Environmental Engineering Reference
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Figure 15.1 (a) Rutile structure of titanium dioxide; (b) Anatase structure of titanium
dioxide.
band and generate e - /h + pairs that degrade the dye molecules. Generally,
nanoparticles are used for the fabrication of noble TiO 2 surface to obtain
high surface areas and a mesoporous structure. However, nanocrystalline
TiO 2 is a promising semiconducting material that has attracted consider-
able interest for its applications as electrodes [12], electronics [13], capaci-
tors [14], optics [15, 16], sensors [17, 18], ceramics [19], solar cells [20-22],
catalysis [23, 24] and photocatalysis [25, 26].
Henceforth, introduction of larger particles with a lower internal sur-
face area on nanoparticles hinders dye adsorption. h e result is an increase
in the electron dif usion path and recombination rate of photogenerated
carriers rather than an enhancement of the ef ect of light scattering.
However, for specii c advanced applications in photocatalysis, especially in
the degradation of organic pollutants, the optical and electrical properties
of TiO 2 have been extensively studied [27-32]. h e possibility of carrying
out selective photooxidations in nonaqueous media is interesting in the
context of Green Chemistry [33, 34]. However, TiO 2 has wide band-gap
energy (3.0-3.2 eV), which means that UV light (wavelength < 387 nm)
can excite anatase TiO 2 to generate e cb /h + vb pairs which cause the photo-
catalytic reactions.
h erefore, lots of research have been done on the photocatalytic activ-
ity of TiO 2 doped with dif erent metal ions such as noble metals (Ag [35],
Au [36], Pt [37] and Pd [38]), transition metals (Mn [39], Fe [40, 41], Co
[42], Ni [43], Cu [44, 45]), and nonmetals (nitrogen, carbon, l uoride,
iodine, nitrate and nitrite [46-51]), which have shown to be good pho-
tocatalyst. Ismail et al. found that TiO 2 microspheres with porous struc-
tures have higher photocatalytic activity and are easily recovered for reuse
[52]. h is breakthrough opened a novel pathway for the elevation of the
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