Environmental Engineering Reference
In-Depth Information
−
2
+
+
−
2
+
Dye
∗+
e
(Fe
)
Dye
+
e
(Fe
)
(15.7)
−
2
+
−
2
+
e(Fe ) O
+
O Fe
+
(15.8)
2(ads)
2
+
Dye
Degradation products
(15.9)
15.4.2
Metal Molybdate Incorporated Titanium Dioxide
Photocatalyst
Dif erent metal molybdates (Metal: Ni, Cu, Zn)
incorporated titanium
dioxide were prepared by the chemical solution decomposition (CSD)
method. Ghorai
et al.
[26] found that among many transition-metal
molybdates, nickel molybdate incorporated titanium dioxide (NMT) was
found to be more photoactive than P25 TiO
2
and other metal molybdate
doped TiO
2
(M
x
Mo
x
Ti
1−x
O
6
) (M= Ni, Cu, Zn;
x
= 0.05), for photocatalytic
oxidation of various dye solutions (MO, RhB, TB and BG) to harmless
decolorized solution at room temperature with the help of a Hg lamp (Fig.
15.13). h e average particle size of NMT1 was found to be 15 nm measured
from TEM (inset Fig. 15.13) and calculated band gap from adsorption edge
is found to be 2.66 eV [26] (Table 15.2). h e UV-Vis dif use rel ectance
spectrum of NiMoO
4
incorporated TiO
2
and pure TiO
2
presented in inset
Figure 15.13, gave distinct band gap absorption edges at 465 nm, 313 nm,
305 nm and 387 nm for doped NMT1, NMT2, NMT3 and pure TiO
2
, and
corresponding band gap energies are 2.66, 3.00, 3.06 and 3.20 eV respec-
tively. By increasing the dopant concentration, the band gap increased; as
a consequence the photocatalytic activities decreased. h e photochemical
reaction proceeds step-by-step. Firstly, the dye is sensitized by the catalyst
in the presence of UV light and the dye cation is formed. Secondly, the dye
cation is unstable and decomposes, injecting an electron on the conduc-
tion band of TiO
2
. Electron goes to conduction band and hole is captured
by Ni
2+
producing Ni
3+
, and helps to degrade the dye molecule faster [26].
15.4.3
Metal Molybdate Doped Bismuth Titanate (NMBT)
Nanocomposites
Various compositions of nanosized metal molybdate (MMoO
4
)
x
-doped
bismuth titanate (Bi
2
Ti
4
O
11
) (M=Ni, Cu; x = 0.01, 0.05, 0.1) composites
have been prepared by chemical solution decomposition (CSD) method
using triethanolamine (TEA) as complexing agent [89]. Yao
et al.
have
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