Synthesis of nano-CuI and its catalytic activity in the thermal decomposition of ammonium perchlorate

Article abstract of DOI:10.1007/s11164-013-1497-1

Nano-CuI was fabricated by an element-direct-reaction route at 40°C in acetonitrile, and used as a catalyst in the thermal decomposition of ammonium perchlorate. The effects of polyvinyl pirrolidone (PVP) as an additive in the preparation of the catalyst and the addition amount of the catalyst in thermal decomposition reaction on the catalytic activity were investigated. Meanwhile, the morphologies and composition of the catalyst were also identified by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The results showed that nano-CuI can remarkably decrease the higher decomposition temperature of ammonium perchlorate by more than 100°C, and that the temperature can be further reduced by using the nano-CuI catalyst with PVP as an additive in preparation. In addition, smaller crystallite size and increasing addition amount of nano-CuI in the thermal decomposition are favorable for improving its catalytic activity.

Full text of DOI:10.1007/s11164-013-1497-1

Res Chem Intermed
DOI 10.1007/s11164-013-1497-1
Synthesis of nano-CuI and its catalytic activity
in the thermal decomposition of ammonium perchlorate
Yaqing Liu
Chunsheng Liu
•
Yun Cheng
•
•
Shiqi Lv
•
•
Junling Lai
Genxiang Luo
Received: 10 October 2013 / Accepted: 25 November 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract Nano-CuI was fabricated by an element-direct-reaction route at 40 °C in
acetonitrile, and used as a catalyst in the thermal decomposition of ammonium
perchlorate. The effects of polyvinyl pirrolidone (PVP) as an additive in the prep-
aration of the catalyst and the addition amount of the catalyst in thermal decom-
position reaction on the catalytic activity were investigated. Meanwhile, the
morphologies and composition of the catalyst were also identified by X-ray dif-
fraction, scanning electron microscopy, transmission electron microscopy, and
energy dispersive X-ray spectroscopy. The results showed that nano-CuI can
remarkably decrease the higher decomposition temperature of ammonium per-
chlorate by more than 100 °C, and that the temperature can be further reduced by
using the nano-CuI catalyst with PVP as an additive in preparation. In addition,
smaller crystallite size and increasing addition amount of nano-CuI in the thermal
decomposition are favorable for improving its catalytic activity.
Keywords Element-direct-reaction ꢀ Nano-CuI ꢀ Ammonium perchlorate ꢀ
Thermal decomposition
Introduction
Ammonium perchlorate (AP) is one of the main oxidizing agents that have been
used in various propellants. The burning behavior of propellants is closely relevant
to the thermal decomposition of AP. The desired lower decomposition temperature
of AP can be obtained by the addition of small amounts of catalyst [1, 2]. The
catalytic activities of transition metal oxides, such as CuO, MgO, Fe O , and Cr O ,
2
3
2 3
Y. Liu ꢀ Y. Cheng ꢀ S. Lv ꢀ C. Liu ꢀ J. Lai ꢀ G. Luo (&)
Department of Chemistry, School of Chemistry and Materials Science, Liaoning Shihua University,
Fushun 113001, People’s Republic of China
e-mail: gxluo1965@163.com
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Y. Liu et al.
have been investigated in the thermal decomposition of AP [3–5]. Freeman and
Anderson [6] proposed that the rate-controlling mechanism was the transfer of an
electron from the perchlorate ion to a positive hole in p-type oxides. The results
have indicated that CuO and Cr O were the most active catalysts in the thermal
2
3
decomposition of AP [7–12]. In addition, transition metal and alloy fine particles
have also attracted much attention due to their catalysis in the thermal decompo-
sition of AP [13].
As an important transition metal compound, CuI has three crystalline phases of a,
b, and c. The low-temperature c-phase (cubic) behaves as a p-type semiconductor.
The direct fundamental band gap of CuI was reported as 3.0 eV [14]. CuI is widely
used in many fields, such as catalysts and adsorbents for some reactions [15–18],
superionic conductor [19], and solid-state solar cells [20–23]. So far, a variety of
physical and chemical approaches have already been developed for preparing nano-
CuI, including electrodeposition [24], hydrothermal [25], pulse laser deposition
[
26–28], and vacuum evaporation [29]. However, all these methods have some
limitations. Therefore, it is important to develop a new and facile synthesis route of
nano-CuI for practical application.
The element-direct-reaction (EDR) route is a synthesis method to comply with
the atom economy and has no byproducts. However, the traditional EDR route
needs a high temperature and obtains the product with relatively large grain size
[
30].
In this paper, nano-CuI was synthesized by a EDR route and its catalytic activity
was evaluated in thermal decomposition of AP. The effects of polyvinyl pirrolidone
PVP) as an additive in the preparation of nano-CuI and the addition amount of the
(
catalyst in the thermal decomposition reaction on catalytic activity were investi-
gated. Some characterizations were also carried out.
Experimental
Materials and preparation of nano-CuI
All the reagents used in this experiment were of analytical grade and used as
received without further purification.
In a typical experiment, 0.3200 g copper powder, 0.6328 g iodine, and 0.2900 g
PVP were all dissolved with 100 mL acetonitrile in a flask under constant stirring at
4
0 °C for 4 h under reflux conditions. The resultant solution was evaporated at
0 °C to remove the acetonitrile solvent. The CuI precipitate was washed with
3
absolute ethanol three times, dried in vacuum at 25 °C for 1 h, and then stored in the
dark.
Characterization
The phase and purity of the as-prepared CuI nanoparticles were identified by X-ray
diffraction (XRD) with CuKa radiation (k = 0.15418 nm) at 40 kV and 100 mA,
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Synthesis of nano-CuI and its catalytic activity
Fig. 1 XRD patterns of CuI catalysts prepared with PVP as an additive (a) and without any additives (b)
and the diffraction patterns were taken in the range of 10° \ 2h \ 70°. The average
particle size of the CuI obtained was calculated by using the Scherrer formula.
D ¼ kk=b cos h;
where D is the crystallite diameter, k is the Scherrer constant (0.89), k is the X-ray
wavelength (0.15418 nm), b is the full width at half-maximum (FWHM) of the
diffraction peak, and 2h is the diffraction angle of the peak.
The morphologies and composition of the nano-CuI were determined by JEOL
500F scanning electron microscopy (SEM) equipped with an energy dispersive
7
X-ray spectroscopy (EDX).
The crystallite sizes were observed on a JEOL 2200FS transmission electron
microscope (TEM) at an accelerating voltage of 200 kV.
Catalytic activity measurements
The catalytic activity of nano-CuI obtained in thermal decomposition of AP was
evaluated with the mass ratio of CuI:AP = 2:98 by thermogravimetric and
differential scanning calorimetric analysis techniques, in the test temperature range
of 25–500 °C under an argon atmosphere. The measurements were performed on a
-
1
SDT 2960 simultaneous DSC-TGA at a heating rate of 10 °C min
.
Results and discussion
Characterization of nano-CuI catalyst
The XRD patterns of CuI catalysts prepared by two different methods are shown in
Fig. 1, from which it can be seen that the diffraction peaks of the two XRD patterns
reveal that CuI exists in the form of c-CuI crytal phase with face-centered cubic
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Y. Liu et al.
Fig. 2 SEM image of the nano-CuI catalyst prepared with PVP as an additive (a) and without any
additives (b)
structure (JCPDS card No. 06-0246). No diffraction peaks of any impurity phase are
identified in the two XRD patterns, indicative of the high phase purity of the nano-
CuI prepared by the EDR method. The average crystallite size is estimated by using
the Scherrer formula. The results showed that the average crystallite size of CuI,
prepared with PVP as an additive, is about 50 nm, and that of CuI, prepared without
an additive, is above 100 nm. The above results demonstrate that PVP as an additive
can play an effective role in decreasing the crystallite size of nano-CuI prepared by
the EDR method.
The morphologies of nano-CuI catalyst prepared with PVP as an additive (a) and
without any additives (b) are shown in Fig. 2 by SEM technique. The CuI particles
generated in the presence of PVP show an average size of 50 nm. However, the CuI
particles show an average size of 100 nm without any additives. It is well known
that PVP can encapsulate the nanoparticles in the solution and prevent their
aggregation. The growth of the nanoparticles may be limited in the course of the
EDR by the space restrictions imposed by the three-dimensional PVP network.
The micro-texture of nano-CuI was identified by the TEM technique and is
displayed in Fig. 3. It can be observed that the nano-CuI has a crystallite size of
about 50 nm, marked by the relatively bright areas. TEM characterization explains
well the role of PVP played in reducing the crystallite size of the nano-CuI. In
addition, the observed crystallite size of nano-CuI prepared with PVP as an additive
by TEM is in good agreement with the result calculated by the Scherrer formula in
XRD patterns.
Elemental composition of nano-CuI prepared with PVP as an additive is analyzed
by EDX technique. In Fig. 4, the characteristic peaks of three elements of Cu, I, and
O can be identified. The quantitative analysis of the EDX spectrum proves the molar
ratio of Cu:I = 1:1, which is in accordance with the stoichiometric compound of
CuI.
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Synthesis of nano-CuI and its catalytic activity
Fig. 3 TEM image of the nano-
CuI catalyst prepared with PVP
as an additive
Fig. 4 EDX spectrum of the nano-CuI prepared with PVP as an additive
Catalytic activity of nano-CuI
Figure 5 shows the thermal decomposition behaviors of pure AP and AP with nano-
CuI catalysts by the DTA technique. For pure AP, an endothermic peak was
observed at about 249 °C, which is assigned to the crystallographic transition of AP
from orthorhombic to cubic crystal [31].With the increasing temperature, AP
underwent two complicated decomposition stages [32], i.e., a low temperature stage
at 340 °C and a high temperature stage at 454 °C. From the comparison between
Fig. 5b, c, it can be seen that, with the addition of the nano-CuI catalyst, the two
separated exothermic peaks of AP decomposition incorporate a strong exothermic
peak that is located at 345 °C, and the temperature of the peak at the high
decomposition temperature stage of pure AP is therefore decreased by 109 °C.
Figure 5a shows that the exothermic peak temperature of AP decomposition can be
further decreased in the presence of the nano-CuI catalyst prepared with PVP as an
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Y. Liu et al.
Fig. 5 DTA curves for (a) AP ? nano-CuI catalyst prepared with PVP as an additive; (b) AP ? nano-
CuI catalyst prepared without additive; (c) pure AP
additive, which indicates that the smaller crystallite size of CuI contributes to its
higher catalytic activity in thermal decomposition of AP. In addition, Fig. 5
demonstrates that the temperatures of the endothermic peaks are almost the same in
all cases, proving that a catalyst has hardly any effect on the crystallographic
transition temperature of AP in the thermal decomposition of AP.
TG analysis on the thermal decomposition behaviors of pure AP and AP with
nano-CuI catalysts is carried out and the results are shown in Fig. 6. It shows that
the decomposition rate of AP is greatly increased with the introduction of nano-CuI
catalyst. Addition of nano-CuI in AP led to a significant reduction of the ending
decomposition temperature of AP. In terms of nano-CuI catalysts prepared with and
without PVP, the ending temperature of AP decomposition decreases by 116 and
1
04 °C, respectively. The above analysis further corroborates the substantial effects
of the nano-CuI catalyst and its crystallite size on the thermal decomposition of AP.
The effect of the addition amount of the nano-CuI catalyst, prepared with PVP as
an additive, on its catalytic activity in the thermal decomposition of AP was also
investigated. Figure 7 shows that the exothermic peak temperature gradually shifts
the low temperature field with the increase of the amount of the nano-CuI catalyst.
Probably, an increasing amount of the catalyst can improve the intermiscibility and
further increase the contact area between AP and the catalyst.
The mechanism of nano-CuI in the catalyzed thermal decomposition of AP can be
understood by an electron transfer process. It was proposed that the transfer of an
electron from the perchlorate ion to a positive hole is the rate-controlling step in p-type
semiconductors [6]. The decomposition of AP can proceed via the following equation:
ꢁ
1
ꢁ
3
jej þ ClO ! O
þ ClO ! = O þ ClO þ e;
4
oxide
3
2
2
where |e| represents a positive hole in the valence band of p-type semiconductors
and Ooxide is an oxygen atom abstracted by the p-type semiconductors of nano-CuI.
1
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Synthesis of nano-CuI and its catalytic activity
Fig. 6 TG curves for (a) AP ? nano-CuI catalyst prepared with PVP as an additive; (b) AP ? nano-CuI
catalyst prepared without additive; (c) pure AP
Fig. 7 DTA curves for AP ? 1 wt% (a), 3 wt% (b) and 5 wt% (c) nano-CuI catalyst prepared with PVP
as an additive
Conclusions
In summary, we have successfully fabricated CuI nanoparticles by an EDR route
at 40 °C with PVP in acetonitrile. As shown by TEM observations, the average
diameter is about 50 nm. It can also be seen from SEM that the CuI nanoparticles
exhibit a crystal schistose shape. The SEM and TEM results are well agreed with
the XRD results. Moreover, the addition of nanoparticles of CuI merges two
exothermic peaks of AP thermal decomposition into one peak, greatly reducing
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Y. Liu et al.
the high temperature decomposition peak. Hence, there is a great potential for the
use of nanoparticles of CuI in catalytic decomposition of AP.
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