Oleksandra A. Khazieieva

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.

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.

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.

Mechanochemical Delamination of Graphite in the Presence of Various Inorganic Salts and Formation of Graphene by Its Subsequent Liquid Exfoliation

Feasibility was demonstrated for the mechanochemical delamination of graphite in the presence of inorganic salts such as NaCl, Na2SO4, and CaCO3 with subsequent liquid exfoliation of the resultant nanostructurized graphite materials to produce graphene. The nature of the inorganic delaminating agents, in particular, their hardness, may have a significant effect on the structural defectivity in the graphenes obtained and their capacity to form stable dispersions in various solvents. Sodium sulfate proved to be the most generally useful agent among the inorganic salts tested. The use of sodium sulfate leads to stable graphene dispersions in N-methylpyrrolidone, dimethylformamide, ethanol, and water.

Mechanochemical Preparation of a MoS2/Polyaniline Nanocomposite with High Electrochemical Capacity

A hybrid polyaniline nanocomposite derived from polyaniline in the emeraldine base state and nanostructurized MoS2was prepared by a mechanochemical method. The electrochemical properties of the MoS2/PAni nanocomposite as the active component of a lithium battery cathode were studied. This material has a high specific capacity of ~270 A·h/kg, which is due to the significantly greater specific capacities of the organic and inorganic components relative to their characteristics in the individual states. This enhancement may be attributed to the effects of the nanocomposite components on the electrochemical behavior of each other.

Nanocomposite of Polyaniline with Partially Oxidized Graphene as the Transport Layer of Light-Emitting Polymer Diodes

Feasibility has been demonstrated for the use of the interpolymer complex of polyaniline with poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (PAni·PAMPSA) and its nanocomposite with partially oxidized graphene (PAni·PAMPSA/POGr) as a material for hole transport layers in the manufacture of polymer light-emitting diodes (PLED). A study was carried out on the functional characteristics of such PLED, which were compared with those of traditional PLED made with poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonate anions (PEDOT/PSS). The PLED made with PAni·PAMPSA/POGr nanocomposites were shown to have better functional characteristics, namely, current density, brightness, current and luminous efficiency, than for the analogous heterostructures derived from the pure PAni·PAMPSA interpolymer complex. The PAni·PAMPSA/POGr nanocomposite may be used instead of PEDOT/PSS in the manufacture of efficient organic optoelectronic devices.

Liquid exfoliation of mechanochemically nanostructured tungsten disulfide to a graphene-like state

The possibility of the efficient preparation of graphene-like 1H-WS2 by the primary solventless nanostructuration of bulk 2H-WS2 by means of its mechanochemical treatment in the presence of a chemically inert agent (NaCl) and the subsequent liquid exfoliation of the nanostructured 2H-WS2 in an organic solvent is shown for the first time. The shear stresses generated during the grinding of the WS2/NaCl mixture caused the formation of WS2 particles with a reduced number of layers, while the stresses normal to their surface led to their cracking and a significant reduction in lateral size. The graphene-like morphology of the 1H-WS2 nanoparticles in the prepared dispersions is confirmed by atomic force microscopy and Raman spectroscopy. The semiconducting character of 1Н-WS2 is supported by electron absorption and x-ray photoelectron spectroscopy data.

Effect of the Mechanochemical Preparation on the Fractional Composition and Spectral Characteristics of Graphene Oxide

Mechanochemically prepared graphene oxide GO|mc consists of a fraction of low-molecular-weight debris and a fraction of rather large graphene sheets (bwGO|mc, bw = base-washed). The content of the low-molecular-weight fraction in dispersions of GO|mc was found to be higher than for GO dispersions prepared by chemical methods. GO|mc exhibited photoluminescence in the visible region of the spectrum, the main contribution to which is made by the debris fraction. Conjugated carbon bonds are retained in the debris, which distinguishes this material from analogs synthesized by the chemical oxidation of graphite.

Effect of the Nature of Exfoliating Agents on the Structure of Graphenes with Various Degrees of Oxidation Obtained by Mechanochemical Treatment

Graphenes with various degree of oxidation and capable of forming stable aqueous dispersions were prepared by a mechanochemical method using Na2SO4, KMnO4, and KMnO4 with the addition of a stoichiometric amount of H2SO4 as exfoliating agents in the mechanochemical treatment of graphite. It was established that the lateral dimension of the predominantly monolayer particles of such graphenes amounts to 100-500 nm and decreases with increase of the degree of oxidation. It was shown that various oxygen-containing groups formed as a result of interaction of the nanostructured graphite with atmospheric oxygen and water are present on the surface of the obtained graphenes. It was found that the initial high specific discharge capacity of graphene oxide is reduced during charge–discharge cycling as a result of the irreversibility of the reduction of the oxygen-containing groups and is stabilized at 90 A·h/kg.