We have collected the IR spectra of two samples, one prepared with commercial graphite (Sigma Aldrich) and with a sonothermal treatment of 2h, the second with the same apparatus Vibracell Bioblock 500 W but in 5 min. We know that the first sample contains larger graphene sheets than the second, as established by TEM. The second is a mixture of 1 to 5 sheets and remaining graphite.
We have been surprised to detect that a strong absorption peak was detected at 7325 cm-1 but only with the smallest sheets. Do you agree with me, it corresponds to a border functionality? The infrared irradiation is removing absorbed water.
In that position, we are no longer in the IR range. Which range are we observing?
Can attributions to OH and peroxyde OOH groups be propose?
Dear Anne,
May I first ask you how you obtained the IR spectra? Some of your bands are inverted, and some are dispersion-like. This could be an effect due to the measurement conditions. I wonder if you have used, by any chance, ATR-spectroscopy with a ZnSe- or diamond ATR-crystal at 45° angle of incidence?
Thomas has pointed out a major problem. Instrument vendors say that they will sell a diamond (or ZnSe) ATR and it is a universal sampling accessory.
Not true!
From those spectra it is obvious that you violated the critical angle constraint on ATR. I just finished recording a webcast for Spectroscopy, where this will be discussed. Single bounce (45° AOI) diamond ATR is not appropriate and even a Ge ATR element at a 45° AOI will still violate the critical angle constraint.
You may get usable spectra with germanium at a very shallow AOI. I would try a GATR or a VeeMax with a Ge element with a face angle of 60°. That should give you a large enough AOI to have it be greater than the critical angle for graphene.
You cannot interpret anything from these spectra until you get usable spectra. If you decide to do an external reflection experiment (which I don't think will work very well) you will need to correct them for the effects of the complex refractive index before you can interpret them.
As to your 7325 cm-1 feature you mention. That is still very much the infrared. It is the near infrared. And your spectra do not show it anyway.
- Badges
- Science topic
- Similar topics
- Mathematics