## 3 Results and Discussion
### Characteristics of the Graphene Materials
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**O (at \%)**} & \multirow{2}{*}{**N (at \%)**} & \multicolumn{4}{c}{**O 1s**} & \multicolumn{4}{c}{**N1s**} & \multirow{2}{*}{**I\({}_{\text{D}}\)/I\({}_{\text{G}}\)**} \\ \cline{3-3} \cline{5-13}  & & & **C-O** & & & **C=O** & & **COOH** & & **H\({}_{2}\)O** & **Pyr** & **Pyrr** & **Quat** & **Nox** \\ \hline rGO\({}_{\text{325-3}}\) & 7.0 & - & 57.0 & 21.1 & 15.7 & 6.2 & - & - & - & - & 0.63 \\ rGO\({}_{\text{100-3}}\) & 7.0 & - & 63.1 & 17.0 & 13.7 & 6.3 & - & - & - & - & 0.39 \\ rGO\({}_{\text{10-3}}\) & 6.8 & - & 54.6 & 20.7 & 18.7 & 6.0 & - & - & - & - & 0.53 \\ NrGO\({}_{\text{325-4}}\) & 4.1 & 3.4 & 54.7 & 23.5 & 17.6 & 4.2 & 40.0 & 21.7 & 22.7 & 15.6 & 0.75 \\ NrGO\({}_{\text{100-4}}\) & 3.6 & 3.3 & 54.2 & 21.2 & 18.9 & 5.7 & 39.5 & 21.7 & 23.6 & 15.3 & 0.63 \\ NrGO\({}_{\text{10}}\)-4 & 3.6 & 3.2 & 56.2 & 17.4 & 18.7 & 7.6 & 38.5 & 20.5 & 28.5 & 12.4 & 0.58 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: XPS deconvolution results and RAMAN I\({}_{\text{D}}\)/I\({}_{\text{G}}\) ratio for rGO\({}_{\text{m}}\)-3 and NrGO\({}_{\text{m}}\)-4 samples. The intensity ratio of the D and G bands (I\({}_{\rm D}\)/I\({}_{\rm G}\)) can be used as a quantitative indicator of the amount of disorder or edges within the structure of the samples. I\({}_{\rm D}\)/I\({}_{\rm G}\) ratios were calculated (Table 2). A comparison of rGO\({}_{\rm m}\) samples with their NrGO\({}_{\rm m}\) counterparts shows that the ratio increases when N  
Figure 5: PZC for rGOm-3 and N-doped reduced graphene oxide (NrGOm-4) samples. Figure 6: Raman spectra for rGO\({}_{\rm m}\)-3 and NrGO\({}_{\rm m}\)-4 samples. is introduced in the reduced graphite oxide. In addition, an increase with N content in the \(\mathrm{N}\mathrm{r}\mathrm{G}\mathrm{O}_{\mathrm{m}}\) series is observed. This is due to a disruption of the symmetry of the lattice produced by the incorporation of heteroatoms into the graphitic structure. This effect has been described previously by [PERSON] et al. [53]. They claimed that the introduction of N into the carbon lattice could produce distortions, transforming the graphitic region into an \(\mathrm{sp}^{3}\) domain. From the Raman spectra, it can be observed that an increment in the N content leads to a shift of the D band to lower frequencies. For a bulk graphite sample, the 2D band consists of two contributions. For single-layer graphene, the 2D band appears as a single sharp peak at the lower frequency (around 2690 cm\({}^{-1}\)). As the number of layers increases, the 2D band changes its shape, width, and position, and the G peak position shifts to lower frequencies [8]. A systematic study of the in-plane crystallite size was carried out in 1970 by [PERSON] and [PERSON] [54]. They found that the ratio of the D and G band intensities (\(\mathrm{I}_{\mathrm{D}}\)/\(\mathrm{I}_{\mathrm{G}}\)) is inversely proportional to the in-plane crystallite sizes (\(\mathrm{L}_{\mathrm{a}}\)). The crystallite sizes (\(\mathrm{L}_{\mathrm{a}}\)) can be calculated from \(\mathrm{L}_{\mathrm{a}}\)(nm) = \((2.4\times 10^{-10})\,\lambda^{4}(\mathrm{I}_{\mathrm{D}}/\mathrm{I}_{ \mathrm{G}})^{-1}\) (\(\lambda\) being the Raman excitation wavelength) [55]. \(\mathrm{L}_{\mathrm{a}}\) were 25.6-33.1 nm for \(\mathrm{N}\mathrm{r}\mathrm{G}\mathrm{O}\) samples and 30.5-49.3 nm for \(\mathrm{r}\mathrm{G}\mathrm{O}\) samples; it is concluded that the crystallite size decreases with the presence of defects, and therefore the doping level. It is consistent with the bibliography [40], which point outs that since \(\mathrm{L}_{\mathrm{a}}\) is the average interdefect distance, the introduction of nitrogen atoms accompanied by defects implies a smaller \(\mathrm{L}_{\mathrm{a}}\). The stability of the prepared graphenic materials in air atmosphere with the temperature was studied by thermal gravimetric analysis (Figure S5, ESI).