ISSN 03615219, Solid Fuel Chemistry, 2010, Vol. 44, No. 2, pp. 118–123. © Allerton Press, Inc., 2010.

Original Russian Text © T.P. Miloshenko, O.Yu. Fetisova, M.L. Shchipko, S.A. Mikhailenko, N.I. Pavlenko, A.M. Zhizhaev, V.F. Kargin, 2010, published in Khimiya Tverdogo
Topliva, 2010, No. 2, pp. 56–60.

Synthesis and Properties of Porous Carbon Materials

from Natural Cryptocrystalline Graphites
T. P. Miloshenko, O. Yu. Fetisova, M. L. Shchipko, S. A. Mikhailenko,
N. I. Pavlenko, A. M. Zhizhaev, and V. F. Kargin
Institute of Chemistry and Chemical Technology, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, Russia
email: fou1978@mail.ru
Received September 14, 2009

Abstract—The applicability of cryptocrystalline graphites as porous carbon materials was studied. The prop
erties of the resulting products were examined with the use of various physicochemical methods of analysis.
DOI: 10.3103/S0361521910020084

The chemical intercalation of natural crystalline Graphite from the Noginsk deposit was a native
graphites followed by thermal treatment is in wide cur sample, pieces of size 100–500 mm. Table 1 summa
rent use for the manufacture of carbon materials with rizes the characteristics of the initial graphite samples.
unique properties, which find increasing use in indus
try. However, according to a dispersion–structure The test natural graphites had high concentrations
classification [1], natural graphites from the Noginsk of mineral impurities. According to published data [2],
and Kureika deposits in Krasnoyarsk krai belong to a the removal of mineral impurities from carboncon
cryptocrystalline type, which is unsuitable for this pur taining raw materials considerably increased the reac
pose. tivity of the raw materials because of the appearance of
an additional pore space and the deblocking of unoc
The aim of this work was to develop new oxidative cupied pores; this was responsible for the appearance
modification and thermal treatment methods for the of additional paths for reagent transport. Upon
manufacture of porous carbon materials (PCMs) from mechanical sample preparation, particles from the
cryptocrystalline graphites. inner surface of a mill, which wore out in the course of
operation, entered into graphite. Therefore, the
ground sample was subjected to magnetic separation
EXPERIMENTAL to remove rubbed and oxidized iron. Then, the sample
Natural graphites from the Noginsk and Kureika was heated to 100°C in order to convert diamagnetic
deposits in Krasnoyarsk krai were used as starting raw components (goethite, hydrogoethite, and hematite)
materials. into a ferromagnetic and the separation was repeated.
The weight of the treated sample after separation was
Graphite from the Kureika deposit was a native about 97–98% on an initial sample basis.
sample, pieces of size 100–500 mm. Mineralogical
studies demonstrated that it had a finegrained texture The subsequent demineralization of graphite sam
with considerable dispersed lamellar (mica and chlo ples was initially performed by treatment with hydro
rite) and round (pyrite and calcite) inclusions with an chloric acid at a ratio of graphite : HCl : H2O = 1 : 3 :
average particle length of 20–40 µm and a width of 2– 3 on boiling for 12 h and then with hydrofluoric acid at
4 µm. a concentration of 38.2% at a ratio of graphite : HF =

Table 1. Characteristics of parent graphites

Proximate analysis, % Ultimate analysis, % on a daf basis

Sample
Wa Ac Vdaf C H S N+O

Kureika graphite 1.30 11.99 1.35 97.76 0.53 0.39 1.32

Noginsk graphite 2.96 16.11 1.34 95.19 1.90 0.32 2.59

118
 SYNTHESIS AND PROPERTIES OF POROUS CARBON MATERIALS 119

1 : 2 with stirring for a day. The sample was thoroughly Table 2. Ultimate analysis of PCM samples from Kureika
washed with distilled water and dried at 105°C to con graphite (KG PCM) and Noginsk graphite (NG PCM), %
stant weight.
Ultimate analysis, % on a daf basis
The following reagents were used in this study: acid Sample
melange (GOST [State Standard] 150078), chemi C H S N+O
cally pure hydrochloric acid (GOST 311877), and
commercial hydrofluoric acid (GOST 256789). KG PCM 65.1 1.18 0.03 33.69
The porous carbon materials were prepared from NG PCM 78.4 2.30 0.05 19.25
Kureika and Noginsk graphites in the following man
ner: 5 g (7.5 ml) of absolutely dry demineralized
graphite with a particle size of 0.2–0.4 mm was placed Table 3. Experimental design for the preparation of PCM
in a 250ml heatresistant glass beaker, and 52.5 ml of from Kureika graphite and the experimental results
melange (water duty of 1 : 7) was added. The beaker
was closed with a cap, and the contents were boiled for Hydro Process KG PCM yield, %
10 h. After cooling, the reaction mass was filtered. The No. modulus time (X2),
dark brown filtrate was centrifuged. The liquid phase (X1) h Y1 Y1
was decanted, and distilled water was added; the con 1 3 2.5 10.0 10.2
tents were centrifuged once again. The steps were
repeated until pH 7 in the liquid phase. The resulting 2 5 2.5 16.0 16.1
solid residue was dried at 105°C to constant weight. 3 7 2.5 15.8 15.8
The thermal expansion of dry material was performed 4 3 6.5 16.0 15.9
in a 90ml stainless steel reactor preheated to 800°C
for 3 min. The yields of thermally treated materials 5 5 6.5 20.8 20.7
from Kureika and Noginsk graphites were 1.015 and 6 7 6.5 20.6 20.7
0.81 g (20.3 and 16.2%), respectively. Table 2 summa
7 3 10.5 14.2 14.3
rizes the ultimate analysis data for the resulting sam
ples. 8 5 10.5 20.6 20.6
9 7 10.5 17.9 18.0
RESULTS AND DISCUSSION
The Experimental design unit from the Statgraphics As a result of decoding the found values, the opti
Plus program package was used for optimizing the mum values of factors in a natural form were found:
conditions of PCM preparation from graphites with Х1 = 5.66 (hydromodulus) and Х2 = 7.49 h (process
consideration for procedures described in a mono duration).
graph [3].
The mathematical treatment of the experimental
The following factors were chosen as independent results for the preparation of PCM from Noginsk
variables: X1, (the volume ratio graphite : melange) graphite was performed in an analogous manner. A
and X2, the process time of graphite treatment with regression equation was obtained; as a result of decod
melange, h. To determine the effects of the above fac ing, the optimum process parameters in a natural form
tors on the yield of PCM, the Ko2 design was imple were determined: Х1 = 5.60 (hydromodulus) and Х2 =
mented. Each of the experiments was performed 7.42 h (process duration).
twice.
Data summarized in Table 3 were used to evaluate Thus, under optimum experimental conditions,
the effects of the above factors on the yield of PCM PCMs were prepared from Kureika and Noginsk
from graphites. graphites in 21.7 and 16.5%, respectively. In this case,
the calculated parameters were consistent with exper
As a result of the computerassisted processing of imental data to demonstrate the adequacy of the
experimental data, the following regression equation model.
was obtained:
A specific feature of graphite matter responsible for
У1 = 21.350 + 2.350Х1 its low reactivity is not only its physical and chemical
(1) stability but also its surface inaccessible to reagents.
+ 1.808Х2 – 3.350Х12 – 0.500Х1Х2 – 3.325Х2 2. The mechanochemical activation of graphite can be
considered as grinding, which increases the specific
Figure 1 shows the response surface of the output surface area by decreasing the geometric sizes of parti
parameter—the yield of PCM from Kureika graph cles and opening previously inaccessible pores. To
ite. increase the yield of PCM, mechanical actions on the

SOLID FUEL CHEMISTRY Vol. 44 No. 2 2010

120 MILOSHENKO et al.

22

KG PCM yield, % (Y1)

20
18
16
14
12 10.5
8.9
10 7.3
3.0 5.7
3.8 4.6 4.1
5.4 6.2 7.0 2.5 Time, h (X2)
Hydromodulus (X1)

Fig. 1. Response surface of the output parameter Y1—PCM yield from Kureika graphite.

initial graphite structure were used, in particular, with Кр = 50 (Кр is the coefficient of thermal expansion).
activator mills [4]. An analysis of relevant published data and the results
of our experiments demonstrated that, in accordance
It was experimentally found that the mechanical with all of the previously known procedures for the
activation of graphites resulted in a considerable preparation of TEG from cryptocrystalline graphites,
increase in the yield of the end product—PCM (to the coefficient of thermal expansion was no higher
73%) (see Fig. 2). At the same time, the stepwise than 10.
mechanical activation and demineralization of sam
ples allowed us to considerably decrease the concen Xray diffraction analysis was performed on a
tration of mineral impurities, as compared with the DRON3 Xray diffractometer (Russia) with the use
initial sample (from 1.56 to 0.30%). It is likely that a of СuKα radiation (λ = 1.541 Å); the pointbypoint
graphite grain containing a mineral component scanning was performed at a step of 0.02 deg, and the
released a portion of this component upon degrada accumulation time at a point was 1 s.
tion (see Fig. 3). The morphology of the parent graphite and the
In addition to a decrease in the ash content of par product prepared from it were studied by scanning
ent graphite and an increase in the yield of the pre electron microscopy (SEM) on a LEO32 instrument
pared PCM, the stepwise mechanical activation and (Germany).
demineralization followed by graphite treatment with The IR spectra were measured on a Vector 22 Fou
melange in accordance with our procedure allowed us rier transform IR spectrometer (Bruker) in a KBr
to obtain thermally expanded graphite (TEG) with matrix at a constant concentration of the test sub

KG PCM yield, % Sample ash content, %

80 3.0
70
2.5
60
2.0
50
1.5
40
1.0
30
0.5
20
0 5 10 15 20 25 30 0
5 10 15 20 25 30
Mechanical activation time, h Mechanical activation time, h

Fig. 2. Effect of mechanical activation time on the yield of Fig. 3. Effect of Kureika graphite mechanical activation
PCM from Kureika graphite. time on the ash content of the sample.

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 SYNTHESIS AND PROPERTIES OF POROUS CARBON MATERIALS 121

stance. The computer processing of spectroscopic Table 4. Texture characteristics of PCM samples from
information was performed with the use of the OPUS graphites according to data on nitrogen adsorption (77 K)
3 program, version 2.2. and sorption activity toward methylene blue (MB)
Information on the electronic states of surface Sorption
atoms in the resulting PCMs was obtained from an SBET, Vtotal, Dpore,
Sample capacity for
analysis of spectra measured by Xray photoelectron m2/g cm3/g nm MG, mg/g
spectroscopy (XPS). A SPECS spectrometer (Ger
many) was used. A vacuum of no lower than 10–9 mbar NG PCM 520 0.291 2.2 33.2
was maintained in the analytical chamber. The optical
absorption spectra of substances in the region of KG PCM 620 0.319 2.0 30.6
300⎯1000 nm were measured on a Shimadzu UV300
spectrometer.
The adsorption measurements were performed of Xrays from less ordered structural fragments. In the
with the use of an ASAP2420 V2.02J instrument. The general case, the distribution of interplanar distances
specific surface areas of samples were determined in (d) is unknown.
accordance with the BET method. The predominant The diffraction pattern changed after chemical
pore diameter was calculated from the desorption demineralization (Fig. 4). A rather narrow and intense
branch of an isotherm with the use of the Barret– peak corresponding to an index of 002 with a maxi
Joyner–Halenda (BJH) model. mum at d = 3.35 Å appeared. Thus, we can state an
The N2 adsorption–desorption isotherms for sam increase in the concentration of ordered carbon struc
ples prepared from Kureika and Noginsk graphites are tures in demineralized graphite, as compared with
generally similar. They have a Langmuir shape, con parent graphite.
tain a capillarycondensation hysteresis loop, and
belong to type IV isotherms (according to the The diffraction patterns of the prepared PCM
Brunauer–Deming–Deming–Teller classification). exhibited a dramatically different behavior. A broad
These isotherms differed in only the capacity of ening of the (002) diffraction line of graphite and the
a monolayer. In a PCM sample prepared from formation of a halo suggest the presence of a finecrys
Kureika graphite, the monolayer capacity was about talline (amorphous) carbontype material. The dif
fraction pattern of the resulting samples was different
180 cm3/g, whereas this value was ~150 cm3/g in a
from those of the wellknown carbon structures (lons
PCM from Noginsk graphite. It is well known [5] that
daleite, graphite, chaoite, carbyne, fullerene, its deriv
the number of active sites is proportional to the capac
atives, etc.). It is believed that the treatment of parent
ity of a monolayer.
graphite with melange released an amorphous carbon
The adsorption volumes given in Table 4 were component of graphite, which formed a product with
determined atР/Р0= 0.97. specific properties in the course of carbonization.
Capillary hysteresis appears because of adsorption
in intermediate pores (2–50 nm) [6], and the loop
area is proportional to the fraction of these pores in the Intensity, arb. units
total pore space volume. Unclosed hysteresis is a sign 5000
of the presence of micropores. In addition, because of
the occurrence of capillary hysteresis, we can hypoth
4000
esize that pores in the test samples have the shape of
bottles or beads. The emptying of these pores comes
into play at a lower vapor pressure than the filling. 3000
In general, the pore structure of the test samples
has a bimodal character with maximums at 20 and 2000
37 Å with almost no macropores. In the case of the
PCM from Noginsk graphite, the pore structure
mainly consisted of mesopores (37 Å). 1000
Additional data on the structures of graphite and
product samples were obtained using Xray diffraction 0
analysis. The analysis of Kureika and Noginsk graphi
tes was difficult to perform because reflections in the 0 10 20 30 40 50 60 70 80
test range of angles 2θ = 5–80° were diffuse and asym Bragg angle, deg
metric. The asymmetry of the (002) reflection on the
side of small angles is usually explained by the contri Fig. 4. Xray diffraction pattern of a demineralized sample
bution of a set of γbands resulting from the scattering of Kureika graphite.

SOLID FUEL CHEMISTRY Vol. 44 No. 2 2010

122 MILOSHENKO et al.

in this region were due to the deformation vibrations of

А phenolic and alcoholic OH groups with the necessary
C–O stretching vibrations of alcohols (1350–
1260 cm–1). Absorption bands in the region of 1250–
1050 cm–1 were due to the vibrations of C–O groups in
esters and ethers.
In the IR spectrum of the PCM prepared from
Kureika graphite, mediumintensity absorption bands
at 1625 and 1740 cm–1 were recognized; these bands
can belong to the absorption of aromatic fragments
containing the carbonyl group (C=O). The intensity
of a characteristic absorption band (~3400 cm–1)
10 µm responsible for intermolecular hydrogen bonds con
siderably increased.
B In the spectral region of 2700–3000 cm–1, the
PCM prepared from Kureika graphite clearly exhib
ited absorption bands at 2848, 2925, and 2975 cm–1
due to the stretching vibrations of aliphatic C–H
bonds. The separate assignment of absorption to ali
phatic groups like CH3 , CH2 , and CH was contradic
tory.
The occurrence of a large number of oxygencon
taining functional groups on the surface of the PCM
prepared from Kureika graphite was supported using
XPS. The binding energy of electrons at C 1s and O 1s
lines found from the analysis of XPS spectra allowed us
10 µm to judge the electronic states of surface atoms.
The deconvolution of the C 1s spectrum of the
Fig. 5. Electron micrographs of (a) parent Noginsk graph PCM prepared from Kureika graphite (KG PCM)
ite and (b) PCM prepared from it (×1000). afforded the following four main peaks: graphitized
carbon (peak I, 284.6 eV); phenolic, alcoholic, and
ether C–O bonds (peak II, 286.1 eV); carbonyl or
According to electronmicroscopic data, the par quinone groups (peak III, 287.5 eV); and carboxyl
ent graphite consisted of differently shaped particles, groups (peak IV, 289.1 eV).
mainly, with sharp edges (Fig. 5a). Particle sizes varied
The O 1s spectrum afforded two main peaks due to
over a wide range from 5 to 70 µm. A developed poros
ketone, lactone, and carbonyl C=O groups (peak I,
ity was not observed visually in the parent graphite. On
531.2 eV) and C–OH and/or C–O–C groups (peak
the contrary, the PCM prepared from Noginsk graph
II, 532.8 eV).
ite exhibited a clearly distinguishable developed pore
system (Fig. 5b).
The PCM particles were roundshaped. The parti CONCLUSIONS
cle size was several times greater than that of the parent A procedure was proposed for converting cryptoc
graphite (from 200 to 400 µm). It is likely that the rystalline graphite into a watersoluble state.
aggregation of dispersed (after chemical modification) The occurrence of an amorphous phase after
graphite particles occurred in the course of carboniza chemical modification was demonstrated using physi
tion with the formation of coarse porous particles. cochemical techniques.
IR spectroscopy was used to qualitatively study the A sorbent with a specific surface area of about
surface states of Kureika graphite and the PCM pre 600 m2/g was prepared.
pared from it.
A comparison between the spectra of parent REFERENCES
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SOLID FUEL CHEMISTRY Vol. 44 No. 2 2010

 SYNTHESIS AND PROPERTIES OF POROUS CARBON MATERIALS 123

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SOLID FUEL CHEMISTRY Vol. 44 No. 2 2010