The ATR-FTIR spectrum shows hydrochar produced by hydrothermal carbonization of sucrose after subsequent pyrolysis at 1000°C in Nitrogen. The powder sample was pressed onto the diamond ATR crystal, scanned 32 times and the spectrum has not been processes in any way.
1.) Which chemical bond is causing the FTIR peak at 2105 cm-1? The only bonds that I found that could cause this peak are (1) alkyne groups, (2) the combination band of water or, as stated without reference in some paper, (3) a C=O bond. (1) seem unlikely as it is not very stable, (2) seems unlikely as no other water-typical peaks are visible and (3) seems unlikely as no other C=O-typical peaks are visible and oxygen shouldnt be in the sample after pyrolysis anyway. Any suggestions?
2.) My second question is: I know that graphitic structures without functional groups do now show FTIR peaks in general. But why? The only explanation I can find is that "no peaks indicate chemical inertness". The sample does absorb IR light and generally aromatic C=C and C-C have distinct FTIR absorption peaks. What is the reason for the absence of distinct peaks at the molecular level?
1. The Si-H band appears around 2100 wavenumber. The spectrum was recorded using Diamond crystal it can't be Si-H. Thus, this can be stretching vibration of hydrogen-bonded C-C band which is often a weak red-shifted band.
You are not observing the vibrational spectrum of your sample. Those peaks are the incompletely compensated strong absorption of the diamond anvil. This weak peak typically appears in diamond ATR.
After heating the material to 1000oC, the majority of chemical groups carbonize. Around 900oC, many heteroatom evaporate. Thus, the IR spectrum become near featureless. For this type of sample, Raman spectroscopy will provide much better information. The well known D and G bands, and overtones will allow you to evaluate the perfection of graphitic structure.
Dear Hatsuo,
thank you for your answer, I allready expected that the sample wouldnt be the origin of that peak. Indeed i recorded Raman spectra and analyzed the D and G peaks. Do you have a reference for that spectral artifact of the diamond ATR??
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