Environmental Engineering Reference
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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
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