Environmental Engineering Reference
In-Depth Information
Fig. 17 a SEM image, b UV-visible spectra (the inset is the band gap (E
g
) of samples estimated
from the absorption edge), and c photodegradation of MB under visible light (1: P25, 2: bare
anatase TiO
2
NPs, 3: graphene-TiO
2
NPs (two-step hydrothermal), 4: graphene-TiO
2
NPs).
d TEM image of TiO
2
-graphene composite, e current-voltage characteristic, and f Nyquist plots
of DSSCs using TiO
2
-graphene composite (the inset is the corresponding Bode plots in
electrochemical impedance spectra (EIS) test). (Reprinted with permission from Ref. a-c [
374
],
d-f [
377
]. Copyright American Chemical Society and Wiley-VCH)
amorphous TiO
2
NPs with GO, followed by continuous GO reduction and TiO
2
crystallization via hydrothermal treatment. The graphene-TiO
2
nanoparticles
possess excellent photocatalytic properties under visible light for the degradation
of MB (Fig.
17
c) [
374
].
In the second method, graphene-TiO
2
photocatalysts are fabricated by an in situ
growth of TiO
2
on graphene sheets [
375
,
376
]. By introducing cetyltrimethylam-
monium bromide (CTAB)-functionalized DMF-soluble graphene into the poly-
meric solution for electrospinning, graphene was successfully integrated into the
TiO
2
rice-shaped nanostructures (Fig.
17
d). The obtained composites displayed
enhanced photovoltaic and photocatalytic properties compared to pure TiO
2
nan-
orices when used in DSSCs (Fig.
17
e, f) and in the photocatalytic degradation of
methyl orange (MO) [
377
]. In addition, a series of graphene-TiO
2
composites with
different graphene contents can be controllably synthesized by a sol-gel method
[
378
]. Graphene-TiO
2
composites demonstrated a higher photocatalytic activity
compared to P25 with respect to hydrogen generation from water splitting. The
highest photocatalytic activity was observed for the sample with 5 % graphene,
suggesting that an excess of graphene will decrease the activity by introducing
electron-hole recombination centers into the composite [
378
].
In the third method, TiO
2
structures are grown in situ onto GO followed by the
reduction of GO in a subsequent reaction step using UV light or microwave
irradiation [
379
,
380
]. For example, novel hollow spheres consisting of Ti
0.91
O
2
nanosheets and graphene nanosheets (Fig.
18
a) were successfully fabricated by a
Search WWH ::
Custom Search