3.1. Characterization of rGO-TiO2Composite Materials
Figure 2 shows that GO has a strong diffraction peak at 11°, which is a characteristic peak (Zhan et al., 2017). With the reaction of GO and tetrabutyl titanate, the composite material rGO-TiO2 is formed. There are characteristic peaks of TiO2, 2 theta is 25.3°, 37.8°, 48.0°, 53.9°, 55.1° and 62.7°. These angles correspond to the 6 crystal planes (101), (004), (200), (105), (211), and (204) of anatase TiO2 (Wang et al., 2017), of which the peak corresponding to the (101) crystal plane is the most. The sharpness and maximum strength indicate that the TiO2 in the composite material is mainly anatase crystal type (Sorrenti et al., 2021; Wang et al., 2021). In this structure, the diffraction peak of graphene is also not observed. This is because the characteristic peak of graphene is at 24.5°, which is easily covered by the strong diffraction peak at 25.3° of the anatase (101) crystal plane.
From Figure 3 (a), (b), and (c), it can be shown that TiO2 nanoparticles have been supported on a thin layer of graphene oxide. The high-resolution lattice phase analysis of the region with nanoparticles is shown in Figure 3(d). It can be observed that the interval of the lattice fringes is 0.352 nm, which corresponds to the anatase TiO2 (101) crystal plane (Wu et al., 2017; Yung et al., 2017). The above results can indicate that the TiO2 nanoparticles were successfully supported on the graphene oxide substrate.
Figure 4(a) shows the XPS full spectrum of GO and nanoparticles rGO-TiO2. The full spectrum of rGO-TiO2nanoparticles contains three elements, of which the characteristic peak of C 1s is at 284.41 eV (Shirazi et al., 2017), the characteristic peak of Ti 2p is at 459.72 eV (Minetto et al., 2017), and the characteristic peak of O 1s is at 530.98 eV (Sendra et al., 2017). Correspondingly, the XPS full spectrum of GO contains only two elements, such as C and O. The characteristic peak of C 1s is at 286.76 eV, and the characteristic peak of O 1s is at 532.50 eV (Madeira et al., 2017). XPS high-resolution analysis was performed on the C 1s of GO and the composite nano-catalyst rGO-TiO2. As shown in Figure 4(b), it is the high-resolution XPS spectrum of GO C 1s. In addition to the symmetrical sp2 hybridized C-C bond at 284.82 eV, it is also observed at 288.30 eV and 289.14 eV. Peaks, these two peaks respectively correspond to epoxy C-O-C, carboxyl HO-C=O, and other oxygen-containing active groups. In the composite structure prepared with GO as the raw material, as shown in Figure 4(b), is the high-resolution XPS spectrum of the composite nano-catalyst rGO-TiO2 with C 1s. The peak is observed at 286.08 eV in the figure, which corresponds to the C-C bond may be due to the solvothermal reaction, other oxygen-containing active groups are gradually reduced. This indicates that GO has been reduced to rGO during the synthesis process of the composite material.