Effect of yttrium oxide on the formation of the phase composition and porous structure of titanium dioxide

Article abstract of DOI:10.1134/S0023158411010174

The formation of the structure of TiO₂ (anatase) doped with 1-5 mol % Y₂O₃ is reported. The dopant changes the anatase structure from regular to nanocrystalline. The nanocruystalline structure consists of incoherently intergrown 5- to 7-nm anatase crystallites (500°C) separated by interblock boundaries accommodating yttrium ions. The formation of the nanocrystalline anatase structure stabilizes small anatase crystallites and raises the anatase-to-rutile phase transition temperature above 900°C. Owing to this structure, the developed specific surface area and fine porous texture of yttrium oxide-doped titanium dioxide survive up to higher temperatures than those of undoped titanium dioxide.

Full text of DOI:10.1134/S0023158411010174

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2011, Vol. 52, No. 1, pp. 111–118. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.A. Shutilov, G.A. Zenkovets, V.Yu. Gavrilov, S.V. Tsybulya, 2011, published in Kinetika i Kataliz, 2011, Vol. 52, No. 1, pp. 113–121.
Effect of Yttrium Oxide on the Formation of the Phase Composition
and Porous Structure of Titanium Dioxide
,
b
,
b
,b
A. A. Shutilova , G. A. Zenkovets*,a , V. Yu. Gavrilova, and S. V. Tsybulyaa
aBoreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
bNovosibirsk State University, Novosibirsk, 630090 Russia
* eꢀmail: zenk@catalysis.ru
Received January 14, 2010
Abstract—The formation of the structure of TiO2 (anatase) doped with 1–5 mol % Y2O3 is reported. The
dopant changes the anatase structure from regular to nanocrystalline. The nanocruystalline structure consists
of incoherently intergrown 5ꢀ to 7ꢀnm anatase crystallites (500
accommodating yttrium ions. The formation of the nanocrystalline anatase structure stabilizes small anatase
crystallites and raises the anataseꢀtoꢀrutile phase transition temperature above 900 C. Owing to this structure,
°C) separated by interblock boundaries
°
the developed specific surface area and fine porous texture of yttrium oxide–doped titanium dioxide survive
up to higher temperatures than those of undoped titanium dioxide.
DOI: 10.1134/S0023158411010174
Titanium dioxide is an object of intent attention of increases, for example, during sintering, the system
researchers because it is widely used as a support for passes into the normal state, in which the rutile phase
heterogeneous catalysts for environmental protection is thermodynamically favorable. On the whole, the
from nitrogen oxides [1] and carbon monoxide [2, 3], relevant experimental data confirm these inferences
for photocatalytic oxidation of hazardous organics in (see, e.g., [11, 14–16]).
air and water [4–6], and for partial oxidation of subꢀ
Some authors report other critical anatase particle
strates into valuable organic compounds [7, 8]. It is
sizes corresponding to the anataseꢀtoꢀrutile phase
also employed in materials converting solar energy
transition. For example, the anataseꢀtoꢀrutile phase
into electricity [9] and in chemical sensors [10]. Titaꢀ
transition was observed when the anatase particle size
nium dioxide used in nearly all of these applications is
reached ~20 nm [15] or even about 40 nm [11, 16].
anatase with a high degree of dispersion, a large speꢀ
This might be due to the presence of anionic or catꢀ
cific surface area, and a porous structure. However, the
ionic microimpurities whose chemical composition
pure anatase phase is metastable. As the temperature is
depends on the synthetic procedure. The microimpuꢀ
raised, anatase turns to rutile, and this is accompanied
rities can occur both in the anatase crystal structure
by a change in its crystal structure, by a dramatic
and on the crystal surface, and this is a factor influencꢀ
decrease in dispersion and in the specific surface area,
ing the free energy of the nanosized anatase and rutile
by a transformation of the porous structure, and by a
phases. However, the general dependence of the phase
marked degradation of the properties of the titanium
transition on the TiO2 particle size is quite evident in
dioxide–based catalyst [3, 11].
all cases.
Therefore, knowledge of the factors stabilizing the
Based on the above data, it would be expected that
anatase phase of TiO2 is quite essential for developing
the regularꢀtoꢀnanocrystalline transition of the anaꢀ
new, heatꢀresistant nanomaterials with an anatase
tase structure will exert a significant effect on the therꢀ
structure.
mal stability of the anatase phase in TiO2. We indeed
A thermodynamic analysis of the phase stability of observed that anatase doped with cerium dioxide or
nanocrystalline TiO2 [12, 13] demonstrated that the silicon dioxide changes its structure from regular to
widespread view that the free energy of rutile is lower nanocrystalline under heating [17, 18]. The nanocrysꢀ
than that of anatase is true only for fairly large crystals, talline structure is formed by incoherently intergrown
while just the reverse is true for nanosized titanium anatase crystallites with the formation of interblock
dioxide. As a consequence, the anataseꢀtoꢀrutile phase boundaries between them. Thee boundaries are stabiꢀ
transition in nanosized titanium dioxide occurs only lized by cerium ions or thin silicon dioxide interlayers.
when the anatase crystal size reaches a certain critical Owing to this structure, the growth of anatase crystalꢀ
value. This critical size is about 14 nm [12], so, for titaꢀ lites is markedly slowed down and they reach their
nium dioxide particles smaller than 14 nm, the anatase critical size at a higher temperature, thus raising the
phase is more stable. As the anatase crystal size anataseꢀtoꢀrutile phase transition temperature.
111

112
SHUTILOV et al.
Table 1. Phase composition of and structural properties of Y2O3ꢀdoped TiO2
Chemical composition, mol % Phase composition
Unit cell parameters
Calcination
D
CSD, nm
temperature, °С
TiO2
100
Y2O3
0
phase
content, wt %
а,
Å
c, Å
500
750
anatase
anatase
rutile
100
60
20
80
85
90
7
3.789
3.787
4.599
4.599
3.791
3.789
3.788
4.592
–
9.524
9.524
2.955
2.957
9.520
9.521
9.529
2.965
–
40
900
500
rutile
100
100
100
100
99
98
1
2
anatase
anatase
anatase
rutile
750
25
40
91
–
900
1000
Y2Ti2O7
anatase
anatase
anatase
Y2Ti2O7
rutile
–
100
100
~100
traces
–
500
750
900
6
3.789
3.790
3.789
10.09
4.597
10.119
3.791
3.791
3.788
10.120
4.598
10.119
9.522
9.521
9.529
22
40
1000
100
20
6
2.959
Y2Ti2O7
anatase
anatase
anatase
Y2Ti2O7
rutile
95
5
500
750
900
100
100
9.519
9.519
9.527
13
35
20
80
50
~100
traces
–
1000
2.957
Y2Ti2O7
It was noted [19, 20] that doping of titanium dioxꢀ
(DCSD) was derived from the halfꢀwidths of the diffracꢀ
ide with yttrium oxide stabilizes the anatase phase at tion peaks of anatase (200), rutile (110) and Y2Ti2O7
fairly high temperatures; however, the causes of this (222) using the Scherrer formula [22]. The unit cell
stabilization were not investigated.
parameters of anatase were refined by least squares
involving all of the observed (seven) reflections, using
the POLIKRISTALL program [23]. The error in the
determination of the unit cell parameter was 0.003 Å.
Transmission electron microscopic images were
obtained on a JEMꢀ2010 microscope (Japan) with
1.4 Å resolution at an accelerating voltage of 200 kV.
Elemental (EDX) analyses were made using a
microanalytical attachment with an EDAX DXꢀ4
energyꢀdispersive Xꢀray detector (Ametek Inc.,
United States). The surface area examined was 150–
300 nm2. The lowest yttrium detection limit was
0.1 at %.
Here, we report the effect of yttrium oxide admixꢀ
tures in titanium dioxide on the formation of the anaꢀ
tase structure and on the genesis of the porous strucꢀ
ture of xerogels during heat treatment in a wide temꢀ
perature range.
EXPERIMENTAL
Titanium dioxide samples doped with Y2O3 (1–
5 mol %) were synthesized by incipientꢀwetness
impregnation. Anatase obtained by the industrial sulꢀ
furic acid technology [21] was impregnated with an
yttrium nitrate solution and was dried in air and then
The specific surface area (SBET) was determined
in a dry box at 110
treated in air between 300 and 1000
Xꢀray diffraction patterns were obtained on a
URDꢀ63 diffractometer (Germany) using monochroꢀ
°C for 12 h. Thereafter, it was heatꢀ from argon thermal desorption data from four sorption
°
C for 4 h.
equilibrium points using a SORBIꢀM device (META,
Russia).
The porous structure of materials was studied by
lowꢀtemperature (77 K) nitrogen sorption using a
mated CuKα radiation (point scanning,
0.05
The coherentꢀscattering domain size for anatase The samples to be examined were pretreated in a vacꢀ
2θ = 10°–60°,
°
increments, counting time of 10 s per point). DigiSorb instrument (Micromeritics, United States).
KINETICS AND CATALYSIS Vol. 52
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EFFECT OF YTTRIUM OXIDE ON THE FORMATION OF THE PHASE COMPOSITION
Intensity, arb. units
T K
113
270
240
210
180
150
120
90
60
30
0
500 nm
(а)
Y L
1.00 1.65 2.30 2.95 3.60 4.25 4.90 5.55 6.20 6.85
Energy, keV
Fig. 2. EDX spectrum of the 2 mol % Y O + 98 mol %
2
3
TiO sample calcined at 500°C.
2
yield rutile until 900
undoped titanium dioxide is detectable starting at
750 C. The calcination of the sample containing
5 mol % Y2O3 at 900 C yields anatase and traces of the
yttrium titanium oxide compound Y2Ti2O7, which has
a cubic structure (space group Fd ) with a unit cell
parameter of = 10.09 Å [25]. In all cases, doped titaꢀ
nium dioxide has a substantially smaller anatase crysꢀ
tallite size ( CSD) than the undoped sample (Table 1).
As the yttrium oxide content is raised, CSD at temperꢀ
atures of 500 to 900 C decreases. For example, raising
the Y2O3 content of doped TiO2 calcined at 750
from 1 to 5 mol % reduces the CSD of anatase from 25
to 13 nm. Note that, for undoped anatase calcined at
the same temperature, CSD is about 80 nm.
°C, while the rutile phase in
10 nm
(b)
°
°
3m
а
D
D
°
°
C
D
D
10 nm
(c)
The unit cell parameters ( and ) of anatase are
a
c
not changed significantly by doping and coincide with
those of the undoped sample (a = 3.787 Å, c =
Fig. 1. Electron micrographs of the 2 mol % Y O
+
2
3
9.524 Å) [17]. This suggests that the Y3+ ions are not
incorporated in the anatase lattice and no anataseꢀ
based solution is formed. The ionic radius of Y3+
98 mol % TiO samples (a) dried at 110°C, (b) calcined at
2
500°C, and (c) calcined at 900°C.
(0.80 Å) Å) [26],
is much larger than that of Ti4+ (0.64
so if yttrium ions had been incorporated in the anatase
structure, there would have been a marked increase in
the unit cell parameters of anatase.
uum (10–4 Torr) at 200
°C for 5 h. The mesopore size
distribution was derived from the desorption branch of
the nitrogen sorption isotherm using the classical Barꢀ
rett–Joyner–Halenda (BJH) method [24].
As was demonstrated earlier [17], the initial titaꢀ
nium dioxide dried at 110°C consists of fine anatase
RESULTS AND DISCUSSION
crystallites loosely packed in larger aggregates up to
1000–1500 nm in size. Electron microscopic data
(Fig. 1a) indicate that titanium dioxide doped with
Table 1 presents the Xꢀray diffraction data for yttrium
oxide–doped titanium dioxide samples. Clearly, yttrium
oxide causes a significant increase in the anataseꢀtoꢀ
rutile phase transition temperature. The calcination of
yttrium oxide and dried at 110°C is morphologically
similar to undoped titanium dioxide and consists of
doped samples containing 1–5 mol % Y2O3 does not large aggregates of fine anatase crystallites.
KINETICS AND CATALYSIS Vol. 52
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114
SHUTILOV et al.
Intensity, arb. units
(а)
TiK
207
184
161
138
115
92
2.32
Å
69
46
23
YL
3.55
Å
0
1.001.652.302.953.604.25 4.905.556.206.85
(b)
TiK
207
184
161
138
115
92
69
46
23
YL
0
10 nm
1.001.652.302.953.604.25 4.905.556.206.85
Energy, keV
Metal content, at %
Y
Ti
(a) 2.17
(b) 0.52
97.83
99.48
Fig. 3. Electron micrograph of the 2 mol % Y O + 98 mol % TiO sample calcined at 900
°C and EDX spectra taken from (a)
2
3
2
interblock boundaries and (b) regular structure.
The micrograph of the titanium–yttrium sample also presents elemental analysis data for the area in
doped with 2 mol % Y2O3 and calcined at 500 which the crystal has a regular structure. The interꢀ
°
C
(Fig. 1b) shows that this sample is nanocrystalline, block region is substantially richer in yttrium. Thereꢀ
while undoped titanium dioxide calcined at the same fore, the greater part of the dopant is localized at the
temperature has a wellꢀordered crystal structure [17]. interblock boundaries, and this is the main cause of
The nanocrystalline structure of doped TiO2 consists the higher thermal stability and nanocrystallinity of
of intergrown fine anatase crystallites 5–7 nm in size doped anatase at fairly high temperatures.
separated by interblock (intercrystallite) boundaries.
The micrograph shows no other crystalline or amorꢀ
phous phases. At the same time, microanalysis data
indicate that the sample contains yttrium, and the eleꢀ
mental makeup of the sample (1.20 at % Y, 32.34 at %
Ti, 66.46 % O) is in agreement with its chemical comꢀ
position (Fig. 2).
According to electron microscopic data, the same
sample calcined at a higher temperature of 750°C has
a larger anatase crystallite size of 20–25 nm, retaining
its nanocrystalline structure. As the calcination temꢀ
The micrograph of the 5 mol % Y2O3 + 95 mol %
TiO2 sample calcined at 750 C (Fig. 4a) indicates the
°
formation of a nanocrystalline anatase structure in
which the crystallite size is smaller (10–15 nm) than
the crystallite size in the sample containing 2 mol %
Y2O3. These data are in agreement with the Xꢀray difꢀ
fraction data (Table 1). Thus, the thermal stability of
the interblock boundaries in the nanocrystalline strucꢀ
ture of titanium dioxide increases with increasing Y2O3
content. The nanocrystalline anatase structure withꢀ
stands calcination at 900°C, but the anatase particle
size increases to 35 nm. In addition, calcination at this
temperature leads to the formation of the Y2Ti2O7
compound as 15–20 nm crystals mostly intergrown
with anatase particles (Fig. 4b).
perature is further raised to 900°C, the nanocrystalline
structure of the titanium–yttrium sample persists, but
the anatase crystallite size increases to 40 nm, which is
in agreement with the
DCSD value for anatase (Fig. 1c).
Figure 3 shows a micrograph of this sample, in which
A comparison between the Xꢀray diffraction data
anatase interblock boundaries are clearly seen. Figure 3 and the electron microscopic data suggests that most
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2011

EFFECT OF YTTRIUM OXIDE ON THE FORMATION OF THE PHASE COMPOSITION
115
10 nm
100 nm
(а)
(а)
(b)
(c)
10 nm
100 nm
(b)
Fig. 4. Electron micrographs of the 5 mol % Y O
+
2
3
95 mol % TiO samples calcined at (a) 750°C and (b)
2
900°C.
of the Y3+ ions in doped anatase are localized at the
interblock boundaries formed by intergrown anatase
particles, where the anatase structure is heavily disorꢀ
dered. As the yttrium oxide content is increased, the
dopant can occupy the anatase particle surface as well,
probably as an Xꢀrayꢀamorphous yttrium–titanium
oxide.
100 nm
The textural characteristics of yttrium oxide–
doped titanium dioxide are somewhat different from
those of undoped titanium dioxide. The textural charꢀ
acteristics of porous materials are known to be deterꢀ
mined by the size and packing density of the primary
particles [27]. Figure 5 also shows the micrographs of
5 mol % Y2O3 + 95 mol % TiO2 samples calcined at
different temperatures, but these images were
obtained at a lower resolution to see the morphology of
Fig. 5. Electron micrographs of the 5 mol % Y O
+
2
3
95 mol % TiO samples calcined at (a) 500, (b) 750°C, and
2
(c) 900°C, obtained at a lower resolution.
60–70 nm and there are many ~30ꢀnm particles and
some particles 90 nm in size. Note that the sample
≈
remains nanostructured.
the particles. The sample calcined at 500°C has irregꢀ
ularly shaped 15ꢀ to 30ꢀnm TiO2 particles consisting of
Figure 6 demonstrates how the specific surface area
still smaller, intergrown particles. These smaller partiꢀ of doped titanium dioxide varies with calcination temꢀ
cles are rather loosely packed into larger aggregates. A perature. As the temperature is raised, the SBET of
similar situation is observed for the sample containing undoped TiO2 decreases sharply. The specific surface
the smaller amount of the dopant. In the 5 mol % Y2O3 + area of doped titanium dioxide also decreases, but less
95 mol % TiO2 sample calcined at 750°C, the TiO2 rapidly. For any calcination temperature, the specific
particle size is 25–45 nm (mainly 35–45 nm), their surface area of titanium dioxide doped with 1–2 mol %
complicated structure is retained, and the particle Y2O3 is larger than that of undoped TiO2. For the samꢀ
packing in the aggregates is less loose. In the sample ple containing 5 mol % yttrium oxide, SBET is larger
calcined at 900°C, the dominant TiO2 particle size is than that of undoped TiO2 only above 400°C. At lower
KINETICS AND CATALYSIS Vol. 52
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116
Specific surface area, m2/g
SHUTILOV et al.
cally independent of the dopant content. It is possible
that the smaller specific surface area of the highly
doped sample (5 mol % Y2O3) calcined below 400 C is
due to the presence of undecomposed yttrium nitrate
in the fine pores of the support.
300
250
200
150
100
°
2
The pore volume (Vs) of the initial TiO2 support
calcined at 300°
C is 0.316 cm3/g [28]. It decreases
with an increasing dopant content to become
0.203 cm3/g for the sample containing 5 mol % Y2O3
(Table 2). The pore volume in all samples increases
slightly as the calcination temperature is raised from
3
300 to 400°C. This can apparently be due to the
decomposition of the yttrium salt in the pores of the
support. The pore volume in the samples containing 1
and 2 mol % Y2O3 is almost unchanged by heat treatꢀ
1
50
0
ment up to 700
ple containing 5 mol % Y2O3 decreases upon heat
treatment above 400 C. In addition, experimental
°C, while the pore volume in the samꢀ
100 200 300 400 500 600 700 800 900 1000
Temperature,
°
C
°
data indicate that titanium dioxide containing 5 mol %
Y2O3 has a substantially smaller pore volume throughꢀ
out the temperature range examined. This is likely due
to the higher TiO2 particles packing density in the
highly doped samples.
Fig. 6. Effect of the calcination temperature on the specific
surface area ( ) undoped titanium dioxide and ( ) titaꢀ
nium dioxide doped with ( ) 2 and ( ) 5 mol % Y O .
1
2, 3
2
3
2
3
Figure 7 shows the differential mesopore size disꢀ
tribution calculated by the BJH method. For the samꢀ
ples containing 1 and 2 mol % Y2O3, raising the calciꢀ
temperatures, this sample has a smaller specific surꢀ
face area than undoped titanium dioxide. In a wide
calcination temperature range (400–900°C), the speꢀ
nation temperature to 700°C causes a gradual increase
cific surface area of doped titanium dioxide is practiꢀ
in the dominant pore size (Table 2). For the sample
containing 5 mol % Y2O3, raising the calcination temꢀ
perature to 600°C does not lead to any significant
increase in the pore size, which remains at the 3–4 nm
level and increases only as the temperature is further
Table 2. Parameters of the porous structure of Y2O3ꢀdoped
TiO2
increased. For all samples, calcination at 1000°C leads
Chemical
composition, mol %
Calcination
temperature, °С
to the total disappearance of the mesopores and
3
**
pore , nm
*
Vs , cm /g
D
diminishes the specific surface area to 2 m2/g.
TiO2
99
Y2O3
1
Figure 8 shows how the porous structure of doped
titanium dioxide calcined at 600°C depends on the
300
400
500
600
700
300
400
500
600
700
300
400
500
600
700
0.257
0.264
0.285
0.269
0.287
0.261
0.278
0.269
0.282
0.282
0.203
0.222
0.208
0.195
0.188
3.3
3.9
4.7
7.3
11.9
3.2
3.9
4.8
7.3
9.5
3.1
3.2
4.0
3.8
4.7
chemical composition of the xerogel. The porous
structure of the samples containing 1 and 2 mol %
Y2O3 is dominated by pores with a uniform diameter of
7.3 nm, and the sample containing 5 mol % Y2O3 has
a finer porous structure with a dominant pore diameter
of 3.8 nm. It is clear from the data presented in Table 2
and Fig. 8 that the persistence of the finer porous texꢀ
ture of the sample containing 5 mol % Y2O3 is accomꢀ
panied by a decrease in the pore volume and is not
accompanied by any significant change in the specific
surface area. This character of the formation and heatꢀ
induced changes of the porous structure of the doped
samples suggests that the dopant is partially redistribꢀ
uted, filling some pores and regions of the pore space,
as is described by Fenelonov et al. [29]. At low Y2O3
concentrations (1–2 mol %), most of the dopant is
localized at the boundaries between intergrown fine
anatase crystallites, which does not allow a sufficient
amount of the surface phase of the dopant to form in
the sample. During heat treatment, this causes a gradꢀ
ual increase in the size of the TiO2 particle without
changing their packing density, and this is accompaꢀ
98
95
2
5
Notes: * Limiting volume of the sorption space, including
micropores and mesopores.
** Dominant mesopore diameter.
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EFFECT OF YTTRIUM OXIDE ON THE FORMATION OF THE PHASE COMPOSITION
117
1
1
dV
/
dDpore, cm3 g−1 nm−
dV/
dDpore, cm3 g−1 nm−
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
(a)
0.08
0.06
0.04
0.02
0
1
2
3
4
5
1
2
3
1
1
1
10
1
10 Pore diameter, nm
(b)
Fig. 8. Differential pore size distribution curves for the
samples containing ( ) 1, ( ) 2, and ( ) 5 mol % Y O calꢀ
cined at 600 C.
0.08
0.06
0.04
0.02
0
1
2
3
1
2
3
4
5
2
3
°
during heat treatment without reducing the specific
surface area and ensures the persistence of the fine
porous structure at higher temperatures.
Thus, it follows from our experimental data that, as
titanium dioxide is doped with yttrium oxide by
impregnation with an aqueous solution of yttrium
nitrate, the dopant penetrates into the particle aggreꢀ
gates. Part of the dopant is adsorbed by the surface of
anatase particles, and the other part occupies the
interparticle space. At the drying and heat treatment
stages, the dopant prevents the sintering of the anatase
10
(c)
1
0.06
0.04
0.02
0
particles. Upon calcination at 500°C, this leads to the
2
3
4
5
formation of a nanocrystalline TiO2 structure consistꢀ
ing of incoherently intergrown fine anatase crystallites
5–7 nm in size. Interblock boundaries accommodatꢀ
ing Y3+ ions form between these crystallites. Note that
the formation of the nanocrystalline anatase structure
occurs only in the presence of the dopant. In the
absence of the dopant, the fine anatase crystallites
accrete coherently during heat treatment at 500
form large crystals with a regular structure.
°C to
As was demonstrated in our earlier works [17, 18],
the formation of the nanocrystalline anatase structure
also takes place in anatase doped with cerium dioxide
or silicon dioxide. The thermal stability of the nanocꢀ
rystalline anatase structure is largely determined by
the nature and concentration of the dopant. Doping
with cerium and silicon dioxides and, as is demonꢀ
strated by this study, yttrium oxide leads to the formaꢀ
tion of thermally stable interblock boundaries between
anatase crystallites. The formation of these boundaries
markedly hampers the growth of the anatase crystalꢀ
lites at high temperatures and, according to [12, 13],
raises the anataseꢀtoꢀrutile phase transition temperaꢀ
ture. The anatase phase in the samples containing
10 Pore diameter, nm
Fig. 7. Differential pore size distribution curves for the
samples containing (a) 1, (b) 2, and (c) 5 mol % Y O calꢀ
2
3
cined at (1) 300, (2) 400, (3) 500, (4) 600, and (5) 700°C.
nied by a decrease in the specific surface area, by an
increase in the dominant pore size, and by no change
in the total pore volume. In the highly doped sample
(5 mol % Y2O3), the dopant is located both at the
interblock boundaries and on the outer surface of
nanocrystalline TiO2 particles. This increases the
packing density of these particles in their aggregates
1⎯5 mol % Y2O3 is indeed stable up to 900°C, while a
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SHUTILOV et al.
7. Nicolov, V., Klissurski, D., and Anastasov, A., Catal.
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considerable part of anatase in undoped TiO2 turns
into rutile starting at 750 C.
°
8. Al’kaeva, E.M., Andrushkevich, T.V., Zenkovets, G.A.,
The formation of the porous structure in the binary
system is also determined by the increase in the phase
transition temperature as a function of the xerogel
composition. Note that the decrease in the total pore
volume with an increase in the percentage of yttrium
oxide is likely due to the dopant occupying pores in the
TiO2 matrix. The thermal stability of the resulting
binary structure is confirmed by the finding that the
pore volume in the samples containing 1 and 2 mol %
Y2O3 does not change as the heat treatment temperaꢀ
Kryukova, G.N., and Tsybulya, S.V., Catal. Today
2000, vol. 61, nos. 1–4, p. 249.
,
9. Park, N.ꢀG., van de Lagemaat, J., and Frank, A.J.,
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ture is raised to 700°C.
The observation that increasing the amount of
dopant at a fixed heat treatment temperature imparts a
finer porous texture to the binary system is explained
by the fact that the smaller titanium dioxide particles
survive at higher Y2O3 contents. Accordingly, the
mesopore space results from the packing of smaller
particles, for which a smaller dominant pore size is
typical. The fine porous texture with a pore diameter
12. Zhang, H. and Banfield, J.F., J. Mater. Chem., 1998,
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Kryukova, G.N., Kinet. Katal., 1999, vol. 40, no. 4,
p. 623 [Kinet. Catal. (Engl. Transl.), vol. 40, no. 4,
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of Dpore ≈ 4.7 nm is stable up to 400°C. Thus, the dopꢀ
ing of titanium dioxide with yttrium oxide using the
procedure suggested here makes it possible to markꢀ
edly enhance the thermal stability of anatase and to
form a heatꢀresistant fine porous texture at fairly high
calcination temperatures.
17. Zenkovets, G.A., Shutilov, A.A., Gavrilov, V.Yu.,
Tsybulya, S.V., and Kryukova, G.N., Kinet. Katal.
,
2007, vol. 48, no. 5, p. 792 [Kinet. Catal. (Engl. Transl.),
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ACKNOWLEDGMENTS
18. Zenkovets, G.A., Shutilov, A.A., Gavrilov, V.Yu., and
Tsybulya, S.V., Kinet. Katal., 2009, vol. 50, no. 5, p. 790
The authors are grateful to A.V. Ishchenko for carꢀ
rying out electron microscopic studies.
[Kinet. Catal. (Engl. Transl.), vol. 50, no. 5, p. 760].
19. He, X., Chen, R., Zheng, X., and Chen, Z., Semicond.
Photon. Technol., 2005, vol. 11, no. 3, p. 192.
This work was supported by the Siberian Branch of
the Russian Academy of Sciences (interdisciplinary
project no. 36) and the Ministry of Education and Sciꢀ
ence of the Russian Federation through state contract
no. P252/23.07.2009 and through the program “Develꢀ
opment of the Scientific Potential of the Higher Educaꢀ
tion Institutions” (project no. 2.1.1/729).
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SSSR, 1988.
22. Guinier, A., Théorie et technique de la radiocristallograꢀ
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2011