V. G. Koshechko

Preparation of graphene oxide by solvent-free mechanochemical oxidation of graphite

Graphenes with different oxidation degrees are prepared by ultrasound assisted aqueous exfoliation of solvent-free mechanochemically treated graphite in the presence of solid oxidants, under comparatively mild conditions without using aggressive concentrated acids.

Improved dispersant-free liquid exfoliation down to the graphene-like state of solvent-free mechanochemically delaminated bulk MoS2

Molybdenum disulfide (MoS2) was recently found to exhibit an indirect-to-direct gap transition when its thickness is reduced to a single S–Mo–S trilayer sheet, which opens up opportunities for a range of novel optoelectronic applications. Here we first report the possibility of dispersant-free efficient liquid exfoliation down to the graphene-like state of solvent-free mechanochemically delaminated bulk MoS2. The graphene-like, single-sheet structure of MoS2 nanoparticles in the dispersions is confirmed by mutually complementary experimental methods. The proposed approach essentially improves the known liquid exfoliation method based on the ultrasound disintegration of bulk MoS2, because the proposed mechanochemical treatment of the initial bulk MoS2 could provide 100% yield of the single-sheet nanoparticles without the use of dispersants.

Electrochemical initiation by sulfur dioxide of radical-chain trifluoromethylation processes of thiophenols with bromotrifluoromethane

Abstract Sulfur dioxide may serve as an efficient catalyst for the electrochemical trifluoromethylation of thiophenols by Freon F13B1 (CF 3 Br), which enables implementation of trifluoromethylation in an energy-saving radical-chain regime.

Ultrasound-free preparation of graphene oxide from mechanochemically oxidized graphite

We propose an ultrasound-free preparation of graphene oxide using spontaneous exfoliation of specifically synthesized graphite oxide in water for the first time. Graphite was mechanochemically oxidized by KMnO4 in the presence of a stoichiometric amount of sulfuric acid. The shear stresses generated during the oxidation lead to primary delamination of the graphite oxide particles and in combination with the presence of the surface oxygen-containing functional groups facilitate their further exfoliation in water without the use of ultrasound disintegration. The synthesized graphene oxide luminesces in the blue region of the spectrum.

Fluoroalkylation of thiophenols with Freons using conjugated electron transfer mediator systems composed of methylviologen-SO2 and I2-SO2

Abstract Methylviologen-sulfur dioxide and iodine (iodide)-sulfur dioxide have been shown to mediate electron transfer from thiophenols to Freons and perform the fluoroalkylation of thiophenols under mild conditions.

Efficient dispersant-free liquid exfoliation down to the graphene-like state of solvent-free mechanochemically delaminated bulk hexagonal boron nitride

It is shown that during mechanochemical treatment of the bulk hexagonal boron nitride (hBN) in the presence of an inert delamination agent the nanostructuring of hBN occurs: its partial delamination, shift of the layers relative to one another, reduction of the particle size. It is established that the reactive paramagnetic defects are formed in the structure of the nanostructured hBN, and their number is significantly reduced under the effect of water. The formation of oxygen-containing functional groups at the outer edge of the nanoparticles, and ability of such nanoparticles to effectively exfoliate in various organic solvents and in water under the effect of ultrasound are shown. The data of electron diffraction, XPS and UV-vis indicated the preservation of the hBN structure in the plane of the nanoparticles. The predominately monolayer morphology of the particles in the dispersions is confirmed by AFM microscopy and Raman spectroscopy.

Advanced electrochemical performance of hybrid nanocomposites based on LiFePO4 and lithium salt doped polyaniline

LiFePO4 (LFP) is one of the commercially usable cathode materials for lithium batteries. To overcome its main drawback—low conductivity—LFP particles are usually covered by carbon shell. But this approach lowers the capacity of the whole cathode due to electrochemical inactivity of the carbon shell at the required potentials. In the present work, we propose a novel approach which is based on mechanochemical insertion of LFP particles inside polyaniline doped with lithium salt. It is established that during charge–discharge of these nanocomposites, both LFP and polyaniline are redox active. It is shown that the prepared nanocomposites exhibit improved electrochemical performance as a cathode in lithium batteries compared with the individual LFP. It is shown that the presence of the polyaniline in the nanocomposite could facilitate the transport of lithium ions inside (outside) the inorganic component during discharge (charge).

Structure and electrochemical properties of multilayer graphene prepared by electrochemical exfoliation of graphite in the presence of benzoate ions

The possibility of obtaining multilayer graphenes–MLGs (11–21 single graphene layers) with slight amounts of oxygen-containing defects (C/O ratio in MLGs ranges from 9 to 25) via the electrochemical exfoliation of graphite in the presence of benzoate anions (MLG1) or benzoate and sulfate anions together (MLG2), under conditions of electrolysis with pulse changing of the electrode polarization potential was established. Composition, morphology, structure and electrochemical properties of MLGs were characterized by CHN-analysis, scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, FTIR and UV-Vis spectroscopy, as well as cyclic voltammetry. It was shown that MLG1 and MLG2 can be used directly as electrode materials, since they provide a fast enough heterogeneous electron transfer without any additional reduction (removing of oxygen-containing groups). In particular, the electrocatalytic activity of MLGs in the processes of electrochemical oxidation of such biomarkers as ascorbic acid (MLG1 and MLG2) and NADH (MLG2) exceeds that established for the electrochemical reduced graphene oxide (ERGO), which may be due to the presence of epoxy, aldehyde, carbonyl and peroxide groups in MLGs, unlike ERGO, which can play the role of active sites.

Polymerization of pyrrole and phenylacetylene under the action of stable radical ions

The possibility of pyrrole polymerization caused by chemically or electrochemically generated radical cations of para-substituted triphenylamines ((XC6H4)3N·+A−, where X=−OCH3, A−=SbCl6− (I); X=−CH3, A−=SbCl6− (II); X=−Br, A−=SbCl6− (III); X=−OCH3, A−=BF4 (VI) and phenylacetylene polymerization in the presence of radical anions of anthracene were explored. Reaction of radical cations, RC(I)–(IV), with pyrrole was shown to result in oxidative polymerization accompanied by simultaneous doping and conductive polymer formation. In the cases of RC(I), (II) and (IV), polypyrrole soluble in organic solvents, particularly in CH3CN, was obtaied. The pyrrole polymerization rate under the action of radical cations and the properties of the resulting polymers were found to be largely dependent on radical cation structure. Increasing radical cation oxidative ability in the trend I<II<III leads to accelerating RC-pyrrole reaction, the resulting polypyrrole conductivity rising, the number of paramagnetic centres changing and the soluble polymer yield declining. It was ascertained that RC(IV) and anthracene radical anions are capable of acting as homogeneous catalysts, mediators of electron transfer in the electrochemical polymerization of pyrrole and phenylacetylene, respectively. This allows the above processes to run at lower potentials.

One-Step Electrochemical Preparation of Multilayer Graphene Functionalized with Nitrogen

A new environmentally friendly one-step method for producing multilayer (preferably 7–9 layers) nitrogen-doped graphene (N-MLG) with a slight amount of oxygen-containing defects was developed. The approach is based on the electrochemical exfoliation of graphite electrode in the presence of azide ions under the conditions of electrolysis with pulse changing of the electrode polarization potential. It was found that usage of azide anions lead not only to the exfoliation of graphite but also to the simultaneous functionalization of graphene sheets by nitrogen atoms (as a result of electrochemical decomposition of azide anions with ammonia evolution). Composition, morphology, structure, and electrochemical properties of N-MLG were characterized by C,H,N analysis, transmission electron microscopy, atomic force microscopy, FTIR, UV–Vis, and Raman spectroscopy, as well as cyclic voltammetry. The perspective of using N-MLG as oxygen reduction reaction electrocatalyst and for the electrochemical analysis of biomarkers (dopamine, ascorbic acid, and uric acid) in their mixtures was shown.