N. F. Yudanov

Fluorinated cage multiwall carbon nanoparticles

Abstract Multiwall carbon nanoparticles from the inner part of a deposit grown onto a cathode in an arc-discharge condition were fluorinated at room temperature using volatile fluoride BrF 3 . The sample produced was characterized by means of X-ray diffraction (XRD), infrared (IR) and X-ray photoelectron spectroscopy (XPS). These methods point to the presence of covalent C–F bonds in the sample with retention of the sp 2 -hybridizated carbon atoms composing the cage tubular or quasi-spherical shells. Transmission electron microscopy (TEM) indicated a decrease of cage nanoparticles in the fluorinated material relative to the pristine sample that may be connected with unrolling the nanotubes during fluorination.

Gas-phase synthesis of nitrogen-containing carbon nanotubes and their electronic properties

Nitrogen-containing carbon nanotubes are synthesized using a gas-phase reaction. The synthesis of nitrogen-doped carbon nanotubes from 100 to 500 Å in diameter is accomplished through pyrolysis of acetonitrile (CH3CN) at a temperature of 800°C. Cobalt and nickel metallic particles formed upon thermal decomposition of a mixture of maleate salts are used as catalysts. The materials synthesized are investigated by scanning and transmission electron microscopy. Analysis of the x-ray photoelectron spectra demonstrates that the content of nitrogen atoms in three nonequivalent charge states is approximately equal to 3%. A comparison of the CKα x-ray fluorescence spectrum of the carbon nanotubes synthesized through electric-arc evaporation of graphite and the x-ray fluorescence spectrum of the nitrogen-containing carbon nanotubes prepared by catalytic decomposition of acetonitrile indicates that, in the latter case, the spectrum contains a certain contribution from the sp3 states of carbon atoms. The temperature dependences of the electrical conductivity for different types of multi-walled carbon nanotubes are compared. The difference observed in the temperature dependences of the electrical conductivity is associated with the presence of additional scattering centers in nitrogen-containing carbon nanotubes.

Transport and magnetic properties of multiwall carbon nanotubes before and after bromination

Bulk samples of oriented carbon nanotubes were prepared by electric arc evaporation of graphite in a helium environment. The temperature dependence of the conductivity σ(T), as well as the temperature and field dependences of the magnetic susceptibility χ(T, B) and magnetoresistance ρ(B, T), was measured for both the pristine and brominated samples. The pristine samples exhibit an anisotropy in the conductivity σ∥(T)/σ⊥>50, which disappears in the brominated samples. The χ(T, B) data were used to estimate the carrier concentration n0 in the samples: n0ini∼3×1010 cm−2 for the pristine sample, and n0Br∼1011 cm\t—2 for the brominated sample. Estimation of the total carrier concentration n=ne+np from the data on ρ(B, T) yields nini=4×1017 cm−3 (or 1.3×1010 cm−2) and nBr=2×1018 cm−3 (or 6.7×1010 cm−2). These estimates are in good agreement with one another and indicate an approximately fourfold increase in carrier concentration in samples after bromination.

Preparation of metal-polymer composites through the thermolysis of Fe(II), Co(II), and Ni(II) maleates

Metal-polymer composites have been prepared through the thermolysis of the [M1(H2O)2(C4H2O4)] · H2O (M1 = Co(II), Ni(II)) neutral maleates and [M2(H2O)4(C4H3O4)2] (M2 = Fe(II), Co(II), Ni(II)) acid maleates. In the polymer matrix of the Fe-containing composite, we identified metal, Fe2O3, and Fe3O4 particles, with slight densification of the matrix around them. The polymer matrix of the cobalt maleate-derived composite contained four types of nanoparticles: α-Co, β-Co, and CoO in polymer shells and Co3O4 with no polymer shell. The decomposition of the nickel maleates yielded homogeneous nickel nanoparticles (4–5 nm) covered with two to five graphene layers. The Co-containing composite was found to be a dielectric. The Ni-containing composite exhibited variable range hopping conduction in the range T ≤ 50 K.

Transition-metal bimaleates and their solid solutions: Synthesis, structural, and thermoanalytical study

Transition-metal hydrogen maleates of composition M(C4H3O4)2 · 4H2O, where M = Mn, Fe, Co, and Ni, and their solid solutions were synthesized and characterized by X-ray crystallography, IR spectroscopy, mass spectrometry, and thermal analysis. X-ray crystallography and IR spectroscopy showed that both intramolecular and intermolecular H-bonds exist in these compounds. The generation of continuous substitutional solid solutions with cation substitution in these compounds was studied. The thermolysis mechanism was studied for both transition-metal hydrogen maleates and their solid solutions. The composite produced by thermolysis is stable up to 1200°C in flowing helium.

LAYERED COMPOUNDS BASED ON PERFORATED GRAPHENE

A method to obtain previously unknown layered structure composed of stacks of perforated graphene sheets is developed. The method consists in the thermal decomposition of graphite oxide in the concentrated H2SO4 and H3PO4 medium. In order to confirm the presence of holes in graphene layers, a large set of chemical and physicochemical analysis methods are applied. Based on a new matrix, treated thermally and chemically, layered compounds are obtained: oxide, fluoride, and fluoroxide of two types. The obtained compounds are analyzed by transmission electron microscopy, infrared absorption spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and powder X-ray diffraction.

Maleates of Mn(II), Fe(II), Co(II), and Ni(II) as precursors for synthesis of metal-polymer composites

Comparison was made for the structural, IR spectral, and thermoanalytical characteristics of normal [M1(H2O)2(C4H2O4)](H2O) (M1 = Co(II) and Ni(II)) and acid maleates [M2(H2O)4(C4H3O4)2] (M2 = Mn(II), Fe(II), Co(II) and Ni(II)). Only structures of acid maleates contain intramolecular asymmetric hydrogen bond whose asymmetry increases in the series of transition metal salts. Thermal decomposition of Co(II), Ni(II) normal maleates, and Mn(II), Fe(II), Co(II), Ni(II) acid maleates proceeds in three stages. Onset decomposition temperatures for the first and second stages decreases in the series of normal maleates Co(II) ≥ Ni(II) and increases in the series of acid maleates Fe(II) < Co(II) < Ni(II) ≈ Mn(II). Onset temperature of the third stage decreases in the series of both normal maleates Co(II) > Ni(II) and acid maleates Mn(II) > Fe(II) > Co(II) > Ni(II).

Growth of carbon nanotubes via chemical vapor deposition on Co catalyst nanoparticles dispersed in CaO

Multiwalled carbon nanotubes (CNTs) have been synthesized by chemical vapor deposition (CVD) from methane and carbon monoxide. The process was catalyzed by cobalt nanoparticles produced via pyrolysis of a solid solution between cobalt and calcium tartrates. The solid solution was characterized by x-ray diffraction, thermogravimetry, and chemical analysis. As shown by transmission electron microscopy, the introduction of water vapor during synthesis increases the CNT content of the resulting material. The field emission current-voltage behavior of the CNTs is shown to depend on CVD conditions.

Thermolysis of copper(II) salts of maleic acid. Synthesis of metal-polymer composites

The thermal decomposition of neutral ([Cu(H2O)(C4H2O4)]) and acidic ([Cu(H2O)4](C4H3O4)2) maleates can conventionally be divided into four stages: (1) dehydration, (2) polymerization, (3) isomerization of the maleate ion to the trans form with the simultaneous reduction Cu(II) → Cu(I), and (4) decarboxylation of copper(I) fumarate. The third and fourth stages of the decomposition of these salts coincide. The residue after the thermolysis of copper(II) maleates in a He flow is a composite consisting of aggregates from 50 nm to several microns in size. Spherical conglomerates (50–200 nm) containing many spherical Cu particles (5–10 nm) are incorporated into the organic polymer matrix of these aggregates.

Thermal decomposition of transition metal biphthalates [M(H2O)6](C8H5O4)2 (M = Fe, Co, Ni) and copper biphthalate [Cu(C8H5O4)2(H2O)2]. Synthesis of metal-polymer composites

The decomposition of transition metal biphthalates [M(H2O)6](C8H5O4)2 (M = Fe, Co, Ni) and copper biphthalate [Cu(C8H5O4)2(H2O)2] was studied by thermal analysis and mass spectrometry. The decomposition was shown to proceed in three stages: the temperature of the third stage of decomposition decreased in the series of iron, cobalt, nickel, and copper biphthalates from 365 to 275°C. The mass spectrometric study showed the evolution of CO2, diphenylene C12H8, and fluorene (C6H4)2CH2 that at this stage. It was shown by electron scanning microscopy, X-ray diffraction analysis, and chemical analysis that the final thermolysis product of transition metal biphthalates was a composite consisting of the polymer and incorporated into it round submicronic aggregates with metallic particles inside.