Synthesis of micro- and nanosized manganese oxides from hydrated manganese oxalates and products of their chemical modification with ethylene glycol

Article abstract of DOI:10.1134/S0036023609070080

The reactions of ethylene glycol with manganese oxalates MnC ₂O₄ · ₂H₂O and MnCO ₄ · 3H₂O on heating in air were studied. At temperature below 100° C, ethylene glycol was found to displace

Full text of DOI:10.1134/S0036023609070080

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 7, pp. 1035–1040. © Pleiades Publishing, Inc., 2009.
Original Russian Text © O.I. Gyrdasova, V.N. Krasil’nikov, G.V. Bazuev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 7, pp. 1097–1102.
COORDINATION
COMPOUNDS
Synthesis of Micro- and Nanosized Manganese Oxides
from Hydrated Manganese Oxalates and Products
of Their Chemical Modification with Ethylene Glycol
O. I. Gyrdasova, V. N. Krasil’nikov, and G. V. Bazuev
Institute of Solid-State Chemistry, Ural Division, Russian Academy of Sciences,
ul. Pervomaiskaya 91, Yekaterinburg, 620219 Russia
Received January 22, 2008
Abstract—The reactions of ethylene glycol with manganese oxalates MnC O · 2H O and MnC O · 3H O on
2
4
2
2
4
2
heating in air were studied. At temperature below 100°C, ethylene glycol was found to displace water from
oxalates to give a new solvate compound according to the reaction MnC O · nH O + HOCH CH OH =
2
4
2
2
2
MnC O (HOCH CH OH) + nH O↑. The crystals of the solvates retain the morphology of the initial oxalates,
2
4
2
2
2
which is then inherited by the products of their thermolysis. Thus, thermolysis of MnC O · 3H O and
2
4
2
MnC O (HOCH CH OH) having quasi-unidimensional structure gave Mn O and Mn O nanowhiskers in air
2
4
2
2
3
4
2 3
and MnO in an inert gas environment. Heating of MnC O · nH O in ethylene glycol at temperatures above
2
4
2
100°C results in anhydrous manganese oxalate.
DOI: 10.1134/S0036023609070080
The development and progress of new effective meth- that MnC O · 3H O precipitates from solution as
2
4
2
ods for the synthesis of new oxide materials with extended slightly pink-colored needle crystals [6, 7]. The
particles (whiskers, rods, fibers, wires, ribbons, tubes) is a replacement of water by ethylene glycol may result
key task of the modern preparative nanochemistry. A [2, 3] in the formation of thinner crystals of the solvate
promising and widely used method for the synthesis of MnC O (HOCH CH OH), which opens up prospects
2
4
2
2
these materials is based on the phenomenon of pseudo-
morphism, i.e., the ability of the initial compound to con-
vert into oxide upon heat treatment without a considerable
change in particle morphology [1]. Previously, we
described methods for the synthesis of micro- and nano-
sized whisker and fiber crystals of complex oxides
for the formation of manganese oxides as nano-sized
whisker crystals upon thermolysis.
EXPERIMENTAL
MCo O (M = Zn, Mn) with the spinel structure from sol-
2
4
The synthesis of MnC O · 3H O was performed by
2
4
2
vates M Co C O (HOCH CH OH) consisting of 20–
1/3
2/3
2
4
2
2
adding a stoichiometric amount of a cooled solution of
5
0-µm long needle- and fiber-shaped crystals with a cross manganese(II) sulfate to a cooled solution of oxalic
section of less than 0.5 µm [2, 3]. On heating in air, sol- acid with continuous stirring. After 20 min, the precip-
vates M Co C O (HOCH CH OH) are converted into itated MnC O · 3H O was separated from the mother
1/3
2/3
2
4
2
2
2
4
2
oxides MCo O with a cubic spinel structure, the mor- liquor, washed with ethanol on a vacuum filter, and
2
4
phology of the parent extended crystals being inherited by dried to constant weight in air at ambient temperature.
the products of thermolysis. The whisker crystals of The solid solution Mg Mn C O · 3H O was synthe-
0.2
0.8
2
4
2
MCo O formed upon thermolysis have a cross section of
2
4
sized in a similar way by adding a mixture of manga-
nese and magnesium sulfates to oxalic acid. The
oxalate MnC O · 2H O was prepared by the following
procedure: a 0.2 M solution of manganese(II) sulfate
heated to 70°C was added from a dropping funnel over
a period of 30–40 min to a 0.2 M aqueous solution of
oxalic acid (taken in a 50% excess) heated to the same
temperature. Precipitation was carried out at a temper-
ature of 70°C with continuous stirring for 60 min. After
maturing for 24 h, the precipitates were washed with
~30–40 nm and a length of not less than 20 µm [3].
2
4
2
Manganese oxides traditionally find use as magnetic
materials, sorbents, catalysts, and semiconductor ter-
mistors [4, 5]. Manganese(II) oxalate is actively used to
produce nanosized manganese oxides in different oxi-
dation states. In this study, micro- and nanocrystal
whiskers of manganese oxides were obtained using
synthesized manganese oxalate MnC O · 3H O and the
2
4
2
solvate MnC O (HOCH CH OH) obtained upon
2
4
2
2
2
4
–
distilled water until the test for SO was negative, and
ylene glycol. This compound was chosen due to the fact dried under ambient conditions to a constant weight.
replacement of water in the trihydrate structure by eth-
1
035

1
036
GYRDASOVA et al.
Mixtures of synthesized manganese oxalates and eth- (to a maximum content of 2.4 wt %) into the MnC O ·
2
4
ylene glycol were heat treated in heat-resistant glass bea-
kers at various temperatures. The initial oxalate powders
were mixed with a fivefold excess of HOCH CH OH until
3
H O structure stabilizes the needle-shaped phase
2
based on the oxalate trihydrate. According to our data,
Mg Mn C O · 3H O stored in a sample bottle for
more than 2 years did not undergo morphological or
2
2
0.2
0.8
2
4
2
a uniform blend formed and stirred for 18 h at 80 and
50°ë. The solid reaction products were separated from
the liquid phase by vacuum filtration, washed with ace- structural degradation, whereas MnC O · 3H O partly
1
2
4
2
tone, dried in air at 40°ë, and placed in tightly closed sam-
ple bottles for storage. The sample with the composition
Mg Mn C O · 3H O was treated only at lower temper-
converted into MnC O · 2H O within one month after
2
4
2
the synthesis.
The products of reaction of MnC O ·nH O with eth-
0.2
0.8
2
4
2
ature.
2
4
2
ylene glycol at low temperatures are individual chemi-
cal compounds. They are formed upon replacement of
two or three water molecules in the oxalate structure by
Phase analysis was performed using a DRON UM-1
X-ray diffractometer (CuK radiation) and a POLAM
α
C-112 polarization microscope in the transmitted light.
Thermogravimetric analysis was carried out on a one ethylene glycol molecule according to the reaction
Q-1500D derivatograph in air with heating from 20 to
MnC O ⋅ nH O + HOCH CH OH
2
4
2
2
2
1
000°C at a rate of 10 K/min. IR spectra were measured on
(
1)
–1
a Spectrum-One spectrophotometer in the 400–4000 cm
MnC O (HOCH CH OH) + nH O↑.
2 4 2 2 2
range. Morphological studies were carried out for the
initial oxalates, products of their treatment with ethyl-
After low-temperature heat treatment, a mixture of
ene glycol, and the products of thermolysis in air and in MnC O · 2H O plate crystals with ethylene glycol
2
4
2
a helium atmosphere at 150–600°ë. The shape and size
of the particles formed upon thermal decomposition
were determined by scanning electron microscopy
gives the solvates MnC O (HOCH CH OH) as very
2
4
2
2
small flattened crystals with a square cross section.
The replacement of water by ethylene glycol in
(
SEM) on a Tesla BS-301 instrument. Elemental analy-
sis for Mn and Mg was carried out by atomic absorption MnC
O · 3H O gives rise to thinner needles and
2
4 2
spectroscopy in an acetylene–air flame on a Perkin- fibers of MnC O (HOCH CH OH). Reaction (1) was
2
4
2
2
Elmer instrument and by inductively coupled plasma
atomic emission spectroscopy on a JY 48 spectral ana-
lyzer.
found to be reversible as MnC O (HOCH CH OH) is
2
4
2
2
hydrolyzed upon contact with water or water vapor at
room temperature. The HOCH CH OH molecule is
2
2
displaced from the solvate by two water molecules to
RESULTS AND DISCUSSION
give MnC O · 2H O. The X-ray diffraction patterns
2
4
2
of MnC O · 2H O formed upon hydrolysis of
According to powder X-ray diffraction, microscopic
2
4
2
examination, IR spectroscopy, thermogravimetric anal- MC
O (HOCH CH OH) show broad lines, indicating
4 2 2
2
ysis, and elemental analysis, the oxalate samples pre- a low degree of crystallinity.
pared by the above-described procedure were single
phases. Powdered MnC O · 2H O is white-colored and
Under a microscope, the precipitates obtained by high-
temperature treatment of manganese oxalate di- and trihy-
2
4
2
looks under a microscope as plate crystals with high drates mixed with ethylene glycol are small platelike crys-
birefringence. The refractive indices are Ng = 1.558 and tals shaped like rectangles and squares with low birefrin-
Np = 1.501. The MnC O · 3H O powder is slightly gence. The refractive indices are Ng = 1.579, Np = 1.564.
2
4
2
pink-colored and looks under a microscope as needle
crystals with a size of ~1 × 50 µm; the refractive indices
are Ng = 1.546 and Np = 1.470. Similar crystals are
formed by the complex oxalate Mg Mn C O · 3H O.
The thermal decomposition in air of
MnC O (HOCH CH OH) fibers prepared from MnC O ·
2
4
2
2
2
4
3
H O occurs in two stages (Fig. 1a). The first exotherm
2
0.2
0.8
2
4
2
corresponds to the removal of ethylene glycol (t ~200–
90°C), and the second one observed in the temperature
MnC O · 3H O is a metastable compound because on
2
4
2
2
storage in air it is gradually converted into the more sta-
ble MnC O · 2H O. The needle morphology of the tri-
range of 290–420°C with a maximum at 310°ë corre-
sponds to the decomposition of magnesium oxalate.
The decomposition of the MnC O (HOCH CH OH)
2
4
2
hydrate is not retained in this process. This feature of
the MnC O · 3H O phase was noted in the literature;
2
4
2
2
2
4
2
sample prepared from MnC O · 2H O also occurs in
2 4 2
two stages (Fig. 1b), the removal of 1 mole of ethylene
glycol and onset of manganese oxalate decomposition
the formula {[Mn(µ-ox)(H O) ] · H O} was proposed
2
2
2
to emphasize the nonequivalent positions of H O mole-
2
cules with respect to the chains of structural polyhedra being reflected by an inflection in the TG curve at
M–C O –M–C O – [7]. The introduction of magnesium ~220°C. Thermal decomposition of manganese oxalate
2
4
2
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 7 2009

SYNTHESIS OF MICRO- AND NANOSIZED MANGANESE OXIDES
1037
∆
m,
(
a)
320
(b)
(c)
mg
TG
TG
TG
3
10
2
4
0
0
DTA
3
00
DTA
6
0
DTA
200
2
00
400
200
400
400 T, °C
Fig. 1. TG and DTA curves of (a) fibrous MnC O (HOCH CH OH), (b) finely crystalline MnC O (HOCH CH OH), and (c) anhy-
2
4
2
2
2
4
2
2
drous MnC O .
2
4
glycolated at 150°ë is exothermic and occurs in one
According to powder X-ray diffraction, thermolysis
stage with a maximum at 300°ë (Fig. 1c). The final of MnC O (HOCH CH OH) fibers in air at tempera-
2
4
2
2
product of themolysis is Mn O .
tures up to 500°C yields Mn O (Fig. 2b, pattern 1).
2 3
2
3
During annealing under these conditions, finely crystal-
The X-ray diffraction patterns of the initial MnC O ·
2
4
line MnC O (HOCH CH OH) decomposes to give
2
4
2
2
3
H O, oxalates subjected to heat treatment under vari-
2
Mn O (Fig. 2a, pattern 2). Analogous dependences
3
4
ous conditions, and thermolysis products obtained in
air and in an inert gas environment are presented in Fig. 2.
Analysis of the X-ray spectra leads to the conclusion
that the solvate MnC O (HOCH CH OH) is an individ-
were found for thermal decomposition of the di- and tri-
hydrate of manganese oxalate [6]. The annealing of
MnC O · 2H O at t ≤ 450°ë gives Mn O , while the tri-
2
4
2
2
3
2
4
2
2
hydrate forms Mn O in the same temperature range. In
3
4
ual compound. According to powder X-ray diffraction
Fig. 2a) and DTA (Fig. 1c), treatment of a mixture of
manganese oxalate di- and trihydrate with ethylene gly-
a helium atmosphere at T ≥ 350°C, thermolysis of
MnC O (HOCH CH OH) gives MnO (Fig. 2b, pattern 3).
(
2
4
2
2
Heating of Mg Mn C O (HOCH CH OH) to 600°ë
0.2
0.8
2
4
2
2
col at 150°ë gives MnC O as the final product. The for-
2
4
induces the formation of the complex Mg Mn O
3
0.4
1.6
mation of anhydrous manganese oxalate occurs in two
having the structure of α-Mn O .
2
3
stages to give intermediately MnC O (HOCH CH OH),
2
4
2
2
which decomposes upon temperature rise according to
the following equation:
According to SEM and optical microscopy, thermal
decomposition of MnC 3H and
MnC O (HOCH CH OH) in air or in an inert gas envi-
ronment completely conserves the crystal shape of the
initial compound. An increase in temperature to 700°ë
does not result in a substantial change in the particle
O
·
O
2
2
4
2
4
2
2
MnC O (HOCH CH OH)
2
4
2
2
(2)
MnC O + HOCH CH OH.
2
4
2
2
Reaction (2) describes an irreversible process, shape or size. Figure 3 shows the SEM images of
because it had been shown that anhydrous oxalates do MnC O · 3H O, MnC O (HOCH CH OH), and the
2
4
2
2
4
2
2
not react with ethylene glycol [2, 3].
products of thermolysis of the solvate in air and in the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 7 2009

1
038
GYRDASOVA et al.
a)
(
(b)
3
3
2
2
1
1
1
0
20
30
40
50
60 10
20
30
40
2θ, deg
50
60
2
θ, deg
Fig. 2. X-ray diffraction patterns of a: (1) MnC O · 3H O, (2) MnC O (OHCH CH OH), (3) MnC O ; b: products of thermolysis
2
4
2
2
4
2
2
2 4
of the solvates MnC O (OHCH CH OH) in air at 450°ë: (1) based on MnC O · 3H O (Mn O ), (2) based on MnC O · 2H O
2
4
2
2
2
4
2
2
3
2
4
2
(
Mn O ), and (3) in an inert gas atmosphere at 600°ë (MnO).
3 4
inert gas environment. Manganese oxalate trihydrate chains connected to one another by hydrogen-bonded
tends to form needles about 1 µm in diameter (Fig. 3a). bridging water molecules. Since the water molecules in
The solvate MnC O (HOCH CH OH) crystallizes as MnC O · 3H O are nonequivalent, its IR spectrum
2
4
2
2
2
4
2
thinner needles and fibers that tend to longitudinally exhibits, in the ν(H O) stretching region, an intense
2
–
intergrow (Fig, 3b). As can be seen from Fig. 3c, heat-
broad band with maxima at 3417, 3317, and 3144 cm
ing of MnC O (HOCH CH OH) in air and in an inert
1
2
4
2
2
. The intense broad band with absorption maxima at
689 and 1606 cm corresponds to asymmetric stretch-
ing vibrations (ν ) of the O–C–O groups of the oxalate
gas environment results in separation of the initial crys-
tals into thinner extended aggregates of Mn O and
–1
1
2
3
as
MnO, respectively.
2–
ion. Usually the bending vibrations C O occur in the
2
4
Analysis of the IR spectra of MnC O · 3H O,
2
4
2
same region but due to the superimposition of more
2
–
MnC O , and MnC O (HOCH CH OH) presented in
2
4
2
4
2
2
intense bands of the C O ion, it is impossible to dis-
2
4
Fig. 4 and in the table indicates that the denticity of the
tinguish them in Fig. 4. The symmetrical δ(H O) vibra-
2
–
2
C O ion in the compounds is retained. According to
2
4
tions are responsible for two narrow intense lines at
–
1
X-ray diffraction data [7], the crystal structure of 1374 and 1318 cm . In the region of bending δ(OCO)
MnC O · 3H O is formed by infinite –M–C O –M–C O – modes and libration modes ρ(OCO) of coordinated
2
4
2
2
4
2
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 7 2009

SYNTHESIS OF MICRO- AND NANOSIZED MANGANESE OXIDES
1039
(
‡)
(b)
5
µm
(
c)
(d)
Fig. 3. SEM images (×2500) of (a) MnC O · 3H O, (b) MnC O (HOCH CH OH), (c) product of thermolysis of the solvate in air at
2
4
2
2
4
2
2
450°ë, (d) product of thermolysis in a helium atmosphere at 600°ë.
3
water molecules, the spectrum contains three bands at
–1
8
09, 759, and 617 cm . The weak bands with maxima
–1
at 496 and 410 cm can be assigned to Mn–O stretch-
ing vibrations in the MnO octahedra.
6
The IR spectrum of MnC O (HOCH CH OH) is a
2
4
2
2
superposition of absorption bands of the tetradentate
2
2
–
C O ion and manganese-coordinated ethylene glycol
2
4
molecules [8, 9]. As a result of ethylene glycol substi-
tution for water in the structure MnC O · 3H O, the
2
4
2
asymmetric stretching bands ν (OCO) in the IR spectra
as
of the solvates MnC O (HOCH CH OH) are split into
2
4
2
2
–1
three components (1699, 1685, and 1619 cm ). Simul-
1
taneously, the band ν(OH) shifts to lower frequency
–1
–1
(
3190 cm ) by approximately 180 cm with respect to
its position in the IR spectrum of liquid ethylene glycol
–
1
(
(
3368 cm [9]) (table). The C–O stretching bands
–1
–1
1087, 1043 cm ) and CH libration bands (883, 864 cm )
2
–1
3600 3200 2400 1800 1400 1000 600
in ethylene glycol [9] also shift to lower (1069, 1029 cm )
–
1
ν, cm
–1
and to higher (891, 878 cm ) frequency, respectively,
in the solvate spectrum. The band shifts noted in the IR
spectrum of MnC O (HOCH CH OH), together with
Fig. 4. IR spectra of (1) MnC O · 3H O, (2)
2
4
2
MnC O (HOCH CH OH), and (3) MnC O .
2
4
2
2
2
4
2
2
2 4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 7 2009

1
040
GYRDASOVA et al.
–
1
IR absorption maxima (cm ) of (1) MnC O · 3H O and (2) the change in the band intensity, attest to a pronounced
2
4
2
MnC O , (3) assignment of bands according to [6], (4)
MnC O (HOCH CH OH), and (5) HOCH CH OH (liquid)
2
4
interaction of ethylene glycol molecules with the man-
ganese cations. The IR spectrum of anhydrous manga-
nese oxalate obtained by heating of the trihydrate in
ethylene glycol, the asymmetric stretching vibrations
2
4
2
2
2
2
1
2
3
4
5
ν (OCO) are manifested as a very broad intense band
as
3
3
3
1
1
1
1
417 (vs)
317 (vs)
141 (vs)
ν(H O)
3190 (sh) 3368 (vs)
2960 (w) 2943 (vs)
2
–1
at 1642 cm , the symmetric vibrations ν (OCO) are
s
–1
responsible for two narrow lines at 1354 and 1317 cm . In
the regions of δ(OCO) bending mode and Mn–O
stretching mode, the spectrum has a very narrow
–1
intense band at 792 cm and a narrow medium-inten-
689 (vs) 1716 (vs) ν (OCO)
as
–1
sity band at 514 cm , respectively.
607 (vs) 1642
δ(H O)
2
Thus, moderate heating (to about 50–100°ë) of
manganese oxalate di- or trihydrate with ethylene gly-
col results in the displacement of water molecules from
the oxalate structure and their replacement by one eth-
ylene glycol molecule, the shape of crystals of the ini-
tial compound being retained. When needle MnC O ·
373 (m) 1354 (m) νs(OCO)
318 (s) 1317 (s) ν(CO)
2852 (w) 2878 (s)
2738 (w)
2
633 (w)
1699 (s)
684 (s)
2
4
3
H O is used as the precursor, the solvates
2
8
09 (m) 791 (m) δas(OCO)
MnC O (HOCH CH OH) are formed as extended
2
4
2
2
1
micro- and nano-sized crystals. As the temperature of
the reaction mixture increases, the solvate is destroyed
to give MnC O . It was shown that intercalation of
7
6
4
4
59 (m)
ρ(H O)
1618 (vs) 1458 (c)
1460 (m) 1408 (s)
2
2
4
MnC O · 3H O with magnesium markedly increases
18 (m)
2
4
2
the stability of the initial compound and the solvates. In
all cases, thermolysis of the solvates in air and in an
inert environment gave simple or complex oxides with
retention of the shape of particles of the initial com-
pounds.
96 (w) 514 (m) ν(MO)(C O ) 1362 (m) 1332 (w)
2
4
10 (w) 496 (m) δs(OCO)
10 (s) ν(MO)
1316 (s) 1255 (w)
1228 (w) 1204 (w)
4
1
069 (s) 1087 (vs)
029 (m) 1043 (vs)
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Note: ρ(H O) are rocking and wagging vibrations of water molecules
2
[
6]; vs is very strong, s is strong, m is medium, w is weak, sh is
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 7 2009