# Synthesis of Nitrogen-Doped Graphene Quantum Dots from Sucrose Carbonization
## 3 Results and Discussion
### Structural Characterization
In the literature, there are several works that deal with the chemical reduction of graphene oxide [45; 46], but there are few that use DMSO as a possible candidate for the reduction of graphene oxide [47]. The Raman spectra obtained for the precursors without and with nitrogen doping (Precursors A and B) and for the GQDs obtained after treatment in DMSO are shown in Figure 5. The spectra of all samples showed a peak located at \(\sim\)1360 cm\({}^{-1}\), associated with the graphene D band, and a peak centered at approximately \(\sim\)1585 cm\({}^{-1}\), referring to the graphene G band. Furthermore, the spectra obtained showed a wide 2D band located at approximately \(\sim\)2750 cm\({}^{-1}\)[24; 48]. Figure 4: XRD results of undoped GQDs and N-GQDs. Figure 5: Raman spectra obtained for (**a**) Precursor A and undoped GQDs and (**b**) Precursor B and N-GQDs. The spectra of the precursors showed broad bands, which are typical of graphene oxide [49; 50], corroborating the observations made in the XRD analyses. In this case, the Id/Ig ratio (considering the integrated intensities) for the precursor that did not go through the doping process (Precursor A) was 4.04 and for the precursor that went through the nitrogen reflux process (Precursor B), the Id/Ig ratio was 3.31. It was also noted that the 2D bands had a low intensity compared with the D and G bands, which is also compatible with the presence of graphene oxide in these samples [49]. The GQDs that did not undergo the nitrogen doping process showed a very similar Raman spectrum to the precursors. In this case, the Id/G ratio was 2.19. It is worth adding that the broadening of the bands in the Raman spectrum is also expected for graphene nanoparticles and nanoribbons, in which the size of the sp\({}^{2}\) domains is also greatly reduced [49]. On the other hand, in the spectrum of the N-GQDs, the Raman bands of graphene were much narrower. The narrowing of the bands reveals that the size of the sp\({}^{2}\) domains should be larger in this sample [49]. The Id/Ig ratio in this case was 1.45. The presence of an intense D band can also occur as a result of light scattering at the edges of graphene nanoparticles [49]. Figure 6 shows the FTIR spectrum of the precursor materials used for the synthesis of GQDs and the spectra of doped and undoped GQDs. In general, some of the absorption peaks were common to all samples: the peak centered at 3400 cm\({}^{-1}\) is associated with the stretching of the -OH group [51; 52]; the peak located at \(\sim\)1710 cm\({}^{-1}\) is associated with the presence of carbonyl groups (C=O) in the GQD structure [52]; at 1640 cm\({}^{-1}\), a peak was observed that is related to the C=C bonds of the aromatic rings that form the base structure of the GQDs [24; 52]; absorption peaks located at 1160 and 1030 cm\({}^{-1}\) are common in graphene oxide and are associated with bond stretching (C-O) of carboxylic acids [24; 52]; and the peak centered at \(\sim\)850 cm\({}^{-1}\) is also common in graphene oxide and is associated with bond deformation (C-O-C) in epoxy groups [51; 52]. In the FTIR spectrum of the precursor that was subjected to nitrogen reflux treatment, it is also possible to notice the appearance of an absorption peak at \(\sim\)1400 cm\({}^{-1}\). This peak is related to deformations of the bonds (C-N) in the amine groups in GQDs [52; 53]. In general, the FTIR spectra of the precursors indicate that the material has a large number of functional groups with oxygen (carboxylic acids, epoxy, and hydroxyl groups) that are also quite common in graphene oxide. The infrared absorption peaks that were observed in the precursors of the GQDs were also observed in the FTIR spectra of the GQDs after the DMSO reflux treatment. However, the emergence of new peaks was observed; namely, the absorption peak at 3020 cm\({}^{-1}\) can be related to the stretching of bonds (C=C) in polycyclic aliphatic hydrocarbons, expected in  
Figure 6: FTIR spectra of (**a**) Precursors A and B and (**b**) undoped GQDs and N-GQDs.