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108Section 7. High energy chemistry
4. Аристова Н. А., Мокино Т. С., Пискарев И. М. Окисление муравьиной и щавелевой кислот в безэлектродной электрохимической реакции.//Журнал общей химии. - 2003. - Т. 73. - Вып. 5. - С. 756-760.
5. Жесткова Т. П., Жукова Т. Н., Макаров И. Е. Особенности радиолитического разложения щавелевой кислоты в аэрированных водных растворах.//Химия Высоких Энергий. - 2001. - Т. 45. -№ 2. - С. 115-118.
6. Isgenderova Z. I., Guliyeva U. A., Mammadov S. G., Gurbanov M. A., Abdullayev, Radiolysis E. T. of aerated formic acid solution.//European J. ofAnalitial and Applied Chemistry. - 2015. - No. 1. - Р. 44-50.
Mahmudov Hokman Movajat, Institue of Radiation Problems, ANAN, the head of Laboratory
Kuliyeva Uviyya Aydin, Institue of Radiation Problems, ANAN, dissertant
Kerimov Valeh Karim, Institue of Radiation Problems, ANAN, leading researcher
Kurbanov Muslum Ahmad, Institue of Radiation Problems, ANAN, the head of Laboratory E-mail: hokman.mahmudov@gmail.com
Water radiolysis on the surface of Al2O3 nano-catalyst
Abstract: Kinetics of molecular hydrogen produced from the radiolysis of the system of water and Al2O3- nanoparticles with different sizes were studied. It was determined that, the molecular hydrogen yield of liquid solutions of smaller-sized catalysts is higher for 1.4-1.6 times than the large-sized catalysts.
Keywords: nanocatalyst, radiolysis, radiation-chemical yield, molecular hydrogen.
Introduction
The analysis of the current situation of nanotechnology raises a number of important directions. Scientific research to be carried out on investigation of nanocomposites, development in nano-and molecular electronics, nanophotonics, synthesis of nanocomponents and effective catalysts were widely justified by Tretyakov and others [1].
Nowadays there is a growing interest to scientific investigations being carried out in the field of a radiation-chemical transformation of the water on the surface of nanocatalysts [1-7]. The purpose of this research is to study the regularities of hydrogen formation at radiolysis of Al2O3 nanoparticles with different sizes in water solutions [3].
Research Methodology
Radiolysis process carried out under the influence ofgamma rays at a room temperature in the presence ofnanoparticles ofdifferent sizes. Nanoparticles
and bidistilled water in a ratio of 1:100 were taken. The experiments were conducted under stationary conditions, samples were irradiated by gamma rays at an isotope 60Co with dose rate P = 1.04 kGy/h. A system composed of d = 5 50 nm-sized and bidistilled water is prepared; 5 ml. of the prepared solution is taken and filled in glass vials (15 ml.). Ready samples are ejected for a few times and made gas-free at a vacuum facility in liquid nitrogen t = -196 °C temperature and shut down.
The hydrogen obtained as a result of radiolysis was analyzed on a gas analyzer.
Results and their discussion
The dependence ofH2 concentration on adsorbed doses is given fig. 1. From the obtained kinetic curves it seems that though in the range of At = 0 + 20 hours the formation of molecular hydrogen rises linearly, in next interval of irradiation time At=20 + 60 hours relatively it goes down to approaching stationary state.
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Water radiolysis on the surface of AI2O3 nano-catalyst
Fig. 1. The kinetic dependence (mcat/mwater = 1:100, meat=0.01 gr.,
T = 300 K, P = 1.04 kGy/h) of molecular hydrogen produced from the radiolysis of water and d = 5, 20, 40, and 50 nm-sized nanoparticles Al2O3
As can be seen from Fig. 1 molecular H2 produced on the surface area of the catalyst within 10 hours of at a linear kinetic region had the rate W = (2.78 ^ 3.89) * *1014 molecules/(g * sec), and the radiation-chemical output as G (H2) = 13.8 ^ 19.8 molecule/100 eV.
The main essence of radiation catalytic processes is transferring the unbalanced charges formed by absorbed ionizing radiation energy on the surface of
the catalyst to the adsorbent adsorbed on the surface of the catalyst or the system [3].
Figure 2 describes the investigation of molecular hydrogen yield depending on the size of the given nano-particle. The obtained schedule can be divided into two parts; the output from the 20 nm-sized nanoparticles is more than that from 40 nm-sized nanoparticles for 1.4-1.6.
Fig. 2. The dependence of molecular hydrogen output formed as a result of Al2O3 + H2O system radolysis dissolved in water at different amounts on the size of nanoparticles (mcat./mwater = 1:50, mcat = 0.05 0.1 grams, d = 5, 20, 40, 50 nm., T = 300 K, P = 1.04 kGy/h, т = 7 hours)
As shown (Fig. 2) the hydrogen output was higher on the surface of the small-sized nanocatalysts, it once again prove that the smaller size of catalyst is, the higher its specific area become
which naturally results in better absorption of ionizing radiation on the surface of the catalyst and the efficient transfer of the energy carriers formed the surface to the system [8; 9].
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Section 7. High energy chemistry
One of the main reasons for higher transmission of ionizing energy to the water system and the decomposition of the system under the influence of the radiation is more likely an equal distribution of catalysts in the system and the system itself being homogenous. If the more water molecules are in contact with the surface of the catalyst, the more rapidly the transmission of the surface energy and water decomposition would take place [8, 9].
In order to increase the probability of the radiation processes we use taking place the amount of catalyst to be used should be selected in a way that it could assist in radiolysis process actively and no sedimentation of the catalyst coagulating in the bottom of the vials could be observed. On this purpose in figure 3 is presented the output of molecular hydrogen formed out of water radiolysis in relation with the mass of the given nanocatalyst.
Fig. 3. The dependence (d = 20 nm., T = 300 K, D = 21 kGy) of molecular hydrogen on the mass of nanocatalyst
As can be seen from Fig. 3, nanoparticles more than 0.1 gram precipitate in a water solution which leads to non-active presence of catalysts in water decomposition process. This can happen due to two reasons: a) the surplus amount of the catalyst
coagulates and precipitates in the bottom of the ampoule; b) in our system the absorbed beam intensity would be adsorbed by this amount of material. In fig. 4 the dependence of the formed molecular hydrogen on the amount of taken water was presented.
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Fig. 4. The dependence (d = 5, 20, 40 and 50 nm., T = 300 K, m = 0.01 gr., т=7 hours, D = 7.31 kGy) of output the formed molecular hydrogen on the amount of water in system
Water radiolysis on the surface of AI2O3 nano-catalyst
It seems from the obtained curves that the formation ofmolecular hydrogen increases linearly for all taken nanoparticles with various sizes, approaches
ionizing radiation
H2O ^ e~, H',
2 eq7 7
Molecular products are mainly formed as a result of recombination processes both inside and outside a spur which can be seen in the form of the reactions 2 and 3.
HO + HOH2O2 (2)
H + H ^H2 (3)
Simultaneously counter recombination takes place inside the spur in the reaction 4 and consequently hydrogen output is reduced.
H + HO — H2O (4)
As can be seen from the general mechanism so far the concentration of the formed radicals grows the speed of 4th type reactions increases as well.
Radiation is mainly absorbed by a catalyst when nanocatalyst is ejected into water s system; consequently additional radiation energy is transmitted to the system which mainly generates due to the catalyst volume and formation of radiation defects. Under the effect of ionizing radiation one or two valence electrons (F+ and F) and hole centers (V, V+, V-2) form in aluminum oxide crystals [11;12;13]. As for relatively bigger-sized catalysts the electrons formed in bulk migrate to the surface, captured by the existing holes on the surface and are recombined (reactions 5 and 6).
F ++ V =product (5)
FS+ + V- =product (6)
2H ++ 2c - = H2 (7)
2OH -+ 2F + = H2O2 (б)
By reducing the sizes of the catalysts the defects formed in bulk migrate to the surface and as the result, the numbers of the defects on the surface of the catalyst are increases. In addition, the electrons formed on the surface migrate to the medium and accelerate the
a saturation state in the ratio of water 1:100 and more. The water radiolysis process leads to formation the following primary products [7: 13, 14]:
HO ,H',HO2,H3O + HH,H2O2,H2. (1)
reactions (7) and (8) in radiation-catalytic reactions the surface defects play a key role in the processes of surface defect formation, adsorption and decomposition resulting in increase in the output of the final product. Excess of electron density formed in radiation defects migrate from the surface to adsorbents and weakens the intramolecular chemical bonds of the adsorbent, water decomposition process accelerates. Under the radiation effect AlO3 , AlO5 type vacancy oxygen clusters generate on the surface of the catalyst and the chemical bond energy of the water molecules (O3Al-OH2) localized on the surface of this cluster is reduced from 1.9 up to 1.5 eV [14], consequently this accelerate water decomposition and raise the output of the (3) and (4) reaction products.
Results
• Thewaterradiolysis at T = 300 K, D = 0.35 Gy/sec, At = 0 ^ 90 hours in the presence of nano-Al2O3 catalysts of different sizes was studied. It was determined that, the radiation-chemical yield of molecular hydrogen is equal to G = 13.3 19.8 molecule/100eV and this value is for several times more than yield ofhydro-gen formed from water radiolysis.
• It was investigated that, the yield of molecular hydrogen formed from the radiolysis of homogeneous liquid solutions of catalysts varies related to the size of the catalyst. Thus, radiation-chemical yield at d = 5-20 nm. small-sized catalysts is higher 1.4 1.6 times than it is at d = 40-50 nm. highsized particles. Depending on the amount of the water in the system the molecular-hydrogen output on the surface of a nanocatalyst of different sizes is growing.
References:
1. Revin A. A. Actual problems of high-energy chemistry. MRCTU conference materials named after Mendeleev. - 2009. - P. 77-78.
2. Tretyakov Y. D., Gudilin E. A. «Main directions of fundamental and oriented investigations in the field of nanomaterials»//Successes of Chemistry. - 78 (9). - 2009. - P 867-888.
3. Garibov A. A. Size effects in radiation-catalytic process of water decomposition and perspectives if applying nanocatalysts. The IV International Conference Perspectives of peaceful use of Nuclear Energy. -November 23-25, 2011. - Baku, Azerbaijan. - P. 12-20.
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4. Seino S., Yamamoto T. A., Hashimoto IK., Okuda S., Chitose N., Ueta S. and Okitsu K. «Gamma-ray irradiation effect on the aqueous solutions of phenol dispersing Al2O3 or TiO2 nanoparticles», rev. Adv. Mater. Sci. 4. - 2003. - P. 70-74.
5. Seino S., Fujimoto R., Yamamoto T. A, Katsura M., Okuda S., Okitsu K., Oshima R. «Hydrogen gas from water dispersing nanoparticles irradiated with gamma-ray evaluation». Mat. Res. Soc. Sympa. Proc. Vol. 608. - 2000. - Materials Research Society. - P. 505-510.
6. Takao Kojima, Kentaro Takayanagi, Ryoichi Taniguchi, Shuichi Okuda, Satoshi Seino and Takao A. Yamamoto «Hydrogen gas formation from the water by pre-irradiated with gamma-ray radiolysis dispersing silica nanoparticles».//Journal of Nuclear Science and Technology. - 2006. - Vol. 43. -No. 10. - P. 1287-1288.
7. Cecal Alexandra, Haut Oana, Macovei Island, Popovici Evelini, Rusu Ioana and Nicoleta Melniciuc Puica «Hydrogen yield from the radiolysis of water in the presence of some pillared Clays».// Revue de Chimie roumaine. - 2008. - 53 (9) - P. 875-880.
8. Mahmudov H. M., Karimov V. K., Nasirova Kh. Y. Regularities of radiation in the process of water radiolysis Al2O3 nano-catalytic system. International Conference «Nuclear Science and its Application». -Samarkand, Uzbekistan, September 25-28, 2012. - P. 199-200.
9. Mahmudov H. M., Karimov V. K., Nasirova Kh. Y, Zalilov Z. Z., Hasanov S. A., Akhundova Kh. Sh. Study of water and Al2O3 nanoparticle system under the effect of y-radiation. The V International Conference Perspectives ofpeaceful use of Nuclear Energy. - November 21-23, 2012. - Baku, Azerbaijan. - P. 47-48.
10. Yufeng Song, Qi Liu, Youmei Sun, Jie Liu, Zhiyong Zhu. Color center formation in a-Al2O3 induced by high energy heavy ions. Original Research Article. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. - Volume 254. - Issue 2. - January 2007. - P. 268-272.
11. Savelev G. G., Yurmazova T. A., Galanov A. I., Sizov S. V., Danilenko N. B., Lerner M. I., Kaledin Te-per F. Adsorption abicapacity of fiber aluminium oxide.//News of Tomsk Technical University. -2004. - V. 307 - № 1. - P. 102-107.
12. Pshejeckaya S. Y. In the book on Mechanism of Radiation-Chemical Reactions. - Moscow “Chemistry”, 1968. - P. 254.
13. Pikaev A. K. In the book on Modern radiation Chemistry. Gas and liquid radiolysis. - Moscow “Chemistry”, 1986. - Р. 73.
14. Kotov A. G., Gromov V. V. Radiation Physics and Chemistry of heterogeneous systems. - Moscow: “Energoatomizdat”, 1988. - Р. 117.
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