## 3 Results and Discussion
### Testing and Characterization  
In order to explore the preparation process of aerogel, we carried out scanning morphology analysis, infrared spectrum analysis, Raman spectrum analysis and XRD analysis. Through SEM analysis, we found that the micro morphology of aerogel gel is a three-dimensional network structure composed of interconnected open-celled microspheres (Figure 3a). FT-IR spectroscopy is a power full technique to characterize the presence of different functional groups. FT-IR spectrum was recorded, and the spectrum of GO obtained confirmed the successful oxidation of the graphite (Figure 3b). Functional groups such as O-H, C-OH, C-O were observed in GO. Due to the carboxyl OH stretching mode, there is a broad peak between 3500 cm\({}^{-1}\) and 2500 cm\({}^{-1}\) in the IR spectrum [28; 29]. The peak at around 1725 cm\({}^{-1}\) is attributed to C=O stretch of carboxyl group [30] while 1230 cm\({}^{-1}\) corresponds to C-OH stretch of alcohol group [29]. The peak at around 1060 cm\({}^{-1}\) is attributed to C-O stretching vibrations of C-O-C [31] and the peak around 1620 cm\({}^{-1}\) is attributed to C=C stretches from unoxidized graphitic domain [28]. All the intensities of the peaks corresponding to the oxygen-containing functional groups of reduced graphene oxide were reduced compared to the intensity of the peaks of graphene oxide, and even the intensities of some peaks disappeared [32]. This suggests that N\({}_{2}\)H\({}_{4}\cdot\)H\({}_{2}\)O successfully reduced graphene oxide. However, all peaks did not disappear, which indicates that the GO was not completely reduced and suggests the presence of some functional groups.  
Raman spectra has long been considered as the simplest and non-invasive tool to characterize the structure of carbon [33]. Figure 3c displays the Raman spectra of graphene  
Figure 3: Characterization of OCGA. (**a**) SEM image of OCGA. (**b**) FTIR spectroscopy, (**c**) Raman spectra and (**d**) XRD patterns of GO before and after reduction.  
Figure 2: Schematic illustrations of the fabrication of the OCGA.  
aerogels with strong D-bands and G-bands centered at 1328 and 1593 cm\({}^{-1}\), respectively. Additionally, the intensity ratio of the two peaks (D and G) in the Raman spectrum of graphene is higher than that of graphene oxide [34; 35], indicating that the number of sp\({}^{2}\) carbon atoms in graphene is higher than that of sp\({}^{3}\) carbon atoms, which means that the average size of the sp hybridized carbon planes in graphene is larger than that of graphene oxide. This shows that when graphene oxide is reduced under the present experimental conditions, only part of its sp\({}^{3}\) carbon atoms are reduced to sp\({}^{2}\) carbon atoms.  
Figure 3d shows the XRD patterns of GO before and after reduction. The GO exhibits a peak at 20 = 11.1\({}^{\circ}\) which corresponds to the reflection of the plane (001) with a corresponding layer to layer distance of 0.796 nm, which is close to in the literature [36]. After reduction of GO, the diffraction peak for graphene oxide was at around 20 = 25.1\({}^{\circ}\), which corresponds to the reflection of the plane (002), corresponding to a layer-to-layer distance of 0.356 nm [37]. This indicates that the inter layer distance was decreased due to the removal of oxygen containing functional groups when GO is reduced to reduced graphene. Through the above analysis, we confirmed that graphene oxide was successfully reduced to graphene.