pressure nonstoichiometric TiO 2-x , compounds can also be obtained. The bulk titania
rutile structure is the most thermodynamically stable phase. However, at the
nanosized level, when the particles size is lower than 11 nm or comprised between
11 and 35 nm, anatase and brookite become the more stable phase, respectively
(Zhang and Banfield 2000). The band gap values of bulk rutile, anatase, and brookite
are 3.0, 3.2, and 3.4 eV, respectively (Table 2.1). The Raman spectrum of bulk
anatase exhibits a very intense band at around 143 cm
-1 (e.g., band), and this mode
shifts to higher wave numbers in nanocrystalline materials (Kelly et al. 1997; Zhang
et al. 2000). As depicted in Table 2.2, due to its properties, titania has been widely
used in the water treatment processes such as adsorption or photodegradation. In
particular, the last one has been widely considered for the removal of either anionic
or cationic dye. In this chapter, we will focus on this method for dye removal from
Fig. 2.3 Structure of the main polymorphs of titanium dioxide: anatase (a), rutile (b), and brookite
(c). (Reprinted with permission from Pelaez et al. 2012. Copyright 2012 Elsevier, Applied Catalysis
B: Environmental)
Table 2.1 Characteristics of the main polymorphs of titanium dioxide
Anatase
Rutile
Brookite
Crystallographic system
Tetragonal
Tetragonal
Orthorhombic
Space group
I4 1 /amd
P4 2 /mnm
Pbca
Cell parameters (Å)
a: 3.793
a: 4.5937
a: 5.456
c: 9.512
c: 2.9618
b: 5.497
c: 5.1
Density (cm
3
/g)
3.89
4.42
4.12
Band gap (eV)
3.2
3.0
3.4
Refractive index
2.561
2.605
2.581
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
41
rutile structure is the most thermodynamically stable phase. However, at the
nanosized level, when the particles size is lower than 11 nm or comprised between
11 and 35 nm, anatase and brookite become the more stable phase, respectively
(Zhang and Banfield 2000). The band gap values of bulk rutile, anatase, and brookite
are 3.0, 3.2, and 3.4 eV, respectively (Table 2.1). The Raman spectrum of bulk
anatase exhibits a very intense band at around 143 cm
-1 (e.g., band), and this mode
shifts to higher wave numbers in nanocrystalline materials (Kelly et al. 1997; Zhang
et al. 2000). As depicted in Table 2.2, due to its properties, titania has been widely
used in the water treatment processes such as adsorption or photodegradation. In
particular, the last one has been widely considered for the removal of either anionic
or cationic dye. In this chapter, we will focus on this method for dye removal from
Fig. 2.3 Structure of the main polymorphs of titanium dioxide: anatase (a), rutile (b), and brookite
(c). (Reprinted with permission from Pelaez et al. 2012. Copyright 2012 Elsevier, Applied Catalysis
B: Environmental)
Table 2.1 Characteristics of the main polymorphs of titanium dioxide
Anatase
Rutile
Brookite
Crystallographic system
Tetragonal
Tetragonal
Orthorhombic
Space group
I4 1 /amd
P4 2 /mnm
Pbca
Cell parameters (Å)
a: 3.793
a: 4.5937
a: 5.456
c: 9.512
c: 2.9618
b: 5.497
c: 5.1
Density (cm
3
/g)
3.89
4.42
4.12
Band gap (eV)
3.2
3.0
3.4
Refractive index
2.561
2.605
2.581
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
41