Volume 52, Nº 4 (2018)

Based on the experimental data obtained by the authors in a number of previous studies, the limits of applicability of positron annihilation lifetime spectroscopy (PALS) and low-temperature gas sorption (LTGS) to determination of nanoporosity (size distribution of nanopores in the range from a few fractions of a nanometer to 50 nm) in polymeric membrane materials and sorbents are discussed. It turns out that none of these methods is universal. The possibility of using each of them is determined by different factors, with the cases considered being finely divided polymer materials and the membranes per se cast from powders. It has been shown that the particle size factor is important for the applicability of LTGS. The possibility of using PALS depends on the concentration of nanopores of a given size.

Relaxation processes in ZnSe quantum dots upon excitation by a 30-fs pulse at a wavelength of 360 nm have been studied by broadband femtosecond absorption spectroscopy. The diameter of ZnSe nanoparticles was 3.7 ± 0.6 nm. A colloidal solution of ZnSe in cyclohexane was used. In the differential spectra, a bleaching band at the edge of the excitonic absorption band of ZnSe, an absorption band of the biexcitonic transition with a peak at about 420 nm, and a broad structureless absorption band in the region from 440 to 750 nm have been revealed. From the analysis of the absorption and luminescence spectra, the shift of the excitonic luminescence band δ_XX = 127 meV has been measured. From the femtosecond photolysis data, an estimate of the biexcitonic interaction Δ_XX ≈ 75 meV has been obtained. It has been shown that the relaxation kinetics of the differential spectra is described by three-exponential dependences with time constants and corresponding amplitude contributions of 1 ps (42%), 13 ps (22%), and 91 ps (17%). The kinetic component of 1 ps (42%) is presumably due to hole transport to surface traps. The kinetic components of 13 ps (22%) and 91 ps (17%) apparently describe the processes of electron transport to shallow and deep traps.

The irradiation of low-density polyethylene with MeV protons leads to a substantial increase in surface free energy, its acid–base component, and surface polarity due to the appearance of functional groups in the surface layer, as confirmed by ATR IR and Raman spectra. It has been shown that the surface energy of the irradiated polymer depends little on the change in proton energy from 1 to 4 MeV at a fluence of 10¹⁵ proton/cm². It has been found that the oxygen content of the irradiated polymer surface increases as a result of oxidative reactions of the radicals generated during radiolysis and the thermal stability of the polymer decreases.

The effect of electron-beam irradiation on the catalytic properties of PdO/CeO₂ has been examined. It has been found that irradiation in the range of 15–30 kGy results in an increase in the concentration of the radical anion [O⁻], thereby enhancing the catalytic activity of PdO/CeO₂.

The decomposition of tetrachloromethane and tetrafluoromethane by air plasma in the presence of methane has been studied using an ac plasma torch of up to 500 kW power with rail electrodes. Methane reacts with air in the partial oxidation mode to form hydrogen, which reacts with a halogen to produce the hydrogen halide.

A device for creating a cold nonequilibrium electron-beam plasma in a supersonic gas flow has been developed. A method proposed for generating this plasma is described. It has been established that methane is activated by direct electron impact in electron-beam plasma under specified conditions. It has been shown that applying an external electromagnetic field leads to a significant increase in the methane decomposition factor due to the involvement of secondary, low-energy beam electrons accelerated in the electromagnetic field.

Hydrogenated graphene has been synthesized in one step by acetylene conversion in a helium plasma jet. A dc plasma torch with a diverging anode channel and a power up to 45 kW has been used to generate plasma. The obtained graphene materials have been studied by scanning electron microscopy, Raman spectroscopy, and elemental analysis. Hydrogen desorption from the samples synthesized has been studied by thermal analysis as a function of temperature. It has been found that during annealing in vacuum, the synthesis products change their morphology because of hydrogen release.

The paper describes the effect of low-temperature annealing in air on the composition and structure of graphene oxide aerogel. It has been found that the concentration of carbon in the aerogel sharply increases, i.e., its carbonization occurs, already at a temperature of 175°C. At the same time, both the outer shape of the aerogel granules and the internal porous structure are preserved.

The product composition of photocatalytic oxidation of vaporized sevoflurane, a next-generation fluorinated inhalation anesthetic, has been studied. It has been found that the final products of oxidation are carbon dioxide and hydrogen fluoride. The possibility of complete chemical absorption of the evolved hydrogen fluoride by a lime absorber during the course of the photocatalytic reaction has been shown. A safe scheme for using photocatalysis is recommended for purifying air to remove vapors of halogen-containing anesthetics under medical hospital conditions.