Environmental Engineering Reference
In-Depth Information
table 24.1
some examples of nanocrystalline semiconductors used in photocatalysis of organic compounds
Nanocatalyst
Organic pollutants
references
Nanocatalyst
Organic pollutants
references
ZnFe
2
O
4
Phenol
[9a]
Polyoxometalates supported
on yttrium-doped TiO
2
(H
3
PW
12
O
40
-y-TiO
2
)
methyl orange
[9u]
TiO
2
films
methyl orange
[9b]
ZnAl
2
O
4
nanoparticles
gaseous toluene
[9v]
ZnO and Pt-ZnO films
Phenol
[9c]
TiO
2
nanoparticles supported
on porous glass beads
methyl orange
[9w]
Core/shell-structured ZnO/
SiO
2
nanoparticles
rhodamine B
[9d]
ZnO-bentonite
nanocomposite
Phenol
[9x]
Hydrophilic ZnS nanocrystals
Basic violet 5BN
[9e]
yttrium Orthovanadate
(yvO
4
) nanoparticles
direct blue
53
[9y]
Ag-loaded TiO
2
nanotube
arrays
methylene blue
[9f]
Nb-loaded ZnO
Nanoparticles
Phenol
[9z]
mWCNTs loaded with
Ag nanoparticles
rhodamine B
[9g]
Pr-doped TiO
2
Phenol
[9aa]
Hydroxyapatite-supported
Ag
3
PO
4
nanoparticles
methylene blue
[9h]
layered la
2
Ti
2
O
7
nanosheets
methyl orange
[9ab]
Bi
3
NbO
7
nanoparticles
rhodamine B
[9i]
SnS
2
methyl orange
[9ac]
Co-doped TiO
2
nanoparticles
2-Chlorophenol
[9j]
moS
2
/TiO
2
Phenol
[9ad]
Nano-aluminum oxide
Pyridine
[9k]
BivO
4
/Bi
2
O
2
CO
3
nanocomposites
rhodamine B
[9p]
lanthanide(la
3+
, Nd
3+
,
or Sm
3+
)-doped ZnO
nanoparticles
4-Nitrophenol
[9l]
CNTs/P-TiO
2
methyl orange
[9ae]
CdS/la
2
Ti
2
O
7
methyl orange
[9m]
m@TiO
2
(m =Au, Pt, Ag)
Benzene
[9af]
TiO
2
/SiO
2
/NiFe
2
O
4
violet 5B
[9n]
CoFe
2
O
4
-Cr
2
O
3
-SiO
2
methylene blue
[9ag]
C-doped Zn
3
(OH)
2
v
2
O
7
nanorods
methylene blue
[9o]
mgFe
2
O
4
/TiO
2
composite
rhodamine B
[9ah]
BivO
4
/Bi
2
O
2
CO
3
rhodamine B
[9p]
Fe
3
O
4
/ZnO
methyl orange
[9ai]
Ag-Agi/Fe
3
O
4
@SiO
2
rhodamine B and
4-chlorophenol
[9q]
NiO/AgNbO
3
methylene blue
[9aj]
CuxS/TiO
2
copper sulphide/
titanium oxide
methylene blue, methyl
orange
[9r]
Fe-Co-TiO
2
rhodamine B
[9ak]
ln
2
Ti
2
O
7
methylene blue
[9s]
Chitosan/CdS
Cango red
[9al]
v-doped TiO
2
nanoparticles
methylene blue and
2,4-dichlorophenol
[9t]
Fe
3+
-TiO
2
-zeolite
methyl orange
[9am]
gap energy of Q-particles is increased by reducing the particle size, which is a great practical advantage. One disadvantage of
nanosized particles is the need for light with a shorter wavelength for photocatalyst activation than for bulk materials [11].
Crystal size and surface area can play an important role in affecting the photocatalytic activity of photocatalysts. Wang
et al. conducted experiments on the decomposition of chloroform and observed an optimal TiO
2
nanoparticle size for maximum
photocatalytic efficiency. The particle's photocatalytic activity increased as the particle size was decreased from 21 to 11 nm,
but when the size was reduced further to 6 nm, the activity decreased [12]. As an explanation to these observations, Zhang
et al. suggested that the high surface area of the nanoparticles increases the photonic efficiency due to the increased interfacial
charge-carrier transfer rates. However, below a certain particle size, charge recombination is faster than interfacial charge-
carrier transfer processes [13]. Thus, there exists an optimum particle size for maximum photocatalytic efficiency. in another
investigation, liao et al. manipulated TiO
2
nanoparticles into spheres, cubes, ellipsoids, and nanorods using various surfac-
tants. Cube-shaped and smaller-sized TiO
2
nanoparticles showed increased red shift in the uv-vis light region. This reduces
the energy needed for photocatalysis [7].
24.2.3
Nanocatalyst enhancements
Among all semiconductors, TiO
2
is the most widely used photocatalyst. it has two stable crystalline phases—anatase
and rutile—which are achieved at synthesis temperatures of typically around 350 and 800°C, respectively. Nanocatalyst
systems that include iron oxides, sulphides, and selenides are considered unstable for catalysis because they readily undergo
