Effects of surfactants on the microstructure characteristics of alumina microfibers

Article abstract of DOI:10.14233/ajchem.2013.14985

Alumina microfibers were synthesized using different types of surfactants (rosin-based quaternary ammonium salt, sodium dodecyl sulphate and triblock copolymer P123 as directing agents. Their structures were characterized with X-ray diffraction, N2 adsorption and desorption, field-emission scanning electron microscope and transmission electron microscopy to investigate the effects of surfactants on the microstructure characteristics of alumina microfibers. The surfactants can not change the intrinsic crystal structure of the as-syntheiszed ammonium aluminium carbonate hydroxide with the composition (NH₄[Al(OH)₂CO₃]) (AACH), but they will alter the way of the growth of the AACH nanocrystals. Because of the strong electrostatic interaction between AACH nanocrystals and ionic surfactants (rosin-based quaternary ammonium salt and sodium dodecyl sulphate), the AACH microfibers grew too fast on the surfactant micelles to form regular fibrous morphologies. When the non-ionic surfactant P123 was used as the template, due to the weak hydrogen bond interaction, the AACH microfibers grew at an appropriate speed to form a uniform fibrous morphology.

Full text of DOI:10.14233/ajchem.2013.14985

Asian Journal of Chemistry; Vol. 25, No. 16 (2013), 9055-9058
http://dx.doi.org/10.14233/ajchem.2013.14985
Effects of Surfactants on the Microstructure Characteristics of Alumina Microfibers
1,*
2
1
1
1
1
PENG WANG , ZHENDONG ZHAO , ZONGDE WANG , MIN HUANG , SHANGXING CHEN and GUORONG FAN
1College of Forest, Jiangxi Agriculture University, Nanchang 330045, P.R. China
2Institute of Chemical Industry of Forest Products, CAF; National Engineering Lab. for Biomass Chemical Utilization; Key and Open Lab. on
Forest Chemical Engineering, SFA, Nanjing 210042, P.R. China
*Corresponding author: Tel: +86 791 83828029; E-mail: pengwang1981@126.com
(Received: 15 December 2012;
Accepted: 16 September 2013)
AJC-14112
Alumina microfibers were synthesized using different types of surfactants (rosin-based quaternary ammonium salt, sodium dodecyl
sulphate and triblock copolymer P123 as directing agents. Their structures were characterized with X-ray diffraction, N2 adsorption and
desorption, field-emission scanning electron microscope and transmission electron microscopy to investigate the effects of surfactants on
the microstructure characteristics of alumina microfibers. The surfactants can not change the intrinsic crystal structure of the as-syntheiszed
ammonium aluminium carbonate hydroxide with the composition (NH4[Al(OH)2CO3]) (AACH), but they will alter the way of the growth
of the AACH nanocrystals. Because of the strong electrostatic interaction between AACH nanocrystals and ionic surfactants (rosin-based
quaternary ammonium salt and sodium dodecyl sulphate), the AACH microfibers grew too fast on the surfactant micelles to form regular
fibrous morphologies. When the non-ionic surfactant P123 was used as the template, due to the weak hydrogen bond interaction, the
AACH microfibers grew at an appropriate speed to form a uniform fibrous morphology.
Key Words: Alumina microfiber, Morphology, Surfactant, Rosin-based quaternary ammonium salt.
three-dimensional dumbbells, flower-like hierarchical super-
structures were obtained by Liu et al.11 using cetyltrimethyl-
ammonium bromide and sodium dodecyl sulphate as directing
agents.
INTRODUCTION
Because of the rich porosities and large surface areas as
well as the outstanding thermal and mechanical stabilities,
mesoporous alumina are widely used in the areas of catalysis,
separation and adsorption1-3. However, the preformances of
mesoporous alumina depend not only on their porosities and
surface areas, but also on their morphologies. Special mor-
phologies often bring mesoporous alumina with varieties of
physical and chemical properties, such as high dielectric
constant, large mechanical modulus, etc.4,5.
We have developed a facile and economic ammonium
carbonate precipitation method for preparing mesoporous
alumina microfibers in our previous work12. In the present
work, different types of surfactants (cationic, anionic and non-
ionic surfactants) were introduced in the process of ammonium
carbonate precipitation method for the synthesis of alumina
microfibers. The influences of the surfactants on the micro-
structure characteristics of the materials were investigated.
Surfactants play a crucial role in the morphology modifi-
cation process of mesoporous aluminas. Several researchers
have demonstrated the synthesis of mesoporous alumina with
various shapes using different kinds of surfactants. Su et al.6
demonstrated the synthesis of lamellate structure mesoporous
alumina with the assistance of non-ionic surfactant PEG6000
usingAl2(SO4)3 and NaAlO2 as aluminum precursors. Bai et al.7
prepared mesoporous alumina microfibers under hydrothermal
conditions using tri-block copolymer P123 as directing agent
and urea as homogeneous precipitation agent. Through the
same method, multilayered alumina microfibers and alumina
nanorods were successfully synthesized by Zhu et al.8-10 using
different kinds of PEG (polyethylene glycol) as directing
agents. Mesoporous aluminas with spheres, rods, fibers and
EXPERIMENTAL
Rosin-based quaternary ammonium salt13 [(RSAC), tech-
nical grade, principal component: abietyltrimethyl ammonium
chloride] was provided by Henan Titaning Chemical Tech-
nology Co., Ltd. Sodium dodecyl sulphate (SDS, AR) was
purchased from Chengdu Kelong Reagent Chemical Factory.
Triblock copolymer (PEO)20-(PPO)70-(PEO)20, namely P123,
was provided by Sigma-Aldrich Co. Aluminium nitrate
nonahydrate (AR) was purchased from Shanghai Zhenxin
Reagent Chemical Factory. Ammonium carbonate (AR) was
provided by Guangdong Chemical Reagent Engineering-
Technological Research and Development Center.

9056 Wang et al.
Asian J. Chem.
General procedure: In a typical experiment, three kinds
XRD patterns of calcined samples are shown in Fig. 2.
The sample of A-RSAC displays diffraction lines of the γ-
Al2O3 phase (JCPDS card No. 10-425). The other two samples
only exhibit two broad humps, implying the existence of
amorphous aluminas.Although the surfactants can not change
the intrinsic crystal structure of precursor, but they have a great
impact on crystalline structure of the samples after calcination.
The season for this phenomenon can be related to the residue
of the Cl– ion from RSAC in calcination.
of surfactants (RSAC, SDS and P123) were dissolved in 50 mL
0.5 mol/L aluminium nitrate solution at 343 K, respectively.
The molar ratio of aluminium nitrate to sufactants was 1:0.02.
150 mL of 0.5 mol/L ammonium carbonate solution was then
added while stirred. After stirring for 2 h, the precipitate was
aged at 343 K for 18 h and washed with water and ethanol for
several times. After drying at 323 K, the template agents were
removed by calcination at 833 K for 4 h at the rate of 1 K/min.
The results were denoted as A-RSAC, A-SDS and A-P123.
Detection method: The crystalline phases of the samples
were recorded by an X-ray diffractometer (D8 Focus, Bucker
AXS Inc., Germany) with CuKα radiation (k = 0.154 nm).
The operating target voltage was 40 kV and the current was
40 mA. The sample was powdered and scanned for 2θ ranging
from 10-80º. Porosity and surface area measurements were
performed following the N2 adsorption on a Micromeritics
ASAP2020 instrument made by Micromeritics Instrument
Corporation. The special surface areas were calculated using
the Brunauer-Emmett-Teller (BET) model. Average pore dia-
meters were calculated using the Barrett-Joyner-Halenda (BJH)
method from the desorption branch of isotherm. The micro-
scopic features of the samples were characterized with a field-
emission scanning electron microscope (S-4800 HITACHI,
Japan) operated at 5 KV. Transmission electron microscopy
images were obtained with a JEOL JEM-2100 instrument
operated at an accelerating voltage of 200 kV. The samples
were ultrasonically dispersed in ethanol and then dropped onto
the carbon-coated copper grids prior to the measurements.
1400
1300
1200
1100
1000
900
800
A-P123
700
600
500
A-SDS
400
300
A-RSAC
200
100
0
10
20
30
40
50
60
70
80
2θ (°)
2 θ (°)
Fig. 2. XRD patterns of calcined alumina microfibers
Fig. 3 shows the N2 adsorption-desorption isotherms of
the calcined alumina microfibers. All the samples exhibit
classical type IV isotherm (classification by IUPAC) which is
a characteristic of mesoporous material. The hysteresis loops
of the samples are different, indicating that there are great
differences in pore structures of the samples. BJH pore size
distributions of the samples are depicted in Fig. 4. The curve
of the A-RSAC sample displays a bimodal pattern. The pores
with the smaller sizes bear concentrate distribution at 3.8 nm,
while those with the larger sizes possess broad distribution in
the range of 5.5-14 nm. The curves of the samplesA-SDS and
A-P123 exhibit a single peak distribution centered at 3.8 nm.
Table-1 summarizes the textural properties of the three samples.
It can be noted that all the samples possess big specific surface
areas. The sample A-SDS shows the biggest specific surface
area (369.45 m2/g), the highest pore volume (0.62 cm3/g) and
the largest pore diameter (5.74 nm).
RESULTS AND DISCUSSION
Fig. 1 shows the XRD patterns of the as-synthesized
alumina microfibers. All the peaks of the samples can be
indexed to the data available in the JCPDS 42-0250 powder
diffraction file, indicating that all the samples contain only a
AACH (NH4[Al(OH)2CO3]) crystalline phase. No distinct dis-
similarity can be observed from the patterns of the as-synthe-
sized samples, suggesting that surfactants can not change the
intrinsic crystal structure of AACH. This result is similar to
Zhu et al.14 report.
25000
20000
15000
Fig. 5 shows the field-emission SEM images of as-synthe-
sized and calcined samples. All the as-synthesized samples
reveal a fibrous morphology (Fig. 5a-e) due to the formation
ofAACH. However, significant differences can also be observed
among the samples. The as-synthesized microfibers directed
by RSAC are various in sizes and wider than the other two
samples (Fig. 5a), while the ones synthesized by SDS are
shorter with an obvious sense of fragmentation (Fig. 5c). Well
dispersed and uniform microfibers can be observed in the
image (Fig. 5e) of the sample templated by P123. Thus, the
surfactants have great effects on the morphologies of the
samples.Although the surfactants can not change the intrinsic
crystal structure of AACH, but they will alter the way of the
growth of theAACH nanocrystals. Different types of surfactants
10000
A-P123
5000
A-SDS
A-RSAC
0
10
20
30
40
50
60
70
80
2θ (°)
2 θ (°)
Fig. 1. XRD patterns of the as-synthesized alumina microfibers

Vol. 25, No. 16 (2013)
Effects of Surfactants on the Microstructure Characteristics of Alumina Microfibers 9057
420
400
380
360
340
320
A-P123
300
280
260
240
220
A-SDS
200
180
160
140
120
A-RSAC
100
80
60
40
0.0
0.2
0.4
0.6
0.8
1.0
Relative Presure (P/P )
0
Fig. 3. N2 adsorption-desorption isotherms of calcined alumina microfibers
0.30
0.28
0.26
0.24
0.22
0.20
0.18
0.16
0.14
0.12
Fig. 5. Field emission SEM images of as-synthesized (a, c, e) and calcined
(b, d, f) alumina microfibers; a, b: A-RSAC; c,d: A-SDS; e,f: A-
P123
0.10
A-P123
0.08
electron microscopy was applied. All the calcined samples
display a fibrous morphology with wormhole-like mesopores
(Fig. 6). It can be seen that the edges of the A-RSAC sample
are rough (Fig. 6a-b), while theA-SDS sample shows obvious
fracture phenomenon of the microfibers (Fig. 6c-d). Only the
A-P123 sample is made of integrated microfibers with smooth
edges (Fig. 6e-f). The results are in good agreement with the
field emission SEM characterizations.
0.06
A-SDS
0.04
0.02
A-RSAC
0.00
-0.02
0
10
20
30
40
50
Pore Diameter (nm)
Fig. 4. BJH pore size distributions of calcined alumina microfibers
TABLE-1
TEXTURAL PROPERTIES OF
CALCINED ALUMINA MICROFIBERS
Sample
A-RSAC
A-SDS
SBET (m2/g)
V (cm3/g)
D (nm)
5.32
323.45
0.33
369.45
0.62
5.74
A-P123
298.75
0.36
4.85
possess various charging properties. When the surfactants of
RSAC and SDS were applied as the directing agents, the as-
synthesizedAACH nanocrystals were bonded to the surfactant
micelles through the electrostatic interaction in order to form
fibrous structures. However, due to this strong interaction, the
AACH microfibers grew so fast that the irregularly fibrous
morphologies were formed. When the surfactant P123 was
used as the template, theAACH nanocrystals and the surfactant
micelles was interacted with hydrogen bond which was weaker
than the electrostatic interaction. Thus, theAACH microfibers
grew at an appropriate speed to form a uniform fibrous morpho-
logy. It can be seen that the morphology of the alumina samples
was not markedly altered after the calcination at 833 K for 4 h
(Fig. 5b-f).
For further investigation of the morphology and micro-
structures of the calcined alumina microfibers, transmission
Fig. 6. TEM images of calcined alumina microfibers; a, b: A-RSAC; c,d:
A-SDS; e,f: A-P123

9058 Wang et al.
Asian J. Chem.
Conclusion
REFERENCES
Different types of surfactants (RSAC, SDS and P123) were
1. M.E. Doukkali, A. Iriondo, P.L. Arias, J. Requies, I. Gandarías, L.
Jalowiecki-Duhamel and F. Dumeignil, Appl. Catal. B, 125, 516 (2012).
2. C. Chen and W.-S. Ahn, Chem. Eng. J., 166, 646 (2011).
3. B. Yahyaei and S. Azizian, Chem. Eng. J., 209, 589 (2012).
4. J. Zou, L. Pu, X. Bao and D. Feng, Appl. Phys. Lett., 80, 1079 (2002).
5. X.S. Fang, C.H. Ye, L.D. Zhang and T. Xie, Adv. Mater., 17, 1661
(2005).
introduced in the process of the synthesis of alumina
microfibers. The effects of surfactants on the microstructure
characteristics of alumina microfibers were investigated. The
surfactants can not change the intrinsic crystal structure of the
as-syntheiszedAACH, but they will alter the way of the growth
of theAACH nanocrystals. Because of the strong electrostatic
interaction betweenAACH nanocrystals and ionic surfactants
(RSAC, SDS), the AACH microfibers grew too fast on the
surfactant micelles to form regular fibrous morphologies. When
the surfactant P123 was used as the template, due to the weak
hydrogen bond interaction, the AACH microfibers grew at an
appropriate speed to form a uniform fibrous morphology.
6. A. Su,Y. Zhou, Y. Yao, C.Yang and H. Du, Micropor. Mesopor. Mater.,
36, 159 (2012).
7. P. Bai, F. Su, P. Wu, L. Wang, F.Y. Lee, L. Lv, Z.F. Yan and X.S. Zhao,
Langmuir, 23, 4599 (2007).
8. Z. Zhu, H. Sun, H. Liu and D. Yang, J. Mater. Sci., 45, 46 (2010).
9. Z. Zhu, H. Liu, H. Sun and D. Yang, Chem. Eng. J., 155, 925 (2009).
10. Z. Zhu, H. Liu, H. Sun and D. Yang, Micropor. Mesopor. Mater., 123,
39 (2009).
11. Q. Liu, A. Wang, X. Wang and T. Zhang, Micropor. Mesopor. Mater.,
100, 35 (2007).
ACKNOWLEDGEMENTS
12. P. Wang, Z.D. Zhao, L.W. Bi,Y.X. Chen, L. Zhang and L.T. Sun, Mater.
Res. Innov., 16, 121 (2012).
This work was supported by the Jiangxi Agriculture
University Starting Foundation for Doctoral Research (grant
No. 09004314), the Natural Science Foundation of China
(grant No. 30972319) and the Joint Innovation of Industries,
Universities and Research Institutes Foundation (grant No.
BY2010112).
13. P. Wang, Z.D. Zhao, L.W. Bi and Y.X. Chen, Asian J. Chem., 24, 3439
(2012).
14. H.Y. Zhu, J.D. Riches and J.C. Barry, Chem. Mater., 14, 2086 (2002).