Design, Fabrication, and Modification of Cost-Effective Nanostructured TiO for Solar Energy Applications - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 13

Fig. 2 a Overview principle of TiO 2 -based photocatalytic water splitting for hydrogen
generation. b Simplified principle of TiO 2 -based photocatalysis of organic pollutants. (Reprinted
with permission from Ref. [ 29 ]. Copyright Simplex Academic Publishers)
Numerous semiconductor materials, for instance (TiO 2 ,Fe 2 O 3 , SrTiO 3 , ZrO 2 ,
WO 3 , CdS, ZnO, NaTaO 3 , BaTi 4 O 9 , BiVO 4 ,CeO 2 ) have been explored for water
splitting into H 2 and O 2 under ultraviolet (UV) or visible light irradiation [ 23 , 28 , 29 ].
Among the various candidates for the photoanode, TiO 2 is considered to be one of
the most promising semiconductor materials as it can fulfill the task of photocatalytic
water splitting in a clean, environmentally friendly and low-cost way, owing to its
favorable band gap energy (3.2 eV in anatase), high photochemical stability, non-
toxic property, and relatively inexpensive cost [ 25 ]. There are however several
drawbacks to TiO 2 . The conversion efficiency of this technology is still low and thus
it is currently only in the research stage. Also, the band gap of anatase TiO 2 is around
3.2 eV, implying that only ultraviolet (UV) light can be used for water splitting.
Lastly, the PEC cell concurrently undergoes a rapid recombination of photogener-
ated electron-hole pairs [ 30 ]. Consequently, many research efforts are made to
reduce these drawbacks in the TiO 2 -based PEC cell.
1.3 Applications in Photocatalytic Degradation of Pollutants
Lastly, solar light may have the potential to solve the environmental contamination
problem. Wastewater pollutants have become a worldwide environmental threat as
a result of burgeoning industry and population [ 31 ]. To date, many techniques
have been developed for the decontamination of many artificial or anthropogenic
organic pollutants, especially those with high toxicity but very low concentration.
A better alternative should be able to chemically transform the organic pollutants
into environmentally benign compounds in an efficient manner [ 31 ].
Recently, numerous studies have been performed on the application of photo-
catalysis in the degradation of organic pollutants from wastewaters due to its
ability to completely mineralize the toxic organic chemicals into nontoxic inor-
ganic minerals [ 29 ]. Photocatalysis is triggered by semiconductor catalysts which