64
T. Rakitskaya et al.
Table 1 Phase compositions and phase parameters for the manganese oxide samples under study
Sample
Phase
Phase
content,
wt%
Lattice
parameters (Å)
Crystallite size
(nm)/V (Å 3 )
OMS-2(SSt)
K x Mn 8 O 16 (cryptomelane)
85.3 (4)
a = 9.8552
10/277.03
c = 2.85231
β-MnO 2 (pyrolusite)
14.72 (4) a = 4.3915
28/55.360
c = 2.8706
OMS-2(Ref)
K x Mn 8 O 16 (cryptomelane)
90.5 (3)
a = 9.8306
15/275.095
c = 2.84655
Mn 2 O 3 -Ht (bixbyite)
9.49 (2)
a = 9.38922
66/827.729
OMS-2(SG)
K x Mn 8 O 16 (cryptomelane)
100.0 (4) a = 9.82216
36/275.476
c = 2.85542
OMS-2(MS)
K x Mn 8 O 16 (cryptomelane)
100.0 (1) a = 9.8389
14/276.527
c = 2.8532
differ in their crystallite sizes. OMS-2(SG) is characterized by the largest crystallite
size of 36 nm, whereas the crystallite sizes for other OMS-2 samples vary from 10
to 15 nm.
Among the impurity phases, bixbyite has the largest crystallite size of 66 nm.
Different parameters and unit cell volumes of the OMS-2 samples synthesized by
different methods give evidence of some structural differences. The largest expansion
of a unit cell is observed for OMS-2(SSt) (Table 1).
3.2 FT-IR Spectroscopy
Figure 2 shows some fragments of FT-IR spectra for the synthesized OMS-2 samples
in the range of 1100-400 cm
−1 . Their analysis and comparison with data reported [36,
38–42] allow us to conclude that these FT-IR spectra are typical for cryptomelane.
Absorption bands in the 700–459 cm
−1 region are assigned to vibrations of the MnO 6
octahedral structure; weak absorption bands at 1046, 1047, 1073, and 1045 cm
−1
are attributed to the Mn-OH structure fragment. The absorption bands of stretching
and deformation vibrations of water molecules are very weak and therefore are not
shown in Fig. 2.
T. Rakitskaya et al.
Table 1 Phase compositions and phase parameters for the manganese oxide samples under study
Sample
Phase
Phase
content,
wt%
Lattice
parameters (Å)
Crystallite size
(nm)/V (Å 3 )
OMS-2(SSt)
K x Mn 8 O 16 (cryptomelane)
85.3 (4)
a = 9.8552
10/277.03
c = 2.85231
β-MnO 2 (pyrolusite)
14.72 (4) a = 4.3915
28/55.360
c = 2.8706
OMS-2(Ref)
K x Mn 8 O 16 (cryptomelane)
90.5 (3)
a = 9.8306
15/275.095
c = 2.84655
Mn 2 O 3 -Ht (bixbyite)
9.49 (2)
a = 9.38922
66/827.729
OMS-2(SG)
K x Mn 8 O 16 (cryptomelane)
100.0 (4) a = 9.82216
36/275.476
c = 2.85542
OMS-2(MS)
K x Mn 8 O 16 (cryptomelane)
100.0 (1) a = 9.8389
14/276.527
c = 2.8532
differ in their crystallite sizes. OMS-2(SG) is characterized by the largest crystallite
size of 36 nm, whereas the crystallite sizes for other OMS-2 samples vary from 10
to 15 nm.
Among the impurity phases, bixbyite has the largest crystallite size of 66 nm.
Different parameters and unit cell volumes of the OMS-2 samples synthesized by
different methods give evidence of some structural differences. The largest expansion
of a unit cell is observed for OMS-2(SSt) (Table 1).
3.2 FT-IR Spectroscopy
Figure 2 shows some fragments of FT-IR spectra for the synthesized OMS-2 samples
in the range of 1100-400 cm
−1 . Their analysis and comparison with data reported [36,
38–42] allow us to conclude that these FT-IR spectra are typical for cryptomelane.
Absorption bands in the 700–459 cm
−1 region are assigned to vibrations of the MnO 6
octahedral structure; weak absorption bands at 1046, 1047, 1073, and 1045 cm
−1
are attributed to the Mn-OH structure fragment. The absorption bands of stretching
and deformation vibrations of water molecules are very weak and therefore are not
shown in Fig. 2.