Improve the catalytic activity of α-Fe2O3 particles in decomposition of ammonium perchlorate by coating amorphous carbon on their surface

Article abstract of DOI:10.1016/j.jssc.2010.12.004

Sphere- and pod-like α-Fe₂O₃ particles have been selectively synthesized using NH₃·H₂O and NaOH solution to adjust the pH value of the designed synthetic system, respectively. The sphere-like α-Fe₂O

Full text of DOI:10.1016/j.jssc.2010.12.004

Journal of Solid State Chemistry 184 (2011) 387–390
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Improve the catalytic activity of
ammonium perchlorate by coating amorphous carbon on their surface
a
-Fe2O3 particles in decomposition of
n
Yifu Zhang a, Xinghai Liu b,n, Jiaorong Nie c, Lei Yu a, Yalan Zhong a, Chi Huang a,
a Engineering Research Center of Organosilicon Compound and Material, Ministry of Education of China, College of Chemistry and Molecular Sciences, Wuhan University,
Wuhan 430072, PR China
b School of Printing and Packaging, Wuhan University, Wuhan 430079, PR China
c Jianghe Chemical Factory of CSSG, Yuan’an 444200, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Sphere- and pod-like
a
-Fe2O3 particles have been selectively synthesized using NH3 ꢀ H2O and NaOH solution to
-Fe2O3 particles with
diameter about 25 nm on average were encapsulated into carbon shells to fabricate a novel core–shell
composite ( -Fe2O3@C) through the coating experiments. The catalytic performance of the products on the
Received 25 July 2010
Received in revised form
24 November 2010
adjust the pH value of the designed synthetic system, respectively. The sphere-like
a
a
Accepted 1 December 2010
Available online 7 December 2010
thermal decomposition of ammonium perchlorate (AP) was investigated by thermal gravimetric analyzer (TG)
and differential thermal analysis (DTA). The thermal decomposition temperatures of AP in the presence of pod-
Keywords:
like
a
a
-Fe2O3, sphere-like
a
-Fe2O3 and
a
-Fe2O3@C are reduced by 72, 81 and 109 1C, respectively, which show
-Fe2O3.
Nanocomposites
Nanomaterials
Core–shell
that
-Fe2O3@C core–shell composites have higher catalytic activity than that of a
& 2010 Elsevier Inc. All rights reserved.
a
a
-Fe2O3@C
-Fe2O3
Ammonium perchlorate
1. Introduction
catalytic performance can be improved by the nanometer-scale
catalysts [10–13]. Recent researches indicate that ferric oxides are
proved to be quite effective on the thermal decomposition of AP
[14–16]. In this paper, we will introduce the novel amorphous
carbon containing aromatic structures as shells to enhance the
catalytic activities of ferric oxides in the decomposition of AP.
In past decades, core–shell nanostructures have been paid more and
more attentions owing to their tunable surface properties, which can
enhance their magnetic, electronic, optical and catalytic properties [1].
The core–shell materials may retain the properties of both cores and
shells, which could afford composite properties in one system. Con-
sequently, these novel materials have potential applications in diverse
technological fields such as semiconductor electronics and biomedical
industries [1–4]. Recently, core–shell structured nanoparticles with a
carbon shell have stimulated great interest. A series of work has been
focused on the synthesis of metal@C and metal oxides@C core–shell
composites (e.g. Ag@C, Fe3O4@C, V2O3@C, etc.), and most of these new
unique materials with amorphous carbon show some novel properties,
which have been widely applied to lithium ion battery and catalyst
[5–9]. However, to our best knowledge, the introduction of this
amorphous carbon containing aromatic structures into the catalytic
decomposition of ammonium perchlorate (AP) has not been reported.
As is well known, AP is one of the most common oxidizing agents that
have been used in various propellants and its thermal decomposition
characteristics influence the combustion behavior of the solid propel-
lant directly. The catalytic activities of some catalysts in the thermal
decomposition of an AP have been reported and it was found that
Herein, we reported that the sphere- and pod-like
were selectively synthesized by a facile hydrothermal approach. Then,
-Fe2O3@C core–shell nanocomposites were prepared using the as-
obtained sphere-like -Fe2O3 as the cores and glucose as the resources
a-Fe2O3 particles
a
a
of carbon by an environmental hydrothermal method. At last, all of the
above products were mixed with AP and their catalytic performances
on the thermal decomposition of AP were investigated by DTA. The
results revealed that the
higher catalytic activity on the thermal decomposition of AP than that
of only -Fe2O3.
a-Fe2O3@C core–shell composites have much
a
2. Experimental section
2.1. Synthesis of sphere- and pod-like a-Fe2O3 nanoparticles
All the reagents purchased from Sinopharm Chemical Reagent
Co., Ltd. were of analytic grade and used without any further puri-
fication. In a typical procedure, 3.00 g of FeCl3, 4.67 g of H2C2O4 ꢀ 2
H2O, 20 mL of distilled water (H2O) and 1.68 g of cetyltriethy-
lammnonium bromide (CTAB: C19H42BrN) were orderly added into
n Corresponding authors. Fax: +86 27 68754067.
E-mail addresses: liuxh@whu.edu.cn (X. Liu), chihuang@whu.edu.cn (C. Huang).
0022-4596/$ - see front matter & 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2010.12.004

388
Y. Zhang et al. / Journal of Solid State Chemistry 184 (2011) 387–390
a 50 mL of beaker and mixed with vigorously magnetic stirring for
30 min. Then, NH3 ꢀ H2O (10 wt%) or NaOH (10 wt%) was added
dropwise to adjust the pH value under continuous stirring. After the
pH value was adjusted to about 4, all the suspension were transferred
into a 40 mL teflon lined stainless steel autoclave, which was sealed
and maintained at 100 1C for 24 h. After cooling to room temperature
naturally, the samples were filtered off, washed with distilled water
and absolute ethanol several times and dried in vacuum at 75 1C for
12 h. Finally,
a-Fe2O3 nanoparticles were obtained by calcining the
above samples at 300 1C for 6 h in air atmosphere.
2.2. Synthesis of
a-Fe2O3@C core–shell nanocomposites
To synthesize
a-Fe2O3@C core–shell structure, the sphere-like
a
-Fe2O3 nanoparticles with small diameter were selected due to their
large specific surface. In the experiment, 0.32 g of the as-obtained
-Fe2O3 nanoparticles were dispersed into 20 mL of distilled water by
ultrasonic wave for 10 min. In order to modify the surface of -Fe2O3
a
a
nanoparticles and improve the coated process, the diluted HNO3 was
dropped slowly to adjust the pH value to about 3 [3]. After the mixture
was filtered off, the substrate solid was dispersed into the glucose
solution (4.00 g of glucose and 30 mL of distilled water) under
ultrasonic wave for 30 min. The suspension was transferred into a
40 mL teflon lined stainless steel autoclave, which was sealed and
maintained at 180 1C for 4 h. After cooling to room temperature
naturally, the samples were filtered off, washed with distilled water
and absolute ethanol several times, and dried in vacuum at 75 1C
Fig. 1. XRD patterns of the products: (a) sphere-like
NH3 ꢀ H2O adjusting pH; (b) pod-like -Fe2O3 nanoparticles with an NaOH adjusting
pH; (c) -Fe2O3@C core–shell composites; and (d) pure carbon.
a-Fe2O3 nanoparticles with
a
a
carbon [3]. Furthermore, the disorganized background results from
amorphous carbon coating on the surface of -Fe2O3 compared
Fig. 1c with Fig. 1d. These results reveal that the as-synthesized
product might be -Fe2O3@C core–shell composites. Further
information about the structure of the carbon shell coating on
the surface of -Fe2O3 was investigated by Raman spectrum, which
was represented in Fig. S1 (Supplementary data). A typical Raman
spectrum of -Fe2O3@C core–shell composites exhibits two main
a
for 12 h. Finally, a-Fe2O3@C core–shell nanoparticles were obtained by
calcining the above samples at 500 1C for 2 h in N2 atmosphere.
a
a
2.3. Characterization
a
The purity and crystalline structure of the resulting products were
peaks. The peaks located at 1360 cmꢁ1 (D-band) and 1599 cmꢁ1
(G-band) are attributed to the in-plane vibration of the disordered
amorphous carbon and the in-plane vibrations of the crystalline
graphite, respectively, which are the same as those of amorphous
carbon [6,18]. The D-band is relatively high, further proving that
the coating comprises disordered carbon. Therefore, the Raman
investigated by the X-ray powder diffraction (XRD, D8 X-ray diffract-
˚
ometer equipment with Cu Ka radiation, l¼1.54060 A). The Raman
spectrum was collected on a RM-1000 spectrometer with an argon-ion
laser at an excitation wavelength of 514.5 nm. The chemical composi-
tion of the as-obtained samples was revealed by use of an energy-
dispersive X-ray spectrometer (EDX) attached to a scanning electron
microscope (SEM; Quanta 200). The morphologies of the products were
observed by the transmission electron microscopy (TEM, JEM-100CXII).
The elemental analysis (EA) of the samples was carried out using Vario
EL III equipment (Germany) with TCD detector to analyze the element
of C, H, N and S. Fourier transform infrared spectroscopy (FT-IR) pattern
was recorded on Nicolet 60-SXB spectrometer from 4000 to 400 cmꢁ1
with a resolution of 4 cmꢁ1. Thermo-gravimetric analysis and differ-
ential thermal analysis (TG/DTA) measurements were performed on
Diamond TG-DTA 6300 at a heating rate of 10 1C minꢁ1 in N2 atmo-
sphere in the range of 25–500 1C with Al2O3 as reference. The
homogeneous mixture of product and AP was used for the DTA
experiment, and the mass ratios of products to AP were 3:97.
spectrum shows that the carbon in
a-Fe2O3@C sample is disor-
dered, in agreement with the XRD pattern observations.
Fig. 2 represents the typical TEM images of the as-synthesized
a
-Fe2O3 nanoparticles and
pH value is adjusted by NH3 ꢀ H2O, the morphology of the
nanoparticles is a sphere with diameter about 25 nm on an average, as
shown in Fig. 2a and b. However, the pod-like -Fe2O3 particles with
a
-Fe2O3@C core–shell composite. When the
a-Fe2O3
a
the major axis of about 314 nm and the minor axis about 138 nm on an
average (Fig. 2c) are synthesized when the pH value is adjusted by an
NaOH solution. Thus, a-Fe2O3 particles with different morphologies are
obtained using NH3 ꢀ H2O and NaOH to adjust the pH value. As is well
known, NH3 ꢀ H2O is a weak base, while NaOH is a strong base, which
might be the reason that the sphere- and pod-like
have been selectively synthesized. The TEM images of
a
a
-Fe2O3 particles
-Fe2O3@C core–
shell composites are shown in Fig. 2d and e. We can observe that the
samples consist of well-dispersed particles with an average size
ranging 30–50 nm, and the contrast grade between core and shell
could even be observed, implying that the core–shell structure (inset
3. Results and discussion
Fig. 1 shows the typical XRD patterns of the resulting products.
All the diffraction peaks in Fig. 1a and b can be readily indexed as
Fig. 2d and e) has been formed. The deep background is a-Fe2O3, while
the rhombohedral crystalline phase (space group R-3c) of a-Fe2O3
with calculated lattice parameters a¼5.026, c¼13.752, which
corresponds to (JCPDS, no. 89-596) already described in the
literature [17]. No peaks of any other phases are detected from
the shallow background is amorphous carbon with thickness of about
12 nm on average. It is worth noting that, after the coating process, the
core–shell particles scatter relatively better than that of sphere-like
the XRD pattern, indicating the as-prepared
high purity. All the diffraction peaks in Fig. 1c could be readily
indexed as rhombohedral -Fe2O3, revealing that the crystalline
phase is pure -Fe2O3. However, the broadened peak ranging
15–301 can also be observed, which is attributed to amorphous
a
-Fe2O3 particles are of
a-Fe2O3 particles and the as-synthesized a-Fe2O3@C core–shell mate-
rials are slightly cross-linked. It is their surface coated the colloidal
carbon that contain lots of active function groups, which is in
accordance with the FT-IR result discussed in the following
a
a
section. The possible formation mechanism of a-Fe2O3@C core–shell

Y. Zhang et al. / Journal of Solid State Chemistry 184 (2011) 387–390
389
Fig. 2. (a) and (b) TEM images of
a
-Fe2O3 with NH3 ꢀ H2O adjusted the pH value; (c) TEM image of
a
-Fe2O3 with NaOH adjusted the pH value; (d) and (e) TEM images of
a-Fe2O3@C core–shell composites, inset enlarged drawings; and (f) schematic illustration of the synthesis of
a
-Fe2O3@C core–shell structure.
composites is schematically illustrated in Fig. 2f. First,
are dispersed into the glucose solution. Then, the glucose molecules are
absorbed on the surface of -Fe2O3 particles. This process can be due to
the surface of -Fe2O3 particles containing some active function groups
a-Fe2O3 particles
a
a
after diluted HNO3 modifying, which is similar with the synthesis of
Fe3O4@C [3]. Last, the glucose is undergoing dehydration, polymeriza-
tion and carbonization, leading to the amorphous carbon with aromatic
structure is finally formed on the surface of
a-Fe2O3 particles, in
agreement with the formation of colloidal carbon spheres [19].
More information about the composition of the core–shell struc-
tured materials was collected by the EDX, EA and FT-IR measurements.
The typical EDX spectrum of
a-Fe2O3@C core–shell composite was
shown in Fig. S2 (Supplementary data), while it reveals that this novel
core–shell composite contains only Fe, C and O elements. An EA of
a
-Fe2O3@C shows that it contains C (12.34 wt%) and H (1.08 wt%),
indicating that this core–shell material probably contains some organic
functional groups, which is further confirmed by FT-IR (Fig. S3,
Supplementary data). According to the spectrum, we find that C¼O
and C¼C groups exist in
a-Fe2O3@C core–shell composites, which
supports the concept of aromatization of glucose during the hydro-
thermal reaction [19]. The peak at 3360 cmꢁ1 implies the existence of
residual hydroxyl groups and the peaks located at 3000–2850 cmꢁ1 is
the characteristic C–H stretches. The results reveal that there are lots of
active function groups such as C¼O, C¼C and –OH groups in this core–
shell composites, which will facilitate the linkage of catalytic species or
biomolecules to the surface in the potential application [8,19,20].
Fig. 3. DTA curves for: (a) pure AP; (b) pod-like
-Fe2O3 and AP; and (d) -Fe2O3@C and AP.
a-Fe2O3 and AP; (c) sphere-like
a
a
a-Fe2O3, sphere-like a-Fe2O3 and a-Fe2O3@C core–shell structure
materials were, represented in Fig. S4 (Supplementary data) and
Fig. 3. It can be observed from Fig. S4 that the addition of the as-
obtained products in AP led to a significant reduction of the ending
decomposition temperature of AP. Only two thermal signals can be
observed for the mixture of AP and products, which compares to the
three obvious peaks for pure AP. The first endothermic peak at 247 1C is
The pod-like
a-Fe2O3, sphere-like a-Fe2O3 and a-Fe2O3@C were
explored as an additive to the thermal decomposition of ammonium
perchlorate (AP), the key component of composite solid propellants.
The TG and DTA curves of pure AP and AP in the presence of pod-like

390
Y. Zhang et al. / Journal of Solid State Chemistry 184 (2011) 387–390
due to the crystal transformation of AP from an orthorhombic to cubic
phase [21] and the additives have little effect on this crystallographic
transition temperature. It is seen that there are two obvious exothermic
peaks centered at about 314 and 452 1C on the DTA curve of pure AP
(Fig. 3a), which are attributed to the low-temperature decomposition
and high-temperature decomposition, respectively [21]. As seen in
Fig. 3b–d, the low-temperature exothermic peak of AP decomposition
has nearly disappeared. However, the high-temperature exothermic
peak of AP shifts to a lower temperature at 380, 371 and 343 1C. From
temperatures of AP in the presence of pod-like
-Fe2O3 and -Fe2O3@C are reduced to 72, 81 and 109 1C, respec-
tively. Thus, the -Fe2O3@C core–shell composites have much higher
catalytic activity on the thermal decomposition of AP than that of
-Fe2O3, indicating the core–shell composites have better potential
a-Fe2O3, sphere-like
a
a
a
a
applications.
Acknowledgments
above analyses, it can be concluded that a-Fe2O3@C has higher catalytic
This work was partially supported by the National Science Fund
for Fostering Talents in Basic Science (J0730426), Natural Science
Foundation of Hubei Province (2005ABA034), Students’ Scientific
Research Program of Wuhan University (2007138), The Fourth
Installment of Science and Technology Development 2010 Program
of Suzhou (SYG201001) and Key Laboratory of Catalysis and
Materials Science of Hubei Province (CHCL06003). We thank Mr.
Shaobo Mo and Mrs. Ling Hu concerning the help of TEM and XRD.
activity towards the thermal decomposition of AP than that of
a-Fe2O3,
which is corresponding with the suggested result of FT-IR.
According to the previous reports [14,15,22], the decomposition
of AP consists essentially of three steps:
(1) 240–250 1C: the crystal transformation from orthorhombic to
cubic phase;
(2) 300–330 1C: the first decomposition step—a solid-gas
multiphase reaction, including decomposition and sublimation
shown as follows:NH4ClO4-NH4+ +ClO4ꢁ-NH3(g)+HClO4(g);
(3) 450–480 1C: the second decomposition step—NH3 and HClO4
react after entering the gas phase, and the products are N2O, O2,
Cl2, H2O and few NO.
Appendix A. Supplementary material
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.jssc.2010.12.004.
From our experimental results, we can deduce that the additives
can catalytically decompose AP via the third step, because the
temperature of the high-temperature exothermic decomposition
process was reduced during the process, indicating that the
catalytic mechanism is probably changed. According to the tradi-
tional electron-transfer theory [13,23], for one thing, the presence
of partially filled 3d orbit in Fe3+ provides help in an electro-
transfer process. Positive hole in an Fe2O3 can accept electrons from
AP ion and its intermediate products enhancing the thermal
decomposition of AP. So, the better catalytic activity of sphere-
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a
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experiments. The carbon shell is amorphous carbon with lots of active
function groups, which promotes the catalytic performance of
a-Fe2O3. The results of DTA illustrate that the decomposition