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INVESTIGATION OF INFLUENCE OF CARBON TUBULES OBTAINING CONDITIONS ON THEIR CHEMICAL STRUCTURE
R. SZARGAN, K.H. HALLMEIER, D. WETT, A.P. KUZNETSOV*, V.I. KODOLOV*
Leipzig University, Willhelm Ostvald Institute of Physical and Theoretical Chemistry, Leipzig, Germany
♦Basic research - High educational center of Chemical Physics and Mesoscopy, Udmurt Scientific Center, RAS, 222 Gorky St., Izhevsk, 426001, Russia.
ABSTRACT. With the help of X-ray photoelectron spectroscopy the chemical composition and the presence of different types of chemical bonds extracted from the reaction mass of carbon products have been determined. The extraction methods have been constant. Products soluble and insoluble in xylene, extracted via 30 minutes intervals, have been investigated. The dependence of the composition on synthesis time is practically insignificant, perhaps, due to great time interval. The carbonization process takes place, apparently, in the first 30 minutes. It is noted that the component in the spectrum referred to carbon in sp2, for the samples insoluble in xylene, is much greater in comparison with line Cls corresponding to sp3. For the samples soluble in xylene this ratio is less than one.
INTRODUCTION
Earlier [1] the investigation on synthesis and examination of tubules in melts of Lewis acids was carried out with the help of electron spectroscopy. It was of interest to determine the influence of tubules formation conditions on their chemical structure. The products were extracted from the reaction mass after heating for 30 minutes. Such interval corresponds with the color change of reaction mass.
EXPERIMENTAL
The samples to be investigated are obtained using the following method: anthracene and anhydrous aluminum, sodium and nickel chlorides taken in molar ratio 1:10:10:1 are ground into a fine powder and heated at 280-300°C. The analysis samples are taken after 30, 60, 90 and 120 minutes. The reaction is stopped by icy water. After inorganic products are removed, the residue insoluble in water is washed by hydrochloric acid and water up to pH=7 and dried at 90-100°C for 24 hours. The dried residue is treated by 3 portions of hot (90-100°C) o-xylene by 50 ml. From the combined extracts xylene is topped till a solid residue is obtained. Powders soluble and insoluble in xylene are used for the investigation. The data of their electron-microscopic investigation indicate tubules formation [1 ].
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INVESTIGATION OF INFLUENCE OF CARBON TUBULES OBTAINING CONDITIONS ON THEIR
CHEMICAL STRUCTURE
The spectra are measured using on X-ray photoelectron spectrometer VG ESCALA 220i XL with AlKa radiation non-monochromatic (12 kV, 20 mA) in case of powder samples. The powders were prepared at double-side adhesive tape. In the measuring process the vacuum is 10~9 torr. The spectra are treated with the software package UNIFIT-32-32.
RESULTS AND DISCUSSION
Two types of samples are used differing in preparation conditions: 1) fraction insoluble in xylene (1.2, 2.1, 3.1, 4.1); 2) fraction soluble in xylene (1.2, 2.2, 3.2, 4.2) after 30, 60, 90 and 120 minutes, respectively.
Table 1 contains the data of spectral components obtained after processing the experimental curves with the help of Voigt maximums.
Table I. Binding energies and amounts of atoms in tubules obtained in different conditions
(1 - soluble in xylene, 2 - insoluble in xylene)
Tu bes C Is O Is C12p A1 2p
No E/eV FWH M/ eV Amou at/ Atomic E/eV FWHM/ eV Amount / Atomic E/eV FWHM/ eV Amou nt/ Atom- % E/eV FWH My eV Amoun t/ Atomic
1.1 284.0 1.9 62.6 284.6 1.9 31.9 530.7 2.9 0.2 532.5 2.9 4.4 198.4 2.7 0.6 74.5 2.2 0.4
2.1 284.0 1.6 57.5 284.8 1.6 37.7 531.2 2.8 0.2 532.4 2.8 4.1 198.3 2.6 0.5
3.1 284.0 1.8 62.1 284.8 1.8 33.2 530.8 2.7 0.6 532.5 2.7 3.3 198.4 3.2 0.8
4.1 284.0 1.7 39.7 285.3 1.7 55.0 531.9 2.9 0.8 532.9 2.9 3.8 198.91 3.3 0.8
1.2 284.0 1.6 44.0 284.7 1.6 52.5 531.3 2.6 0.8 532.5 2.6 2.7
2.2 284.0 1.7 30.9 284.6 1.7 65.6 531.7 2.7 1.1 532.8 2.7 2.4
3.2 284.0 1.6 39.0 284.7 1.6 56.7 531.8 2.0 2.5 533.0 2.0 1.7
4.2 284.0 1.6 40.2 284.7 1.6 54.9 531.7 2.6 2.1 532.7 2.6 2.8
Using the sensitivity factors the relative quantities of the components (atomic %) are calculated. In table 2 the data of yields of insoluble and soluble fractions occur.
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R. SZARGAN, K.H. HALLMELER, D. WETT, A.P. KUZNETSOV, V.l. KODOLOV
Table 2. Yield change of soluble and insoluble fractions
Time, min % of soluble fraction % of insoluble fraction
0 100 0
30 98 2
60 22 78
90 14 86
120 9 91
Analyzing the Cls-spectra and in agreement with previous measurements two binding forms of carbon could be identified:
1. 284,0 eV (sp2-carbon, which can refer to nanotubes, taking the charging into account).
2. 284,6-285,3 eV (parts of amorphous carbon or C-H - groups).
We have found the dependence from the preparation conditions. Samples 1.1-3.1 have amounts of the sp2 carbon of approximately 60% (referred to all determined elements). This components decreased to 40% in the spectra of the samples soluble in xylene, with the exception 2.2 (31%). In these cases the resulting component from amorphous carbon (or C-H - groups) increases considerably. Ols-spectrum has two components, which can be from oxide (530,7-531,9 eV) and hydroxide (532,4-533,0 eV) parts, respectively.
Besides, in the spectra of series 1 the chlorine component higher than 0,8% appears. In all cases bond energies indicate chlorides presence. Sample 1.1 gives low aluminum quantity, perhaps, AICI3 (0,4%). According to the spectra the amount of tubules carbon is increased during 90 min, and then it is decreased.
CONCLUSIONS
Carbon content (in atomic %), which can be referred to tubules, depends on obtaining conditions. In case of fraction insoluble in xylene, this component is always higher in comparison with sp3- hybrid carbon. This ratio Csp2/Csp3 is inverted for the samples soluble in xylene. The dependence on time has not been found, perhaps, due to large time-step interval.
REFERENCE
1. V.I. Kodolov, A.P. Kuznetsov, A.A. Didik, L.G. Makarova, I.N. Shabanova, A. Yu. Volkov, E.G. Volkova Formation of carbon nanotubes and nanoparticles in the process of stimulated carbonization of aromatic hydrocarbons. / 2nd International Internet Conference on synthesis, investigation and application of metal-containing tubules june-july 2001.
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