Synthesis and characterization manganese oxide nanobundles from decomposition of manganese oxalate

Article abstract of DOI:10.1016/j.ica.2009.04.022

The present investigation reports, the synthesis of manganese oxide (α-Mn₂O₃) nanobundles using thermal decomposition and its physicochemical characterization. The α-Mn₂O₃ nanobundles have been prepared using ma

Full text of DOI:10.1016/j.ica.2009.04.022

Inorganica Chimica Acta 362 (2009) 3663–3668
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Inorganica Chimica Acta
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Synthesis and characterization manganese oxide nanobundles
from decomposition of manganese oxalate
Fatemeh Davar a,b, Fatemeh Mohandes b, Masoud Salavati-Niasari a,b,
*
a Institute of Nano Science and Nano Technology, University of Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran
b Department of Chemistry, Faculty of Science, University of Kashan, P.O. Box. 87317-51167, Kashan, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The present investigation reports, the synthesis of manganese oxide (
a
-Mn2O3) nanobundles using ther-
Received 4 October 2008
Received in revised form 4 April 2009
Accepted 17 April 2009
Available online 3 May 2009
mal decomposition and its physicochemical characterization. The
a-Mn2O3 nanobundles have been pre-
pared using manganese oxalate dihydrate powders as precursor in the presence of oleylamine and
triphenylphosphine as solvent and capping agent. Transmission electron microscopy (TEM) analysis
demonstrated Mn2O3 nanobundles compose of nanospheres with diameter 30 nm. The products were
characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray
(EDX), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy.
Manganese oxide nanocrystals have been prepared under different condition. The controlled experimen-
tal results showed that the use of oleylamine and triphenylphosphine as the solvent and capping agent in
the chemical process played important role in the formation of the final products.
Keywords:
Nanobundles
Mn2O3
Thermal decomposition
Inorganic materials
Chemical synthesis
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Mn2O3 (50 nm) by autoclaving b-MnO2 with ethanol at 130 °C for
24 h under autogenous pressure. Nanosize crystals of Mn2O3 have
Manganese oxide materials are of considerable importance in
technological applications, including catalysis, ion-exchange,
molecular adsorption, and electrode materials for lithium cathodes
due to their structural flexibility combined with novel chemical
and physical properties [1–5]. A large number of different manga-
nese oxides are possible owing to the availability of various oxida-
tion states of manganese (II, III and IV). The most commonly known
manganese oxides MnO, Mn2O3 and Mn3O4 have a wide range of
applications in catalysis and battery technologies [6]. Among the
series of manganese oxides Mn3O4 is known to be an active cata-
lyst in various oxidation and reduction reactions e.g. it can be used
as a catalyst for the oxidation of methane [7].
Up to now, various nanostructures of Mn3O4, such as nanopar-
ticles [8], nanorods/nanowires [9,10], mesoporous/hollow struc-
tures [11,12] urchins/coral-like and other structures [13] have
been synthesized by different methods. Gui et al. [14] synthesized
Mn2O3 nanocrystals (9–12 nm in diameter) by direct reduction of
aqueous KMnO4 with hydrazine solution at ambient temperature.
been prepared by a precipitation process using dilute aqueous
solutions of manganese sulfate and ammonia in the presence of so-
dium lauryl sulfate, a surface active agent [16].
One method to prepare nanosized Mn2O3 is the thermal decom-
position.
MnO2 or MnCO3 in air at temperatures of 600–800 °C [17]. Sphere-
or cube-like -Mn2O3 was obtained at 550 °C through the decom-
position of the MnCO3 precursors synthesized via a hydrothermal
reduction process [18]. Nanofiberous -Mn2O3 was prepared by
calcination of -MnO2 nanowires at the temperature above
a-Mn2O3 particles were usually prepared by heating
a
a
c
600 °C [5]. Monodisperse nanocrystals of MnO of length 7 nm have
been synthesized by thermal decomposition of [Mn(ac)2],
(ac = acetate), in the presence of oleic acid at high temperature
[19]. Seo et al. [20] prepared Mn3O4 nanocrystals from [Mn(acac)2],
(acac = acetylacetonate). Zhang and coworkers prepared nanocrys-
tals MnO and Mn3O4 via thermolysis of manganese formate in
coordinating solvent at temperatures ranging from 170 to 250 °C
[21].
c
-Mn2O3 nanowires synthesized by treatment of
a
-MnO2 with
A major interest at the moment is in the development of orga-
nometallic or inorganic compound for preparation of nanoparti-
cles. Using of the novel compound can be useful and open a new
way for preparing nanomaterials to control nanocrystal size, shape
and distribution size. Recently, the synthesis of metal oxide nano-
particles via thermal decomposition of novel precursor has been
reported [22–27]. Metal carboxylates are good precursors to obtain
pure metal oxides. Ahmad et al. [28] have prepared manganese
ethanol at 140 °C [10]. He et al. [15], prepared nanocrystals of
c
-
* Corresponding author. Address: Institute of Nano Science and Nano Technology,
University of Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran. Tel.:
+98 361 5555333; fax: +98 361 5552935.
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.04.022

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F. Davar et al. / Inorganica Chimica Acta 362 (2009) 3663–3668
oxalate by the reverse-micellar method using cetyltrimethylam-
monium bromide as the surfactant. These manganese oxalates
when decomposed in air at 450 °C for 6 h led to the formation of
an ESCA-3000 electron spectrometer with nonmonochromatized
Mg K X-ray as the excitation source. Thermogravimetric–differ-
ential thermal analysis (TG–DTA) were carried out using a thermal
a
a
-Mn2O3 about 45 nm.
Herein, we report on the facile synthesis of
gravimetric analysis instrument (Shimadzu TGA-50H) with a flow
a
-Mn2O3 nanobun-
rate of 20.0 mL minꢁ1 and a heating rate of 10 °C minꢁ1
.
dles via thermolysis of manganese (II) oxalate dihydrate
[Mn(O4C2)ꢀ2H2O] in coordinating solvent oleylamine and triphen-
ylphosphine (TPP) (Scheme 1). To the best of our knowledge, this
is the first report on the synthesis of Mn2O3 nanobundles via ther-
mal decomposition of manganese oxalate in coordination solvent.
In this process, oleylamine was used as both the medium and the
stabilizing reagent.
2.3. Synthesis of Mn2O3 nanobundles
The current synthetic procedure is a modified version of the
method developed by Hyeon and others for the synthesis of nano-
crystals for metals that employs the thermal decomposition of
transition metal complexes [30,31]. The synthetic pathway is
shown in Scheme 1. In this synthesis, Mn2O3 nanobundles were
prepared by the thermal decomposition of manganese (II) oxa-
late-oleylamine, [Mg(O4C2)ꢀ2H2O]-oleylamine complex as precur-
sor. First, the [Mn(O4C2)ꢀ2H2O]-oleylamine complex was
prepared by reaction 0.6 g of [Mn(O4C2)ꢀ2H2O] and 5 mL of oleyl-
amine. The mixed solution was placed in a 50 mL two-neck distil-
lation flask and heated up to 150 °C for 120 min. The resulting
metal-complex solution was injected into 5 g of triphenylphos-
phine (TPP) at 250 °C. The color of the solution changed from peal
dark pink to milky-white, indicating that colloidal products were
generated. The milky-white solution was aged at 245 °C for
90 min, and was then cooled to room temperature. The black nano-
particles products were precipitated by adding excess ethanol to
the solution. The final products were washed with ethanol for at
least three times to remove impurities, if any, and dried at
100 °C. These products could easily be re-dispersed in nonpolar or-
ganic solvents, such as hexane or toluene (Scheme 1). The synthe-
sized nanobundles were characterized by XRD, SEM, TEM, FT-IR
and XPS.
2. Experimental
2.1. Materials
All the chemicals reagents used in our experiments were of ana-
lytical grade and were used as received without further purifica-
tion. Manganese(II) oxalate dihydrate, [Mn(O4C2)ꢀ2H2O],
precursor was synthesized according to this procedure: the man-
ganese acetate tetrahydrate (CH3COO)2Mnꢀ4H2O (2 mmol) was
dissolved into 10 mL of distilled water to form a homogeneous
solution. A stoichiometric amount of potassium oxalate dissolved
in an equal volume of distilled water was dropwise added into
the above solution under magnetic stirring. The solution was stir-
red for about 30 min and pink precipitate was isolated, washed
with ethanol several times and dried at 50 °C. The [Mg(O4C2)ꢀ2H2O]
was characterized by elemental analyses, FT-IR, powder X-ray dif-
fraction (XRD) and thermo gravimetric analysis (TGA) [29]. Anal.
Calc. for [Mn(O4C2)ꢀ2H2O]: C, 13.42; H, 2.25; Mn, 30.69. Found: C,
13.35; H, 2.17; Mg, 30.61%.
3. Results and discussion
2.2. Characterization
The TGA curve of the [Mn(O4C2)ꢀ2H2O] is shown in Fig. 1. It can
be seen that there are two distinct weight loss steps. The first
weight loss occurs at 130 °C, which corresponds to the evaporation
of crystallized water, that is to say, manganese oxalate dehydrate
in the stage. The second weight loss step occurs at the temperature
range 300–400 °C. The weight loss at 300–400 °C may be ascribed
to the decomposition of the oxalate. The weight loss of two steps is
about 19.60% and 49.41%, which is close to the theoretical value
[29].
Fig. 2a and b shows the XRD patterns of the precursor of man-
ganese oxalate and Mn2O3 nanobundles. In Fig. 2a, all the reflec-
tions in the pattern could be indexed on the basis of an
monoclinic cell reported for manganese oxalate dihydrate (JCPDS
XRD patterns were recorded by a Rigaku D-max C III, X-ray dif-
fractometer using Ni-filtered Cu K
a radiation. Elemental analyses
were obtained from Carlo ERBA Model EA 1108 analyzer. The com-
positional analysis was done by energy dispersive X-ray (EDX, Ke-
vex, Delta ClassI). Scanning electron microscopy (SEM) images
were obtained on Philips XL-30ESEM equipped with an energy dis-
persive X-ray spectroscopy. Transmission electron microscopy
(TEM) images were obtained on a Philips EM208 transmission elec-
tron microscope with an accelerating voltage of 100 kV. Fourier
transform infrared (FT-IR) spectra were recorded on Shimadzu Var-
ian 4300 spectrophotometer in KBr pellets. X-ray photoelectron
spectroscopy (XPS) of the as-prepared products was measured on
Scheme 1. Schematic diagram illustrating the formation of Mn2O3 nanobundles.

F. Davar et al. / Inorganica Chimica Acta 362 (2009) 3663–3668
3665
pared samples contain Mn, and O elements and no other impurities
are observed in Fig. 3.
The microstructures of the products have been examined by
scanning electron microscopy (Fig. 4a and b). The as-prepared con-
tains numerous rods of nearly the same diameters. As shown in
Fig. 4c, nanobundles with a diameter of ca. 30 nm have been ob-
served. These nanobundles have likely been formed by the aggrega-
tion of Mn2O3 nanospheres drawn together. Further observation at
higher magnification reveals that each nanobundle actually con-
sists of nanoparticles that are individually ca. 30 nm in diameter
(Fig. 4d). These nanoparticles are sequentially connected together
to form nanobundles with lengths on the order of ca. 20 lm.
FT-IR spectroscopy is a useful tool to understand the functional
group of any organic molecule. The infrared spectra of free TPP,
oleylamine, manganese oxalate dihydrate and Mn2O3 nanobundles
are shown in Fig. 5. By comparing the infrared spectra of the nano-
particles with free surfactants in Fig. 5, we can see that the organic
molecules have indeed become a part of the nanoparticles. As
shown in Fig. 5a and b, peaks corresponding to P–ph stretching
at 1710 cmꢁ1, rocking and bending mode of the methylene group
Fig. 1. TGA plot for the decomposition of manganese oxalate precursor.
No. 25–0544, a = 12.016 Å, b = 5.632 Å, c = 9.961 Å), indicating the
pure manganese oxalate dihydrate precursor was obtained. All of
the reflections of the XRD pattern in Fig. 2b can be indexed to
x
(CH2) at 1270 cmꢁ1, bending mode of the phenyl group
at 742 cmꢁ1and (benzene ring) at 697 cmꢁ1 can be seen. The only
c(@CH)
the standard pattern of the pure cubic phase of
a-Mn2O3 which
m
is in good agreement with the reported data (JCPDS No. 78–
0390). This revealed that the Mn2O3 sample produced a single-
phase cubic structure. From XRD data, the crystallite size (Dc) of
as-prepared Mn2O3 particles was calculated to be 21 nm using
the Debey–Scherrer equation [32],
difference among these characteristic peaks is either the peak
intensity or a slight shift in the peak position. For example, the
peak position of the longitudinal modes of oleylamine and TPP
shifts to lower wavenumbers after TPP and oleylamine are ad-
sorbed on the surface of the Mn2O3 nanobundles. The FT-IR spec-
trum of [Mg(O4C2)ꢀ2H2O] is shown in Fig. 5c. The broad
absorption band around 3410 cmꢁ1 corresponds to the mO–H
stretching vibrations. This observation provides evidence for the
presence of chemically bound H2O in the manganese oxalate. The
two absorption bands around 2970 and 2850 cmꢁ1 are due to sur-
face–OH stretch arising from hydroxyl groups in dissociated state
or C–H stretch of organic residue [33]. In Fig. 5c, double absorption
peaks appeared at 1645 and 1610 cmꢁ1 caused by the symmetrical
and asymmetrical vibrations of the carbonyl group, which are re-
lated to the existence of the [Mn(O4C2)ꢀ2H2O] compound. The
deformational mode of water usually seen around 1600 cm–1 is,
however, masked by the above doublet. The uncoordinated COO,
characterized by a single stretching absorption band at 1750–
1700 cmꢁ1, shifts towards the lower frequency and splits into
two bands (as observed above) when it combines with metal ions
as (C2O4)ꢁ2 ion [33]. Thus, IR absorption confirms the formation of
[Mn(O4C2)ꢀ2H2O]. The sharp absorption peaks at 1384 and
Kk
b cos h
Dc ¼
ð1Þ
where b is the breadth of the observed diffraction line at its half-
intensity maximum, K is the so-called shape factor, which usually
takes a value of about 0.9, and k is the wavelength of X-ray source
used in XRD.
The as-prepared Mn2O3 particles have been found to be of high
purity by EDX measurements. EDX results indicate that the as-pre-
1317 cmꢁ1 are assigned to ms(C–O)+d(OC@O) modes.
A peak at
795 cmꢁ1 is attributed to bending mode of O@C@O. In Fig. 5d,
the peaks at 3435 and 1637 cmꢁ1 can be assigned to the EtOH used
in the separation step. From these results, a chemical bond can be
formed between N and Mn atoms and a coordinate bond between P
and Mn atoms on the surface of the nanobundles. Thus, the phenyl
stretching mode m
(P–ph) at 1460 cmꢁ1 is still visible in Fig. 5d. So the
oleylamine and TPP serves as the capping ligand that controls
growth. The phenyl groups in TPP can provide greater steric hin-
drance than straight-chained alkyl groups such as tributyl and tri-
octyl to control the size of nonmagnetic metal and metal oxide
nanoparticles and to stabilize efficiently the magnetic nanoparti-
cles. The FT-IR of the Mn2O3 nanobundles shows the intense
adsorption peaks at 2920 and 2850 cmꢁ1 attributed to the alkyl
chains of oleylamine. This indicates that oleylamine is bound on
the surface through the unpaired electron couple of the amine
group [33]. The peaks around 668 and 576 were attributed to
mMn–O stretching vibration of Mn2O3, 525 cmꢁ1 were attributed to
mMn–O bending vibration of Mn2O3 [9]. This pattern further con-
firmed that the products prepared from thermal decomposition
are Mn2O3 phase, which is in agreement with analysis result of
XRD.
Fig. 2. XRD patterns of the obtained (a) manganese oxalate precursor and (b)
Mn2O3 nanobundles.

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F. Davar et al. / Inorganica Chimica Acta 362 (2009) 3663–3668
Fig. 3. EDX pattern of the as-prepared sample.
Fig. 4. (a and b) SEM and (c and d) TEM images of Mn2O3 nanobundles.
The growth mechanism could be well understood on the basis
[34]. The addition of TPP into the mixture of oleylamine and com-
plex as an additional surfactant reduced the particle size much fur-
ther and resulted in nanocrystals with very thin arrays. Oleylamine
is known as a ligand that binds tightly to the metal nanoparticles
surface. The combined effects of TPP and oleylamine were much
more profound than those of individual contributions. When the
triphenylphosphine (TPP) was used as the complexing agent, the
circumference of produced nuclei was capped by this surfactant,
leading to the increase of surface energy of some crystallographic
of the following reactions and the crystal habits of Mn2O3. In the
presence of oleylamine as solvent [Mn(O4C2)ꢀ2H2O]-oleylamine
were synthesized. After addition of TPP to these solutions at high
temperature [Mn(O4C2)ꢀ2H2O]-oleylamine will decomposed. TPP
was widely used in the synthesis of phosphine-stabilized gold or
other metal nanoparticles. The phenyl groups in TPP can provide
greater steric hindrance than straight-chained alkyl groups such
as tributyl and trioctyl to control the size of metal nanoparticles

F. Davar et al. / Inorganica Chimica Acta 362 (2009) 3663–3668
3667
Fig. 6. XPS spectra of the Mn2O3 nanobundles.
Table 1
Preparation of Mn2O3 under different conditions.
Sample
Capping agent
Temperature (°C)
Time
Particles size
1
2
3
450
150
245
6 h
90 min
90 min
50 nm [28]
Agglomeration
30 nm
Oleylamine
Oleylamine + TPP
uct to be 653.23 and 641.53 eV, respectively. A full survey scan did
not reveal other element peaks. The results are in accord with the
data for Mn2O3 in the literature [36].
In addition, the manganese oxide nanocrystals have been pre-
pared under different condition (Table 1). By controlling the qual-
ity of nanocrystals, Mn2O3 with various sizes can be formed.
[Mn(O4C2)ꢀ2H2O] (sample 1) was calcined at 450 °C for 6 h, in this
case Mn2O3 with particle size about 50 nm and irregular shapes
was obtained. We decided to use of solvent for preparing manga-
nese oxides with small particle size and use of low reaction tem-
perature so, 0.6 g of [Mn(O4C2)ꢀ2H2O] and 5 mL of oleylamine,
(sample 2), was mixed and heated in 150 °C for 90 min so led to
agglomerated nanoparticles Mn2O3 with particle size 45–60 nm.
To prepare Mn2O3 nanobundles (sample 3), the procedure men-
tioned in experimental section, including oleylamine and TPP,
was done. Considering different condition employed to prepare
these samples, it is obvious that using both oleylamine and TPP
as capping agent is preferred for Mn2O3 nanobundles synthesis.
Fig. 5. FT-IR spectra of (a) TPP, (b) oleylamine (c) manganese oxalate dihydrate and
(d) Mn2O3 nanobundles.
faces. From the TEM images, we believe that the Mn2O3 nanobun-
dles have been formed by the assembly of obtained nanospheres.
On the other hand the reaction involves the decomposition of
[Mn(O4C2)ꢀ2H2O]-oleylamine, and the nucleation and growth of
Mn2O3 nuclei into nanospheres. In this step, a high concentration
of Mn2O3 nanoparticles with a size of ca. 30 nm has been formed.
These nanoparticles are then oriented along together and are
assembled into short rod likes. Meanwhile, decomposition occurs
at the junctions between the nanospheres and the newly-formed
nanoparticles connect to the short nanobundles to yield longer
nanobundles. At extended reaction times, the nanobundles in-
crease in length until the manganese oxalate is completely con-
sumed [35]. The growth of the Mn2O3 nanoparticles can be
explained on the basis of the schematic view presented in Scheme
1. The Mn2O3 nanoparticles agglomerated together to form a
nanobundles.
4. Conclusion
In summary, we have demonstrated the synthesis of
a-Mn2O3
nanobundles from the manganese oxalate dihydrate powders via
a thermal decomposition process. The nanobundles actually con-
sist of nanospheres that are individually ca. 30 nm in diameter.
These nanoparticles are sequentially connected together to form
nanobundles with lengths on the order of ca. 20 lm. The controlled
experimental results showed that the use of oleylamine and TPP as
the solvent and capping agent in the chemical process played
important role in the formation of the final products. This method
employed an inexpensive, reproducible process for the large-scale
To further confirm the oxidation state of Mn, the products were
characterized by X-ray photoelectron spectroscopy (XPS). Fig. 6
shows the XPS for the as-synthesized samples. The XPS gives the
binding energies of Mn 2p1/2 and Mn 2p3/2 for the obtained prod-
synthesis of
a-Mn2O3 nanobundles. We expect that it would be a
promising route to synthesize some other metal oxides with vari-
ous nanostructures.

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F. Davar et al. / Inorganica Chimica Acta 362 (2009) 3663–3668
[16] N. Chandra, S. Bhasin, M. Sharma, D. Pal, Mater. Lett. 61 (2007) 3728.
Acknowledgement
[17] M. Tabuchi, K. Ado, J. Electrochem. Soc. 145 (1998) L49.
[18] S.J. Lei, K.B. Tang, Z. Fang, Q.C. Liu, H.G. Zheng, Mater. Lett. 60 (2006) 53.
[19] M. Yin, S. O’Brien, J. Am. Chem. Soc. 125 (2003) 10180.
[20] W.S. Seo, H.H. Jo, K. Lee, B. Kim, S.J. Oh, J.T. Park, Angew. Chem. Int. Ed. 43
(2004) 1115.
Authors are grateful to council of University of Kashan for pro-
viding financial support to undertake this work.
[21] X. Sun, Y.-W. Zhang, R. Si, C.-H. Yan, Small 1 (2005) 1081.
[22] M. Salavati-Niasari, F. Davar, M. Mazaheri, M. Shaterian, J. Magn. Magn. Mater.
320 (2008) 575.
References
[23] N. Bouropoulos, G.C. Psarras, N. Moustakas, A. Chrissanthopoulos, S. Baskoutas,
Phys. Stat. Sol. A 205 (2008) 2033.
[24] S. Baskoutas, P. Giabouranis, S.N. Yannopoulos, V. Dracopoulos, L. Toth, A.
Chrissanthopoulos, N. Bouropoulos, Thin Solid Films 515 (2007) 8461.
[25] M. Salavati-Niasari, F. Davar, M. Mazaheri, Polyhedron 27 (2008)
3467.
[26] M. Salavati-Niasari, F. Davar, N. Mir, Polyhedron 27 (2008) 3514.
[27] M. Salavati-Niasari, Z. Fereshteh, F. Davar, Polyhedron 28 (2009) 126.
[28] T. Ahmad, K.V. Ramanujachary, S.E. Lofland, A.K. Ganguli, J. Mater. Chem. 14
(2004) 3406.
[29] B. Donkova, D. Mehandjiev, Thermochim. Acta 424 (2004) 141.
[30] T. Hyeon, S.S. Lee, J. Park, Y. Chung, H.B. Na, J. Am. Chem. Soc. 123 (2001)
12798.
[1] A.R. Armstrong, P.G. Bruce, Nature 381 (1996) 499.
[2] A.E. Fischer, K.A. Pettigrew, D.R. Rolison, R.M. Stroud, J.W. Long, Nano Lett. 7
(2007) 281.
[3] Z. Yang, Y. Zhang, W. Zhang, X. Wang, Y. Qian, X. Wen, S. Yang, J. Solid State
Chem. 179 (2006) 679.
[4] J. Fei, Y. Cui, X. Yan, W. Qi, Y. Yang, K. Wang, Q. He, J. Li, Adv. Mater. 20 (2008)
452.
[5] Z.Y. Yuan, Z.L. Zhang, G.H. Du, T.Z. Ren, B.L. Su, Chem. Phys. Lett. 378 (2003)
349.
[6] O. Giraldo, S.L. Brock, W.S. Willis, M. Marquez, S.L. Suib, J. Am. Chem. Soc. 122
(2000) 9330.
[7] K. Ramesh, L. Chen, F. Chen, Z. Zhong, J. Chin, H. Mook, Y.-F. Han, Catal.
Commun. 8 (2007) 1421.
[31] M. Salavati-Niasari, F. Davar, M. Mazaheri, Mater. Lett. 62 (2008) 1890.
[32] R. Jenkins, R.L. Snyder, in: Chemical Analysis: Introduction to X-ray Powder
Diffractometry, John Wiley and Sons Inc., New York, 1996, p. 90.
[33] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compound,
fourth ed., Chemical Industry Press, Beijing, 1991.
[34] H.T. Yang, Y.K. Su, C.M. Shen, T.Z. Yang, H.J. Gao, Surf. Interface Anal. 36 (2004)
155.
[35] F. Jia, L. Zhang, X. Shang, Y. Yang, Adv. Mater. 20 (2008) 1050.
[36] A.A. Audi, P.M.A. Sherwood, Surf. Interface Anal. 33 (2002) 274.
[8] Z.W. Chen, J.K.L. Lai, C.H. Shek, J. Non-Cryst. Solids 352 (2006) 3285.
[9] Y. Chen, Y. Zhang, Q.-Z. Yao, G.-T. Zhou, S. Fu, H. Fan, J. Solid State Chem. 180
(2007) 1218.
[10] X. Chen, X. Li, Y. Jiang, C. Shi, X. Li, Solid State Commun. 136 (2005) 94.
[11] T.-Z. Ren, Z.-Y. Yuan, W. Hu, X. Zou, Micropor. Mesopor. Mater. 112 (2008) 467.
[12] Z. Yang, W. Zhang, Q. Wang, X. Song, Y.T. Qian, Chem. Phys. Lett. 418 (2006) 46.
[13] Y.-F. Han, L. Chen, K. Ramesh, Z. Zhong, F. Chen, J. Chin, H. Mook, Catal. Today
131 (2008) 35.
[14] Z. Gui, R. Fan, X.H. Chen, Y.C. Wu, Inorg. Chem. Commun. 4 (2001) 294.
[15] W.L. He, Y.C. Zhang, X.X. Zhang, H. Wang, H. Yan, J. Cryst. Growth 252 (2003)
285.