TiO 2 nanotubes on reduced graphene oxide sheets via hydrothermal synthesis under
basic conditions. As shown in Fig. 5.1b, it could be clearly seen that the color of the
TiO 2 /GO dispersion became dark black after the hydrothermal treatment. The
prepared TiO 2 nanotubes/GO composite exhibits much higher photocatalytic activity toward the degradation of malachite green than TiO 2 nanotubes itself.
Among all the preparation methods, the simplest route is mixing and sonication,
owing to that the GO would be exfoliated when added to an aqueous or organic
solution. Although the mixing method is very simple, in most cases the interaction
between the two phases is very weak, since chemical bonding is not expected
[46]. In our previous work, we designed ternary P25/GO/Pt hybrid photocatalysts,
which were prepared in different orders by employing different methods and using
Degussa’s TiO 2 (P25), GO, and chloroplatinic acid as precursors [47]. For instance,
we prepared the (Pt/P25) + mGO and (Pt/mGO) + P25 by using the mechanical
mixing method. A certain amount of Pt/P25 particles were dispersed into an aqueous
suspension of GO, stirred for 24 h at room temperature, centrifuged, washed, and
dried, which was denoted as (Pt/P25) + mGO, where “m” represents the quality ratio
of GO/P25. 0.05 g chloroplatinic acid was dissolved into a solution containing GO,
ethanol, and deionized water, stirred for 30 min at room temperature, and illuminated
for 3 h. Then 0.5 g P25 was dispersed into the above mixture and stirred for 24 h at
room temperature, centrifuged, washed, and dried. The obtained catalyst was
denoted as (Pt/mGO) + P25. Though there is absence of a strong chemical bonding
between TiO 2 and GO by using a physical mixing technology, the photo-generated
electrons also can transfer from TiO 2 to the GO owing to the intermolecular forces.
In our investigation, the (Pt/mGO) + P25 gave a better photocatalytic activity than
other catalysts prepared by different methods. After that, we continued employing
the simple mixing method to load the P25 nanoparticles on the surface of borondoped graphene nanosheets [48]. Firstly, the vacuum activation method was
employed to prepare the boron-doped graphene nanoribbons, and then the TiO 2
was successfully embedded into the boron-doped graphene nanosheets by a mechanical stirring and ultrasonic treatment. The loading of TiO 2 on graphene surface gave
a distinct pressure stress on the surface of graphene, which caused the rupture of C–C
bonds that is close to Ti–O–C in B–GR nanoribbons by a shear force from the
ultraphonic treatment. The ultraphonic energy could cut some large-sized graphene
nanoribbons into smaller nanosheets.
Guo et al. [49] reported a simple method by mechanical mixing TiO 2 nanosheets
and reduced graphene oxide (rGO) powder to prepare a series of TiO 2 @rGO
composite electrodes for the first time, as shown in Fig. 5.2a. Yamashita and his
coworkers reported that the TiO 2 nanoparticles supported on a mesoporous silica
surface (TiO 2 /MCM-41) were selectively coated with graphene through the formation
of
surface
complexes
between
TiO 2
nanoparticles
and
2,3-dihydroxynaphthalene [50]. And then the complex was carbonization under N 2
flow at a high temperature of 1073 K, as shown in Fig. 5.2b.
Sol–gel is an advanced technology, which usually employs the compounds with
high activity as the precursors. Chen et al. [36] prepared the GO/TiO 2 composites by
using TiCl 3 and GO as reactants through a sol–gel method. The authors found that
110
5 Graphene-Modified TiO 2 with Enhanced Visible Light Photocatalytic Activities
basic conditions. As shown in Fig. 5.1b, it could be clearly seen that the color of the
TiO 2 /GO dispersion became dark black after the hydrothermal treatment. The
prepared TiO 2 nanotubes/GO composite exhibits much higher photocatalytic activity toward the degradation of malachite green than TiO 2 nanotubes itself.
Among all the preparation methods, the simplest route is mixing and sonication,
owing to that the GO would be exfoliated when added to an aqueous or organic
solution. Although the mixing method is very simple, in most cases the interaction
between the two phases is very weak, since chemical bonding is not expected
[46]. In our previous work, we designed ternary P25/GO/Pt hybrid photocatalysts,
which were prepared in different orders by employing different methods and using
Degussa’s TiO 2 (P25), GO, and chloroplatinic acid as precursors [47]. For instance,
we prepared the (Pt/P25) + mGO and (Pt/mGO) + P25 by using the mechanical
mixing method. A certain amount of Pt/P25 particles were dispersed into an aqueous
suspension of GO, stirred for 24 h at room temperature, centrifuged, washed, and
dried, which was denoted as (Pt/P25) + mGO, where “m” represents the quality ratio
of GO/P25. 0.05 g chloroplatinic acid was dissolved into a solution containing GO,
ethanol, and deionized water, stirred for 30 min at room temperature, and illuminated
for 3 h. Then 0.5 g P25 was dispersed into the above mixture and stirred for 24 h at
room temperature, centrifuged, washed, and dried. The obtained catalyst was
denoted as (Pt/mGO) + P25. Though there is absence of a strong chemical bonding
between TiO 2 and GO by using a physical mixing technology, the photo-generated
electrons also can transfer from TiO 2 to the GO owing to the intermolecular forces.
In our investigation, the (Pt/mGO) + P25 gave a better photocatalytic activity than
other catalysts prepared by different methods. After that, we continued employing
the simple mixing method to load the P25 nanoparticles on the surface of borondoped graphene nanosheets [48]. Firstly, the vacuum activation method was
employed to prepare the boron-doped graphene nanoribbons, and then the TiO 2
was successfully embedded into the boron-doped graphene nanosheets by a mechanical stirring and ultrasonic treatment. The loading of TiO 2 on graphene surface gave
a distinct pressure stress on the surface of graphene, which caused the rupture of C–C
bonds that is close to Ti–O–C in B–GR nanoribbons by a shear force from the
ultraphonic treatment. The ultraphonic energy could cut some large-sized graphene
nanoribbons into smaller nanosheets.
Guo et al. [49] reported a simple method by mechanical mixing TiO 2 nanosheets
and reduced graphene oxide (rGO) powder to prepare a series of TiO 2 @rGO
composite electrodes for the first time, as shown in Fig. 5.2a. Yamashita and his
coworkers reported that the TiO 2 nanoparticles supported on a mesoporous silica
surface (TiO 2 /MCM-41) were selectively coated with graphene through the formation
of
surface
complexes
between
TiO 2
nanoparticles
and
2,3-dihydroxynaphthalene [50]. And then the complex was carbonization under N 2
flow at a high temperature of 1073 K, as shown in Fig. 5.2b.
Sol–gel is an advanced technology, which usually employs the compounds with
high activity as the precursors. Chen et al. [36] prepared the GO/TiO 2 composites by
using TiCl 3 and GO as reactants through a sol–gel method. The authors found that
110
5 Graphene-Modified TiO 2 with Enhanced Visible Light Photocatalytic Activities