## 3 Results and Discussion  
### Characterizations of the Samples  
The morphologies and nanostructures of the SiO\({}_{2}\) and rGO/SiO\({}_{2}\) nanocomposites were examined via FE-SEM and TEM. In Figure 1a,b, the primary SiO\({}_{2}\) was a microsphere with a diameter of approximately 10 nm. Nanosilica could effectively reduce agglomeration by using the surface-active agent PEG2000. In Figure 1d, the TEM image clearly shows that the rGO/SiO\({}_{2}\) composites had a spherical shell structure similar to a core-shell structure, and the inner layer of nanosilica was wrapped by the outer layer of graphene. A similar structure was observed in the SEM image in Figure 1c, where SiO\({}_{2}\) was wrapped in graphene powder with a rough surface. The distributions of the elements in the SiO\({}_{2}\) and rGO/SiO\({}_{2}\) nanocomposites were determined by EDS, as shown in Figure 1. In the rGO/SiO\({}_{2}\) composite, the weight percentages of C and Si were 11.09 and 37.33%, respectively. Figure 2 shows the TG/DTA of the SiO\({}_{2}\) and rGO/SiO\({}_{2}\) samples. In regard to SiO\({}_{2}\), the thermal decomposition temperature was 479 \({}^{\circ}\)C. Free water and CO\({}_{2}\) in the pores or on the surface were first lost from 30 to 110 \({}^{\circ}\)C. Then, from 110 to 666 \({}^{\circ}\)C, the surface groups of silica gradually decomposed, and the reaction was exothermic. Next, from 666 to 720 \({}^{\circ}\)C, the reaction was exothermic, which might be because of the removal of the structural water by two Si-OH groups in the silica to form Si-O-Si bonds. Finally, from 720 to 800 \({}^{\circ}\)C, the silica continued to decompose. In regard to the rGO/SiO\({}_{2}\) sample, the thermal decomposition temperature was 436 \({}^{\circ}\)C. The free water and CO\({}_{2}\) in the pores or on the surface were lost from 30 to 100 \({}^{\circ}\)C, and the silica and rGO gradually decomposed from 100 to 800 \({}^{\circ}\)C.  
The powder XRD patterns of the rGO, SiO\({}_{2}\), and rGO/SiO\({}_{2}\) samples are shown in Figure 3. SiO\({}_{2}\) exhibited characteristic diffraction peaks at 20 values of 23\({}^{\circ}\), and rGO showed characteristic diffraction peaks at 20 values of 43\({}^{\circ}\). In the rGO/SiO\({}_{2}\) sample, the same peaks were shown at 20 values of 23\({}^{\circ}\) and 43\({}^{\circ}\), confirming that the rGO/SiO\({}_{2}\) composites were prepared successfully. The nanopore structures were evaluated by nitrogen physical adsorption measurements at 77 K on the SiO\({}_{2}\), GO, and rGO/SiO\({}_{2}\) samples, as shown in Figure 4. The Brunner\(-\)Emmet\(-\)Teller (BET) specific surface areas of SiO\({}_{2}\) and GO were 130 and 21 m\({}^{2}\) g\({}^{-1}\), respectively. After the composite was prepared, the BET specific surface area of the rGO/SiO\({}_{2}\) samples was 54 m\({}^{2}\) g\({}^{-1}\). The adsorption total pore volumes of SiO\({}_{2}\), GO, and rGO/SiO\({}_{2}\) were 0.090, 0.016, and 0.113 cm\({}^{3}\) g\({}^{-1}\), respectively. The adsorption at P/P\({}_{0}\)\(<\) 0.1 suggested the presence of micropores, and the adsorption at P/P\({}_{0}\)\(>\) -0.4 (to \(\sim\)1) indicated the presence of stacked mesopores in the rGO/SiO\({}_{2}\) samples. Therefore, the rGO/SiO\({}_{2}\) sample had a porous structure with both micro- and meso-pores. Figure 1: (**a**) SEM image of SiO\({}_{2}\) and (**b**) TEM image of SiO\({}_{2}\). (**c**) SEM image of the rGO/SiO\({}_{2}\) nanocomposite and (**d**) TEM image of the rGO/SiO\({}_{2}\) nanocomposite. Figure 2: Thermogravimetric (TG)/differential thermal analysis (DTA) of the (**a**) SiO\({}_{2}\) and (**b**) rGO/SiO\({}_{2}\) samples. Figure 4: Nitrogen adsorption/desorption isotherms of the SiO\({}_{2}\), GO and rGO/SiO\({}_{2}\) samples at 77 K.  
Figure 3: XRD patterns of the rGO, SiO\({}_{2}\), and rGO/SiO\({}_{2}\) samples. To characterize the bonding of the samples, XPS was used to study the functional groups on their surfaces.