The comparative study of sorption of polar substances acetonitrile and water into powders and membranes (>10 μm thick) of modified Hummers (HGO) and Brodie (BGO) graphite oxides was performed using isopiestic method (IM) and differential scanning calorimetry (DSC). Additional sorption data were obtained for pyridine and 1-octanol. Sorption measurements were accompanied by conventional XRD and XPS control. Electron paramagnetic resonance (EPR) was additionally used to characterize ordering of the membranes. The impact on sorption of synthetic procedure (Brodie or Hummers), method of making membranes, chemical nature of the sorbent, and method of sorption was systematically examined. It was demonstrated that variations in synthetic procedures within both Hummers and Brodie methods did not lead to changes in the sorption properties of the corresponding powders. Sorption of acetonitrile and pyridine was reduced by approximately half when switching from powders to membranes at ambient temperature. DSC measurements at a lower temperature gave equal sorption of acetonitrile into HGO powder and membranes. Water has demonstrated unique sorption properties. Equal sorption of water was measured for HGO membranes and powders at T = 298 K and at T = 273 K. It was demonstrated that lowering the orientational alignment of the membranes led to the increase of sorption. In practice this could allow one to tune sorption/swelling and transport properties of the GO membranes directly by adjusting their internal ordering without the use of any composite materials.

Reversible phase transformation in the Brodie graphite oxide-acetonitrile system, which is intercalation or release of part of the sorbed liquid from the interplanar space accompanied by an increase or a decrease in interplanar distances, is commonly observed in twice-oxidized materials. We observed this phenomenon for once-, twice- and thrice-oxidized materials using the EPR spin probe technique, DSC, and temperature programmed XRD. It was shown that all materials under study formed similar low temperature (LT) and high temperature (HT) swollen structures with acetonitrile. The phase transformation of these structures is observed for materials with different oxidation levels in the same temperature range (∼20 K). The twice- and thrice-oxidized Brodie graphite oxides form swollen structures with the same parameters, while the once-oxidized material sorbs less acetonitrile at lower temperatures, but shows the same interplanar distances as those in twice- and thrice-oxidized materials. The spin probe technique has proven its sensitivity to the appearance of small amounts of the new forming swollen structures, which makes this method useful in studies of phase transformations.

The multispectral modality and technique for optically dense samples of optoacoustic spectroscopy were applied to measure spectra and high absorbances of concentrated aqueous dispersions of undoped nanodiamonds. The data from optoacoustic and optical transmission measurements and DSC data of the mean particle size by the Gibbs-Kelvin equation are compared to estimate the difference in composition of various nanodiamond trademarks. Optoacoustic spectra confirm the contribution of surface dimer chains into the absorption of nanodiamonds in the long wavelength range. Optoacoustic and conventional absorption spectra of aqueous solutions of nanodiamond fractions after centrifugation (15300g) and ultracentrifugation (130000g) revealed a separation of a highly absorbing non-diamond sp(2) phase. The two-step separation by ultracentrifugation followed by extra centrifugation made it possible to isolate a highly absorbing and soluble nanodiamond phase with the particle size of 3.6 nm, showing a change in spectra compared to the starting nanodiamond material.

The ultrasound-assisted solvent-exchange technique for aqueous fullerene dispersions (AFD) of C-60 (10(-4) - 10(-6) M) have been improved for high-yield synthesis, thereby achieving AFDs with total recovery over 90 %. Using ICP-AES, HPLC-UV, HGC-MS, the elemental and residual organic compounds have been estimated as not exceeding 3 ppm. The possible structure of fullerene clusters in AFD was assumed as {n[C-60]mC(6)H(5)COO(-) (m - x)Na+}xNa(+).

Thermal-lens spectrometry was used to characterize thermal diffusivity and thermal conductivity of aqueous nanodiamond dispersions at the level of mg/mL, accompanied by heat capacity, density, and viscosity measurements and modelling.The data from thermal lensing corresponding to thermal equilibrium show 3 -7 % increase in thermal conductivity of the studied dispersions, show good precision and agree with the existing data.

The work considers a possibility of creating standard reference samples of aqueous dispersions of unmodified fullerenes and endohedral fullerenes. Procedures for preparing highly concentrated dispersions and methods for determining the concentration of the main component, elemental impurity composition, organic composition, and dimensional characteristics are discussed. Commercially available fullerenes C60 and C70 and endohedral fullerene Y@C82 (C2v isomer) synthesized by the electric arc method were used as the starting materials. Aqueous fullerene dispersions (AFDs) were prepared by replacing the organic solvent (toluene) under additional ultrasonic treatment. The maximum concentrations of fullerenes C60, C70, and Y@C82 were 150 ± 3, 55 ± 2, and 2.8 ± 0.1 mg/L, respectively. The long-term stability of solutions (more than 5 years) on storage was found. A set of methods and procedures that enable the determination of the main components of AFDs (fullerenes) and accompanying components (impurities of organic solvents and metals at the level of trace concentrations) is discussed. The sizes of fullerene clusters in solutions (from 100 to 120 nm for all solutions) are characterized; the stability of dispersions is estimated based on the electrokinetic potential (ca. –40 mV). The combined use of spectrophotometry, determination of total organic carbon, inductively coupled plasma atomic emission spectrometry, headspace gas chromatographic analysis, and HPLC offers a complete description of the physicochemical properties of AFDs, which further ensures the validation of AFDs as standard reference samples.

A thermal-lens spectrometer implementing back-synchronized detection technique with a mode-mismatched optical scheme was constructed. Steady-state and transient signals of thermal-lens spectrometry are used to characterize concentration parameters of aqueous fullerene dispersions (AFDs) at the level of 10(-7) - 10(-5) M and to assess thermophysical properties of AFDs. The detection limits of fullerenes in AFDs are 100 nM for C-60, 80 nM for C-70 and C-78 - C-88, and 60 nM for Y@C-82, which are 20-fold lower than for spectrophotometry. Suitable precision of measurements of thermal diffusivity and thermal effusivity for AFDs is shown.

An improved technique of the ultrasound-assisted reversible liquid liquid transfer of pristine (unmodified) C-60 and C-70 fullerenes between organic solutions and aqueous fullerene dispersions (AFD; another notation in general use, nC(60), nC(70)) without any additional reagents (media modifiers) was developed. To our knowledge, this is the first report of such a fullerene transfer from an AFD to an organic phase. Based on the observation of this fullerene reversible transfer, their distribution between the aqueous and organic phases was considered. A quasi-equilibrium transfer mechanism was proposed, which makes it possible to estimate distribution constants, K-D, as 6 and 2, for C-60 and C-70 respectively, in a water toluene system. Under the optimum conditions, AFDs of C-60 and C-70 with the concentrations 180 +/- 20 and 70 +/- 20 mu M, respectively, were obtained from the corresponding solutions in toluene. Based on UV/vis spectroscopy, total organic carbon, headspace GC-MS, and MALDI measurements, a reliable analytical procedure to measure fullerene concentrations and to monitor the concentration of residual toluene in AFDs was proposed. AFDs of a mixture of fullerenes C-60 and C-70 were characterized by the developed technique. (C) 2016 Elsevier Ltd. All rights reserved.

The solvent-exchange process from toluene was used for preparing aqueous dispersions of C60 and C70 without preconcentration with final concentrations of 180 ± 2 and 62 ± 1 μM, respectively, which exceeds the previously reported maximum concentrations for C60 more than 6-fold; for C70 such an aqueous dispersion is prepared for the first time. The residual quantity of the organic solvent and low-molecular compounds determined by headspace GC-MS was not more than 1 ppb. The procedure for the determination of fullerenes in aqueous dispersions is developed using a total organic carbon analyzer and absorption spectra; LOD, 50 nM, LOQ, 200 nM by TOC. Spectrophotometric determination of fullerenes in their aqueous dispersions was optimized: for C60 at 268 nm: LOD, 0.1 μM, LOQ, 0.3 μM, for C70 at 218 nm: LOD, 0.1 μM, LOQ, 0.3 μM. RSD mixture quantification by Vierordt’s method in the range of 2 – 20 μM does not exceed 0.14 for C60 and 0.09 C70. RSD for toluene fullerene mixtures by Vierordt’s method in the range of 2 – 20 μM does not exceed 0.10 for C60 and 0.06 for C70.

The C60 and C70 fullerene-cluster size distribution in aqueous solutions and a physiological medium is studied via dynamic light scattering. The initial aqueous solutions of fullerenes obtained via different methods are found to contain clusters with a characteristic size of about 100 nm. The additional aggregation of fullerenes is observed after their transfer into a physiological medium (0.9% NaCl) and is established to depend on the preparation method. The cluster-size distribution in a fullerene–pectic-acid mixture is found to vary in water and a physiological medium. The results reveal the need for additional studies of the structure and properties of C60 and C70 molecules, as well as their complexes with medicines, in a physiological medium for medical applications.

The results of researches concerning the cluster state in a number of disperse carbonic materials that are widely used in modern applications, including fullerenes and detonation nanodiamonds, are reported. With the help of the small-angle neutron scattering (SANS) method, some basic aspects of clustering in such systems are elucidated. At the same time, for the most effective and reliable description of a cluster structure under various conditions, a complex analysis involving complementary experimental and calculation techniques is applied. The experimental aspects of SANS applications are emphasized, and a qualitatively new idea of the structure of analyzed systems is formulated.

In this paper, two types of fullerene C60 solutions are compared with respect to their structural features and toxic properties. The results are discussed in terms of their potential in medical and biological applications. The fullerene cluster state at the nanoscale in these solutions is analyzed by small-angle neutron scattering. Experiments on the cytotoxicity of these systems on Chinese-hamster V-79 cells showed no toxic effects of the solutions.

A set of 20 commercially available nanodiamond samples of eight manufacturers of various countries, which are most frequently used in basic and applied studies, was analyzed for the concentration of Hg. Conditions of mercury determination by flameless atomic absorption spectroscopy with thermal sample decomposition (pyrolysis) at 800°C were proposed and confirmed by wavelength-dispersive X-ray fluorescence analysis. It was found that nanodiamonds have a significant diversity of amounts of mercury, from 20μg/kg to higher than 0.7g/kg. Thus, the need to control Hg impurity in nanodiamonds, especially for biological and medical research, was demonstrated. The precision of flameless pyrolysis atomic absorption determination of mercury in nanodiamonds is discussed.