## 3 Results and Discussion  
### Characterization of Photocatalyst  
The successful preparation of materials by the combination of the hydrothermal method and calcination can be demonstrated with detailed characterization of the obtained TiO\({}_{2}\)@rGO nanomaterials. The FT-IR spectra of natural graphite GO and rGO are presented in Figure 1A, while the spectra of TiO\({}_{2}\) and the nanocomposites are shown in Figure 1B. The GO spectrum present the following peaks at 3372 cm\({}^{-1}\) corresponded to the stretching vibration of the carboxyl group (\(-\)OH), which was ascribed on the attendance of alcohol groups and absorbed water molecules, 2857 cm\({}^{-1}\) and 2925 cm\({}^{-1}\) vibrations corresponded to the symmetric and asymmetric CH\({}_{2}\) stretching of GO [34, 35]. The stretching vibration at 1715 cm\({}^{-1}\) ascribed to the C=O from carbonyl and carboxyl group and the vibration at 1622 cm\({}^{1}\) (C=C) as skeletal vibration of unoxidized graphitic materials [35]. The deformation vibration of C-OH stretch from the alcohol group was displayed at 1376 cm\({}^{-1}\)[36, 37]. The stretching vibrations at 1221 cm\({}^{-1}\) were assigned to the C-O-C of epoxy groups, and at 1039 cm\({}^{-1}\) were ascribed to the C-O from the alkoxy group [37]. By comparing the GO and rGO spectra, displayed in Figure 1A, it could be seen that in the rGO sample, that the intensity of peaks attributed to oxygen functional groups, e.g., O-H, C=O, and C-O, were reduced [38]. The TiO\({}_{2}\)@rGO nanocomposite spectra exhibited peaks between 450-900 cm\({}^{-1}\), which belonged to the stretching vibration of Ti-O-Ti and Ti-O-C bonds, affirming the effective interaction between Ti and C [39, 40]. The Raman spectrum of TiO\({}_{2}\) is shown in Figure 2A (inset), highlighting five sharp peaks for the anatase-phase of TiO\({}_{2}\). These peaks are located at 147 cm\({}^{-1}\), 198 cm\({}^{-1}\), and 641 cm\({}^{-1}\) as Eg, 399 cm\({}^{-1}\) as B1g, and 517 cm\({}^{-1}\) as A1g + B1g [41]. As the figures show, these peaks appeared for all prepared nanocomposites, but in comparison to pure TiO\({}_{2}\) nanoparticles, the intensity of the anatase phase was strongly reduced in the nanocomposites. Figure 2A shows, the prepared nanocomposites with a smaller amount (5 wt.%) of rGO had sharper peaks than the prepared nanocomposites with a higher amount (15 wt.%). The crystalline phase of the nanocomposite was disturbed because of the content of rGO. Figure 2B presents the Raman spectra of GO, rGO, and nanocomposites. The GO spectrum showed the presence of the two characteristic peaks at 1329 cm\({}^{-1}\) as D-band and 1585 cm\({}^{-1}\) as G-band. On the rGO spectrum, two peaks appeared at 1347 cm\({}^{-1}\) (D-band) and 1593 cm\({}^{-1}\) (G-band). The vibrations of the peaks in rGO materials were shifted significantly in relation to GO materials. The reason for the shift is the structure of the graphene material, where the G band corresponds to the sp\({}^{2}\) hybridization in C-C bonds, and D band  
Figure 1: FTIR spectra of (**A**) natural graphite, GO, rGO; (**B**) TiO\({}_{2}\) and TiO\({}_{2}\)@rGO nanocomposites prepared with different amounts of GO (5 wt.% and 15 wt.%). matches the sp\({}^{3}\) defects in carbon atoms as associated with structural defects [42; 43]. The spectra of the prepared nanocomposites show characteristic peaks of anatase-phase TiO\({}_{2}\) and the presence of the D and G band. The binding of TiO\({}_{2}\) nanoparticles into rGO, as well as the intensities of anatase-phases in the nanocomposites, showed a significant decrease (Figure 2A,B). As Figure 2B shows and Table 1 confirms, the content of graphene has an influence on the intensity of G and D bands in the nanocomposites. The reason for the high-intensity ratio between D and G bands was the presence of a lot of sp\({}^{2}\) hybridization in C-C bonds [41]. The rGO shows a higher ratio than GO, indicating that the rGO contained more defects.