A study of the oxidation and fluorination of single-walled carbon nanotubes by the MNDO method

This paper reports on the results of MNDO calculations of the atomic adsorption of oxygen and fluorine on the surface of armchair and zigzag single-walled carbon nanotubes with a cylindrical symmetry. The calculations are carried out within the molecular cluster and ion-incorporated covalent-periodic cluster models at the modern quantum-mechanical semiempirical MNDO level. The electronic and energy characteristics of the oxidation and fluorination processes are analyzed, and the most energetically favorable oxide structure of the (6, 6) nanotube is determined. It is found that narrow-gap tubulenes show a tendency to metallic behavior as their surface is saturated with oxygen atoms.     

Carbon nanotubes, new material for purification of water-ethanol mixtures from isomers of propanol

The possibility of purification of water-ethanol mixtures from the unwanted admixtures of higher alcohol, in particular, of the isomeric propanols, with the help of carbon nanomaterial is discussed. Results of quantum-chemical calculations of n-propanol and isopropanol on the surface of the single-walled carbon nanotube of the “armchair” type are presented. Investigations are carried out within the frame of model of molecular cluster using semi-empirical quantum chemical MNDO method. The possibility of adsorption of molecules of propanol isomers on the outer surface of nanotubes of small diameter as well the absence of adsorption of ethanol molecules on them is shown. It indicates the possibility of selective sorption with carbon nanotubes. Main geometric, electronic, and energy characteristics of obtained adsorption complexes are evaluated. A conclusion is made on the possibility to use carbon nanotubes for superfine purification of water-ethanol mixtures from the unwanted admixtures of n- and isopropanol.     

Adsorption of atomic hydrogen on the surface of the boron-carbon nanotubes

Results of theoretic studies of geometrical, electronic, and energy composition of monolayer boron-carbon BC₃ nanotubes of the zig-zag type (n, 0) and the cylindrical symmetry are presented. The mechanism of adsorption of atomic hydrogen on the outer surface of the boron-containing BC₃-nanotubes of the (6, 0) type is studied. The calculations are carried out on the basis of models of the ion-incorporated covalent-cyclic cluster using the semiempiric MNDO scheme and density functional (DFT) methods.     

Characteristic features of the sorption of light atoms on the surface of a single-layer carbon tubelene

The mechanisms of sorption of H, O, C, and Cl atoms on the surface of a single-layer carbon tubelene are studied, and a comparison is made with the case of sorption of these atoms on graphite. Three versions of the position of the adatoms above the surface were studied. A cyclic-cluster model and an appropriately modified MNDO computational scheme are used. The optimal geometry of the sorption complexes and the sorption energies are obtained. The high hydrogen accumulation efficiency in a material consisting of single-layer carbon nanotubes is explained. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 799–804 (25 December 1997)     

Metal-Polymer Nanocomposites Based on Pyrolyzed Polyacrylonitrile with Fe–Ni–Co Inclusions

Russian Physics Journal - The paper presents the results of the computational modeling and quantum-chemical investigations of metal-polymer composites based on pyrolyzed polyacrylonitrile (PAN)...     

Proton conductivity of single-walled carbon nanotubes: A semiempirical study

The possibility of using single-walled carbon nanotubes as materials with proton conductivity is investigated. Two possible mechanisms of migration of a proton over the surface of single-walled carbon nanotubes are proposed. The proton transfer over the outer surface of carbon nanotubes is calculated at the semiempirical quantum-mechanical level. The surface profiles of the potential energy are constructed and used to calculate the activation energy of proton hopping from one carbon atom to another carbon atom. This activation energy can be useful for determining a temperature dependence of the relative hopping conductivity of a nanotube.     

Internal investigation of saturation carbon nanotubes molecular hydrogen

The electron-energy characteristics of the saturation of the cavity of carbon nanotubes of armchair and zig-zag types with molecular hydrogen are theoretically studied. The calculations are performed based on a model of a molecular cluster with the use of the MNDO and PM3 methods, which proved to be effective in predicting the electronic structure of molecules and periodic solids. Two mechanism of saturation of the cavity of single-walled carbon tubulenes with hydrogen molecules were proposed and examined: (1) the mechanism of surface wetting and (2) the capillary mechanism of filling.     

Sensor activity with respect to alkali metals of a carbon nanotube edge-modified with amino group

The work is devoted to the theoretical study of sensor activity of nanosystems based on a carbon nanotube modified with a functional amino group, with respect to certain metal atoms and ions. The calculations were performed within the molecular cluster model using the semiempirical MNDO scheme and density functional theory DFT. The mechanism of attachment of an amino group to the open edge of zigzag single-walled carbon nanotubes possessing cylindrical symmetry was studied to design a chemically active sensor based on them. The key geometric and electron-energy characteristics of the constructed systems have been determined. The interaction of the sensors thus constructed with atoms and ions of some metals—potassium, sodium, and lithium—has been studied. The scanning of arbitrary surfaces containing selected atoms or ions has been modeled; from the interaction energies, and the activity of the single-walled carbon nanotube + amino group probe system has been determined with respect to the selected elements to be initialized. Analysis of the charge state of the system has established that the sensor action mechanism is realized, as a result of which the number of charge carriers in the resulting nanotubular system serving as a sensor probe changes, which provides the appearance of conductivity in the system. The presence of metallic atoms can be experimentally detected by the change in the potential in a probe system based on a nanotube with a functional group. The theoretical studies have proved the possibility of creating highly sensitive sensors based on the most promising nanomaterial— carbon nanotubes functionalized with active chemical groups, including the amino group NH₂.     

Electronic structure of carbon nanotubes modified by alkali metal atoms

The electronic structure and parameters of the energy band structure of (n, 0)-type nanotubes modified by alkali metal atoms (Li, Na) and intercalated by potassium atoms are studied. The quantum-chemical semiempirical MNDO method and a model of the covalent cyclic cluster built in via ionic bonding are used to model infinitely long nanotubes. The electronic density of states of modified nanotubes is found. It is shown that semiconductor-metal transitions can occur in semiconductor nanotubes and that semimetal nanotubes can undergo metal-metal transitions.