**4. Conclusions and outlook**

In the Raman spectra for the raw material (GO-COOH), GO-TYR and final monomers GO-Bz obtained by both methods, the characteristics of the graphene structure are noticed, namely the intense signals D and G, which proves the presence of the graphene structure in the final compound (**Figure 11**). At the same time, it is worth mentioning the appearance of the 2D band that characterizes the arrangement and the number of graphene plans. Graphene, the two-

tion of researchers in recent years due to its excellent thermal, mechanical, electrical and barrier. All these excellent properties have been shown to the monolayer graphene, the increase of the number of layers leading to the decrease of its properties. For this reason graphene structure has been extensively studied. Raman spectroscopy allows the investigation and determination of the number of layers of the graphene, this information being extracted from the 2D spectrum band. Thus, for products obtained by the EDC/NHS method, the band is wider even in the final benzoxazine product, indicating aggregation in the form of multiple layers of the graphene plans, provided that a part of the benzoxazine monomer did not polymerize and therefore, there was no driving force needed to move the graphene aggregates into independent layers.

**Figure 11.** Raman spectra of GO-COOH, GO-TYR, GO-Bz obtained by: a) EDC/NHS activation method; b) chlorination

hybridized carbon atoms has attracted the atten-

dimensional form of graphite, consisting of sp2

194 Raman Spectroscopy

with SOCl2

(Biru I et al. (2016) copyrights).

Raman spectroscopy is a powerful instrument for investigating carbon nanomaterials. As a highly sensitive technique Raman spectroscopy is recommended for detection of small changes in structural morphology of various carbon nanomaterials playing an important role as a direct or complementary tool in any laboratory working with carbon allotropes. Raman spectrum shows specific signals for each carbon allotrope when the monochromatic radiation interacts with the sample. Diamond and graphite exhibit significant differences in the Raman spectrum even if both are entirely made of C-C bonds. The Raman spectrum of pure diamond exhibits an extremely sharp signal at ~1332 cm−1 which arises from the stretching of the C-C bond. Instead, in the Raman spectrum of graphite two distinguishable peaks are revealed at ~1350 cm−1 (D band) and ~1580 cm−1 (G band) revealing that the graphite is not as uniform in structure as diamond.

Also more complex structures can be investigated by Raman spectroscopy. The Raman spectrum of C60 fullerene exhibits strong signals at 1467 cm−1 and 1567cm−1 revealing that C60 is composed of sp2 bonded carbon. The sharpness of the signal shows that C60 exhibits a uniform structure. On the contrary, the Raman spectrum of C70 exhibits numerous other peaks. In case of C70 sample, the main peaks are located at 1564 cm−1and 1228 cm−1 due to a reduction in molecular symmetry which results in more Raman bands.

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nn100946q

With this technique it is easily possible to distinguish graphite from diamond, SWCNTs from MWCNTs or graphene form bulk graphite. The stretching of the C-C bond in graphitic materials gives rise to the G-band Raman feature which is common to all sp2 carbon systems. The G-band of SWCNTs splits in two band components because of large diameter nanotubes and it can be used to distinguish metallic and semiconducting nanotubes. In case of CNTs the D band is significantly increased compared to graphite indicating that some disorder of the graphene sheets is induced. The radial breathing mode (RBM) is particularly important for the determination of the diameter of CNT, its frequency being related to the aggregation state of SWCNTs. The RBM band is unique to SWNCTs and corresponds to the expansion and contraction of the nanotubes.

Raman spectroscopy could be even used to discriminate single layer graphene from multilayer graphene and to determine number of graphene sheets. In case of pure graphene a sharper 2D band situated at ~2700 cm<sup>−</sup>**<sup>1</sup>** is observed. The 2D band originates from a twophonon double resonance process and it is interrelated to the band structure of graphene layers. The 2D peak evolves as the number of graphene layers increases to about ten layers upon its profile resembles with that of graphite. Moreover, as a non-destructive characterization technique Raman spectroscopy is frequently used to investigate graphene nanocomposites in order to prove successfully graphene functionalization.
