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
Wang, Peng
