M. N. Efimov

Carbon nanostructures based on IR-pyrolyzed polyacrylonitrile

For the first time, it is shown that IR pyrolysis of a composite based on polyacrylonitrile and gadolinium chloride produces a metal-carbon nanocomposite where metal particles with a size of 4–11 nm form a fine dispersion in the structure of the carbon matrix. The carbon phase of the composite is a carbon-carbon nanocomposite with a structure in which carbon nanoparticles (bamboolike carbon nanotubes, carbon nanospheres, or octahedral carbon nanoparticles) are incorporated into the matrix graphite-like material.

The formation of Pt-Ru alloy nanoparticles in a carbon matrix under IR pyrolysis conditions

Nanosized Pt-Ru alloy and Pt13Ru27 intermetallic compound particles dispersed in a carbon matrix were obtained for the first time directly during the preparation of the composite. The alloying of the Pt and Ru particles occurred at IR pyrolysis intensities corresponding to temperatures above 700°C over the whole homogeneity range of solid solutions based on platinum. Metallic nanoparticles were round-shaped (the mean size 6–8 nm) and had a narrow particle-size distribution.

Metal-Polymer Nanocomposites Based on Polydiphenylamine and Cobalt Nanoparticles

It is shown for the first time that the infrared heating of polydiphenylamine in the presence of cobalt (II) acetate Co(CH3CO2)2 · 4H2O in an inert atmosphere at a sample temperature of T = 250−600°C leads to the formation of a metal-polymer nanocomposite in which Co nanoparticles are dispersed in a polymer matrix at the expense of condensation of diphenylamine crystalline oligomers with hydrogen release, promoting the reduction of Co2+ to Co0. The formation of Co nanoparticles is confirmed by X-ray phase analysis. According to data from transmission electron microscopy, Co nanoparticles have sizes of 2 < d < 8 nm. The investigation into the magnetic and thermal properties of Co/polydiphenylamine nanocomposite has shown that the nanocomposite obtained is superparamegnetic and thermostable.

A magnetic metal/polymer nanocomposite material based on poly(diphenylamine) and Fe3O4 nanoparticles

It was discovered that IR heating of poly(diphenylamine) in the presence of FeCl3•6H2O in an inert atmosphere at 300–700 °C produces a metal polymer nanocomposite with Fe3O4 nanoparticles dispersed in polymer matrix. This is achieved by condensation of crystalline diphenylamine oligomers with evolution of hydrogen that promotes iron reduction. The formation of Fe3O4 nanoparticles was confirmed by X-ray powder diffraction. The magnetic and thermal properties of the Fe3O4—poly(diphenylamine) nanocomposite were examined. This nanocomposite material shows superparamagnetism and thermal stability.

Formation of nanoparticles of platinum group metal alloys in composites based on nanodiamonds

Metal-carbon nanocomposites were synthesized from detonation nanodiamonds (ND) and platinum group metals under the IR pyrolysis conditions. The metal interacted with the nanodiamond surface. The size of metal nanoparticles was shown to depend on the amount of the metal introduced in the precursor. In ND/Pt-Ru, ND/Pt-Rh, ND/Pd-Ru, and ND/Pd-Rh nanocomposites, the metal phase was a solid solution. The lattice constants of the metal phases in the nanocomposites were determined. The quantity of the dissolved metal in the solid solution was evaluated.

Structural variation in palladium nanoparticles of the C-Pd system when dissolving hydrogen in them

The structure of nanocomposites of the C-Pd system has been studied by X-ray diffraction analysis and transmission electron microscopy. Variations in the lattice period of nanosized palladium, the average amount of hydrogen dissolved in it, and the size distribution of palladium nanoparticles have been analyzed as functions of the nanocomposite fabrication temperature. Based on the structural data, the solubility of hydrogen in nanosized palladium has been estimated.

Phase formation in nanocomposites of the C-Pd-Fe system

Metal-carbon nanocomposites consisting of a carbon matrix with dispersed nanosize bimetallic Pd-Fe particles were obtained. It was established that at 500–700°C, the bimetallic particles form a solid solution of iron in palladium. It was concluded that raising the intensity of infrared pyrolysis to 800–1100°C leads to the formation of intermetallic compounds whose composition depends on the temperature of nano-composite fabrication.

Complexation in the polyacrylonitrile-amide solvent-PtCl4 system

Complexation in the polyacrylontrile-amide solvent-PtCl4 solvent system has been studied by IR and electronic absorption spectroscopy. It has been shown that Pt is involved in complexation between the amide group of the solvent and the nitrile group of the polymer, thereby promoting retention of the residual solvent in it. Upon full removal of the solvent, Pt forms complexes with the conjugated system of C=N bonds being formed.

Metal–carbon C/Co nanocomposites based on activated pyrolyzed polyacrylonitrile and cobalt particles

A new way of synthesizing metal–carbon nanocomposites via simultaneous pyrolysis and the chemical activation of a precursor based on polyacrylonitrile and cobalt carbonate under IR radiation is proposed. Structural characteristics of samples synthesized both without alkali and in the activation process are compared. The effect the metal has on the structure of the carbon and the size of its specific surface area is shown. The specific surface area of the sample synthesized with the simultaneous formation of the carbon matrix, its activation, and the reduction of the metal is 1232 m2/g. Cobalt nanoparticles are found to have cubic face-centered and hexagonal close-packed lattices.

Effect of IR Radiation on the Properties of Polyacrylonitrile and Membranes on Its Basis

The effect of processing of polyacrylonitrile membranes by IR radiation at a temperature of 100–150°С is studied. The influence of the processing temperature on the film structure is ascertained. In a film heated at 100°С, a small amount of the double C=N bonds is found. Its further heating to 120°С is accompanied by a change in the chain conformation and an increase in the content of C=N bonds. It is shown that, upon IR processing at 120°С, polyacrylonitrile ceases to dissolve in N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. Heating at 150°С gives rise to the appearance of conjugated С=N–C=N bonds. The analysis of AFM micrographs demonstrates that the processing of the membranes by IR radiation makes their surface rougher, while the size of pores changes slightly. The permeability of the membranes in various media is measured.