Synthesis and characterization of chromium doped boehmite nanofibres

Article abstract of DOI:10.1016/j.tca.2008.10.024

Thermogravimetric and differential thermogravimetric analysis has been used to study synthesised chromium doped boehmite. The dehydroxylation temperature increases significantly from 0 to 5% doping, after which the dehydroxylation temperature shows a smal

Full text of DOI:10.1016/j.tca.2008.10.024

Thermochimica Acta 483 (2009) 29–35
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Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Synthesis and characterization of chromium doped boehmite nanofibres
Jing (Jeanne) Yang , Ray L. Frost , Yong Yuana,b
a
a,∗
a
Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia
Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Thermogravimetric and differential thermogravimetric analysis has been used to study synthesised
chromium doped boehmite. The dehydroxylation temperature increases significantly from 0 to 5% doping,
after which the dehydroxylation temperature shows a small steady increase up to the 20% doping level.
The temperature of dehydroxylation increases with time of hydrothermal treatment. Chromium doped
boehmite nanofibres were also characterised by X-ray diffraction and transmission electron microscopy.
Hydrothermal treatment of doped boehmite with chromium resulted in the formation of nanofibres over
a wide dopant range. Nanofibres up to 500 nm in length and between 4 and 6 nm in width were produced.
Received 8 September 2008
Received in revised form 27 October 2008
Accepted 28 October 2008
Available online 6 November 2008
Keywords:
Boehmite
Chromium doping
Nanofibres
©
2008 Elsevier B.V. All rights reserved.
Nanomaterial
Transmission electron microscopy
Thermal analysis
Thermogravimetry
1. Introduction
have been undertaken, for example, boehmite (AlOOH) nanofibers
were reported to be assembled with the assistance of poly(ethylene
Compared to their micro and macro counterparts, nanosized
materials have received wider attention because of their intrin-
sic properties, which are determined by their composition, size,
shape, and structure [1]. Nanosized materials such as nanofibers,
nanotubes, nanoribbons and nanorods, one dimensional (1D)
nanoscale inorganic materials have attracted intensive interest due
to their distinctive geometries, novel physical and chemical prop-
erties, and the potential applications in many fields. [2] Boehmite
oxide) (PEO) surfactant [8] and tubular ꢀ -Al O3 was fabricated
2
via soft solution route using N-cetyl-N,N,N-trimethylammonium
bromide (CTAB) surfactant [9]. Shen et al. published a report
showing a steam-assisted solid-phase conversion of amorphous
aluminium hydroxides wet gel to well crystallised 1D nanostruc-
ture of boehmite AlOOH nanorods without using surfactants and
solvents [10]. The process is unique in the simplicity of preparation
and the high efficiency of crystal growth, which can be operated at
a large scale.
(
ꢀ -AlOOH) and its oxide derivatives such as ˛-Al O3 and ꢀ -Al O3
2 2
have been studied extensively because they can be used as catalysts,
adsorbents, flame retardants and optical materials [3–6].
As for doping clays, the addition of other metal ions into
boehmite, especially into nanostructured boehmite would have
great potential to contribute the further application of these inor-
ganic nanomaterials due to the enhancement of its properties, and
there have been reports on boehmite doped by Fe, Ga and Eu
[11–13]. It is also reported that materials doped with chromium
could obtain special electric, magnetic or optical properties and
gain more application [14–17]. This paper reports our research
on Cr-doped boehmite. Such concepts have not been previously
reported.
Synthesis forms an essential component of nanoscience and
nanotechnology. While nanomaterials have been generated by
physical methods such as laser ablation, arc-discharge and evap-
oration, chemical methods have proved to be more effective,
as they provide better control as well as enable different sizes,
shapes and functionalization. Among these methods, hydrolysis
and precipitation are the most common. John Bugosh first syn-
thesised the boehmite nanofibers by a hydrothermal method in
1
961 [7]. Since then, numerous studies on boehmite nanofibers
Thermal analysis has been proved as the most useful method
for the analysis of minerals and related materials. In this work,
boehmite nanofibers based on Shen’s methodology [10] were
synthesised by introducing chromium as dopant and a series of
chromium doped boehmite nanofibers with different chromium
∗ Corresponding author. Tel.: +61 7 3138 2407; +61 7 3138 1804.
E-mail address: r.frost@qut.edu.au (R.L. Frost).
0
040-6031/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2008.10.024

3
0
J. Yang et al. / Thermochimica Acta 483 (2009) 29–35
◦
Fig. 1. (a) XRD patterns of undoped boehmite and 1% Cr-doped boehmite nanofibers with different hydrothermal treatment time at 170 C. (b) XRD patterns of undoped
◦
boehmite and various Cr % doped boehmite nanofibers, after hydrothermal treatment at 170 C for 3 days.
content percentage and varying hydrothermal treatment time have
been systematically studied with the thermo gravimetric tech-
niques.
produced from a line focused PW3373/10 Cu X-ray tube, operating
at 40 kV and 40 mA, wavelength of 1.54 Å.
2.3. TEM analysis
2
. Experimental
A Philips CM 200 transmission electron microscopy (TEM) at
00 kV was used to investigate the morphology of the boehmite
2
2.1. Synthesis of chromium doped boehmite nanofibers
nanofibers. All samples were dispersed in absolute ethanol solution
and then dropped on copper grids.
A
total amount of 0.02 moles of aluminium nitrate and
chromium nitrate was mixed before being dissolved in ultra-pure
water. To make a comparison, mixtures with chromium molar per-
centage of 0, 1, 3, 5, 10 and 20% were prepared separately and then
dissolved in ultra-pure water to form solutions with a metal ion
2.4. Thermal analysis
Thermal decomposition of the Cr-doped boehmite was car-
ried out in a TA® Instrument incorporating a high-resolution
thermo gravimetric analyser (series Q500) in a flowing nitrogen
to H O molar ratio of 1:35. At room temperature, 10% by weight
2
ammonia solution was added dropwise into the metal ions solution
while stirring vigorously. The addition of the ammonia solution was
ceased when the pH value of the reaction mixture reached 5. The
mixture was then stirred at room temperature for 1 h. The obtained
gel was filtrated to obtain the wet gel-cake, which was then trans-
ferred into a 25 mL glass beaker. Before putting the beaker with
gel-cake into a Teflon vessel (125 mL), 2 ml ultrapure water was
poured to the bottom of each vessel separately. The Teflon vessels
3
−1
atmosphere (60 cm min ). Approximately 20 mg of each sample
◦
underwent thermal analysis, with a heating rate of 5 C/min, with
resolution of 6 from 25 to 1000 C. With the isothermal, isobaric
heating program of the instrument, the furnace temperature was
regulated precisely to provide a uniform rate of decomposition in
the main decomposition stage.
◦
◦
were sealed and heated at 170 C for 1, 3, 5 and 10 days. The resulting
3. Results and discussion
materials were washed several times with ultrapure water, cen-
◦
trifuged, and dried in air at 35 C for 2 days.
3.1. X-ray diffraction
2.2. X-ray diffraction
X-ray diffraction was normally used to determine the phase
and purity of the synthesised materials. Fig. 1a and b displays
well-defined XRD patterns observed and all diffraction peaks
were perfectly indexed to the XRD pattern of undoped boehmite
XRD analyses were performed on a PANalytical X’Pert PRO X-
ray diffractometer (radius: 240.0 mm). Incident X-ray radiation was

J. Yang et al. / Thermochimica Acta 483 (2009) 29–35
31
Fig. 2. TEM images of the synthetic nanofibers with 3-day hydrothermal treatment: (a) undoped boehmite, (b) 3% Cr-doped and (c) 5% Cr-doped.
(
JCPDS card 01-083-2384). No XRD peaks representing other crys-
shows the TEM images of (a) undoped boehmite, (b) 3% Cr-doped
talline phases were detected, indicating that the chromium doped
nanofibers of the synthetic boehmite exhibited excellent crys-
tallinity and a high purity. Fig. 1a shows that the peaks are higher
and narrower with the increase of the hydrothermal treatment time
to 10 days, which means the crystals grew better as synthesis time
getting longer.
and (c) 5% Cr-doped. The figure clearly shows that the boehmite
is fibrous with very long narrow fibres often exceeding 500 nm in
length and with width of between 2 and 6 nm. Many of the fibres
are curved or bent as may be observed in Fig. 2c for the 5% Cr-doped
boehmite.
3.3. Thermogravimetric analysis
3.2. Transmission electron microscopy
The thermogravimetric analysis and the differential thermal
The transmission electron microscopy images of the synthesised
undoped and Cr-doped boehmite are shown in Fig. 2. The figure
analysis of nanostructured undoped boehmite and doped boehmite
with varying amounts of chromium dopant from 0 to 20% are

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J. Yang et al. / Thermochimica Acta 483 (2009) 29–35
shown. The thermal analysis pattern of undoped boehmite is
displayed in Fig. 3a. Fig. 3b reports the effect of hydrothermal treat-
ment time on the formation of boehmite nanofibres. Fig. 4 shows
the effect of the % of doping on the thermal analysis of Cr doped
boehmite. The results of the thermal analyses are summarised in
Table 1.
mass loss of 15.8%. The thermal decomposition occurs as fol-
lows: 2AlO(OH) → Al O + H O. This major decomposition step is
2
3
2
attributed to the dehydroxylation of the boehmite. Two low mass
◦
loss steps at 45 and 260 C with mass losses of 1.5 and 1.7% are also
observed. The first mass loss step is assigned to the dehydration of
boehmite (Column 1 in Table 1)
The TG of the undoped boehmite shows a strongly asym-
The thermal decomposition of 1% doped boehmite with 1 day
hydrothermal treatment shows three mass loss steps at 46, 311
◦
metric curve with
a
peak temperature of 406.5 C and
a
Fig. 3. Thermal analysis patterns of (a) undoped boehmite nanofibres and 1% Cr doped boehmite nanofibers with different hydrothermal treatment time: (b) 1 day, (c) 3
days, (d) 5 days, and (e) 10 days.

J. Yang et al. / Thermochimica Acta 483 (2009) 29–35
33
Fig. 3. (Continued ).
◦
and 403 C with mass losses of 1.7, 6.6 and 11.0% (Fig. 3b). The
The variation in the % chromium doping on the thermal analysis
patterns and decomposition of boehmite is explored in Fig. 4a–d.
The thermal analysis patterns of 3% Cr doped boehmite hydrother-
mally treatment for 3 days shows three mass loss steps at 46,
asymmetry observed in Fig. 3a is no longer observed but a second
peak at 311 C is found. The thermal decomposition of 1% doped
boehmite with 3 day hydrothermal treatment shows three mass
loss steps at 50, 321 and 419.5 C with mass losses of 1.0, 4.8 and
◦
◦
◦
315 and 427 C with mass losses of 1.1, 2.9, and 12.4%. The
◦
1
1.5% (Fig. 3c). The thermal decomposition of 1% doped boehmite
dehydroxylation peak at 427 C is sharp indicating that the dehy-
with 5 day hydrothermal treatment shows three mass loss steps at
droxylation occurs over a very narrow temperature range. For the
5% Cr doped boehmite the dehydroxylation step is observed at
430.5 C with a mass loss of 13.1%. For the 10% Cr doped boehmite
◦
51, 328 and 423 C with mass losses of 0.8, 3.9 and 12.1% (Fig. 3d).
◦
The results of the 1% Cr doped boehmite hydrothermally treated
◦
for 10 days (Fig. 3e) shows a large mass loss step at 435 C with
hydrothermally treated for 3 days results in a sharp mass loss
◦
◦
a mass loss of 12.2%. In addition two smaller mass loss steps at
peak at 433 C with minor mass loss steps at 50 and 380 C.
◦
◦
5
4 and 342 C with mass losses of 0.7 and 3.1% are observed. It is
The temperature for the Cr 20% doped boehmite is 436.5 C. The
apparent that thermal decomposition temperature of the Cr doped
boehmite varies with the hydrothermal treatment time. This vari-
ation is reported in Fig. 5.
variation in the temperature of the decomposition of boehmite
as a function of % doping is reported in Fig. 6. It is apparent
that as the % of Cr is increased in the boehmite the dehy-
Table 1
Results of the thermal analysis of the undoped and various % Cr doped boehmite nanofibers.
Sample
Decomposition steps
Step 1
Peaks
Total mass loss
Step 2
Step 3
Peak 1
Peak 2
Peak 3
406.5
◦
◦
◦
◦
Boehmite
1.5%
1.7%
1.0%
0.8%
0.7%
1.1%
0.8%
0.8%
1.0%
1.7%
6.6%
4.8%
3.9%
3.1%
2.9%
2.1%
–
15.8%
11.0%
11.5%
12.1%
12.2%
12.4%
13.1%
15.1%
15.0%
45
46
50
51
54
46
48
50
50
C
C
C
C
C
C
C
C
C
260
311
321
328
342
315
325
380
330
C
C
C
C
C
C
C
C
C
C
C
19.0%
19.3%
17.3%
16.8%
16.0%
16.4%
16.0%
15.9%
16.0%
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
1% – 1 d
1% – 3 d
1% – 5 d
1% – 10 d
3% – 3 d
5% – 3 d
403 C
419.5
◦
◦
◦
423
435
427
C
C
C
◦
◦
430.5
C
C
◦
10% – 3 d
433
C
2
0% – 3 d
–
436.5
*“d” means “days of hydrothermal treatment”.

34
J. Yang et al. / Thermochimica Acta 483 (2009) 29–35
Fig. 4. Thermal analysis patterns of various % Cr-doped boehmite nanofibers with 3-day hydrothermal treatment: (a) 3%, (b) 5%, (c) 10%, and (d) 20%.

J. Yang et al. / Thermochimica Acta 483 (2009) 29–35
35
dehydroxylation temperature shows a small steady increase up
to the 20% doping level. The associated mass loss decreases and
then shows a constant mass loss. The variation of mass loss and
dehydroxylation temperature with hydrothermal treatment time is
illustrated in Fig. 7. The temperature of dehydroxylation increases
with time of hydrothermal treatment.
4. Conclusions
Boehmite and chromium doped boehmite were synthesised
by low temperature precipitation from aqueous solution and
hydrothermally treated for differing time intervals. Very long
nanofibres were produced often exceeding 500 nm in length. Nor-
mally at above the 5% doping level a mixture of nanofibres are
produced.
Fig. 5. Dehydroxylation temperature of the DTG peak as a function of added Cr
content and with the hydrothermal treatment time.
Doping with chromium resulted in an increase in the dehy-
◦
droxylation temperature of boehmite from ∼406.5 to 436.5 C. The
temperature of dehydroxylation increases with time of hydrother-
mal treatment. The dehydroxylation temperature increases sig-
nificantly from 0 to 5% doping, after which the dehydroxylation
temperature shows a small steady increase up to the 20% doping
level.
Acknowledgements
The financial and infra-structure support of the Queensland Uni-
versity of Technology Inorganic Materials Research Program of the
School of Physical and Chemical Sciences is gratefully acknowl-
edged. The Australian Research Council (ARC) is thanked for funding
the instrumentation.
Fig. 6. Temperature of the main dTGA peak and the total mass loss percentage as a
function of added Cr content.
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