Olga A. Kozarenko

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.

Effect of monomer/oxidant mole ratio on polymerization mechanism, conductivity and spectral characteristics of mechanochemically prepared polypyrrole

The effect of the composition of the initial reaction mixture – pyrrole/oxidant mole ratio – on the mechanism of mechanochemical polymerization of pyrrole was studied. Experimental evidence in favor of the chain mechanism for mechanochemical formation of the highly conducting PPy at high monomer/oxidant mole ratio was first obtained. Interrelation between polymerization mechanism and structure, conductivity and spectral characteristics of the prepared polypyrrole samples was considered.

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).

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.

Effect of the Composition and Post-Synthesis Heat Treatment on the Electrochemical Characteristics of Polypyrrole/V2O5 Nanocomposites Prepared by a Mechanochemical Method

Effects were shown for the composition and post-synthesis heat treatment in an oxygen atmosphere on the electrochemical properties of nanocomposites derived from polypyrrole (PPy) and a V2O5 xerogel with host–guest structure. PPy0.05V2O5 was found to have the highest specific discharge capacity of about 290 mA·h/g and high stability upon prolonged charge-discharge cycling among the PPyxV2O5 nanocomposites prepared (where x = 0.1, 0.05, 0.025). Post-synthesis heat treatment in an oxygen atmosphere leads to oxidation of the reduced portion of the inorganic nanocomposite component and nanostructurization of the composite with formation of nanofibers that facilitate a considerable increase in the specific capacity and stability upon cycling.

Metallic Conductivity of Mechanochemically Doped Polyaniline

It was shown that the conductivity of polyaniline can be increased significantly as a result of mechanochemical doping with camphorsulfonic acid and secondary doping with m-cresol in comparison with the conductivity of the polymer synthesized by the traditional method. The obtained polymer has a nanofibrillar structure and is characterized by a metallic type of temperature dependence of the conductivity over a wide range of temperatures.

Mechanochemically Prepared Nanocomposites Based on Polyaniline and Molybdenum and Tungsten Disulfides as Electrode Materials for Supercapacitors

Hybrid nanocomposites with different composition prepared from polyaniline (PAni) and exfoliated MoS2 and WS2 were prepared by a mechanochemical method and studied as electrodes of symmetrical supercapacitors (SSC). Nanoparticles of MoS2 and WS2 have been found to promote electrochemical reversibility of redox conversion in PAni at high potentials and contribute to the stability of these nanocomposites during prolonged charge-discharge cycling. The specific capacity of such materials can reach 600 F/g and the specific power of SSC can reach ~4.1 kW/kg for specific energy ~23.5 W·h/kg.

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.