Yu. A. Kukushkina

Synthesis of monodispersed mesoporous spheres of submicron size amorphous silica

A technique has been developed for synthesis of submicron monodispersed mesoporous spheres of amorphous silica from an alcohol-water-ammonia mixture by means of tetraethoxysilane hydrolysis in the presence of hexadecyltrimethylammonium bromide. The mechanism of sphere formation from aggregates of close-packed surfactant cylindrical micelles coated by silica has been proposed. The specific surface area in the synthesized spheres is higher than 800 m2/g, whereas the pore volume and average diameter are equal to 0.63 cm3/g and 3 nm, respectively. The average size of particles is shown to decrease twice after the temperature of the synthesis is increased twice. According to the data of atomic force spectroscopy and dynamic light scattering, the average diameter of mesoporous spheres can be controllably varied in the range 300–1500 nm with a root-mean-square deviation of no more than 6%.

Structure of Nanodiamonds Prepared by Laser Synthesis

A study is reported of nanodiamonds obtained by a new method—pulsed laser ablation of a specially prepared carbon target. In the mechanism employed to produce a diamond phase, this method is similar to that of detonation synthesis of nanodiamonds. The main structural characteristics of the material have been determined and compared with the corresponding characteristics of detonation nanodiamonds.

Nanofiltration and sorption of organic solvents in poly(1-trimethylsilyl-1-propyne) samples of different microstructures

For two PTMSP samples synthesized on various catalytic systems (TaCl5/TIBA and NbCl5) and having different chain configurations (the ratio of cis/trans units is equal to 50/50 or 63/37 for PTMSP/Ta and PTMSP/Nb, respectively), sorption and organic solvent nanofiltration (OSN) behavior is studied. Equilibrium sorption (a homological series of linear alcohols C1-C10, diols and ketones for PTMSP/Ta and a homological series of linear alcohols C1-C10 for PTMSP/Nb) and equilibrium swelling of polymers in the above solvents are estimated. Nanofiltration of dilute ethanol solutions of three dyes (Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R) is studied for the PTMSP/Ta sample, and the resultant nanofiltration characteristics of this sample are compared with the earlier data on PTMSP/Nb. Analysis of the experimental results on sorption and swelling of the PTMSP/Ta samples makes it possible to conclude that PTMSP contains sorption sites which are able to coordinate two hydroxyl groups. Structure of the PTMSP/Ta and PTMSP/Nb samples is studied by the methods of vibrational IR spectroscopy and quantum chemistry. The nature of sorption sites in PTMSP is likely to be related to an exceptionally high polarity of the C=C and Si-C bonds in the repeat polymer units. Computational simulation for the model composed of five PTMSP units in the presence of ethanol monomer shows that, in this system, a complex with ΔE = 18 kJ/mol is formed. Nanofiltration studies indicate that, for the PTMSP/Ta sample, the permeability coefficient of ethanol and overall flux of dye-containing ethanol solutions are nearly two times lower than those for PTMSP/Nb. For both PTMSP samples, dye retention increases in the following order: Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R, and this tendency agrees with the increase in the partition coefficients of the above dyes. For the PTMSP/Ta sample, dye retention of Solvent Blue 35 and Safranine O dyes with molecular masses of 350 g/mol appears to be lower than that of the PTMSP/Nb samples. Sorption and nanofiltration behavior of PTMSP/Ta and PTMSP/Nb can be reasonably explained in line with the existing approaches which treat glassy amorphous polymers as microheterogeneous systems containing structural regions with different ordering of polymer chains, and the observed difference in their sorption behaviour and membrane characteristics can be explained by the fact that packing of polymer chains in the PTMSP/Ta is more loosened as compared with that of the PTMSP/Nb sample.

Structure of nanoporous carbon produced from titanium carbide and carbonitride

Scanning electron microscopy, X-ray diffraction and adsorption structural analyses, and helium pycnometry were used to study the structure of nanoporous carbon produced by chlorination of powdered titanium carbide and carbonitride and of titanium carbide synthesized by chemical-vapor deposition. The results obtained were used to make suggestions about the type of organization of the nanoporous structure of these materials. The evolution of the structure of nanoporous carbon was analyzed in relation to the chlorination temperature. The effect of the chlorination temperature on the structure of the nanoporous carbon obtained and on its pore volume was examined.

On fractal nature of the structure of nanoporous carbon obtained from carbides

The curves describing small-angle x-ray scattering at npor-C nanoporous carbon samples obtained from polycrystalline α-SiC, TiC, and Mo2C and a 6H-SiC single crystal have been analyzed. An algorithm is developed for taking into account the corrections to experimental curves for the intensity of the primary beam transmitted through the sample and the height of the inlet slit in these measurements. Two systems of nanoclusters observed in the npor-C structure differ in the type of stacking of structural elements: small-scale mass fractals of a dimension 1<D2<3 and a size L2=50–90 Å, which depend on the type of the initial carbide, and large-scale nanoclusters having a size L1>550 Å. In most samples, large-scale nanoclusters can be regarded as objects with a fractal surface and a dimension 2<D1<13, which also depends on the type of the initial carbide. Large-scale nanoclusters in npor-C obtained from Mo2C prove to be mass fractals with a dimension D1>2. Peculiarities of the structure formation of nanoporous carbon obtained from various carbides are discussed.

Fluorescent monodisperse spherical particles based on mesoporous silica containing rhodamine 6G

Fluorescent monodisperse spherical silica (SiO2) particles with a regular mesoporous structure containing encapsulated Rhodamine 6G (R6G) dye have been synthesized. The as-synthesized particles have been coated with SiO2 and SiO2-CTAB (cetyltrimethylammonium bromide, C16H33N(CH3)3Br) shells in order to prevent uncontrolled release of the dye from pores. The kinetics of R6G release from the pores of silica particles has been studied. It has been found that the particles synthesized by adding CTAB and R6G to the reaction mixture, as well as the particles coated with the SiO2-CTAB shell, are characterized by the maximum duration of dye release from the pores, which is probably associated with the formation of chemical bonds between R6G and CTAB molecules.

Monodisperse spherical silica particles with controlled-varied diameter of micro- and mesopores

A method of fast (1 hour) synthesis of monodisperse spherical silica particles with pore sizes of diameters 0.8 and 2.3–4.5 nm has been developed based on the realization of an aggregate model of particle formation. Cethyl trimethyl ammonium bromide, decyl trimethyl ammonium bromide, and 1,3,5-trimeth-ylbenzene and rhodamine 6G were chosen as the pore-forming agents. The morphological and adsorptive-structural properties of the synthesized materials were studied. The mean-square deviations were no more than 15% for micro- and mesopore diameters, and 10% for the particle diameters. The pore volume and the specific surface of the particles were 0.5–0.8 cm3/g and 600–1100 m2/g.

Thermal oxidation of carbon nanomaterials

The process of the thermal oxidation of various carbon nanomaterials (multiwalled carbon nanotubes, carbon black, nanoporous carbon and graphite) used in the catalytic layers of electrochemical energy converters (electrolyzers, fuel cells) has been studied. The thermal stability of these materials has been determined. Relationships between the structural characteristics of carbon nanomaterials and the parameters of their thermal oxidation in air have determined using the methods of differential thermal analysis and adsorption-structure analysis.

Analysis of porous structure of furfurol-based active carbons with application of the density functional theory

Isotherms of nitrogen low-temperature adsorption on active FAS carbons and coconut-shell carbons were studied by the method of the density functional nonlocal theory. Distribution curves of micropore volumes in their width were obtained.m dodecyl sulfate in the presence of hydrogen peroxide under the action of UV light was studied.

Electron spin resonance of nanoporous carbon with embedded cobalt clusters

Cobalt clusters were embedded into a nanoporous carbon powder (with pores about 2 nm in size) prepared from a B4C carbide powder. Electron spin resonance (ESR) measurements were carried out within a broad temperature range. At all temperatures, the ESR spectrum consisted of two overlapping resonance Lorentzian lines. The temperature dependences of the integrated intensities and linewidths and of the resonance fields were determined. A theoretical analysis of these dependences shows that they can be described in terms of the theory of a disordered magnetic medium with two spin systems with different properties.