XPS characterization of sodium percarbonate granulated with sodium silicate

Article abstract of DOI:10.1134/S0036023609090198

Granular sodium percarbonate has been characterized by X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The O1s binding energy for the solvating hydrogen peroxide molecules is 535.8 eV. Sodium percarbonate is s

Full text of DOI:10.1134/S0036023609090198

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 9, pp. 1455–1458. © Pleiades Publishing, Inc., 2009.
Original Russian Text © A.V. Zhubrikov, E.A. Legurova, V. Gutkin, V. Uvarov, N.V. Khitrov, O. Lev, T.A. Tripol’skaya, P.V. Prikhodchenko, 2009, published in Zhurnal Neor-
ganicheskoi Khimii, 2009, Vol. 54, No. 9, pp. 1526–1529.
PHYSICAL METHODS
OF INVESTIGATION
XPS Characterization of Sodium Percarbonate Granulated
with Sodium Silicate
A. V. Zhubrikova, E. A. Legurovab, V. Gutkinc, V. Uvarovc, N. V. Khitrova,
O. Levc, T. A. Tripol’skayab, and P. V. Prikhodchenkob
a OAO Khimprom, Promyshlennaya ul. 101, Novocheboksarsk, 429952 Chuvash Republic, Russia
b Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
c Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem, Israel
Received October 30, 2008
Abstract—Granular sodium percarbonate has been characterized by X-ray powder diffraction, scanning elec-
tron microscopy, and X-ray photoelectron spectroscopy. The O1s binding energy for the solvating hydrogen
peroxide molecules is 535.8 eV. Sodium percarbonate is stabilized by sodium silicate and polyphosphate.
DOI: 10.1134/S0036023609090198
Sodium percarbonate (sodium carbonate peroxyhy- ate in a spray drier at OAO Khimprom. The material
drate, Na2CO3 · 1.5H2O2, PCS), both alone and in com-
bination with other chemicals, is employed as a solid
source of active oxygen in the textile, chemical, and
other industries and as a bleaching agent in synthetic
detergents [1]. PCS, known for over a century [2], was
characterized by various physicochemical methods.
The PCS structure was determined by X-ray crystallog-
raphy. It was found that the hydrogen peroxide mole-
cules in PCS are solvating and are bound to the carbon-
ate ion by hydrogen bonds [3, 4]. In PCS production,
granulating and stabilizing agents are introduced into
the product. PCS granulation is most often ensured by
adding sodium metasilicate. PCS granules can be stabi-
lized by encapsulation into a substance unaffected by
humid air.
Here, we report XPS data for PCS obtained at the
research center of OAO Khimprom (Novochebok-
sarsk). The purpose of this study was to elucidate the
roles of the components of the product in PCS stabili-
zation. In addition to clarifying this practical issue, we
address the fundamental problem of obtaining XPS
data for the oxygen atoms in the hydrogen peroxide
molecule. This problem is of vital importance because
XPS is widely used in the study of semiconducting
nanomaterials, whose properties depend on the oxida-
tion state of their oxygen atoms, which varies upon the
adsorption of atmospheric oxygen on the surface [5, 6].
No XPS data have been reported for peroxysolvates to
date, and this makes XPS data for other oxygen-con-
taining compounds difficult to interpret.
examined in this work was 1-mm spherical granules
made up of fine PCS crystals (Fig. 1).
As determined by permanganatometry [7], the
active oxygen content of PCS is 12.8 wt % (the calcu-
lated active oxygen content of Na2CO3 · 1.5H2O2 is
15.3 wt %).
The phase composition of PCS was determined by
X-ray powder diffraction on a D8 Advance diffracto-
meter (Bruker AXS, Karlsruhe, Germany) using CuKα
radiation. It was found that the PCS granules contain
orthorhombic Na2ëé3 · 1.5ç2é2 (Fig. 2) [3, 4]. No
other crystalline phases were detected in PCS.
X-ray photoelectron spectra were recorded on a
Kratos Axis photoelectron spectrometer equipped with
an X-ray monochromator and an AlKα source (1486.7 eV).
In the surface analysis of PCS granules, the samples
were the granules themselves. In order to determine the
bulk composition of the granules, they were ground and
the surface of the resulting powder was examined. The
charging effect arising from photoemission was taken
into account using the internal standard technique. The
internal standard was the C1s- spectrum of sodium per-
carbonate, in which the 1s binding energy was taken to
be equal to that of sodium carbonate [8]. An analysis of
photoemission spectra and calculation of relative ele-
ment contents were carried out using the Vision Pro-
cessing program (Kratos Analytical Ltd.) and the
CasaXPS program (Casa Software Ltd.). Peak decon-
volution into components and determination of their
positions and integrated intensities were carried out by
fitting to a combination of symmetric Gaussian and
EXPERIMENTAL
PCS samples were obtained by crystallization from
a water–hydrogen peroxide solution of sodium carbon- Lorentzian functions (30 and 70%, respectively).
1455

1456
ZHUBRIKOV et al.
2 mm
500 µm
Fig. 1. SEM images of sodium percarbonate granules.
I
5
10
20
30
40
2θ, deg
50
60
70
Fig. 2. X-ray powder diffraction pattern from sodium percarbonate (ꢀ—reflections from orthorhombic Na CO · 1.5H O ).
2
3
2 2
RESULTS AND DISCUSSION
interesting that the silicon content of the granule bulk is
over 2.5 wt %; hence, the Na2SiO3 content will be at
least 10 wt % even if the water of crystallization is
ignored. Nevertheless, no crystalline phases other than
orthorhombic PCS were detected by X-ray diffraction
(Fig. 2). This is indirect evidence that X-ray-amor-
phous, gellike sodium persilicate forms during the pro-
duction of the material and it is this compound that
binds the sodium percarbonate crystals into granules.
Although the sodium persilicate structure and forma-
tion conditions have not been determined for certain
[9–12], an analysis of preliminary data together with
the PCS synthesis conditions suggests that the product
contains sodium persilicate.
The results of elemental analysis of PCS samples by
XPS are presented in the table. According to these XPS
data, the major elements of PCS are carbon, sodium,
and oxygen. The relative amounts of these elements are
consistent with the elemental composition of PCS, the
main phase of the samples. The surface is poorer in
oxygen than the sample bulk. This can be explained by
PCS decomposition to sodium carbonate on the surface
and by the stabilization of peroxo compounds in the
granule bulk. It follows from the elemental analysis
data and PCS synthesis conditions that the samples
contain sodium silicate, sulfate, chloride, and poly-
phosphate. The sulfate, chloride, and silicate percent-
ages are higher in the granule bulk, while most of the
phosphate is on the granule surface. Therefore, the PCS
granules are encapsulated in sodium polyphosphate.
No other elements were detected in the samples. It is
The X-ray photoelectron spectrum of PCS shows
Na1s, C1s, Cl2p, S2p, P2p, and Si2p lines (Fig. 3), which
are due to the Na+, CO32–, Cl–, SO24–, phosphate, and
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 9 2009

XPS CHARACTERIZATION OF SODIUM PERCARBONATE GRANULATED
1457
XPS elemental analysis data for PCS
silicate ions, respectively, and also a complex é1s peak
(Figs. 3, 4). This peak has two maxima of different
intensities; however, it cannot be deconvolved satisfac-
torily into only two components (even when asymmet-
ric functions are used). The é1s peak can be decon-
volved into three components at binding energies of
531.1, 532.6, and 535.8 eV with integrated intensity
ratios of 4.6 : 1.1 : 1.0. The strongest peak, which
occurs at a binding energy of 531.1 eV, is due to the
oxygen atoms in the carbonate ions of sodium carbon-
ate [8, 13].
PCS granules
(surface analysis)
Peak
PCS powder
(bulk analysis)
Atomic con- Weight con- Atomic con- Weight con-
centration, % centration, % centration, % centration, %
Na1s
O1s
28.12
54.19
15.70
0.37
36.65
49.15
10.69
0.75
23.60
58.03
15.95
0.37
31.26
53.51
11.04
0.76
C1s*
Cl2p
S2p
The component occurring at the highest binding
energy, 535.8 eV, should be assigned to the peroxide
oxygen atoms in PCS. The comparatively low intensity
of this component is likely due to PCS decomposition
on the sample surface under conditions of a high vac-
uum and X-ray irradiation. This yields sodium carbon-
ate, gives rise to a strong peak from the oxygen atoms
in the carbonate ion, and reduces the é1s peak compo-
nents due to the initial compound. No XPS data have
been reported for solvating hydrogen peroxide, and the
data available on peroxo derivatives are scanty. This is
0.01
0.02
0.24
0.44
P2p
1.03
1.82
0.26
0.47
Si2p
0.58
0.92
1.56
2.52
pounds under the severe conditions of XPS measure-
ments. We obtained the first data for compounds con-
taining hydrogen peroxide molecules. The é1s binding
energy for PCS (535.8 eV) is much higher than the
same binding energy for sodium and strontium perox-
likely explained by the instability of most peroxo com- ides (530.8 and 531.1 eV, respectively) [14]. Our data
I, arb. un.
100000
60000
20000
0
1200
1000
800
600
400
200
0
Binding energy, eV
Fig. 3. X-ray photoelectron spectrum of the sodium percarbonate powder.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 9 2009

1458
ZHUBRIKOV et al.
ACKNOWLEDGMENTS
I
This study was supported by the Russian Foundation
for Basic Research (project nos. 08-03-00537 and OFI 07-
03-12199) and by the Russian FederalAgency for Science
and Innovation (grant no. MK-3120.2008.3).
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1.5ç2é2 (1 : 1).
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