Dear Ranjeet Kumar Mishra ,

I recommend the excellent papers by @John McDonald-Wharry (https://www.researchgate.net/profile/John_McDonald-Wharry)

Article Carbonisation of biomass-derived chars and the thermal reduc...

Article Reviewing, Combining, and Updating the Models for the Nanost...

as well as

Marco Keiluweit

Article Dynamic Molecular Structure of Plant Biomass-Derived Black C...

McDonald-Wharry et al. (2013) used oxygen-rich precursors (Pinus radiata wood, Phormium tenax leaf fibres, and sucrose crystals) and carried out carbonisation at 420 to 1000°C. The authors also produced thermally reduced graphene oxides as well as air-oxidised synthetic graphite. The materials were then studied using Raman spectroscopy, and the ID/IG, IA/IG, and IV/IG height intensity ratios determined. In Figure 10, the authors showed that the ID/IG ratio increased between 400 and 900°C decreasing slightly at 1000°C. The ID/IG ratios of chars produced from all 3 oxygen-rich precursors was closer to graphene oxide than graphite. This is why chars from oxygen-rich precursors are often referred to as non-graphitisable carbons. However, Keiluweit used the term turbostratic chars for chars produced at temperatures > 700°C, which are said to be dominated by disordered graphitic crystallites.

Salisu Nasir et al. (2017) used oil palm leaf and oil palm kernel shell and investigated the effect of temperature on IG/ID ratio of the carbonised material (Article Oil Palm Waste-Based Precursors as a Renewable and Economica...

I suggest you try to carbonise your material at lower temperatures if you want to see a change in the ID/IG ratio with temperature. At the temperatures you selected I believe you are in the equilibrium zone.

In addition to Raman spectroscopy, you can go for XRD and 13C NMR to study the structure of your material.

Hope this helps?

All the best, Rob.

Hi Ranjeet,

I think the possible reason you got the same ID/IG ratio at those temperatures is that high temperature treatment remove nearly all of the non-graphitic phase in the sample. The propensity to graphitize is plausibly controlled by the chemical composition and micro texture of the organic precursor. Biomass-derived precursors are known to consist of complex biomatrix encompassing various polysaccharides, phenolic polymers, and proteins in their structure. Thus, in the course of pyrolysis, the biomass liquid and solid are thermally decomposes. As a consequence, large hydrocarbon molecules of biomass are broken down into smaller molecules. The process removes moisture, water, gases and other non-carbon components at different stages of the pyrolysis and produces a more energy dense product. This when combined with the decomposition of cellulose, hemicellulose and lignin which also occur at different decomposition temperature will give you better understanding of the trend you observed in your sample.

On the whole, as temperature is increased to graphitization regime (starting from 800 to 900 degree Celsius as we observed previously, Salisu Nasir et al. 2017 and 2018), the IG/ID ratio of the sample stabilize and finally converged. This suggests increase in ordering of sp2 bonded graphitic domains.

As for the second part of your question on how you can determine the graphitic content of biocarbon, you can use the reciprocal of ID/IG i.e. IG/ID. This depend on your area of concentration. If your emphasis is to determine defect you can use ID/IG ratio. However, both ratios can work for defect and graphitic content interchangeably. I stand to be corrected...

Hope this will help. Good luck.

Biochar is one kind of ash but it is special type of ash. It is interesting treatment for your research. All the best.

Hi Ranjeet,

It is a very interesting question. Actually, there is a misunderstanding about the correlation between the ID/IG and the biochar graphitization degree. The ID/IG not monotonous changes with the heat treat temperature (HTT) of the biochar, because for the highly disordered carbon materials, the D band and G band can be also related to the aromatic rings. With the increase of the HTT, the carbon structure of the biochar changes from the very highly disordered to ordered aromatic rings and then graphitization. Generally, the ID/IG can firstly decrease or be unchanged at low HTT (~300-~400℃). At this temperature region, the change of the ID/IG can be easily affected by the changes of the minor bands near the D band and G band. With the further increase of the HTT, the ID/IG can firstly increase (~500-~1000℃) and then decrease corresponding to the increase of the La of the biochar. The turning point is depended on the precursor of the biochar and the laser wavenumber of the Raman test. For the 532 nm, the turning point is mainly at about 2-4 nm of the La. I think the similar ID/IG for your biochar obtained at 1000, 1200 and 1400 ℃ is mainly because the La of your biochar is in the range of the turning point. I suggest you to further calculate the D band FWHM, G band FWHM, 2D band intensity or FWHM and IV/ID of your chars, and compare the difference between them. These Raman parameters can be also useful to reflect the carbon structures.

Some references may help you to understand your results.

[1] Carbon 161 (2020) 359-372

[2] Raman Spectroscopy as a Versatile Tool for Investigating Thermochemical Processing of Coal, Biomass, and Wastes: Recent Advances and Future Perspectives. https://dx.doi.org/10.1021/acs.energyfuels.0c03298.

[3] Interpretation of Raman spectra of disordered and amorphous carbon, PHYSICAL REVIEW B, 2000.

Hope this can help you.

All the best, Jun.

Hi, element analysis

http://analizator.pro/analizers/elementnyy-chn-analizator-serii-5e

Or the established standard methods, their essence in the release of compounds flying away during calcination. These are ASTM D5142, ISO 17246 methods

Depending on the intended use of the derived biochar, I think the temperature used is way higher than usual. Most constituent functional groups on the biochar might be lost at such temperatures, and may likely show less variation compared to biochar produced between 250-800 oC

Hi Ranjeet Kumar Mishra

In many previous publications it is suggested that at high temperature graphitic structure will generate. However it is very much depending on decomposition of feedstock and heating rate.

I suggest you have a look at this work which reviewed graphitic biochar preparation accurately.

https://pubs.rsc.org/en/content/articlelanding/2020/ta/c9ta11618d#!divAbstract

Also in case you would like to have more evidence of graphite sheets in your samples, TEM analysis and image is quite common. Mostly you are able to see well ordered stream of carbon between porous carbon or near the edge. Lastly , XRD analysis is another suitable method to check peaks at 26 for all your samples and compare the effect of HHT on graphitization.

Good luck

Thank you so much.