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6Hydrogen in metals and alloys
PECULIARITIES OF NANOPARTICLES FORMATION IN SYSTEMS
CONTAINING METAL IONS
V. I. Kodolov, N. V. Khokhryakov, A. P. Kuznetsov, A. A. Didik, L. G. Makarova,
S. M. Ferrer1, E. G. Volkova2
BRHE Centre of Chemical Physics and Mesoscopy, Udmurt Scientific Centre, Ural Division Russian Academy of Sciences; Gorky str., 222, Izhevsk, 426000
E-mail: kodol@istu.udm.ru 1 Granada University, Institute of Biotechnology, Granada, Spain 2 Institute of Metal Physics, Ural Division, RAS, Ekaterinburg
The paper describes a nanoreactor as the region on the phase separation boundary and in lamellar matrixes with the nano dimensions. The peculiarity of the formation of nanoparticles and chemical processes in nanore-actors lies in the catalytic action of their walls followed by the activation energy decrease in the processes proceeding in them, as well as in the determination of the process direction due to more favorable location of chemical particles for the formation of activated complexes with a certain structure. Based on quantum-chemical investigations and experimental results the formation hypothesis of carbon nanostructures with included metals or their compounds is proposed.
In self-organizing media there are many different chemical reactions including organic ones. A significant number of publications about the proceeding of organic reactions in inorganic and element-organic interface spaces appeared during the last forty years. The precursors of carbon fiber «embryos» or tubules in these works were aromatic hydrocarbons dispersed in metal chloride melts, polyphosphoric or aryl(alkyl)phosphonic acids [1-3]. The formation of polymeric aromatic compounds due to de-hydropolycondensation with a proton transfer into the medium was marked by Berlin et al [4]. At last time the carbon nanotubes and other carbon nanostructures attract the enormous attention of researchers.
Our investigation concerns to the creation of theory and methodology for the low temperature synthesis of nanostructures into nanoreactors.
Advantages of this trend:
— decrease of energy and substances isolation into surroundings;
— decrease of energetic expenses;
— path of synthesis process;
— products orientation in nanoreactor.
There are the following stages of trend development:
1. Modeling of nanostructure stability and their formation processes by quantum-chemical methods.
2. Method development of low temperature synthesis.
3. Nanostructure composition and morphology investigations and also properties study of nanostructures obtained.
4.Nanostructures application for the improvement of inorganic and polymeric composites.
Results of quantum-chemical investigations of the mechanism for low-temperature synthesis of carbon nanostructures in media containing organic substances in the presence of metal salts under the medium aligning action upon carbon clusters being formed are reported. First, the mechanism of dehydropolycondensation reaction of aromatic hydrocarbons in the presence of metals and their salts is investigated. The role of metals as reaction stimulators is discussed and the comparative analysis of processes in media containing ions of different transition metals is carried out. Secondly, interaction of vanadium oxide lamellar structures and polyvanadic acid fragments with ethanol is considered, which is chosen as the interaction model of polyvinyl alcohol with poly-vanadic acid, containing metal ions. In both cases it is proved that the metals and their salts act as stimulators of carbonization process being in accordance with experimental data. The common feature of the processes discussed is the transition of hydrogen atoms from organic molecules onto the clusters of metal salts with further formation of C-C bonds and polymerization under the aligning action of electric field and metal particles. It is experimentally shown that in the frameworks of the methods given carbon tubes, their compounds, as well as metal nanowires and spherical nanoparticles are formed in carbon shells.
Based on quantum-chemical investigations and experimental results the formation hypothesis of carbon nanostructures containing metals or their compounds is proposed. The hypothesis is based on simultaneous reduction of metal ions and oxidation of hydrocarbons. For example, the scheme of tubules formation in lamellar systems with nanoreactors disposed up in electric field is shown in Fig.1. Here the picture for transformation of polyvinyl alcohol through polyene to tubules is given.
Quantum chemical investigations of model systems «hydrocarbon compounds-metal ions» have been done. The energy of hydrogen atom removal from organic compounds and the possi-bilities of geometry compounds changes under the metal and metal ion action are determined. The calculations in framework Hartry-Fock meth-
ISJAEE Special issue (2003)
Second International Symposium «Safety and Economy of Hydrogen Transport»
IFSSEHT-2003
Fig. 1. Scheme of polyvinyl alcohol transformation in polyvanadic acid under the action of electric field
od with the using of program product GAMESS have been carried out.
For complex investigation of dehydropolyconden-sation the optimization is realized by semi em-pirical method MINDO. In result the defective structures formation were predicted. In addition to sp2 hybridization there are sp- and sp3 — hybridization types for Carbon atoms. The probability of carbon shell formation on the surface of growing metallic nanoparticles was obtained. Proposed models are confirmed by experimental data.
Organic and inorganic substances with a lamellar and lamellar-like structure, such as polyvanadic acid with Cr, Mo or W ions, polyphosphoric acid with copper ions or polyvinyl alcohol with distributed copper, cobalt or nickel chlorides, are used as nanoreactors. It is found out that carbon-metal containing tubules are obtained in such systems with a relatively great yield when layer negative charges do not exceed -2.5.
The lamellar structure of polyvanadic acid bring to the acceleration of tubules formation processes as well as to the increasing of the tubules growth center numbers. In this case there is the formation of defective structures consisting from tubes that coalescence in different directions. The individual tubes were formatted as scrolls.
If nanostructures are obtained from polyvinyl alcohol the strong intermolecular interactions of OH groups stimulates to the orientation of polymeric chains and the formation of packets, which contain the few sets of chains. During the dehydration and the dehydrogeniza-tion of polyvinyl alcohol the macromolecules of this
polymer can be bend. The transformation of intermediate structures flowing with surface energy decreasing put to the formation of long tubules.
Depending on the system chosen carbon and carbon-metal containing nanostructures of different shapes are obtained: branched and multi-layer nanotubes, «scrolls», «onions», «bamboo-like» tubules, metal nanowires and globular nanoparticles in carbon shells. For instance, the tubules, included electrolytes, are obtained (Fig. 2). The nature of metal and metal contain-
Fig. 2. Carbon multi-wall nanotube with electrolyte
ing compound participating in the process sufficiently influence the size and shape of nanostructures being produced in nanoreactors.
Supported by INTAS No. 97-30810
References
1. E. Ota, S. Otani. Chem., 1975, No 3, p. 241.
2. H. F. Mark, S. M. Atlas et al. Polym. News, 1975, v. 2, No 5-6, p. 3.
3. V. I. Kodolov et al. Journal Phys. Chem., 1977, T. 53, No 4, S. 944 (in Russian).
4. A. A. Berlin et al. Vysokomol. Soed., 1970, T. 12A, S. 2541 (in Russian).
