long-term stability, and environmental friendliness (Ni et al. 2007). TiO 2 , especially
in the form of anatase, as photocatalyst is widely used for wastewater treatment and
hydrogen generation. TiO 2 exhibits a wide band-gap energy (Eg ~ 3.2 eV) and is a
semiconductor corresponding to radiation in the near-UV range. This is one of the
advantages compared to other semiconductor photocatalysts. When the TiO 2 surface
is irradiated, it is rapidly excited and generates a (e
À /h
+
) pair. The hole (h
+
) adsorbs
the surrounding water molecules and gets oxidized to form a hydroxyl radical. The
generation of hydroxyl radical is a cyclic process and initiates the series of reactions
on the TiO 2 surface as shown in Fig. 7.6. Some recombination processes, which
may reduce the photocatalytic effectivity of titanium oxide are also possible
(Fig. 7.6).
As an alternative to titanium oxide in photocatalysis, various TiO 2 nanoarchitectonic topographies have been extensively studied for enhancing the performance of photoelectrochemical cells (PEC) (Yang et al. 2011; Zhang et al. 2012a;
Chen et al. 2013; Wang et al. 2014a; Huang et al. 2015). In general, a predominant
PEC cell relies on two factors: the efficient usage of solar energy and the instant
transportation/separation of charges. To date, many hierarchical TiO 2 nanostructures
based on nanowires (NWs) and nanotubes (NTs) have been synthesized for
enhanced photoelectric efficiency in solar energy harvesting, conversion, and pollutants purification (Cho et al. 2011; Lee et al. 2013; Bai et al. 2013).
Fig. 7.6 Reactions that may occur over irradiated TiO 2 suspensions under conditions of water
splitting. (Illustration adapted from Yang et al. (2013))
226
A. Boudjemaa and S. Gómez-Ruiz
in the form of anatase, as photocatalyst is widely used for wastewater treatment and
hydrogen generation. TiO 2 exhibits a wide band-gap energy (Eg ~ 3.2 eV) and is a
semiconductor corresponding to radiation in the near-UV range. This is one of the
advantages compared to other semiconductor photocatalysts. When the TiO 2 surface
is irradiated, it is rapidly excited and generates a (e
À /h
+
) pair. The hole (h
+
) adsorbs
the surrounding water molecules and gets oxidized to form a hydroxyl radical. The
generation of hydroxyl radical is a cyclic process and initiates the series of reactions
on the TiO 2 surface as shown in Fig. 7.6. Some recombination processes, which
may reduce the photocatalytic effectivity of titanium oxide are also possible
(Fig. 7.6).
As an alternative to titanium oxide in photocatalysis, various TiO 2 nanoarchitectonic topographies have been extensively studied for enhancing the performance of photoelectrochemical cells (PEC) (Yang et al. 2011; Zhang et al. 2012a;
Chen et al. 2013; Wang et al. 2014a; Huang et al. 2015). In general, a predominant
PEC cell relies on two factors: the efficient usage of solar energy and the instant
transportation/separation of charges. To date, many hierarchical TiO 2 nanostructures
based on nanowires (NWs) and nanotubes (NTs) have been synthesized for
enhanced photoelectric efficiency in solar energy harvesting, conversion, and pollutants purification (Cho et al. 2011; Lee et al. 2013; Bai et al. 2013).
Fig. 7.6 Reactions that may occur over irradiated TiO 2 suspensions under conditions of water
splitting. (Illustration adapted from Yang et al. (2013))
226
A. Boudjemaa and S. Gómez-Ruiz