Environmental Engineering Reference
In-Depth Information
development of three-dimensional polymeric skeletons leads to loosely
packed i rst-order particles. Polymeric Ti-O-Ti chains are developed in the
presence of a large excess of water. Closely packed i rst order particles are
yielded via a three-dimensionally developed gel skeleton [103-119]. From
the study on the growth kinetics of TiO
2
nanoparticles in aqueous solution
using titanium tartarate as precursor, it is found that the rate constant for
coarsening increases with temperature due to the temperature dependence
of the viscosity of the solution and the equilibrium solubility of TiO
2
[104].
Secondary particles are formed by epitaxial self-assembly of primary par-
ticles at longer times and higher temperatures, and the number of primary
particles per secondary particle increases with time. h e average TiO
2
nanoparticle radius increases linearly with time, in agreement with the
Lifshitz-Slyozov-Wagner model for coarsening [104].
Titania adapted chromium-niobate nanocatalysts Cr
x
Nb
x
Ti
1-2x
O
2-x/2
(x =
0.01-0.2) were synthesized by Ghorai
et al.
for the i rst time by the sol-
gel method by using
N,N,N',N'
-tetrakis(2-hydroxyethyl)ethylenediamine
(edteH
4
) precursors in CH
3
OH/H
2
O medium [57]. h e Cr
x
Nb
x
Ti
1-2x
O
2-x/2
(x = 0.01) (CNT1) nanocatalysts display good photocatalytic activity for
degradation of Rhodamine B in the presence of UV light because they have
high surface area (S
BET
= 162m
2
g
−1
), small particle sizes (12 ± 1 nm) and
lower band gap energy (1.85 eV) compared to TiO
2
. h e reaction proce-
dure of nano Cr
x
Nb
x
Ti
1-2x
O
2-x/2
catalysts is shown in Figure 15.7.
h e i ner details of the particles and their morphologies have been inves-
tigated by TEM. h e bright-i eld (BF) electron micrograph of the CNT1
powder produced at 500
C rel ects a narrow distribution of particles, with
an average particle diameter of 12 ± 1 nm, which is shown in Figure 15.8.
h e particle sizes were obtained from multiple TEM images: Figure 15.8a
(particle size distribution histogram inset in 15.8a), Figure 15.8b represents
the SAED pattern of CNT1, Figure 15.8c indicates the mesoporous struc-
tures of CNT1 observed from HRTEM and Figure 15.8d represents the
°
O
O
O
Nb
Nb
(NH)
4
Cr
2
O
7
OO
+
CH
3
OH
edteH
4
Ti
O
O
Figure 15.7
Reaction procedure of nano Cr
x
Nb
x
Ti
1-2x
O
2-x/2
catalysts.
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