Hello respected members, Can anyone comment about the Interpretation of Raman Spectra of fluorescent Carboxyl Functionalized Carbon nanomaterial? Is it relatable with the Raman Spectra of Polycyclic Aromatic Hydrocarbons? The spectrum is very different from conventional graphitic materials.
Looking for expert opinion.
The Raman Spectra of the powdered material is recorded with red laser having 633nm wavelength and energy of 3mW.
Please see the attached figure for more detailed information about the peak positions.
Thank you!
The major peak at 1677 cm-1 could be a g-mode if it still has a major aromatic system. Unfortunately, carboxylic acids also have their vibrations in that segment of the spectrum, so if your carboxy functionalization is in that segment you have an interpretation conflict. Anyway, the "side peaks" in the enhanced cutout are on the noise level, so I would not even start to interpret those.
For other functional groups, here is an overview:
http://www.wysri.com/wp-content/uploads/2014/12/FunctionalGroupsTeachingLab.pdf
I agree with Jürgen Weippert's comment and yet we have to have the knowledge of the wet-chemistry and the standards for safe interpretation of the spectra!
Thank you Jürgen Weippert
Hi Irfan Nadeem
Polycyclic aromatic hydrocarbons, defined here as molecules consisting exclusively or predominantly of carbon and hydrogen arranged in multiple aromatic (phenyl) rings. Raman spectroscopy has proven to be a useful technique for the characterization of PAHs based on its ability to inelastically (Raman) scatter incident light of a particular wavelength. Raman scattering refers to cases where a change in the vibrational or rotational state of a molecular vibration occurs simultaneously with electron cloud distortion. A change in the vibrational or rotational state of the molecule results in the emission of either more or less energy than was supplied by the incident radiation. The intensity of Raman peaks is inversely proportional to the fourth power of the excitation wavelength although a shorter excitation wavelength may generate Raman peaks of higher intensity, it also has a greater likelihood of causing thermal decomposition and photodissociation in samples. The strength of the signal which reaches the detector of a Raman spectrometer is also highly dependent on the physical properties of a target, such as grain size, internal boundaries, surface texture, and the presence of coatings. In general, it has been found that a fine-grained sample provides a better signal when irradiated with a shorter excitation wavelength. Functional groups such as nitryls (RNO2), nitriles (RCN), and carbonyls (RCOR‟) create a negative mesomeric effect by withdrawing electrons from the ring system of the PAH. In contrast, functional groups such as hydroxyls (ROH), amines (RNH2), and ethers (ROR‟) create a positive mesomeric effect by contributing nonbonding electrons to the ring system. In order for a functional group to exert a positive mesomeric effect, one or more pairs of nonbonding electrons must be present on the atom which directly connects it to the ring system. However, a negative mesomeric effect requires that this atom instead engages in multiple bonding with one or more highly electronegative atoms in the functional group. The peaks around ~1400 cm-1 and 1500-1600 cm-1 indicate sp3 domains of carbon layers and sp2 in-plane carbon vibrations i.e., the D band and G band also indicate the vibrational modes in the Raman spectra which represent A1g breathing mode and the E2g in-plane vibrations respectively for carbonaceous materials vibrations. Thus, the peak at 1677 cm-1 is for the G band vibration of the material. The above I can say from my side. For more details please look at this paper 10.1016/j.icarus.2016.03.023.
Regards
Hi Jürgen Weippert
The peaks in red from (1115-1450) are considered peaks or could be noise?
Also, the peak between 862 &725, is it a peak? and the peaks below 725 what about them?
Thanks
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