Synthesis and properties of titanium glycolate Ti(OCH2CH 2O)2

Article abstract of DOI:10.1134/S0036023608070152

A new efficient method for the synthesis of extended micro-and nano-sized crystals (whiskers, fibers) of titanium glycolate Ti(OCH₂CH ₂O)₂ has been suggested. The method implies the reaction of hydrated titanium dioxide with ethylene glycol on heating in air. Thermolysis of Ti(OCH₂CH₂O)₂ in air gives titanium dioxide as anatase (400-500°C) and rutile (T > 700°C), the morphology of titanium glycolate crystals being inherited by the oxide. The pseudocrystals of the thermolysis product in an inert gas medium (T = 500-950°C) represent aglomeration of nano-sized titanium dioxide particles and amorphous carbon. At temperatures up to 1300°C, the formation of the TiO_2-x C _x phase with a rutile structure is probable. In a wet air environment, titanium glycolate is partially hydrolyzed to give TiO _x (OCH₂CH₂O)_2-2x (OH)_2x ?xH ₂O (0 ≤ x ≤ 1) and on keeping in water at room temperature, ethylene glycol is completely displaced from the crystals. This process is also not accompanied by changes in the particle morphology.

Full text of DOI:10.1134/S0036023608070152

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2008, Vol. 53, No. 7, pp. 1065–1069. © Pleiades Publishing, Ltd., 2008.
Original Russian Text ©V.N. Krasil’nikov, A.P. Shtin, O.I. Gyrdasova, E.V. Polyakov, G.P. Shveikin, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 7,
pp. 1146–1151.
COORDINATION
COMPOUNDS
Synthesis and Properties of Titanium Glycolate Ti(OCH2CH2O)2
V. N. Krasil’nikov, A. P. Shtin, O. I. Gyrdasova, E. V. Polyakov, and G. P. Shveikin
Institute of Solid-State Chemistry, Ural Division, Russian Academy of Sciences,
ul. Pervomaiskaya 91, Yekaterinburg, 620219 Russia
Received May 4, 2007
Abstract—A new efficient method for the synthesis of extended micro- and nano-sized crystals (whiskers,
fibers) of titanium glycolate Ti(OCH2CH2O)2 has been suggested. The method implies the reaction of hydrated
titanium dioxide with ethylene glycol on heating in air. Thermolysis of Ti(OCH2CH2O)2 in air gives titanium
dioxide as anatase (400–500°C) and rutile (T > 700°C), the morphology of titanium glycolate crystals being
inherited by the oxide. The pseudocrystals of the thermolysis product in an inert gas medium (T = 500–950°C)
represent aglomeration of nano-sized titanium dioxide particles and amorphous carbon. At temperatures up to
1300°C, the formation of the TiO2 – xCx phase with a rutile structure is probable. In a wet air environment, tita-
nium glycolate is partially hydrolyzed to give TiOx(OCH2CH2O)2 – 2x(OH)2x · xH2O (0 ≤ x ≤ 1) and on keeping
in water at room temperature, ethylene glycol is completely displaced from the crystals. This process is also not
accompanied by changes in the particle morphology.
DOI: 10.1134/S0036023608070152
Titanium dioxide is widely used in many fields of with hydrated titanium dioxide on heating under ambi-
ent conditions.
modern technology, the development of nanotechnol-
ogy giving rise to its new promising applications. This
refers to the production of special ceramics, pigment
materials, membranes, sorbents, luminophores, cata-
lysts, including materials for the photocatalytic oxida-
tion of organic compounds [1–10]. In recent years, the
attention of researchers has been focused on the search
EXPERIMENTAL
Titanium glycolate was prepared by an original pro-
cedure [15] based on a conditional reaction in which
ethylene glycol serves as both a reactant and the reac-
for and development of efficient methods for the syn- tion medium
thesis of titanium dioxide as nano-sized extended
Ti(OH)4 + 2HOCH2CH2OH
= Ti(OCH2CH2O)2 + 4H2O↑.
(quasi-one-dimensional) objects—wires, fibers, whis-
kers, tubes, and rods—with unique electrical, magnetic,
optical, and catalytic properties [2–10]. The most effi-
cient known method for the synthesis of TiO2 with
extended particles is based on thermolysis of titanium
glycolate Ti(OCH2CH2O)2, which has a chain structure
and, under certain conditions, can be obtained as about
~50 nm-thick crystals with a length of up to 40 µm [3,
4, 11]. Thermolysis of titanium glycolate in air is
accompanied by transfer of the precursor morphology
to the product. Currently, method for the synthesis of
extended Ti(OCH2CH2O)2 nanocrystals consists of
many-hour hydrothermal treatment of mixtures of eth-
ylene glycol (EG) and titanium alkoxides Ti(OR)4 in a
Teflon-lined autoclave at 160–180°C [1, 3, 4, 11]. A
main drawback of this method hampering its wide use
is high cost and environmental hazard of the alkoxides
Ti(OR)4 [12–14], which stimulates the search for alter-
native methods for the synthesis of titanium glycolate
without the use of titanium alkoxides. In this paper, we
report the results of studies dealing with formation con-
ditions and properties of Ti(OCH2CH2O)2 obtained by
(1)
Ethylene glycol was added to titanium hydroxide in
the molar ratios Ti(OH)4 : HOCH2CH2OH = 1 : 20, 1 :
30, and 1 : 50. The mixtures were placed in thermally
stable conical flasks, heated under vigorous stirring to
170°ë, kept at this temperature for 2–6 h, and cooled to
room temperature. The products were separated from
unreacted ethylene glycol by vacuum filtration using a
glass filter, washed with acetone or acetonitrile, washed
in a drying chamber at 50°ë for 30 min, and placed into
bottles with ground stoppers for storage. Mixtures with
the composition Ti1 – xSix(OH)4 + 20HOCH2CH2OH,
where x = 0.1 and 0.2, were treated in a similar way.
Titanium hydroxide was prepared by precipitation from a
sulfuric acid solution of titanium containing 0.25 mol/L of
TiOSO4 and 0.57 mol/L of H2SO4. Ammonium hydrox-
ide was added with vigorous stirring as the precipitat-
ing agent. The process was carried out at room temper-
ature up to pH 7.5–8. The precipitate was separated
from the mother liquor by filtering and washed by dis-
tilled water up to negative test for sulfate ions. Both wet
a basically new procedure based on the reaction of EG and air-dry precipitates were used. Silicon-containing
1065

1066
KRASIL’NIKOV et al.
1 µm
5 µm
(‡)
(b)
5 µm
(c)
(d)
Fig. 1. SEM images of titanium glycolate and products of its thermolysis: (a) fibrous Ti(OCH CH O) ; (b) thermolysis product of
2
2
2
plate form of Ti(OCH CH O) in air at 900°C; (c) thermolysis product of plate form of Ti(OCH CH O) under argon at 900°C;
2
2
2
2
2
2
(d) photographic image of the thermolysis product of plate form of Ti(OCH CH O) annealed at 1300°C under argon.
2
2
2
samples were precipitated by adding the required ysis,
the
formation
of
mixed
glycolate
amount of sodium silicate Na2SiO3. The phase control Ti0.96Si0.04(OCH2CH2O)2 was established; the silicon
was accomplished by a DRON-2 diffractometer (CuKα concentration in all samples did not depend on its con-
centration in the initial mixture. According to SEM and
optical microscopy data, all the synthesized samples
were formed as extended crystals with linear dimen-
sions decreasing with an increase in the EG concentra-
tion in the reaction mixture. Figure 1 shows the SEM
image of the Ti(OCH2CH2O)2 sample synthesized by
heat treatment of the reaction mixture with Ti(OH)4 :
HOCH2CH2OH ratio of 1 : 50. At low titanium hydrox-
ide concentrations in the initial mixture,
Ti(OCH2CH2O)2 is formed as thin filament crystals
(Fig.1a) with diameters within 100 nm. At higher con-
centrations, the reaction gives flattened crystals with
dimensions of 0.5–2 × 10–30 µm that tend to inter-
grow as crosses, bundles, or hedgehog type structures.
Intergrowth and twinning along the direction parallel
to crystal elongation are also possible. The longitudi-
nal intergrowth of titanium glycolate fibers was
observed by a high resolution electron microscope [3].
The presence of twinning is supported by inhomoge-
neous extinction of some flattened Ti(OCH2CH2O)2
crystals oriented in the Ng–Np section. Meanwhile,
radiation) and a POLAM S-112 transmission polariza-
tion microscope using the optical immersion control
technique. Thermogravimetric analysis was carried out
on a Q-1500D derivatograph in air at a heating rate of
10 K/min in the temperature range of 20–1000°ë. The
IR spectra were recorded on a Spectrum-One spectro-
photometer in the range 4000–400 cm–1. The particle
size and shape of the samples were determined by scan-
ning electron microscopy (SEM) on a Tesla BS-301
instrument. Elemental analysis of samples was carried
out by standard procedures. All experiments were car-
ried out under conditions either excluding or minimiz-
ing the effect of air moisture.
RESULTS AND DISCUSSION
According to powder X-ray diffraction, micro-
scopic, thermogravimetric and elemental analysis, the
reaction products comprised one chemical compound
Ti(OCH2CH2O)2. The weight loss on heating in air to
900°C estimated from the TG curve, taking into
account the formation of TiO2, corresponded to the the- Ti0.96Si0.04(OCH2CH2O)2 does not tend to undergo inter-
oretical value and was 52.56 wt %. By elemental anal- growth or twining; this phase crystallizes as rods
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 7 2008

SYNTHESIS AND PROPERTIES OF TITANIUM GLYCOLATE
1067
~0.5−1 µm in diameter and up to 10−15 µm in length.
The extinction of colorless Ti(OCH2CH2O)2 crystals
relative to their elongation is direct; the refractive indi-
ces are as follows: Ng = 1.737 0.005, Nm = 1.689
0.002, and Np = 1.676 0.002.
1
According to published data [4], the chain quasi-
one-dimensional structure of Ti(OCH2CH2O)2 in which
the zigzag chains are formed from TiO6 octahedra con-
nected by bridging –OCH2CH2O– groups is readily
transformed on heating in air into TiO2 with retention of
the crystal morphology of precursors. It can be seen
from SEM images (Fig. 1) that particles of the thermol-
ysis products of titanium glycolate synthesized at the
ratio Ti(OH)4 : HOCH2CH2OH = 1 : 20 retain the
appearance of the initial crystals upon heating at
10 K/min to 900°C in air (Fig. 1b) or under argon (Fig. 1c).
The powder obtained on annealing in air is colorless
and, according to X-ray diffraction data, this is the
high-temperature (rutile) modification of titanium
dioxide and, after annealing under inert gas, the product
becomes black (Fig. 1d). Examination under a trans-
mission polarized light microscope shows black non-
transparent extended objects pseudomorphous to the
titanium glycolate precursor crystals.
2
3
10
20
30
40
50
60
2θ, deg
Fig. 2. X-ray diffraction patterns of thermolysis products of
Ti(OCH CH O) obtained under argon at (1) 500; (2) 900;
2
2
2
(3) 1300°C.
Figure 3 demonstrates the TG and DTA curves of
the (a) fibrous Ti(OCH2CH2O)2 sample and (b) the
same sample kept preliminarily at 600°C under argon
Figure 2 shows the X-ray diffraction patterns of the
products of thermolysis of titanium glycolate recorded
after keeping under argon at 500, 900, and 1300°C for for 2 h. Thermal decomposition of titanium glycolate
2 h. It can be seen from Fig. 2 that heat treatment of
Ti(OCH2CH2O)2 at 500°C yields TiO2 with the anatase
structure. The sample heat treated, at 900°C contains
two titanium dioxide modifications (anatase and rutile).
A similar result is obtained upon heat treatment of tita-
nium glycolate in air; however, in this case, titanium
dioxide formed initially as anatase (400−500°C) is con-
verted into rutile on heating to 700°C. As the tempera-
ture of annealing under argon increases, the sample
becomes more and more X-ray amorphous. On the
basis of reflections present in the X-ray diffraction pat-
tern of the sample, one can suggest the presence of a
rutile phase only with a high degree of admission. The
image (Fig. 1d) obtained in the reflected light shows the
pseudocrystals of the thermolysis product obtained by
heating Ti(OCH2CH2O)2 to 1300°C and keeping for 2 h
under argon. The annealing of this sample in air does
not change the particle morphology but its color
becomes bluish-gray, which attests to incomplete
removal of carbon or partial reduction of titanium to
give, for example, nonstoichiometric oxide TiO2 – x
[16]. According to powder X-ray diffraction, the sam-
ple contains titanium dioxide mainly as rutile with
some anatase. It was shown [12] that heating of finely
dispersed anatase mixed with carbon under argon does
not induce its transformation into rutile even above
1000°C. The X-ray diffraction pattern of the sample
heated to 1050°C showed new lines assigned to the
oxycarbide TiCxOy.
occurs in two steps (Fig. 3a) and is completed by for-
mation of TiO2 (anatase) at ~500°C. The weight loss
above 300°C and the corresponding exotherm in the
DTA curve with a maximum at 405°C can be attributed
to oxidation of the solid phase, preferably, amorphous
∆m, mg
0
(b)
(‡)
TG
TG
330
20
40
60
405
675
537
DTA
DTA
200
400
600 200
400
600 t, °C
Fig. 3. TG and DTA curves of (a) titanium glycolate
Ti(OCH CH O) and (b) the same sample kept under argon
2
2
2
at 600°C.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 7 2008

1068
KRASIL’NIKOV et al.
carbon. The TG curve of the sample kept under argon
shows the weight loss of up to 20 wt % accompanied by
an exotherm with a maximum at 330°C in the DTA
curve. Complete removal of the combustible compo-
nents is accompanied by the formation of titanium
dioxide with rutile structure. Since the particle mor-
phology remains unchanged during all operations, the
pseudocrystals formed upon thermolysis of
Ti(OCH2CH2O)2 under inert gas atmosphere can be
considered as containers incorporating separate nano-
particles of titanium dioxide and amorphous carbon. It
is quite probable that the above-noted amorphization of
the thermolysis product at 1300°C under argon is due to
the reaction of TiO2 particles and carbon to give phases
like TiO2 – xCx with a structure similar to that of rutile,
which is converted into rutile upon maintenance in air
at 450°C.
1
2
Previously [3, 4, 11], in order to remove EG impu-
rity from the synthesized titanium glycolate precipitate,
the samples were washed with distilled water and then
with ethanol. In our experiments, we found that the
Ti(OCH2CH2O)2 crystals can sorb atmospheric mois-
ture, the fibrous crystals being most hygroscopic. Keep-
ing nano-sized titanium glycolate fibers in a desiccator
over water transforms them into an amorphous gel-like
material. Figure 4 shows the X-ray diffraction patterns
of Ti(OCH2CH2O)2 and the sample obtained by keeping
this compound in a closed desiccator over water for a
week at room temperature followed by washing by ace-
tone and drying at 50°C. Comparison of X-ray diffrac-
tion patterns unambiguously attests to degradation of
titanium glycolate caused by the action of water vapor.
This occurs as a result of EG displacement from
Ti(OCH2CH2O)2 crystals by water. It is important that,
in this case too, the change in the sample composition
does not affect the particle morphology, which remains
invariable throughout all stages of hydration; the mor-
phology remains the same even after almost complete
removal of EG by keeping the Ti(OCH2CH2O)2 sample
in distilled water for 2 weeks. Annealing in air at 350–
500°C affords titanium dioxide with the anatase struc-
ture and with particles that inherited the precursor mor-
phology.
10
20
30
40
50
60
2θ, deg
Fig. 4. X-ray diffraction patterns of fibrous
Ti(OCH CH O) (1) before and (2) after keeping in a closed
desiccator over water.
2
2
2
3
2
1
The IR spectra of titanium glycolate treated with
water vapor in an open vessel in air or in a closed des-
iccator over water, and those kept directly in water are
presented in Fig. 5. The IR spectrum of the sample kept
in air differs from the spectrum of the initial titanium
glycolate by the presence of new bands in the vibration
frequencies of water molecules [17]. The ν(H2O)
stretching vibrations are responsible for a broad band
with an absorption peak at 3285 cm–1 and the δ(H2O)
bending vibrations are responsible by one more broad
band at 1646 cm–1. In the IR spectra of samples that
have been kept in the desiccator over water and in
water, these bands are more clear-cut and, in addition,
they are shifted to lower frequencies (3230, 3190 cm–1
1800
1400
1000
600
ν, cm
–1
Fig. 5. IR spectra of Ti(OCH CH O) samples kept (1) in
air, (2) in a desiccator over water, or (3) in water.
2
2
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 7 2008

SYNTHESIS AND PROPERTIES OF TITANIUM GLYCOLATE
1069
and 1638, 1633 cm–1). The bands corresponding to
−OCH2CH2O– group vibrations are absent from the IR
spectrum of the sample kept in water, indicating com-
plete displacement of EG from the titanium glycolate
crystals. After annealing at 900°C under argon, this
sample remained colorless, while the samples kept pre-
liminarily in desiccator over water or in water became
black or bluish-gray, respectively, which is related to
different contents of carbon in them. Thus, washing of
titanium glycolate with water followed by heat treat-
ment under an inert gas or in air can be used to control
the carbon content in the extended pseudocrystals thus
formed, which is quite significant for the formation of
titanium dioxide-based catalysts photoactive in the vis-
ible region [18–20]. The presence of rather broad
δ(H2O) band with an absorption peak at 1647 cm–1 in
the IR spectrum of Ti(OCH2CH2O)2 kept in air (Fig. 5)
is indicative of a complicated route of its reaction with
water vapor differing from the mere substitution of OH
groups for the –OCH2CH2O– groups. In the IR spectra
of samples kept in an atmosphere of saturated water
vapor and in water, the δ(H2O) band becomes more
intense; in addition, these spectra exhibit a very
intense broad band at ~1000–500 cm–1, which is usu-
ally attributed to Ti–O and Ti–O–Ti vibrations and OH
bending vibrations [14, 17, 21]. The IR spectra
recorded for intermediate periods of keeping the sam-
ples in water represent superpositions of bands
observed for the initial titanium glycolate and for
hydrated titanium dioxide [14, 21], the contribution of
the band at ~1000−500 cm–1 regularly increasing and
that of the bands for –OCH2CH2O– regularly decreasing.
Correspondingly, the intensity of the exotherm with DTA
maximum at ~400°C also decreases (see Fig. 3a). Thus,
on the basis of IR spectroscopy data, the products of
titanium glycolate hydration can be represented as
TiOx(OCH2CH2O)2 – 2x(OH)2x · xH2O, where 0 ≤ x ≤ 1.
Federation for support of Scientific Schools (grant
no. NSh-8380.2006.3.
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