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.