Anton S. Ivanov

Carboxylated and decarboxylated nanotubes studied by X-ray photoelectron spectroscopy

Carbon nanotubes (CNTs) of the conic and cylindrical structure were studied by X-ray photoelectron spectroscopy in the initial state and after carboxylation and decarboxylation reactions. The O=C—O and C—O groups were revealed on the surface of the chemically modified samples. It was found that both the carboxylated and decarboxylated cylindrical CNTs contain a smaller amount of oxygen than the corresponding conic CNTs apparently due to differences in their structures.

MULTIWALLED CARBON NANOTUBES AND NANOFIBERS: SIMILARITIES AND DIFFERENCES FROM STRUCTURAL, ELECTRONIC AND CHEMICAL CONCEPTS; CHEMICAL MODIFICATION FOR NEW MATERIALS DESIGN

Present work points out the differences between possible tubular carbon structures: nanotubes and nanofibers, as well as describes ways of their modification for utilization for new materials design. For material characterization, XRD, XPS, Raman spectroscopy, thermal analysis, HRTEM and SEM, pore size distribution, EELS, elemental analysis and adiabatic bomb calorimetry were used. Heats of formation for nanotubes and nanofibers and their dependence on carboxylation extent as well as properties of the modified materials are also discussed. The perspectives of applications of modified carbon nanotubes in catalysis and polymers chemistry are given.

Kinetic characteristics of the synthesis of multiwall carbon nanotubes by aerosol pyrolysis of a ferrocene solution in benzene

Approximating the experimental data on the mass distribution of multiwall carbon nanotubes (MCNT) along a reactor, a three-step kinetic model of their synthesis in the aerosol pyrolysis of a ferrocene solution in benzene is proposed. The values of effective rate constants upon the introduction of a catalyst in situ for the reactions that are the basis for synthesizing MCNT via the pyrolysis of hydrocarbons are obtained for the first time.

Sulphur-free synthesis of helical carbon nanotubes

Unique three-dimensional structure of helical carbon nanotubes renders them important in polymer composites, electrode materials of electrochemical devices and microwave absorbers. The most thoroughly studied synthetic method involves hydrocarbon pyrolysis in the presence of sulphur-containing compounds which provide coiling effect. However, sulphur compounds are toxic and are usually undesirable in the coils obtained. The present work describes a novel method for the synthesis of coiled nanotubes by the aerosol pyrolysis of ferrocene solution in methanol, which is easily scalable for high-quantity production and uses no sulphur. The results of systematic investigation of the synthetic procedure with the use of other metal nanoparticle precursors and oxygen sources as well as oxygen role are discussed in details.

New Effective Catalytic Materials based on Modified Heterosubstituted Multiwall Carbon Nanotubes

Present work deals with development of the synthetic procedures for nitrogen and phosphorous substituted multiwall carbon nanotubes (MWCNT) by pyrolytic technique followed by surface modification by cobalt nanoparticles and utilization of the composite obtained in Fischer-Tropsch (FT) synthesis. It is shown that heterosubstitution in CNT structure changes the electron capacity and acid-based properties of the system, allow effectively stabilize metal nanoparticles of 2-4 nm size and yields to thermally stable and effective catalyst for cobalt FT synthesis.

Features of the oxidation of multiwalled carbon nanotubes

Features of the functionalization of multiwalled carbon nanotubes (MWCNTs) with a conical (Ni precursor) and cylindrical (Fe precursor) arrangement of graphene layers using various oxidizing agents are studied. The initial diameter of pyrolytically prepared tubes varies from 20 to 80 nm with a maximum at 40–45 nm and from 10 to 30 nm with a maximum at 18 nm in the first and second cases, respectively. Oxidative modification of the MWCNT surfaces is conducted using HNO3 and H2O2 with ultrasound activation, ozonation in a glow discharge plasma of oxygen, and treatment with liquid ozone. Thermal and elemental analyses and IR spectroscopy show that the highest content of functional groups is achieved in the samples treated with nitric acid, where the conical MWCNTs are subject to surface functionalization. It is concluded that in order to achieve a similar result, cylindrical tubes must be treated with liquid ozone.

NMR spectroscopic investigation of multi-walled carbon nanotubes modified by amino groups

The results of the functionalization of multi-walled carbon nanotube surface by amines containing different substituents at the nitrogen atom, namely, primary n-hexylamine, secondary izadrine, and tertiary N-benzylmorpholine and dithiline, are presented. It was shown by NMR spectroscopy, thermal analysis, mass spectrometry, X-ray photoelectron spectroscopy, and elemental analysis that the interaction of primary and secondary amines with modified nanotubes results in the formation of a covalent bond with the nitrogen atom of amines, while the reactions with tertiary amines afford quaternary ammonium salts; diamine is attached covalently through both amine groups.

Mathematical modeling of the multi-walled carbon nanotube growth by the pyrolysis of a ferrocene solution in benzene

The possibility of scaling up the growth of multi-walled carbon nanotubes (MWCNTs) synthesized by the pyrolysis of aerosol of a ferrocene solution in benzene was experimentally and theoretically studied. The morphology and yields of the reaction products and the influence of the volume of the introduced solution and ferrocene concentration on the duration of the process were investigated. A quantitative mathematical model of the nanotube growth process was proposed, and the possibility of using the model in scaling up the synthesis was analyzed. The experimental and model curves of the distribution of sample weights over the reactor length were compared and showed that the proposed model is correct.

The Composition of Iron-Containing Microphases in the Structure of Multiwalled Carbon Nanotubes

The phase composition of carbon nanotubes (CNTs) with encapsulated iron atoms was studied by 57Fe Mössbauer spectroscopy. The synthesis of CNTs was shown to stabilize iron atoms as both thermodynamically stable iron carbide and oxide phases and phases not characteristic under synthesis conditions (γ-Fe and γ-Fe2O3). In addition, an analysis of the data obtained led us to suggest the existence of Fe-CNT atomic complexes in interlayer positions. CNTs and iron-containing phases were shown to be stable when subjected to prolonged annealing in air at temperatures up to 670 K.

3D Frameworks with Variable Magnetic and Electrical Features from Sintered Cobalt-Modified Carbon Nanotubes

3D frameworks of carbon nanotubes (CNTs) uniformly decorated by cobalt oxide or carbon-encapsulated cobalt nanoparticles were obtained by spark plasma sintering for the first time. The influence of the sintering temperature ( TS) and Co content on the morphology, structure, and electrical and magnetic properties of the obtained materials was investigated by Raman spectroscopy, electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and in situ magnetometry. It was shown that application of the SPS technique allowed simultaneous compaction of the material, formation of CNT framework, and Co oxide reduction. The appearance of the carbon shell around 4-10 nm Co particles was observed at TS > 600 °C. At higher TS, the Co particle size increased (up to 300 nm at 1400 °C), whereas the carbon shell ordered and thickened. The formation of large-size few-layers graphene sheets was observed at TS = 1400 °C. Electrical conductivity of the composites was found to be higher than that of sintered pristine CNTs and varied in the range of 500-12 500 Sm/m. Magnetic experiments demonstrated soft magnetization of the samples and the coercivity of 200-300 Oe. Thus, the obtained CNT-based material is simultaneously compact, formable, electroconductive, and ferromagnetic. Its properties can be tuned by variation of the sintering parameters. Synthesized cobalt-modified carbon 3D structures are promising for the application in magnetic separation, catalysis, fuel cells, and electromagnetic shielding.