be for this article. In the paragraphs below !! -quality of life in terms of threatening water supplies, compromising ecosystems and impeding growth for future generations. The environment around us is an essential part of human survival. The more we don't care about our nvironment, the more it will become intoxicated with contaminants and toxins that have a harmful impact on our lives in numerous ways -"In particular, the pace of global economic growth during the past decades, paved the way to a continuous decline in the availability of natural resources such as forests (cut down for agriculture/demand for wood), air/land/water pollution. This in turn imposes severe health problems, damage to the productivity of land and seas, sources of oil/coal/gas, loss of fishing stocks due to overfishing and loss of species diversity etc. to the mankind. Our environment is composed of some basic components such as water, air, soil, flora, fauna, and human beings and hence economic development must move forward with the stability between these componen"t 2)See the statements below a)On satellite observations as na additional or alternative tool for the detection and monitoring of anthropogenic GHGs emissions such as CO2, CH4, NOx etc b)NMOS-based sensors have been shown to be sensitive to a large range of GHGs, mainly to CO2, CH4, NOx and O3, c)It is noteworthy here that the presente review centred around only on the performance analysis of available NMOS GHGs (CO2, CH4, NOx, O3 etc.) sensors NOx !!!! it's greenhouse gas?
In the section 'Concentration of GHGs in earth's environment" In the first paragraph -Look, nitrous oxide (N2O), greenhouse gas 'The primary GHGs in the atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone'.

3)Concentração de GEEs no meio ambiente da Terra
Reference 28 is presented in the article, where the consultation was made 2020, but data are very old.
4)It has a section 3.3 MOS-based NOxgas sensors, entirely dedicated to NO2 gas, which is not a greenhouse! It is a dangerous gas for human health, it generates acid rain and attacks the ozone layer. But the title of the article is sensors for greenhouse gases. Nothing is talked about sensors for N2O gas 5) It has a section 4. Status of global GHGs emissions during the COVID -19 pandemic lockdown. The theme is important (of course), but it may not be for the central theme of the article (gas sensors)

Review form: Reviewer 2 (Nitin Shelke)
Is the manuscript scientifically sound in its present form? Yes

Are the interpretations and conclusions justified by the results? Yes
Is the language acceptable? Yes

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s)
The manuscript can be accept with minor revision.

Decision letter (RSOS-201324.R0)
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Dear Dr Sharma:
Title: Nanostructured Metal Oxide Semiconductor-based Sensors for Greenhouse Gas Detection: Progress and Challenges Manuscript ID: RSOS-201324 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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https://www.ipcc.ch/ 2)When only the title of the article is read, we have the impression of a review on greenhouse gas sensors based on metallic oxide semiconductor (MOS). But the article has lost its focus, and makes further revisions on the achievements of climate change and its solutions (renewable energies). These themes could be approached as a justification and motivation for the article. But it has an excess of pages, sometimes in a simple language but more suitable for a book than for a scientific text (article). The review (MOS) does not mention other gas detection techniques such as photoacoustic spectroscopy and chemiluminency etc ... There could be a comparison of the advantages and disadvantages with other techniques. The NO2 gas sensors (which is not a greenhouse) are widely discussed, so it is beyond the scope of the article. The greenhouse gas that is (N2O), has no comment in the text, nor reference !! .And the article still lacked comments on the part of the sensors (MOS).
3)"The article needs a new writing that defines its objectives well" 4)Nothing is said about other GHC sensors, only satellite sensing. Why ? there are many gas detection techniques . (The introduction) 5)Let's see the statements in the abstract a) "GHGs sensors and their sensing mechanism have been discussed briefly" This should be better discussed, rather than discussing details of climate change.
b)'The status of global GHGs emissions during the COVID-19 pandemic lockdown has also been discussed'.
Why discuss this topic in the article? I don't see this essential topic for a sensor review.

The introduction
1)This topic is about environmental sustainability, this topic is really important, but it will be for this article.
In the paragraphs below !! -quality of life in terms of threatening water supplies, compromising ecosystems and impeding growth for future generations. The environment around us is an essential part of human survival. The more we don't care about our nvironment, the more it will become intoxicated with contaminants and toxins that have a harmful impact on our lives in numerous ways -"In particular, the pace of global economic growth during the past decades, paved the way to a continuous decline in the availability of natural resources such as forests (cut down for agriculture/demand for wood), air/land/water pollution. This in turn imposes severe health problems, damage to the productivity of land and seas, sources of oil/coal/gas, loss of fishing stocks due to overfishing and loss of species diversity etc. to the mankind. Our environment is composed of some basic components such as water, air, soil, flora, fauna, and human beings and hence economic development must move forward with the stability between these componen"t 2)See the statements below a)On satellite observations as na additional or alternative tool for the detection and monitoring of anthropogenic GHGs emissions such as CO2, CH4, NOx etc b)NMOS-based sensors have been shown to be sensitive to a large range of GHGs, mainly to CO2, CH4, NOx and O3, c)It is noteworthy here that the presente review centred around only on the performance analysis of available NMOS GHGs (CO2, CH4, NOx, O3 etc.) sensors NOx !!!! it's greenhouse gas?
In the section 'Concentration of GHGs in earth's environment" In the first paragraph -Look, nitrous oxide (N2O), greenhouse gas 'The primary GHGs in the atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone'.

3)Concentração de GEEs no meio ambiente da Terra
Reference 28 is presented in the article, where the consultation was made 2020, but data are very old.
4)It has a section 3.3 MOS-based NOxgas sensors, entirely dedicated to NO2 gas, which is not a greenhouse! It is a dangerous gas for human health, it generates acid rain and attacks the ozone layer. But the title of the article is sensors for greenhouse gases. Nothing is talked about sensors for N2O gas 5) It has a section 4. Status of global GHGs emissions during the COVID -19 pandemic lockdown. The theme is important (of course), but it may not be for the central theme of the article (gas sensors) 6)The conclusions must be completely rewritten, according to the objectives of the work (focus). It is certainly not renewable energy or the consequences of climate change. It is a pleasure to accept your manuscript in its current form for publication in Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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Yours sincerely, Dr Laura Smith Publishing Editor, Journals
Royal Society of Chemistry Thomas Graham House Science Park, Milton Road Cambridge, CB4 0WF Royal Society Open Science -Chemistry Editorial Office justification and motivation for the article. But it has an excess of pages, sometimes in a simple language but more suitable for a book than for a scientific text (article).
The review (MOS) does not mention other gas detection techniques such as photoacoustic spectroscopy and chemiluminency etc. There could be a comparison of the advantages and disadvantages with other techniques. The NO2 gas sensor (which is not a greenhouse) are widely discussed, so it is beyond the scope of the article. The greenhouse gas that is (N2O), has no comment in the text, nor reference !!. And the article still lacked comments on the part of the sensors (MOS).

Response:
We agree with the reviewer. We have removed the excess of pages on the achievements of climate change and its solutions (renewable energies) in the revised manuscript accordingly. As per reviewer' suggestion, authors have mentioned other gas detection techniques such as photoacoustic spectroscopy, chemiluminency, electrochemical sensor, thermometric sensors, catalytic sensor, gas chromatography, chemical sensor and mass resistive sensor in the revised manuscript. Authors have given a comparison of the advantages and disadvantages of MOS-based technique with other techniques as per the suggestion of reviewer and highlighted by yellow colour in Table-2 of the revised manuscript.
Authors are very much thankful to the reviewer for the comment on the NO2 gas sensors. We agree with the reviewer. As NO2 is not a greenhouse gas. Therefore, authors have removed the given content for NO2 gas sensors.
In the revised manuscript, authors have included a wide discussion about the various studies/reports available on MOS-based sensors for N2O (greenhouse gas). Authors have also introduced the other recent available techniques for N2O detection as per the reviewer suggestion/expectation.
Comment 3: "The article needs a new writing that defines its objectives well"

Response:
We are agreeing with the reviewer. In the revised manuscript, authors have rewritten the objectives of this review and highlighted that with yellow colour.

Comment 4:
Nothing is said about other GHC sensors, only satellite sensing. Why? there are many gas detection techniques. (The introduction) Response: Although satellite sensing is an emerging interest of climate scientists in order to have a wide spatial and temporal coverage of GHGs emission globally. But authors agree completely with the reviewer's concern on the theme of this review and therefore authors have removed satellite sensing paragraph in the introduction of revised manuscript. Instead other GHG gas sensors have been included in introduction of revised manuscript and highlighted in yellow colour.
Comment 5: Let's see the statements in the abstract; a) "GHGs sensors and their sensing mechanism have been discussed briefly" This should be better discussed, rather than discussing details of climate change.

Response:
We agree with the reviewer. In the revised manuscript, authors have rewritten the abstract as per the suggestion of the reviewer and highlight the rewrite part with yellow color. b)'The status of global GHGs emissions during the COVID-19 pandemic lockdown has also been discussed'. Why discuss this topic in the article? I don't see this essential topic for a sensor review.

Response:
We agree with the reviewer. Authors have discussed the status of global GHGs emissions during the COVID-19 pandemic lockdown because of the interest and motivation followed by the reduction of global GHGs emissions level. However, authors have removed this section 4 in the revised manuscript as per the reviewer suggestion.

Reviewer: 2 (Minor revision)
Comments to the Author(s)

The introduction
Comment 1: This topic is about environmental sustainability, this topic is really important, but it will be for this article.
In the paragraphs below !! -quality of life in terms of threatening water supplies, compromising ecosystems and impeding growth for future generations. The environment around us is an essential part of human survival. The more we don't care about our environment, the more it will become intoxicated with contaminants and toxins that have a harmful impact on our lives in numerous ways -"In particular, the pace of global economic growth during the past decades, paved the way to a continuous decline in the availability of natural resources such as forests (cut down for agriculture/demand for wood), air/land/water pollution. This in turn imposes severe health problems, damage to the productivity of land and seas, sources of oil/coal/gas, loss of fishing stocks due to overfishing and loss of species diversity etc. to the mankind. Our environment is composed of some basic components such as water, air, soil, flora, fauna, and human beings and hence economic development must move forward with the stability between these componen"t.

Response:
We agree with the reviewer. In the revised manuscript, authors have removed all the above said statements/paragraphs about the environment sustainability and modified part of introduction is highlighted by yellow colour as per the reviewer's suggestion. In the section 'Concentration of GHGs in earth's environment" In the first paragraph -Look, nitrous oxide (N2O), greenhouse gas 'The primary GHGs in the atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone'.