Gross R., Sidorenko A., Tagirov L. Nanoscale Devices - Fundamentals and Applications
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360 Z. A. Mansurov
Such increase of the gold (III) sorption velocity by means of the sorbent
CAS-2 can be explained by a catalytic effect: the sorbent CAS-2 reduces
iron (III) to iron (II), and copper (II) to copper (I). The ions of iron (II) and
copper (I) are formed at the surface of the sorbent and at once react with
gold (III) ions in oxidative-reducing interaction. As the reduction of gold
(III) by iron (II) and copper (I) ions occurs in the surface layer of the
sorbent, the metallic gold is extracted on this surface.
The process of gold (III) sorption in the presence of iron (II) salts
practically can be represented as following:
CAS-Red + Fe(III) → CAS + Fe(II) + Ox.
Au(II) + Fe(II) → Au
0
+ Fe(III)
In the presence of copper (II) salts:
CAS-Red + Cu(II) → CAS + Cu(I) + Ox
Au(III) + Cu(I) → Au
0
+ Cu(II)
The easiness of gold (III) sorption by iron (II) is widely used in analytical
methods of gold determination.
Thus, our study of gold (III) sorption on the sorbents CAS-1, CAS-2,
CAS-3 in a muriatic medium has shown that the sorbent CAS-2 has the
strongest sorption ability. As long as gold (III) sorption occurs it it reduced
to the metallic state. The stationary oxidative-reducing potentials of the
sorbents have been measured. The potentials ranged between 0.20 and
0.25 V. This demonstrates the possibility of oxidative-reducing interaction
with gold (III). The sorption velocity is decreased in the sequence CAS-2 >
CAS-1 > CAS-3. When studying the influence of Au (III) concentration,
sorbent mass and particle size on the sorption process it was found that the
gold (III) sorption velocity on the sorbents CAS is directly proportional to
the gold (III) concentration and the sorbent mass, whereas it is inversely
proportional to the particle diameter. It is shown that superior amounts (in
100-800 times) of the metal ions Fe(III), Cu(II), Cd(II), Zn(II), Hg(II),
Pt(IV), and Fe(III) do not impede to gold (III) sorption on the sorbent
CAS-2.
Mechanochemical Encapsulation of Quartz Particles in
Metalcarbon Films [6-7]
When one aims at obtaining composition nanomaterials, usually special
attention is paid to carbon- and silicon containing systems due to the
peculiarities of their properties and a wide range of applications. Surface
Some Applications of Nanocarbon Materials for Novel Devices 361
nanostructures play a significant role in such objects as highly disperse
adsorbents, catalysts, filling agents of composition materials as well as in
the materials for electronic industry. Mechanochemical synthesis has
several advantages compared to other methods in the production of highly
disperse nanostructured materials based on silicon containing materials. As
it was shown [6-7], it is possible to obtain quartz-based highly disperse
materials by mechanochemical synthesis, which exhibit simultaneously
interesting magnetic, dielectric and electric properties depending on the
regimes of treatment and the conditions of subsequent application.
In order to clarify why quartz-based highly disperse materials display the
abovementioned properties, structural investigations of the synthesized
material were carried out. EPR-spectroscopy has shown the presence of
para- and ferromagnetic centers in quartz particles after mechano-chemical
treatment. The presence of ferromagnetic part of the quartz EPR spectrum
indicates the presence of Fe-containing clusters on the surface of the
particles. The formation of Fe compounds connected with the quartz
surface was proven by Mössbauer spectroscopy. The applied methods of
our structural research have shown that structural and phase transformation
occurred on the surface of the quartz particles during the mechano-chemical
treatment. The detected compounds are composites of a modified quartz
surface and polymers formed on its surface.
The structure of the modified quartz particle and its transformation in the
process of mechano-chemical treatment is vividly shown by the results of
scanning electron microscopy studies. After grinding in a mill without
modifying the organic additives, the surface layer of the particle becomes
partially amorphous and the ultradisperse iron being ground is introduced
into the surface from the walls of the milling vessel and balls. These
structural changes were analyzed in detail in [6-7]. The main volume part of
such particles remains crystalline. This fact has been verified by the results
of electron microdiffraction (Fig. 4a). When using a dispersing organic
additive to the quartz during grinding in a centrifugal-planetary mill, the
structure of the particles undergoes considerable changes. The surface layer
is a dense or porous multilayer system of a different structure. The electron
microdiffraction analysis shows the process of transformation of the quartz
particles (see Fig. 4a) into a composition material containing particles with
a partially amorphous and modified structure (see Fig. 4b) up to the
formation of dense carbonaceons structures on the quartz surface (see
Fig. 4c).
362 Z. A. Mansurov
Fig. 4. Electron microscopic pictures and electron diffraction of modified particles
of quartz.
It is found that there is a certain regularity in the structural
transformations taking place on the surface of a quartz particle with the
carbon of the organic additives during the treatment of the material in a
mechanical reactor: from thin dense films with the introduced ultradisperse
particles of iron to porous multilayer structures with the formations of
different configurations grafted to the surface of the particles.
Films, fibers or nanotubes (see Figs. 4a-c) are formed on the surface
depending on the kind of the carbon containing modifier being used
(alcohols, polystyrene) and the time of treatment. Ultradisperse iron
introduced into the surface of the quartz particles catalyzes the growth of
carbon nanotubes on the particle surface. After mechano-chemical
treatment, the quartz particles become encapsulated by a thin coating film
with a thickness ranging between 10 and 50 nm, which is strongly bound to
the surface of the particle. Carbon enters into the composition and structure
of this cover layer. The carbon content can be determined by an adsorption-
weight method. This carbon was defined as in content of a homopolymer
(i.e. in not bound state with surface). Its content varies from 1.5 to 3.5%.
When making an activated coal input of 5%, after mechano-chemical
treatment 3.03% of the carbon was found to be in a chemically bound state.
When using butanol and polystyrene as modifiers, the amount of carbon
was equal to 1.76 and 2.49%, respectively.
Thus, the structure of the quartz particle surface layer after a
mechanochemical treatment may be interpreted as a nanostructural
formation containing carbon, silicon, and iron and having a complex
structure encapsulating a particle. Finally, a composition material is
formed consisting of a carbon surface layer with introduced inclusions of
iron, a transition amorphous layer on the basis of silicon and a crystalline
quartz base.
Some Applications of Nanocarbon Materials for Novel Devices 363
Such structural rearrangements of the surface layers of the quartz
particles being dispersed result in a change of the physical properties of the
material. The measurement of the specific resistance of a quartz powder
after a mechanochemical treatment showed a decrease by more than an
order of magnitude. The modified quartz powder after a mechanochemical
treatment also exhibits magnetic properties (Table 1).
Table 1. The change of specific resistance and magnetic permeability of quartz
powder depending on the time of weathering. Grinding was carried out during 5
specific resistance,
ρ×10
6
, Ω×m
magnetic permeability
time of weathering
τ
st
, 24 hours
time of weathering
τ
st
, 24 hours
Material
0 30 0 30
Quartz 1.1 6 2.0 2.0
Quartz + butanol 6. 15.0 4.0 3.0
Quartz + polystyrene 2.6 3.5 29.0 27.0
Both the electric and magnetic characteristics of mechano-chemically
treated quartz are found to change with time, i.e. the material "ages".
However, if such "aged" material is placed into an electromagnetic field of
definite intensity, its ferromagnetism and conducting characteristics are
recovered. This most likely is the result of the interaction of a piezoelectric
quartz nucleus with the carbon nanostructural film containing ultradisperse
inclusions of iron.
Production of Carbongraphite Cathodes for Chemical
Sources of Current [8-9]
A coalgraphite layer was grown on metal current taps with the aim to
develop an optimal method for production of coalgraphite cathodes for
lithium chemical sources of current. The obtained electrodes were tested for
the discharge of pure nickel screens, electrodes of fibrous carbon materials
and electrodes produced according to conventional technology using
polyethylene as a binder. It is shown that the obtained carbonized material
is not inferior in its characteristics to a traditional one.
minutes.
364 Z. A. Mansurov
In order to measure electrochemical characteristics of cathodes made
according to the proposed method, we created a model of a chemical source
of current with a lithium anode and an electrolyte containing 1.6 mole/L of
lithium chloraluminate in thionyl-chloride (the electrolyte composition
corresponds to that used in commercial samples for this purpose). The
electrodes were tested in a galvanostatic regime using two-sided
polarization of the cathode. The latter was wrapped in a separator of non-
woven glass fibre, placed into a slot cell between two lithium electrodes in
the electrolyte, and the electrodes of the unit were tightly compressed. After
assembling the unit, under galvanostatic conditions, polarization of the
model was carried out by a current corresponding to current density on the
electrodes of 25 mA/cm
2
. The discharge of the model was carried out until
a sharp decrease of the cell voltage appeared. Our investigations showed
that the above mentioned decrease in voltage corresponds to the filling of
pores in the carbon material with electrolyte reduction products. The major
reduction product is lithium chloride which is slightly soluble under these
conditions.
For comparison, the tests on the discharge of pure initial nickel screens,
electrodes of fibrous carbon materials using different materials as
electrodes made according to conventional technology using polyethylene
as a binder were carried out. The discharge of the nickel screen at a current
density of 6 mA/cm
2
showed almost an instant passivation of the electrode
by the reaction products that result in a quick decrease of voltage. The
discharge of a soot electrode with a polyethylene binder lasted 30 minutes
at current density of 12 mA/cm
2
.
The test showed that the discharge characteristics of the models of
current sources of the lithium-thionylchloride practically did not depend on
which of the metals the fibrous carbon was deposited. Discharge curves
were obtained for samples with coated layers of fibrous carbon in three
different regimes (see Fig. 5). The mass of the deposited coating varied
from 0.01 to 0.05 g. It was shown that the time of the electrode discharge
before a sharp decrease of voltage on the cell directly depended on the
amount of the coated carbon material and the time of the layer growth. At
the discharge in thionylchloride solution with current density of 6 mA/cm
2
the time of discharge reaches 4 minutes.
Some Applications of Nanocarbon Materials for Novel Devices 365
Fig. 5. Discharge characteristics depending on cathode material (obtained by
carbonization at 750°C), j = 20 mA/cm
2
: 1 - carbonized iron net; 2 - cathode by the
standard technology.
Multifunctional Catalysts of Oil Hydrofining [10]
Multifunctional catalysts of hydrofining were developed by modifying
alumocobaltmolybdenum catalyst with hardened zeolites. Catalysts were
prepared by the conventional impregnation method. After moulding, the
catalysts had been dried at 393-420 K (4 hours) and calcinated at 823 K
during 5 hours. Then, the catalysts were exposed to the process of
carbonization to obtain active forms of carbon as a carrier. Activation of the
catalysts was carried out in the process of sulphurizing by free sulphur first
at 393-423 K, at a hydrogen pressure of 0.7-1.0 MPa during 3 hours, then
sulphurizing was continued at 473 K, at a pressure of 2.5 MPa for 2.5-3
hours.
The catalysts were investigated by different physico-chemical methods.
Specific surface and porosity were determined by the BET method. The
types of adsorbed forms of hydrogen and activation energy were
determined with the help of thermo-programmed desorption of hydrogen.
The texture of catalysts was determined with the help of electron
microscopy. The reaction products were analyzed by highly effective gas-
liquid chromatography with a capillary column on the chromatograph of
"Perkin Elmer" company. Chromatograms were computed by "Total
Chrom Arneld" software. A detailed hydrocarbon analysis was carried out
366 Z. A. Mansurov
within the framework of "DHA Win" program. The content of sulphur in
the samples was determined by the X-ray fluorescence analyzer "Oxford
Lab-X-3500".
The activity of catalysts was tested in a laboratory flowing plant in the
processes of hydrofining gasoline and diesel fractions of oil at a pressure
ranging form 2.0-4.5 MPa, temperature 593-673 K, and volume rate of raw
material feed 1-4 hour
-1
. The characteristics of the commercial catalyst GO-
70 were taken under equal conditions in order to compare the catalytic
activity. Butyl-mercaptan and thiophene diluted in n-decane were used as a
model compound. The isomerization activity was tested in the reactions of
cracking of hexane and decane. The developed catalysts showed higher
indices than commercial catalyst GO-70. With the increase of temperature
from 593 to 673 K the degree of hydrodesulphurization increases from 75.3
to 98.2%, and isomerization degree increases from 18.3 to 41.7%.
According to the data of the detailed hydrocarbon analysis the estimated
octane number increased from 70.83 to 83.48 (see Table 2).
Obtaining of active forms of carbon on catalysts results in the formation
of more highly dispersed systems having correspondingly a higher catalytic
activity in hydrofining and hydroisomerization processes. The study of the
surface and porosity of catalysts by the BET method showed the increase of
the specific surface of catalysts from 80 to 240 m
2
/g. Catalysts, mainly,
have pores with a size less than 50 nm. Electron microscopy studies showed
carbon coated catalysts to be highly disperse. The metal particle size was
found to vary within 20-40 nm.
Table 2. Effect of the influence of over-carbonized industrial CoMo - catalyst on
the characteristics of straight-run benzine, concentration of carbon - 10%.
concentration
octane
level
boiling-
point
°C
paraffin
(mass.%)
naphthenes
concentratio
n of S-
compound
initial straight-run
benzene (SB)
70.83 88.1 21.42 12.95 0.12
SB after
overcarbonized
catalyst
83.48 36.06 1252 16.05 0.001
Some Applications of Nanocarbon Materials for Novel Devices 367
Carbonization of Vegetative Raw Material [4]
The raw material on the basis of the treatment of agricultural products
belongs to quickly renewable sources and is ecologically more friendly.
When carbonizing (pyrolysis in an inert medium) samples of walnut shells
(WS), apricot (AS) and grape stones (GS) the main mass loss takes place in
the temperatures range 200-500°C. At 500°C during 1 hour, about 50% of
mass is lost and, finally, at 950°C the loss reaches approximately 75%.
The specific surface of the samples is reaching 830 m
2
/g and was
determined by the method of thermal desorption of argon. Electron
microscopy analysis showed a change in morphology and structure of the
carbon containing sorbents depending on the temperature and time of
carbonization.
The mechanism of sorption of heavy metal ions by carbonized sorbents
was stated by physico-chemical methods of analysis. Carbonized sorbents
were found to be effective for adsorption of heavy metal ions, organic
compounds and sulphur dioxide.
Carbon Containing Refractories [11]
Introduction of chromite sludge increases the density and mechanical
strength in comparison with the refractory "Furnon-3XP", slightly
increasing refractoriness. Formation of fibrous carbon and carbides of
metals accounts for the improvement of physico-chemical indices of carbon
refractories on the basis of clay and chromite sludge. The obtained
refractory materials have a high slag-resistance that allows forecasting their
use in metallurgical processes of precious metals production.
On quartz basis, by a mechano-chemical treatment powder material with
new properties was obtained. After mechano-chemical treatment quartz was
found to become ferromagnetic. The magnetic permeability of quartz
reaches µ = 30 depending on the chosen carbon containing modifier and the
regime of mechanical treatment. Electroconductivity of the obtained
material increases by 2-3 orders of magnitude.
A coalgraphite layer was grown on metal current taps with the aim to
develop an optimal method for production of coalgraphite cathodes for
lithium chemical sources of current. The obtained electrodes were tested for
the discharge of pure nickel nets, electrodes of fibrous carbon materials and
electrodes produced according to conventional technology using
polyethylene as a binder. It is shown that the obtained carbonized material
is not inferior in its characteristics to a traditional one.
368 Z. A. Mansurov
Poly-functional carbon containing catalysts which may simultaneously
carry out hydroforming, hydro-desulphurization and hydroisomerization of
petrol and diesel fractions were synthesized. The developed catalysts allow
obtaining petrol of low-sulphur content and diesel fuel with improved
properties.
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