N. N. Rozhkova

From stable aqueous dispersion of carbon nanoparticles to the clusters of metastable Shungite carbon

Aqueous dispersion of Shungite carbon (ShC) condensation is followed by aggregation of carbon nanoparticles and further net formation. Data obtained by adsorption methods that characterized changes in porosity of natural shungites when transformed into aqueous dispersion and precipitated, were investigated. Pore size distribution determined for natural shungites is characterized by micro- and submesopores of <0.7–5.0 nm in size predominantly. It correlates with values of basic structural elements (0.4–0.7 nm) releasing into aqueous dispersion and with the primary ShC globular aggregates less than 6.0 nm in size. Decreasing of specific surface and total pore volume while the mean pore radii remains constant, were observed when oxidizing (ozonating) and heating of carbonaceous net. Different stages of ShC nanoparticles aggregation in nature were modeled in laboratory under concentration of stable aqueous dispersion.

Effect of ozone on the structure and physicochemical properties of ultradisperse diamond and shungite nanocarbon elements

A comparative study of the effect of ozonization on the physicochemical properties of naturally and synthetically generated nanocarbon materials, shungite carbon (ShC) and ultra-disperse diamond (UDD) after special treatment in the form of monodisperse single nano-diamond particulates (mdsn-D), that have a similar two-level structural pattern (hierarchical system structure) and curved graphene shells or their fragments contribute to the formation of the structure and surface properties of both ShC and mdsn-D particles, was conducted. The ozonization kinetics of ShC and mdsn-D showed their high catalytic activity during ozone decomposition. Upon ozonization, the graphene shell is removed selectively from the surface of the diamond core of mdsn-D, as shown by Fourier transform-infrared (FT-IR) spectroscopy and derivatography data. A distinctive characteristic of ShC is a substantial change in structural parameters upon ozonization: structural porosity increases and the size of coherent scatter domains decreases in the direction perpendicular to graphene layers [as shown by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) data], which agrees with adsorption experiments that showed an increase in ultramicroporosity and mesoporosity upon ozonization of ShC. The molecular probe technique was used to monitor changes in microporosity of ShC and mdsn-D.

Fullerene-containing phases obtained from aqueous dispersions of carbon nanoparticles

The hydration of fullerenes and shungite carbon nanoclusters in aqueous dispersions at various carbon concentrations is studied on frozen samples by EPR with spin probes. It is found that, for stable dispersions of both substances (at carbon concentrations of 0.1 mg/ml), the probe rotation frequency versus 1/T dependences exhibit a plateau in the range 243–257 K, which is probably associated with the peculiarities of freezing of water localized near hydrophobic structures of carbon nanoclusters. Solid phases isolated from supersaturated aqueous dispersions of fullerenes and shungites by slow evaporation of water at temperatures higher than 0°C are examines by electron diffraction and electron microscopy. It is established that obtained films of fullerenes contain at least two phases: fullerite with a face-centered cubic lattice and a phase similar in interplanar spacing and radically different in distribution of intensities of diffraction peaks. It is concluded that this phase is formed by the interaction of fullerenes and water (an analogous phase is found in shungite carbon films). It is found that the morphology of the new crystal phase is characterized by globules of size 20 to 70 nm, for fullerenes, and 10 to 400 nm for shungites. It is established that processes of crystallization of fullerites and fullerene-containing phases are very sensitive to temperature: a decrease in the temperature (within the range from 40 to 1°C) is accompanied by an increase in the new phase content.

Effect of the conditions of structure formation on the physicochemical properties of ozonated shungites

It was investigated the influence of ozone on the physicochemical properties of shungites (type 1) (75–98% C) from Nigozero and Chebolaksha deposits (Karelia) formed by hydrothermal (Nigozero) and high-temperature (Chebolaksha) processes. Ozonation was found to affect the specific surface and the total pore volume of shungites considerably. The pore size distribution pattern depends on the volume morphology (texture) of the sample. An increase in the temperature and pressure during the structure formation of shungite (Chebolaksha) led to a shift of the maximum on the distribution pattern towards the formation of mesopores. The size distribution of pores with the dominant contents of micro- and submesopores for both shungites correlated with the basic structural nanoelements of shungite carbon. The peculiarities of the ozonation of shungite nanocarbon found previously (the non-steady state vibrational kinetics of ozonation and the absence of carbon(II) oxide among the reaction products) were confirmed.

Do Primary Particles of Detonation Nanodiamond Form a Secondary Structure

Gels and dried powders of the single-nano buckydiamond (SNBD) have been studied by means of differential scanning calorimetry (DSC) and gas adsorption methods. Nanophase of water (NPhW) (D = 8.4 ± 0.5 nm) was confirmed in SNBD hydrogel by DSC. Nitrogen adsorption isotherms of the dried powder demonstrated the presence of nano voids (D = 7 nm). The characteristic size and volume of the nano voids were almost equal to those of NPhW. Based on DSC and adsorption data, it was concluded that SNBD material though originally divided into individual diamond crystals (d = 5.2 nm) in the water dispersion forms stable networks as gel and dried powder.

Catalytic Activity of Nanodiamonds in Redox Process

Properties and chemical composition of detonation nanodiamonds (ND) vary with production conditions and degree of purification. The presence of catalytically active metals in ND suggests that they could be regarded as ready-made nanostructured metallic catalysts on carbon carriers. Catalytic activity in ozone decomposition as a model reaction of redox processes was studied on ND offered by various authors. The specific surface and volume of pores are observed to change slightly during ozonation, whereas the average radius of micropores remains constant and does not depend on the method of synthesis and the ND purification details. However, they are shown to exert a substantial effect on the ND microstructure and chemical composition and, consequently, catalytic activity and adsorptive properties.