## 3 Results and Discussions  
### Characterization of HNH-rGO  
The XRD pattern of GO, HNH and HNH-rGO samples were presented in Figure 3. As shown in Figure 3a, the interlayer space of GO was about 0.751 nm when calculated by the Bragg diffraction equation. As for HNH-rGO samples displayed in Figure 3b, the wide peak of graphene that appeared at about 26\({}^{\circ}\) represented the (002) and the peak of GO at about 11\({}^{\circ}\) disappeared, which indicated that GO was entirely reduced to graphene by HNH. Additionally, the interlayer space of HNH-rGO was extraordinarily enlarged to about 1.921 nm, which was almost triple the interlayer space of GO. This result was mainly attributed to the surface of HNH-rGO successfully grafted with HNH. Via covalent modification reaction, the molecular chain of HNH was grafted on the surface of graphene and inserted into graphene layers, resulting in the increase of layer interspace and decrease of Van der Waals' force. Compared with the authors' previous research about HBS-rGO [43], the interlayer space of rGO was enlarged by 30% from 1.478 nm to 1.921 nm mainly owing to the extended length of molecular chain of the modifier. Figure 4 displayed the morphology of GO and HNH-rGO samples. It was clear that the two samples both took on layered structure. As shown in Figure 4, GO was more inclined to get aggregations compared with HNH-rGO due to smaller interlayer space resulting in stronger Van der Waals' force, which accord  
Figure 3: The X-ray diffraction (XRD) patterns of GO (**a**) and HNH-rGO (**b**). Figure 5 showed the Raman spectroscopy of graphene, GO and HNH-rGO. As for graphene, the typical Raman scattering features of graphene are G peak, 2D peak, and D peak. The G peak (1580 cm\({}^{-1}\)) is due to the doubly degenerate zone center \(E_{2g}\) mode and originated from the vibration in plane of sp\({}^{2}\) hybrid carbon atoms. The 2D (2700 cm\({}^{-1}\)) peak is the second order of zone-boundary phonons. The defects in graphene will be reflected on the D peak (1350 cm\({}^{-1}\)). As presented in Figure 5, the G band of HNH-rGO (1585 cm\({}^{-1}\)) compared with GO shifted closer to graphene (1563 cm\({}^{-1}\)), which indicated a successful functionalization of reduced GO and a recombination of sp\({}^{2}\)-hybridized graphitic network at mean time. Besides, the intensity ratio of D/G peaks that generally imply the defect concentration of graphene and the defect concentration of graphene can be calculated by: \(n_{D}\)\((cm^{-2})=(7.3\pm 2.2)\times 10^{9}E_{L}^{4}(\frac{I_{D}}{I_{G}})\)[44]. The results showed that the \(I_{D}\)/\(I_{G}\) ratio of HNH-rGO was 0.46 smaller than that of GO (0.93), so the surface defects of HNH-rGO was reduced by half and the sp\({}^{2}\)-hybridized degree was improved. However, the \(I_{D}\)/\(I_{G}\) ratio of HNH-rGO was a little bigger than that of graphene (0.09) and the authors' previous research (0.29) [43], mainly due to the defects resulting from HNH groups grafted on rGO and some remaining unstable structure defects. Moreover, the intensity of G peak, the intensity ratio of G/2D peaks and the peak curve of 2D peak are usually the criterions to confirm the layers of graphene. As the layers increase, the intensity of G peak increases and the 2D peak evolves into 4 and 6 lorenz curves corresponding to bilayers and three layers, respectively [45]. In the research, the HNH-rGO was three-layer, as shown in Figure 5b, and the intensity of G peak increased compared with graphene. All the results gave adequate reasons for a sufficient reduction of GO by HNH and modification of reduced GO. Fourier transform infrared spectrum (FTIR) is an effective method to detect organo-functional group and can give proof to the successful modificaton. As displayed in Figure 6, the characteristic  
Figure 4: The scanning electron microscope (SEM) images of GO (**a**) and HNH-rGO (**b**). Figure 5: The Raman spectroscopy of G, GO and HNH-rGO (**a**) and the 2D peak of HNH-rGO (**b**).