Finger-Like Carbon-Based Nanostructures Produced by Combustion of Flour-Based Sticks (Spaghetti)
Round 1
Reviewer 1 Report
The article describes an unusual study about the formation of carbon material from the combustion of spaghetti. I would not assume that the use of a treated material like spaghetti can be a suitable example as biomass since their use is different. However it can be a reasonable curiosity just to understand the behaviour of such a peculiar material. Unluckily, the design of the experiments isexceedingly simple. Why use a candle to burn the sample? The carbonaceous residues of the flame might interfere with the analysis of the material? which is the temperature of the combustion? Higher or lower is not a good differentiation. a careful morphological analysis of the surface of spaghetti would help in rationalise the results, the authors attempted it but no results could be obtained. The speculation on the mechanism for the formation of the observed structures should be supported by more data
Author Response
The article describes an unusual study about the formation of carbon material from the combustion of spaghetti. I would not assume that the use of a treated material like spaghetti can be a suitable example as biomass since their use is different.
Reply: We agree with the Reviewer, that our “biomass” has been processed, so we have changed the term “starch-rich biomass” into “flour-based” in the title.
We have made changes accordingly: See yellow highlight in line 3 of resubmitted manuscript.
However it can be a reasonable curiosity just to understand the behaviour of such a peculiar material. Unluckily, the design of the experiments isexceedingly simple. Why use a candle to burn the sample?
Reply: The design of the experimental set-up for combustion was straightforward, yet despite this simplicity, the end material provided a rich structure to investigate, and the results were reproducible.
We have made changes accordingly: See lines 67-68 in the highlighted version of the manuscript.
The carbonaceous residues of the flame might interfere with the analysis of the material? which is the temperature of the combustion? Higher or lower is not a good differentiation. a careful morphological analysis of the surface of spaghetti would help in rationalise the results, the authors attempted it but no results could be obtained.
Reply: We do not feel that any soot produced from the flame would have any direct influence of the finger formation for the following reasons: (a) an overpressure is built inside the material and at the surface interface from the gases being formed there, building a barrier, that would hinder diffusion external soot particles to diffuse into the closest region around the surface; (b) for the case when the stick burns without the assisting flame, the amount of soot is relatively small and will be of even less importance; (c) the density of bulk is approximatively 1000 times denser than the surrounding gas so the supply of precursors from the bulk to the surface would be expected to dictate the kinetic rates of dynamics in the formation of the nanostructures.
We have made changes accordingly: See lines 281-284; 285-288; and 312-319 in the highlighted version of the manuscript.
which is the temperature of the combustion? Higher or lower is not a good differentiation.
Reply: We recently measured the candle temperature and that of the self-sustaining flame with a thin thermocouple. Despite the difficulty of measuring exact temperatures (e.g., no radiation correction, and using small volumes), we managed to get indicative results: 1230 ± 30 and 1160 ± 30 °C.
We have made changes accordingly: See lines 72-76 in the highlighted version of the manuscript.
a careful morphological analysis of the surface of spaghetti would help in rationalise the results, the authors attempted it but no results could be obtained.
Reply: We have performed additional SEM measurement that, show the surface of a fresh stick of spaghetti, comparing it with that of the burnt one from the same stick. In the intermediate (heated, but not carbonized) surface we can see, micrometer sized bulging structures that indicates softening and build-up of pressure in the bulk. In the carbonized material region, we see porous inner material in those areas where part of the surface was mechanically broken off. We also obtained ~ 50% increase in diameter going from unburnt to burnt region of the spaghetti stick. We have inserted additional pictures a support to the manuscript and adapted the text.
We have made changes accordingly: See lines 245-264, which includes Fig. 11 (pictures and figure caption) in the highlighted version of the manuscript.
The speculation on the mechanism for the formation of the observed structures should be supported by more data.
Reply: We feel that we have added additional support to the mechanisms we propose with the material and explanations described above.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This is an interesting study on the carbon nanostructrues created by the burning of the hydrocarbon materials (food). The characterization is deliberate and the claims are generally supported by the experimental results. I suggest publish after a few minor revisions as follows:
Figure 5b is supposed to show the carbon lattice but it is really hard to tell with the noisy background. Please take better images or revise the claims.
Does the characterized carbon nanostructures only be generated from the burnt spaghetti? Is there anything special about the spaghetti that facilitate the generation of the nanostructure? In the manuscript it has been mentioned that the mineral elements are concentrated to the inner shell. I think it worth investigating more.
What are the potential applications of such special nanostructure made of carbon and mineral elements? I understand it is not required to have the scientific research immediately "useful" but it will step up a notch if the applications could be significant.
Author Response
This is an interesting study on the carbon nanostructrues created by the burning of the hydrocarbon materials (food). The characterization is deliberate and the claims are generally supported by the experimental results. I suggest publish after a few minor revisions as follows:
Figure 5b is supposed to show the carbon lattice but it is really hard to tell with the noisy background. Please take better images or revise the claims.
Reply: We agree that the resolution in Fig. 5b is very limited. We have replaced Fig.5 with a new figure showing another region on the same finger with a fringe spacing of 0.42 nm. We have also added Fig. 5c showing the corresponding line spectrum of the carbon density in a layered region.
Does the characterized carbon nanostructures only be generated from the burnt spaghetti? Is there anything special about the spaghetti that facilitate the generation of the nanostructure? In the manuscript it has been mentioned that the mineral elements are concentrated to the inner shell. I think it worth investigating more.
Reply: That is a very important point. We feel that the main cause for finger formation is reaching high temperature in the biomass that leads to gas formation (including water vapor) inside the decomposing biomass and then carbonization. This is also supported by a reference that came to our attention very lately in the last days, See Ref. 14, in the new version of the manuscript where their reactor reached 750°C. We recently measured the temperature at the burning surface with a thin thermocouple and found 1000 °C as our highest value. Regarding the minerals, we have already started utilizing different dopants in the biomass.
What are the potential applications of such special nanostructure made of carbon and mineral elements? I understand it is not required to have the scientific research immediately "useful" but it will step up a notch if the applications could be significant.
Reply: We have added a final paragraph at the end of our discussion where we propose different applications, which include nanoscale reactors, capturing waste and toxic materials from environment, produce magnetic elongated nanoparticles for remote control of transportation and rotation, and high surface-to-volume microelectrodes, and nano-electronic/ionic interfaces with biologicals cells.
Author Response File: Author Response.docx
Reviewer 3 Report
The authors found interesting nanostructures on the surface of burnt spaghetti using Scanning Electron Microscopy, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDX) for analysis. The topic should be eye-catching to general readers. The manuscript is well organized. However, the references relevant to Transmission Electron Microscopy is not sufficient. It's advised that the authors cite Nano letters 18 (11), 7238-7246 and Nano Letters 16 (10), 6008-6013.
Author Response
The authors found interesting nanostructures on the surface of burnt spaghetti using Scanning Electron Microscopy, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDX) for analysis. The topic should be eye-catching to general readers. The manuscript is well organized. However, the references relevant to Transmission Electron Microscopy is not sufficient. It's advised that the authors cite Nano letters 18 (11), 7238-7246 and Nano Letters 16 (10), 6008-6013.
Reply: We agree that the introduction is short on details on the power of electron microscopy, in particular since it is the main instrument in our investigation. We have added four references that are relevant to TEM studies of the structure of carbon-related materials. Regarding the suggested papers by the Reviewer, we think it is interesting work, but we do not see the connection to our work: reading these two papers carefully, we find little to connect them with our work. They report on properties that our work does not cover namely electrical and photoresponses , on materials that are unlike our materials - Ge/Si and CdSe semiconductors and on a type of in situ TEM work which is very different to what we briefly mention for a future direction. If there is a link that we have missed, maybe we could kindly ask the reviewer to clarify his/her advice.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have improved their work and it can be accepted for publication
