performance compared to the bulk TiO 2 . Min et al. (2013) successfully fabricated
N-TiO 2 /graphene composite for the photocatalytic decomposition of benzoic acid.
The as-fabricated composites showed high photocatalytic activity over pristine TiO 2 .
The photodegradation activity of MB dye by TiO 2 /graphene is two and six times
faster than that of TiO 2 /graphene oxide and P25, respectively (Ismail et al. 2013).
This improvement was ascribed to the effective charge transfer from TiO 2 to
graphene layers, as well as the better contact between TiO 2 and graphene. The
good contact of graphene with TiO 2 nanoparticles enhances the photoelectron
conversion of TiO 2 by reducing the charge carriers’ recombination rate (Guo et al.
2011). Through, the hydrothermal process, novel graphene/TiO 2 composite efficiently photodegrades MO dye over pure TiO 2 (Khalid et al. 2013a). The efficient
charge separation due to the 2D planar structure and π-conjugation system of
graphene, as well as the high adsorptivity of MO dye, influences the enhanced
performance of the composite. The TiO 2 /graphene composite nanosheets, which
was fabricated via a facile one-pot solvothermal route, showed improved adsorption
capacity and much enhancements toward the photocatalytic decomposition of MB
dye compared to P25 (Zhang et al. 2012c). The superiority of graphene sheets
compared to carbon nanotubes toward the photocatalytic activity of TiO 2 was
investigated (Zhang et al. 2011c). Comparison between carbon nanotubes/TiO 2
and graphene/TiO 2 reveals the prominent advantage of graphene over carbon
nanotubes on both enhancing the photocatalytic activity and controlling the morphology of TiO 2 . Using a sol–gel method, Fe-doped TiO 2 photocatalyst nanowire
arrays were embedded on the surface of functionalized graphene sheets (Farhangi
et al. 2011). The photocatalytic performance improved with increasing the
Fe-doping concentration between 0.6 and 0.8% of Fe. The as-fabricated composites
exhibited high a photodegradation of 17β-estradiol over Fe-doped TiO 2 and TiO 2 /
functionalized graphene sheet composites. Moreover, surface modification of
graphene/semiconductor composite with metal ions, such as Au (Wang et al.
2013b), Pt (Neppolian et al. 2012), Nd (Khalid et al. 2013b), Ag (Tang et al.
2012), and Fe (Khalid et al. 2012a), can enhanced their photocatalytic performance.
These metals can enhance the lifetime of charge carriers by restraining their recombination rate. Wang et al. (2013e) revealed that coupling SnO 2 with graphene
promoted the performance of SnO 2 for the photodegradation of pendimethalin.
This improvement was ascribed to the excitation of an electron from pendimethalin
at the excited states to SnO 2 at the interface and the large potential difference
between SnO 2 and pendimethalin. The underlying mechanism behind the
photocatalytic performance of ZnO/graphene sheet composite was investigated by
Xu et al. (2011). They observed that the presence of O 2
À•
, OH, and h
+ active species
is responsible for the photocatalytic decomposition toward methylene blue dye. Li
and Cao (2011) observed that the ZnO/graphene composite revealed a high
photoactivity toward the decomposition of RhB dye. The incorporation of graphene
on the semiconductor surface promotes the performance and stability of the semiconductor photocatalysts by reducing their photo-corrosion (Fan et al. 2012). The
photocatalytic activity of a semiconductor is influenced by the morphology of the
photocatalyst. One-dimensional WO 3 /graphene nanorod composites exhibited three
18
F. Opoku et al.
N-TiO 2 /graphene composite for the photocatalytic decomposition of benzoic acid.
The as-fabricated composites showed high photocatalytic activity over pristine TiO 2 .
The photodegradation activity of MB dye by TiO 2 /graphene is two and six times
faster than that of TiO 2 /graphene oxide and P25, respectively (Ismail et al. 2013).
This improvement was ascribed to the effective charge transfer from TiO 2 to
graphene layers, as well as the better contact between TiO 2 and graphene. The
good contact of graphene with TiO 2 nanoparticles enhances the photoelectron
conversion of TiO 2 by reducing the charge carriers’ recombination rate (Guo et al.
2011). Through, the hydrothermal process, novel graphene/TiO 2 composite efficiently photodegrades MO dye over pure TiO 2 (Khalid et al. 2013a). The efficient
charge separation due to the 2D planar structure and π-conjugation system of
graphene, as well as the high adsorptivity of MO dye, influences the enhanced
performance of the composite. The TiO 2 /graphene composite nanosheets, which
was fabricated via a facile one-pot solvothermal route, showed improved adsorption
capacity and much enhancements toward the photocatalytic decomposition of MB
dye compared to P25 (Zhang et al. 2012c). The superiority of graphene sheets
compared to carbon nanotubes toward the photocatalytic activity of TiO 2 was
investigated (Zhang et al. 2011c). Comparison between carbon nanotubes/TiO 2
and graphene/TiO 2 reveals the prominent advantage of graphene over carbon
nanotubes on both enhancing the photocatalytic activity and controlling the morphology of TiO 2 . Using a sol–gel method, Fe-doped TiO 2 photocatalyst nanowire
arrays were embedded on the surface of functionalized graphene sheets (Farhangi
et al. 2011). The photocatalytic performance improved with increasing the
Fe-doping concentration between 0.6 and 0.8% of Fe. The as-fabricated composites
exhibited high a photodegradation of 17β-estradiol over Fe-doped TiO 2 and TiO 2 /
functionalized graphene sheet composites. Moreover, surface modification of
graphene/semiconductor composite with metal ions, such as Au (Wang et al.
2013b), Pt (Neppolian et al. 2012), Nd (Khalid et al. 2013b), Ag (Tang et al.
2012), and Fe (Khalid et al. 2012a), can enhanced their photocatalytic performance.
These metals can enhance the lifetime of charge carriers by restraining their recombination rate. Wang et al. (2013e) revealed that coupling SnO 2 with graphene
promoted the performance of SnO 2 for the photodegradation of pendimethalin.
This improvement was ascribed to the excitation of an electron from pendimethalin
at the excited states to SnO 2 at the interface and the large potential difference
between SnO 2 and pendimethalin. The underlying mechanism behind the
photocatalytic performance of ZnO/graphene sheet composite was investigated by
Xu et al. (2011). They observed that the presence of O 2
À•
, OH, and h
+ active species
is responsible for the photocatalytic decomposition toward methylene blue dye. Li
and Cao (2011) observed that the ZnO/graphene composite revealed a high
photoactivity toward the decomposition of RhB dye. The incorporation of graphene
on the semiconductor surface promotes the performance and stability of the semiconductor photocatalysts by reducing their photo-corrosion (Fan et al. 2012). The
photocatalytic activity of a semiconductor is influenced by the morphology of the
photocatalyst. One-dimensional WO 3 /graphene nanorod composites exhibited three
18
F. Opoku et al.